how does nature and nurture influence human behavior essay

The Influence of Nature and Nurture on Human Behavior Research Paper

Introduction, historical background, debate in support of nature, interaction of nurture and nature, iq and personality debate.

According to (Moore, 2003), the issue of whether nature has more impact than nurture on ways in which human beings behave has been debated upon for quite some time, where each individual is found to support either of the two according to experience or perceptions. Nature concerns itself with the natural internal qualities possessed by human beings. On the other hand, nurture concerns itself with experiences that human beings have acquired from the environment in which they live. The debate involves how these two factors determine the behavioral as well as physical characteristics of human beings and ways in which they vary. The particular roles of nurture and nature are portrayed in various areas and stages of lives of human beings.

The debate on how nurture as well as nature contributes to behavior of human beings can be traced to historical times. From the nineteenth century to early the twentieth century, opinions were found to consider nature as the determinant of human behavior. This was mainly supported by scientific research on the role played by genes that are inherited by offsprings. Another study that supported nature is natural selection that was conducted by Charles Darwin. Galton wrote a book called “hereditary nature” where he argued that, those people who possessed various gifts were found to originate from parents or family backgrounds that had similar kinds of gifts. He supported his arguments by an analysis that he carried on concerning talents and various professions where he concluded that, they were inherited from particular parents who possessed such talents. He also argued that, character traits improve or get worse throughout generations depending on the traits of parents. However, after the First World War, more research was carried out on the issue of the roles of nurture as well as nature. This particular research challenged the views that were in support of nature as the sole determinant of human beings’ behavior and argued that nurture was a major contributing factor to ways in which human beings behaved (Moore, 2003).

According to (Bouchard, 1997), supporters of nurture argue that, the manner in which human beings behave is primarily determined by the environment in which they are brought up. This particular argument has been supported by several studies performed on the various types of temperaments possessed by children. For example, John Watson, an American psychologist performed an experiment on a young boy which showed that, phobia is as a result of classical conditioning. He argued that, if he was to be given some healthy infants, he would apply his own knowledge to equip them with skills of his choice and they would end up in different specializations regardless of their abilities, race, genetic characteristics and talents.

(Steele, 1981), found that the theory of nurture was also supported by Skinner, another psychologist, who performed experiments using pigeons. He took his time to train them on various dancing styles, which they imitated and after some time they could dance as directed. He also trained them on how to play tennis and twist their bodies to make figure eight which they did as well. These experiments made him to be considered as the founder of the science that deals with behavior. From experiments that he carried out on animals, he inferred that it’s possible to condition the behavior of human beings in a similar manner. This inference supported the fact that human behavior is a product of what is learnt through experience acquired in one’s surroundings.

Another study done by scientists, show that human beings acquire their humor through learning. Acquisition of humor is influenced by the type of culture that one grows up in or the kind of family set up that one is brought up in. For example, if one grows up in a family where people are jovial, peaceful and make a lot of jokes, then he/she will grow up a jovial person who is full of humor which will have been learnt from the environment surrounding him. A study of the behavior portrayed by identical twins show that, when brought up in different environments, they acquire very different behavioral traits showing that nurture plays a very big role in determining the type of traits acquired by human beings. (Bridgeman, 2003)

(Maroni, 2000), found that, the color of hair as well as that of eyes is determined by genes. Supporters of the theory of nature also argue that, traits such as aggression, sexual orientation and intelligence are determined by genes. Therefore, various types of genes have been studied so as to show how nature plays its role in determination of behavior. However, these arguments are feared to be used by some people as an excuse for their bad behavior. This is because; some people are found to argue that, since one or both of their parents or someone in their extended family was a criminal, he/she can do nothing to his/her criminal behavior because its inherited. Others argue that, since their parents are divorced, they too cannot escape it because; even if they marry they will have to divorce. This is a negative application of the transfer of genes through inheritance as people tend to stick to negative behavior since their parents had the same. Possession of the gene that makes people to become gay has also been used to explain the role of nature in its determination of behavior. Studies have shown that, genes determine the ways in which various people are oriented sexually. It is argued that, sexual behavior is usually encoded in one’s genes and that, one does not choose whether to become gay or not. Gay individuals are therefore believed to be naturally attracted to people of a similar sex which comes out without their knowledge and cannot be controlled.

However, debate suggests that, both nurture and nature play essential roles in determining the manner in which human beings behave. This is because; some behavior is usually engrained in human beings before birth, while others develop during interaction with their surrounding environment. Therefore, it is agreed that, the way in which genes are related to behavior greatly differs with the way in which causes are related to their consequential effects. This is because; one’s genes may give a probability of a certain behavior but does not guarantee or restrict someone to behave in that particular manner. This gives individuals an opportunity to decide what they want to become, where environment and their effort takes charge (Lindsay, 2000).

It has been found that, there exist minimal instances where behavior can be taken to be entirely caused by nurture or entirely as a result of nature. For example, a study on some “genetic” diseases like Huntington disease show that, there is a high percentage of possession of the gene that causes it as well as the disease which is similar to the percentage that shows a lack of both. However, the lives of those animals that already have this disease entirely depend on the level of care they get. That is, those that get quality animal husbandry live for a longer time than those that are not taken good cared of. Therefore, though nature causes Huntington’s disease, nurture takes control of the length of life that the sick animals will live. On the contrary, some characteristics of human beings are determined by nurture among them being someone’s native language. It is argued that, children have the ability to learn languages of their choice when they are provided with the necessary facilities to enable them learn. This means that, the language spoken by any individual is not in any case determined by genes or inherited but by the environment in which people leave. Therefore, nurture and nature work together in the determination of behavior in human beings.

Another example of their interaction is an experiment that was carried out by Pinker on the religion as well as language spoken by human beings. Results to his experiment showed that, one’s religion, language as well as political party is not determined by genes. However, on acquisition of the specific choices, characteristics that show temperaments and skills in the form of how well one can communicate in a certain language, how one behaves in his /her political party or the level of commitment to a certain religion are to some extent determined by one’s inherited genes (Lindsay, 2000).

Therefore, when characteristics of human beings’ behavior are caused by interactions of nurture and nature, the level of heritability can only be measured through variations that exist in a given population. But there are cases where scientists have been noticed to assume that, if a particular level of heritability is noticed in a certain trait, that trait has been purely determined by nature, not taking into account the possibility of nurture been involved in some way. However, this should not be case as both determinants play roles in determination of the traits acquired by human beings though their levels of association or involvement vary in different traits (Stuart, 1999).

This debate has attracted a wide range of arguments and suggestions where studies of twins who are identical and fraternal are used. Adopted children are also used for comparison purposes. Studies that support the role played by nature in determination human beings’ IQ argue that, the IQ of those twins who are identical has a high level of similarity even when the two are reared separately. Those supporting nature say that the high level of similarity is caused by their shared genes from the environment they were inside their mothers’ womb. Further studies show that, similarity of IQ diminishes as one moves from twins, to fraternal, to adopted children and finally to strangers. On the contrary, studies supporting nurture argue something different altogether. For example, James Flynn, a political scientist noticed that, the level of human beings’ IQ was accelerating with time. His arguments suggested that, the level of IQ is determined by environmental factors that children are exposed to as they grow up. These environmental factors include, diet, education and the level of IQ of those people with whom children interact with.

Flynn argued that, the complexity of visual images that people are exposed to through advertisements, computer games and posters increase their levels of IQ. Other environmental aspects that tend to affect IQ levels include infant malnutrition where those children who suffer malnutrition possess low levels of IQ as they lack enough energy to reason as well as other nutrients required in reasoning. The profession of parents also matters as it tends to motivate the child in one way or another if it happens to be good. Consequently, studies show that most children tend to follow the professions of their parents as children are likely to imitate their parents. This trend makes the IQ of those children to be determined by the profession and not genes acquired from parents. Another factor that may affect children’s level of IQ is the parental ambition as well as rigidity. A child whose parents are ambitious is likely to be exposed to issues that would in one way or another increase his/her IQ while rigid parents are likely to cause rigidity in their children resulting to lowering their IQ levels (Stuart, 1999).

The manner in which people behave is caused or determined by both nurture and nature. However, involvement of each of them varies depending on the kind of trait in question. Scientists have contributed to this particular debate by performing studies that are directed at differentiating roles played by nature and those played by nurture. Though it is not possible to give an exact estimation of their involvement, it can be concluded that, genes only determine one’s behavior up to a certain age where environment in which he/she is brought up takes over. (Becker, 2002)

• Becker B. (2002): Behavioral endocrinology : MIT Press pp33-38
• Bouchard C. (1997): Genetics of fitness and physical performance : Human Kinetics pp. 23-27
• Bridgeman B. (2003): Psychology and evolution : Sage Publications pp. 31-36
• Lindsay S. (2000): Adaptation and Learning : Wiley-Blackwell pp. 54-59
• Maroni G. (2000): Molecular and genetic analysis of human traits : Wiley-Blackwell pp. 13-16
• Moore D. (2003): The Fallacy of nature Vs Nurture : Henry Holt pp. 59-65
• Steele J. (1981): On the inheritance of acquired characters : University of Chicago Press pp. 19-24
• Stuart I. (1999): Key ideas in psychology : Jessica Kingsley publishers pp. 11-16
• Chicago (A-D)
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Nature vs. Nurture Debate In Psychology

Saul Mcleod, PhD

Editor-in-Chief for Simply Psychology

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul Mcleod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.

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Olivia Guy-Evans, MSc

Associate Editor for Simply Psychology

BSc (Hons) Psychology, MSc Psychology of Education

Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

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The nature vs. nurture debate in psychology concerns the relative importance of an individual’s innate qualities (nature) versus personal experiences (nurture) in determining or causing individual differences in physical and behavioral traits. While early theories favored one factor over the other, contemporary views recognize a complex interplay between genes and environment in shaping behavior and development.

Key Takeaways

• Nature is what we think of as pre-wiring and is influenced by genetic inheritance and other biological factors.
• Nurture is generally taken as the influence of external factors after conception, e.g., the product of exposure, life experiences, and learning on an individual.
• Behavioral genetics has enabled psychology to quantify the relative contribution of nature and nurture concerning specific psychological traits.
• Instead of defending extreme nativist or nurturist views, most psychological researchers are now interested in investigating how nature and nurture interact in a host of qualitatively different ways.
• For example, epigenetics is an emerging area of research that shows how environmental influences affect the expression of genes.

The nature-nurture debate is concerned with the relative contribution that both influences make to human behavior, such as personality, cognitive traits, temperament and psychopathology.

Examples of Nature vs. Nurture

Nature vs. nurture in child development.

In child development, the nature vs. nurture debate is evident in the study of language acquisition . Researchers like Chomsky (1957) argue that humans are born with an innate capacity for language (nature), known as universal grammar, suggesting that genetics play a significant role in language development.

Conversely, the behaviorist perspective, exemplified by Skinner (1957), emphasizes the role of environmental reinforcement and learning (nurture) in language acquisition.

Twin studies have provided valuable insights into this debate, demonstrating that identical twins raised apart may share linguistic similarities despite different environments, suggesting a strong genetic influence (Bouchard, 1979)

However, environmental factors, such as exposure to language-rich environments, also play a crucial role in language development, highlighting the intricate interplay between nature and nurture in child development.

Nature vs. Nurture in Personality Development

The nature vs. nurture debate in personality psychology centers on the origins of personality traits. Twin studies have shown that identical twins reared apart tend to have more similar personalities than fraternal twins, indicating a genetic component to personality (Bouchard, 1994).

However, environmental factors, such as parenting styles, cultural influences, and life experiences, also shape personality.

For example, research by Caspi et al. (2003) demonstrated that a particular gene (MAOA) can interact with childhood maltreatment to increase the risk of aggressive behavior in adulthood.

This highlights that genetic predispositions and environmental factors contribute to personality development, and their interaction is complex and multifaceted.

Nature vs. Nurture in Mental Illness Development

The nature vs. nurture debate in mental health explores the etiology of depression. Genetic studies have identified specific genes associated with an increased vulnerability to depression, indicating a genetic component (Sullivan et al., 2000).

However, environmental factors, such as adverse life events and chronic stress during childhood, also play a significant role in the development of depressive disorders (Dube et al.., 2002; Keller et al., 2007)

The diathesis-stress model posits that individuals inherit a genetic predisposition (diathesis) to a disorder, which is then activated or exacerbated by environmental stressors (Monroe & Simons, 1991).

This model illustrates how nature and nurture interact to influence mental health outcomes.

Nature vs. Nurture of Intelligence

The nature vs. nurture debate in intelligence examines the relative contributions of genetic and environmental factors to cognitive abilities.

Intelligence is highly heritable, with about 50% of variance in IQ attributed to genetic factors, based on studies of twins, adoptees, and families (Plomin & Spinath, 2004).

Heritability of intelligence increases with age, from about 20% in infancy to as high as 80% in adulthood, suggesting amplifying effects of genes over time.

However, environmental influences, such as access to quality education and stimulating environments, also significantly impact intelligence.

Shared environmental influences like family background are more influential in childhood, whereas non-shared experiences are more important later in life.

Research by Flynn (1987) showed that average IQ scores have increased over generations, suggesting that environmental improvements, known as the Flynn effect , can lead to substantial gains in cognitive abilities.

Molecular genetics provides tools to identify specific genes and understand their pathways and interactions. However, progress has been slow for complex traits like intelligence. Identified genes have small effect sizes (Plomin & Spinath, 2004).

Overall, intelligence results from complex interplay between genes and environment over development. Molecular genetics offers promise to clarify these mechanisms. The nature vs nurture debate is outdated – both play key roles.

Nativism (Extreme Nature Position)

It has long been known that certain physical characteristics are biologically determined by genetic inheritance.

Color of eyes, straight or curly hair, pigmentation of the skin, and certain diseases (such as Huntingdon’s chorea) are all a function of the genes we inherit.

These facts have led many to speculate as to whether psychological characteristics such as behavioral tendencies, personality attributes, and mental abilities are also “wired in” before we are even born.

Those who adopt an extreme hereditary position are known as nativists.  Their basic assumption is that the characteristics of the human species as a whole are a product of evolution and that individual differences are due to each person’s unique genetic code.

In general, the earlier a particular ability appears, the more likely it is to be under the influence of genetic factors. Estimates of genetic influence are called heritability.

Examples of extreme nature positions in psychology include Chomsky (1965), who proposed language is gained through the use of an innate language acquisition device. Another example of nature is Freud’s theory of aggression as being an innate drive (called Thanatos).

Characteristics and differences that are not observable at birth, but which emerge later in life, are regarded as the product of maturation. That is to say, we all have an inner “biological clock” which switches on (or off) types of behavior in a pre-programmed way.

The classic example of the way this affects our physical development are the bodily changes that occur in early adolescence at puberty.

However, nativists also argue that maturation governs the emergence of attachment in infancy , language acquisition , and even cognitive development .

Empiricism (Extreme Nurture Position)

At the other end of the spectrum are the environmentalists – also known as empiricists (not to be confused with the other empirical/scientific  approach ).

Their basic assumption is that at birth, the human mind is a tabula rasa (a blank slate) and that this is gradually “filled” as a result of experience (e.g., behaviorism ).

From this point of view, psychological characteristics and behavioral differences that emerge through infancy and childhood are the results of learning.  It is how you are brought up (nurture) that governs the psychologically significant aspects of child development and the concept of maturation applies only to the biological.

For example, Bandura’s (1977) social learning theory states that aggression is learned from the environment through observation and imitation. This is seen in his famous bobo doll experiment (Bandura, 1961).

Also, Skinner (1957) believed that language is learned from other people via behavior-shaping techniques.

Evidence for Nature

• Biological Approach
• Biology of Gender
• Medical Model

Freud (1905) stated that events in our childhood have a great influence on our adult lives, shaping our personality.

He thought that parenting is of primary importance to a child’s development , and the family as the most important feature of nurture was a common theme throughout twentieth-century psychology (which was dominated by environmentalists’ theories).

Behavioral Genetics

Researchers in the field of behavioral genetics study variation in behavior as it is affected by genes, which are the units of heredity passed down from parents to offspring.

“We now know that DNA differences are the major systematic source of psychological differences between us. Environmental effects are important but what we have learned in recent years is that they are mostly random – unsystematic and unstable – which means that we cannot do much about them.” Plomin (2018, xii)

Behavioral genetics has enabled psychology to quantify the relative contribution of nature and nurture with regard to specific psychological traits. One way to do this is to study relatives who share the same genes (nature) but a different environment (nurture). Adoption acts as a natural experiment which allows researchers to do this.

Empirical studies have consistently shown that adoptive children show greater resemblance to their biological parents, rather than their adoptive, or environmental parents (Plomin & DeFries, 1983; 1985).

Another way of studying heredity is by comparing the behavior of twins, who can either be identical (sharing the same genes) or non-identical (sharing 50% of genes). Like adoption studies, twin studies support the first rule of behavior genetics; that psychological traits are extremely heritable, about 50% on average.

The Twins in Early Development Study (TEDS) revealed correlations between twins on a range of behavioral traits, such as personality (empathy and hyperactivity) and components of reading such as phonetics (Haworth, Davis, Plomin, 2013; Oliver & Plomin, 2007; Trouton, Spinath, & Plomin, 2002).

Implications

Jenson (1969) found that the average I.Q. scores of black Americans were significantly lower than whites he went on to argue that genetic factors were mainly responsible – even going so far as to suggest that intelligence is 80% inherited.

The storm of controversy that developed around Jenson’s claims was not mainly due to logical and empirical weaknesses in his argument. It was more to do with the social and political implications that are often drawn from research that claims to demonstrate natural inequalities between social groups.

For many environmentalists, there is a barely disguised right-wing agenda behind the work of the behavioral geneticists.  In their view, part of the difference in the I.Q. scores of different ethnic groups are due to inbuilt biases in the methods of testing.

More fundamentally, they believe that differences in intellectual ability are a product of social inequalities in access to material resources and opportunities.  To put it simply children brought up in the ghetto tend to score lower on tests because they are denied the same life chances as more privileged members of society.

Now we can see why the nature-nurture debate has become such a hotly contested issue.  What begins as an attempt to understand the causes of behavioral differences often develops into a politically motivated dispute about distributive justice and power in society.

What’s more, this doesn’t only apply to the debate over I.Q.  It is equally relevant to the psychology of sex and gender , where the question of how much of the (alleged) differences in male and female behavior is due to biology and how much to culture is just as controversial.

Polygenic Inheritance

Rather than the presence or absence of single genes being the determining factor that accounts for psychological traits, behavioral genetics has demonstrated that multiple genes – often thousands, collectively contribute to specific behaviors.

Thus, psychological traits follow a polygenic mode of inheritance (as opposed to being determined by a single gene). Depression is a good example of a polygenic trait, which is thought to be influenced by around 1000 genes (Plomin, 2018).

This means a person with a lower number of these genes (under 500) would have a lower risk of experiencing depression than someone with a higher number.

The Nature of Nurture

Nurture assumes that correlations between environmental factors and psychological outcomes are caused environmentally. For example, how much parents read with their children and how well children learn to read appear to be related. Other examples include environmental stress and its effect on depression.

However, behavioral genetics argues that what look like environmental effects are to a large extent really a reflection of genetic differences (Plomin & Bergeman, 1991).

People select, modify and create environments correlated with their genetic disposition. This means that what sometimes appears to be an environmental influence (nurture) is a genetic influence (nature).

So, children that are genetically predisposed to be competent readers, will be happy to listen to their parents read them stories, and be more likely to encourage this interaction.

Interaction Effects

However, in recent years there has been a growing realization that the question of “how much” behavior is due to heredity and “how much” to the environment may itself be the wrong question.

Take intelligence as an example. Like almost all types of human behavior, it is a complex, many-sided phenomenon which reveals itself (or not!) in a great variety of ways.

The “how much” question assumes that psychological traits can all be expressed numerically and that the issue can be resolved in a quantitative manner.

Heritability statistics revealed by behavioral genetic studies have been criticized as meaningless, mainly because biologists have established that genes cannot influence development independently of environmental factors; genetic and nongenetic factors always cooperate to build traits. The reality is that nature and culture interact in a host of qualitatively different ways (Gottlieb, 2007; Johnston & Edwards, 2002).

Instead of defending extreme nativist or nurturist views, most psychological researchers are now interested in investigating how nature and nurture interact.

For example, in psychopathology , this means that both a genetic predisposition and an appropriate environmental trigger are required for a mental disorder to develop. For example, epigenetics state that environmental influences affect the expression of genes.

What is Epigenetics?

Epigenetics is the term used to describe inheritance by mechanisms other than through the DNA sequence of genes. For example, features of a person’s physical and social environment can effect which genes are switched-on, or “expressed”, rather than the DNA sequence of the genes themselves.

Stressors and memories can be passed through small RNA molecules to multiple generations of offspring in ways that meaningfully affect their behavior.

One such example is what is known as the Dutch Hunger Winter, during last year of the Second World War. What they found was that children who were in the womb during the famine experienced a life-long increase in their chances of developing various health problems compared to children conceived after the famine.

Epigenetic effects can sometimes be passed from one generation to the next, although the effects only seem to last for a few generations. There is some evidence that the effects of the Dutch Hunger Winter affected grandchildren of women who were pregnant during the famine.

Therefore, it makes more sense to say that the difference between two people’s behavior is mostly due to hereditary factors or mostly due to environmental factors.

This realization is especially important given the recent advances in genetics, such as polygenic testing.  The Human Genome Project, for example, has stimulated enormous interest in tracing types of behavior to particular strands of DNA located on specific chromosomes.

If these advances are not to be abused, then there will need to be a more general understanding of the fact that biology interacts with both the cultural context and the personal choices that people make about how they want to live their lives.

There is no neat and simple way of unraveling these qualitatively different and reciprocal influences on human behavior.

Epigenetics: Licking Rat Pups

Michael Meaney and his colleagues at McGill University in Montreal, Canada conducted the landmark epigenetic study on mother rats licking and grooming their pups.

This research found that the amount of licking and grooming received by rat pups during their early life could alter their epigenetic marks and influence their stress responses in adulthood.

Pups that received high levels of maternal care (i.e., more licking and grooming) had a reduced stress response compared to those that received low levels of maternal care.

Meaney’s work with rat maternal behavior and its epigenetic effects has provided significant insights into the understanding of early-life experiences, gene expression, and adult behavior.

It underscores the importance of the early-life environment and its long-term impacts on an individual’s mental health and stress resilience.

Epigenetics: The Agouti Mouse Study

Waterland and Jirtle’s 2003 study on the Agouti mouse is another foundational work in the field of epigenetics that demonstrated how nutritional factors during early development can result in epigenetic changes that have long-lasting effects on phenotype.

In this study, they focused on a specific gene in mice called the Agouti viable yellow (A^vy) gene. Mice with this gene can express a range of coat colors, from yellow to mottled to brown.

This variation in coat color is related to the methylation status of the A^vy gene: higher methylation is associated with the brown coat, and lower methylation with the yellow coat.

Importantly, the coat color is also associated with health outcomes, with yellow mice being more prone to obesity, diabetes, and tumorigenesis compared to brown mice.

Waterland and Jirtle set out to investigate whether maternal diet, specifically supplementation with methyl donors like folic acid, choline, betaine, and vitamin B12, during pregnancy could influence the methylation status of the A^vy gene in offspring.

Key findings from the study include:

Dietary Influence : When pregnant mice were fed a diet supplemented with methyl donors, their offspring had an increased likelihood of having the brown coat color. This indicated that the supplemented diet led to an increased methylation of the A^vy gene.

Health Outcomes : Along with the coat color change, these mice also had reduced risks of obesity and other health issues associated with the yellow phenotype.

Transgenerational Effects : The study showed that nutritional interventions could have effects that extend beyond the individual, affecting the phenotype of the offspring.

The implications of this research are profound. It highlights how maternal nutrition during critical developmental periods can have lasting effects on offspring through epigenetic modifications, potentially affecting health outcomes much later in life.

The study also offers insights into how dietary and environmental factors might contribute to disease susceptibility in humans.

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Plomin, R., & DeFries, J. C. (1985). The origins of individual differences in infancy; the Colorado adoption project. Science, 230 , 1369-1371.

Plomin, R., & Spinath, F. M. (2004). Intelligence: genetics, genes, and genomics.  Journal of personality and social psychology ,  86 (1), 112.

Plomin, R., & Von Stumm, S. (2018). The new genetics of intelligence.  Nature Reviews Genetics ,  19 (3), 148-159.

Skinner, B. F. (1957). Verbal behavior . Acton, MA: Copley Publishing Group.

Sullivan, P. F., Neale, M. C., & Kendler, K. S. (2000). Genetic epidemiology of major depression: review and meta-analysis.  American Journal of Psychiatry ,  157 (10), 1552-1562.

Szyf, M., Weaver, I. C., Champagne, F. A., Diorio, J., & Meaney, M. J. (2005). Maternal programming of steroid receptor expression and phenotype through DNA methylation in the rat .  Frontiers in neuroendocrinology ,  26 (3-4), 139-162.

Trouton, A., Spinath, F. M., & Plomin, R. (2002). Twins early development study (TEDS): a multivariate, longitudinal genetic investigation of language, cognition and behavior problems in childhood . Twin Research and Human Genetics, 5(5) , 444-448.

Waterland, R. A., & Jirtle, R. L. (2003). Transposable elements: targets for early nutritional effects on epigenetic gene regulation . Molecular and cellular biology, 23 (15), 5293-5300.

Further Information

• Genetic & Environmental Influences on Human Psychological Differences

Evidence for Nurture

• Classical Conditioning
• Little Albert Experiment
• Operant Conditioning
• Behaviorism
• Social Learning Theory
• Bronfenbrenner’s Ecological Systems Theory
• Social Roles
• Attachment Styles
• The Hidden Links Between Mental Disorders
• Visual Cliff Experiment
• Behavioral Genetics, Genetics, and Epigenetics
• Epigenetics
• Is Epigenetics Inherited?
• Physiological Psychology
• Bowlby’s Maternal Deprivation Hypothesis
• So is it nature not nurture after all?

Evidence for an Interaction

• Genes, Interactions, and the Development of Behavior
• Agouti Mouse Study
• Biological Psychology

What does nature refer to in the nature vs. nurture debate?

In the nature vs. nurture debate, “nature” refers to the influence of genetics, innate qualities, and biological factors on human development, behavior, and traits. It emphasizes the role of hereditary factors in shaping who we are.

What does nurture refer to in the nature vs. nurture debate?

In the nature vs. nurture debate, “nurture” refers to the influence of the environment, upbringing, experiences, and social factors on human development, behavior, and traits. It emphasizes the role of external factors in shaping who we are.

Why is it important to determine the contribution of heredity (nature) and environment (nurture) in human development?

Determining the contribution of heredity and environment in human development is crucial for understanding the complex interplay between genetic factors and environmental influences. It helps identify the relative significance of each factor, informing interventions, policies, and strategies to optimize human potential and address developmental challenges.

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4 Human Behavior: Nature or Nurture?

Learning Objectives

After reading this chapter, you should be able to:

• Describe Galton’s contributions towards the Nature and Nurture theory.
• Differentiate between the influence of genes and environment, as well as a combination of both.
• Define and Describe Epigenetics.
• Explain the difference between Social Learning Theory and Genetic Inheritance Theory.
• Explain the findings of the Bobo doll experiment.
• Understand the Grizzly Bear article.
• Understand the Beyond Heritability: Twin Studies article.
• Understand key concepts and definitions pertaining to nature vs nurture.

Introduction: What Do We Mean By Nature Vs Nurture?

In this chapter it is discussed that nature vs nurture is the debate of whether we are a product of nature (genetics) or nurture (environment). There is evidence supporting both sides of the debate. By the end of this, you should be able to determine that both nature and nurture play a key role in humans and animal behaviour.

Memory Match

The memory match game allows you to identify keywords pertaining to nature and nurture. The goal is to click a card and match the word on the card, with another card that has the same word. Now that you know how to play, let’s see how many you can match!

When we refer to nature, we are talking about our genetics that we inherit from our parents.  A fairly recent study (Kamran, 2016) conducted in Pakistan suggests that the parallels drawn regarding the temperament of siblings are due to their genetics. The results of this study states that the genetic makeup of relatives of the family (even deceased) also influence how the child acts. These behaviours of the child are identifiable by the family members even though the deceased family member no longer is present.

Browse through Galton’s timeline and discover his story!

Pair the Pioneer

The following pioneers play a key role in what we know about nature and nurture today! The goal of the game is to pair the correct pioneer with the correct fact pertaining to the pioneer. If you place your mouse above the pioneer, there is a fun fact that has a clue to help. Be careful, there is a trick pioneer!

• Nature:  refers to all of the genes and hereditary factors that influence who we are- from our physical appearance to our personality characteristics (definition retrieved from verywellmind.com on November 17, 2019).
• Epigenetics : the study of heritable changes in gene function that do not involve changes in DNA sequence (definition retrieved from MerriamWebster.com on November 17, 2019)

When we refer to nurture, we are talking about all the environmental factors that influence us. Environmental factors include but aren’t limited to parenting style, birth order, peers, family size, culture, language, education, etc. The main argument for nurture is that the environment is what makes us who we are. Those who are on the extreme side of nurture are empiricists. They believe humans are born as blank slates and acquire all information from their environment with their 5 senses.

Behaviorism, established by John Watson, is the theory that all behavior is a result of stimulation from the environment or a consequence of the individual’s previous conditioning. Behaviorism is a school of psychology that is on the side of nurture.

A study in 2019 performed an experiment on Bonobos (a species of chimpanzee) to observe social learning. The results of the experiment found supporting evidence that Bonobos are able to learn from observing others of their species just like humans.

Albert Bandura’s Social Learning Theory states that people learn by observing, imitating, and modeling behavior. In 1961, Bandura’s famous Bobo doll experiment’s findings support the argument for nurture in that our environment influences our behavior.

Key Terms: 

• Nurture: Environmental factors that influence our growth and behaviour.
• Empiricism: The belief that people are born as a blank slate learn everything from their environment.

Nature or Nurture? Or Both?

Given what we have discussed so far, is it genes or environment that influences behaviour? It is actually both genetic and social influences that contributes to an individual’s behaviour. Below is a video that explains how both components contribute to an individual.

Now that you understand how genes and environment work together, is it possible for one component to influence an individual more than the other? Below is an article that explains how grizzly bears’ conflict behaviour may attribute to genetic inheritance or social learning… talk about beary bad behaviour!

 Beary Bad Behaviour

Grizzly bear den

Welcome to the Grizzly Bear den. Inside there are paws, click any paw to learn key concepts within the article! Don’t worry, the bears won’t bite!

A study done in Alberta, Canada analyzed the genetic and environmental relationship of grizzly bears, pertaining to their offspring’s conflict behaviour. The study predicts that aggression is determined genetically from either biological parents. If the cub’s conflict behaviour is inherited from the father’s genes, then necessary relocation of wildlife protection is necessary to avoid human-conflict interaction. If the cub’s behaviour is inherited from the mother’s genes, then relocation of female bears is much more difficult to do as there are legal wildlife implications.

The study genotyped 213 grizzly bears, most of which were males. The study described conflict-beahviour or “problem bear” as those that exemplified invasive or aggressive behaviour on private property, public property, or had an incident with an individual. The results of the study indicated that the offspring of the female parent displayed a negative interaction more so than the offspring from the male parent.

According to Morehouse et al., (2016), “ results support the social learning hypothesis, but not the genetic inheritance hypothesis as it relates to the acquisition of conflict behaviour. If human-bear conflict was an inherited behaviour, we would have expected to see a significant relationship between paternal conflict behaviour and offspring behaviour.  Social learning has the potential to perpetuate grizzly bear conflicts highlighting the importance of preventing initial conflicts, but also removing problem individuals once conflicts start” (p.7). 

 Beyond Heritability: Twin Studies

In this study, it talks about the general observations of 50 study samples regarding over 800,000 pairs of twins and how their behavior may have been impacted by genes or by their environment. Due to the ethical limitations of human experimentation, there can only be a conclusion that there are mild causal effects. Heritable estimations are quite frankly useless in these studies because the results purely depend on the environmental conditions of the study participants, and it only becomes applicable when all participants are in the same environment.

If a separated teen is brought up in a rich environment, their gene makeup has a higher likelihood of being a factor in their upbringing. If his or her counterpart twin, in contrast, is brought up in a poor environment, the influence of their genes will be insignificant because of a less nurturing surrounding. Another example is the first sexual encounter on separated twins; do their shared genetics influence them to take action around the same time? The answer is no, because such events are a result of the environmental influences of delinquency.

Psychologist Eric Turkheimer states that there are essentially Three Laws of Behaviour Genetics:

“First Law: All human behavioural traits are heritable.

Second Law: The effect of being raised in the same family is smaller than the effect of the genes.

Third Law: A substantial portion of the variation in complex human behavioural traits is not accounted for by the effects of genes or families.”

He explains that genes only make up ~50% of our behaviours while the rest is influenced by our environment.

“The omnipresence of genetic influences does not [mean] that behaviour is less psychological or more biologically determined”, but it’s the facilitation of the environmental conditions that allows people to bring out their full behaviouristic tendencies to light; and even then, our genes are only half the story.

The following video is a study that looked at the effects of nature and nurture on twins. In short, there are many coincidences that may seem that their actions come from genetic relations.

• To answer the question of whether we are a product of Nature or Nurture, we are both. We are a product of our genetics, and our environment. Through our genetics, we have a certain baseline personality, but that changes over time due to the influence of our surroundings: the people we hang out with and the overall level of nourishment in our growing environment.
•  In summary, based on several studies and research it can be concluded that human behaviour is both nature and nurture. In addition, evidence also supports that animal behaviour specifically (grizzly bears) is also due to nature and nurture. Many aspects of the nature vs. nurture theory argues that various behaviours in humans are based both on genetics and the environment of an individual. However, it is possible that one variable from the theory may contribute more of an effect on the individual.

Chapter References

ABC News (2018, Mar 10) 20/20 Mar 9 Part 2: Adopted twins were separated and then part of a secret study. Retrieved November 17, 2019, from https://youtu.be/0-2FFsuitO4

Benjamin, J. (2017, March 31). Cancer: Nature Vs. Nurture. Retrieved November 17, 2019, from https://marybird.org/blog/olol/cancer-nature-vs-nurture

Biography.com Editors. (2019, August 28). Charles Darwin Biography. Retrieved November 17, 2019, from https://www.biography.com/scientist/charles-darwin.

Cherry, K. (2019, July 1). The Age Old Debate of Nature vs. Nurture. Retrieved November 19, 2019, from https://www.verywellmind.com/what-is-nature-versus-nurture-2795392.

David L, “Social Learning Theory (Bandura),” in Learning Theories, February 7, 2019, https://www.learning-theories.com/social-learning-theory-bandura.html .

Det medisinke fakultet. (2016, January 26). Epigenetics: Nature vs nurture. Retrieved November 17, 2019, from https://youtu.be/k50yMwEOWGU

Everywhere Psychology. (2012, August 28). Bandura’s Bobo Doll Experiment. Retrieved November 19, 2019, from https://youtu.be/dmBqwWlJg8U .

FuseSchool-Global Education. (2019, August 27). Nature vs Nurture | Genetics | Biology | FuseSchool Retrieved November 18, 2019 from https://www.youtube.com/watch?v=EmctxRcmloc

Gervais, M. (2017, August 31). Dr. Albert Bandura – The Theory of Agency. Retrieved November 19, 2019, from https://art19.com/shows/minutes-on-mastery/episodes/a1cef11d-e32c-4f03-ba4a-262a91268f4c.

Johnson W, Turkheimer E, Gottesman II, Bouchard TJ Jr. Beyond Heritability: Twin Studies in Behavioral Research.  Curr Dir Psychol Sci . 2010;18(4):217–220. doi:10.1111/j.1467-8721.2009.01639.x

Kamran, F., PhD. (2016). Are siblings different as ‘day and night’? parents’ perceptions of nature vs. nurture.  Journal of Behavioural Sciences, 26 (2), 95-115. Retrieved from https://ezproxy.kpu.ca:2443/login?url=https://search-proquest-com.ezproxy.kpu.ca:2443/docview/1864042019?accountid=35875

Merriam-Webster. (2019). Retrieved November 17, 2019 from https://www.merriam-webster.com/dictionary/epigenetics

McLeod, S. A. (2016, Feb 05). Bandura – social learning theory . Simply Psychology. https://www.simplypsychology.org/bandura.html

McLeod, S. A. (2018, Dec 20). Nature vs nurture in psychology. Simply Psychology. https://www.simplypsychology.org/naturevsnurture.html

Miko, I.  (2008)  Gregor Mendel and the principles of inheritance.  Nature Education   1( 1 ) :134

Morehouse, A. T., Graves, T. A., Mikle, N., & Boyce, M. S. (2016). Nature vs. nurture: Evidence for social learning of conflict behaviour in grizzly bears. PLoS One, 11 (11) doi:http://dx.doi.org.ezproxy.kpu.ca:2080/10.1371/journal.pone.0165425

Rose, H., & Rose, S. (2011). The legacies of francis galton. Lancet, the, 377 (9775), 1397-1397.doi:10.1016/S0140-6736(11)60560-6

Shorland, G., Genty, E., Guéry, J.-P., & Zuberbühler, K. (2019). Social learning of arbitrary food preferences in bonobos. Behavioural Processes, 167. https://doi-org.ezproxy.kpu.ca:2443/10.1016/j.beproc.2019.103912

TED-Ed. (2013, March 12). How Mendel’s pea plants helped us understand genetics. Retrieved November 17, 2019, from https://youtu.be/Mehz7tCxjSE.

Thesaurus.Plus . (n.d.). Retrieved November 17, 2019, from https://thesaurus.plus/thesaurus.

Turkheimer, E. (2000). Three laws of behavior genetics and what they mean.  Current Directions in Psychological Science ,  9 (5), 160–164. https://doi-org.ezproxy.kpu.ca:2443/10.1111/1467-8721.00084

Winch, J. (2012, Mar 08). Genius with a finger on the pulse of discovery: Birmingham-born sir francis galton was a victorian genius. but today he would be thought a racist because of the controversial interest for which he is best remembered – eugenics. jessica winch reports. Birmingham Post. Retrieved from https://ezproxy.kpu.ca:2443/login?url=https://search-proquest-com.ezproxy.kpu.ca:2443/docview/926809806?accountid=35875

Wikipedia. (2019, November 16). Francis Galton. Retrieved November 17, 2019, from https://en.wikipedia.org/wiki/Francis_Galton.

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The Nature vs. Nurture Debate

Genetic and Environmental Influences and How They Interact

Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

Verywell / Joshua Seong

• Definitions
• Interaction
• Contemporary Views

Nature refers to how genetics influence an individual's personality, whereas nurture refers to how their environment (including relationships and experiences) impacts their development. Whether nature or nurture plays a bigger role in personality and development is one of the oldest philosophical debates within the field of psychology .

Learn how each is defined, along with why the issue of nature vs. nurture continues to arise. We also share a few examples of when arguments on this topic typically occur, how the two factors interact with each other, and contemporary views that exist in the debate of nature vs. nurture as it stands today.

Nature and Nurture Defined

To better understand the nature vs. nurture argument, it helps to know what each of these terms means.

• Nature refers largely to our genetics . It includes the genes we are born with and other hereditary factors that can impact how our personality is formed and influence the way that we develop from childhood through adulthood.
• Nurture encompasses the environmental factors that impact who we are. This includes our early childhood experiences, the way we were raised , our social relationships, and the surrounding culture.

A few biologically determined characteristics include genetic diseases, eye color, hair color, and skin color. Other characteristics are tied to environmental influences, such as how a person behaves, which can be influenced by parenting styles and learned experiences.

For example, one child might learn through observation and reinforcement to say please and thank you. Another child might learn to behave aggressively by observing older children engage in violent behavior on the playground.

The Debate of Nature vs. Nurture

The nature vs. nurture debate centers on the contributions of genetics and environmental factors to human development. Some philosophers, such as Plato and Descartes, suggested that certain factors are inborn or occur naturally regardless of environmental influences.

Advocates of this point of view believe that all of our characteristics and behaviors are the result of evolution. They contend that genetic traits are handed down from parents to their children and influence the individual differences that make each person unique.

Other well-known thinkers, such as John Locke, believed in what is known as tabula rasa which suggests that the mind begins as a blank slate . According to this notion, everything that we are is determined by our experiences.

Behaviorism is a good example of a theory rooted in this belief as behaviorists feel that all actions and behaviors are the results of conditioning. Theorists such as John B. Watson believed that people could be trained to do and become anything, regardless of their genetic background.

People with extreme views are called nativists and empiricists. Nativists take the position that all or most behaviors and characteristics are the result of inheritance. Empiricists take the position that all or most behaviors and characteristics result from learning.

Examples of Nature vs. Nurture

One example of when the argument of nature vs. nurture arises is when a person achieves a high level of academic success . Did they do so because they are genetically predisposed to elevated levels of intelligence, or is their success a result of an enriched environment?

The argument of nature vs. nurture can also be made when it comes to why a person behaves in a certain way. If a man abuses his wife and kids, for instance, is it because he was born with violent tendencies, or is violence something he learned by observing others in his life when growing up?

Nature vs. Nurture in Psychology

Throughout the history of psychology , the debate of nature vs. nurture has continued to stir up controversy. Eugenics, for example, was a movement heavily influenced by the nativist approach.

Psychologist Francis Galton coined the terms 'nature versus nurture' and 'eugenics' and believed that intelligence resulted from genetics. Galton also felt that intelligent individuals should be encouraged to marry and have many children, while less intelligent individuals should be discouraged from reproducing.

The value placed on nature vs. nurture can even vary between the different branches of psychology , with some branches taking a more one-sided approach. In biopsychology , for example, researchers conduct studies exploring how neurotransmitters influence behavior, emphasizing the role of nature.

In social psychology , on the other hand, researchers might conduct studies looking at how external factors such as peer pressure and social media influence behaviors, stressing the importance of nurture. Behaviorism is another branch that focuses on the impact of the environment on behavior.

Nature vs. Nurture in Child Development

Some psychological theories of child development place more emphasis on nature and others focus more on nurture. An example of a nativist theory involving child development is Chomsky's concept of a language acquisition device (LAD). According to this theory, all children are born with an instinctive mental capacity that allows them to both learn and produce language.

An example of an empiricist child development theory is Albert Bandura's social learning theory . This theory says that people learn by observing the behavior of others. In his famous Bobo doll experiment , Bandura demonstrated that children could learn aggressive behaviors simply by observing another person acting aggressively.

Nature vs. Nurture in Personality Development

There is also some argument as to whether nature or nurture plays a bigger role in the development of one's personality. The answer to this question varies depending on which personality development theory you use.

According to behavioral theories, our personality is a result of the interactions we have with our environment, while biological theories suggest that personality is largely inherited. Then there are psychodynamic theories of personality that emphasize the impact of both.

Nature vs. Nurture in Mental Illness Development

One could argue that either nature or nurture contributes to mental health development. Some causes of mental illness fall on the nature side of the debate, including changes to or imbalances with chemicals in the brain. Genetics can also contribute to mental illness development, increasing one's risk of a certain disorder or disease.

Mental disorders with some type of genetic component include autism , attention-deficit hyperactivity disorder (ADHD), bipolar disorder , major depression , and schizophrenia .

Other explanations for mental illness are environmental. This includes being exposed to environmental toxins, such as drugs or alcohol, while still in utero. Certain life experiences can also influence mental illness development, such as witnessing a traumatic event, leading to the development of post-traumatic stress disorder (PTSD).

Nature vs. Nurture in Mental Health Therapy

Different types of mental health treatment can also rely more heavily on either nature or nurture in their treatment approach. One of the goals of many types of therapy is to uncover any life experiences that may have contributed to mental illness development (nurture).

However, genetics (nature) can play a role in treatment as well. For instance, research indicates that a person's genetic makeup can impact how their body responds to antidepressants. Taking this into consideration is important for getting that person the help they need.

Interaction Between Nature and Nurture

Which is stronger: nature or nurture? Many researchers consider the interaction between heredity and environment—nature with nurture as opposed to nature versus nurture—to be the most important influencing factor of all.

For example, perfect pitch is the ability to detect the pitch of a musical tone without any reference. Researchers have found that this ability tends to run in families and might be tied to a single gene. However, they've also discovered that possessing the gene is not enough as musical training during early childhood is needed for this inherited ability to manifest itself.

Height is another example of a trait influenced by an interaction between nature and nurture. A child might inherit the genes for height. However, if they grow up in a deprived environment where proper nourishment isn't received, they might never attain the height they could have had if they'd grown up in a healthier environment.

A newer field of study that aims to learn more about the interaction between genes and environment is epigenetics . Epigenetics seeks to explain how environment can impact the way in which genes are expressed.

Some characteristics are biologically determined, such as eye color, hair color, and skin color. Other things, like life expectancy and height, have a strong biological component but are also influenced by environmental factors and lifestyle.

Contemporary Views of Nature vs. Nurture

Most experts recognize that neither nature nor nurture is stronger than the other. Instead, both factors play a critical role in who we are and who we become. Not only that but nature and nurture interact with each other in important ways all throughout our lifespan.

As a result, many in this field are interested in seeing how genes modulate environmental influences and vice versa. At the same time, this debate of nature vs. nurture still rages on in some areas, such as in the origins of homosexuality and influences on intelligence .

While a few people take the extreme nativist or radical empiricist approach, the reality is that there is not a simple way to disentangle the multitude of forces that exist in personality and human development. Instead, these influences include genetic factors, environmental factors, and how each intermingles with the other.

Schoneberger T. Three myths from the language acquisition literature . Anal Verbal Behav . 2010;26(1):107-31. doi:10.1007/bf03393086

National Institutes of Health. Common genetic factors found in 5 mental disorders .

Pain O, Hodgson K, Trubetskoy V, et al. Identifying the common genetic basis of antidepressant response . Biol Psychiatry Global Open Sci . 2022;2(2):115-126. doi:10.1016/j.bpsgos.2021.07.008

Moulton C. Perfect pitch reconsidered . Clin Med J . 2014;14(5):517-9 doi:10.7861/clinmedicine.14-5-517

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By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

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What Are Nature vs. Nurture Examples?

How is nature defined, how is nurture defined, the nature vs. nurture debate, nature vs. nurture examples, what is empiricism (extreme nurture position), contemporary views of nature vs. nurture.

Nature vs. nurture is an age-old debate about whether genetics (nature) plays a bigger role in determining a person's characteristics than lived experience and environmental factors (nurture). The term "nature vs. nature" was coined by English naturalist Charles Darwin's younger half-cousin, anthropologist Francis Galton, around 1875.

In psychology, the extreme nature position (nativism) proposes that intelligence and personality traits are inherited and determined only by genetics.

On the opposite end of the spectrum, the extreme nurture position (empiricism) asserts that the mind is a blank slate at birth; external factors like education and upbringing determine who someone becomes in adulthood and how their mind works. Both of these extreme positions have shortcomings and are antiquated.

This article explores the difference between nature and nurture. It gives nature vs. nurture examples and explains why outdated views of nativism and empiricism don't jibe with contemporary views. 

Thanasis Zovoilis / Getty Images

In the context of nature vs. nurture, "nature" refers to genetics and heritable factors that are passed down to children from their biological parents.

Genes and hereditary factors determine many aspects of someone’s physical appearance and other individual characteristics, such as a genetically inherited predisposition for certain personality traits.

Scientists estimate that 20% to 60% percent of temperament is determined by genetics and that many (possibly thousands) of common gene variations combine to influence individual characteristics of temperament.

However, the impact of gene-environment (or nature-nurture) interactions on someone's traits is interwoven. Environmental factors also play a role in temperament by influencing gene activity. For example, in children raised in an adverse environment (such as child abuse or violence), genes that increase the risk of impulsive temperamental characteristics may be activated (turned on).

Trying to measure "nature vs. nurture" scientifically is challenging. It's impossible to know precisely where the influence of genes and environment begin or end.

How Are Inherited Traits Measured?

“Heritability”   describes the influence that genes have on human characteristics and traits. It's measured on a scale of 0.0 to 1.0. Very strong heritable traits like someone's eye color are ranked a 1.0.

Traits that have nothing to do with genetics, like speaking with a regional accent ranks a zero. Most human characteristics score between a 0.30 and 0.60 on the heritability scale, which reflects a blend of genetics (nature) and environmental (nurture) factors.

Thousands of years ago, ancient Greek philosophers like Plato believed that "innate knowledge" is present in our minds at birth. Every parent knows that babies are born with innate characteristics. Anecdotally, it may seem like a kid's "Big 5" personality traits (agreeableness, conscientiousness, extraversion, neuroticism, and openness) were predetermined before birth.

What is the "Big 5" personality traits

The Big 5 personality traits is a theory that describes the five basic dimensions of personality. It was developed in 1949 by D. W. Fiske and later expanded upon by other researchers and is used as a framework to study people's behavior.

From a "nature" perspective, the fact that every child has innate traits at birth supports Plato's philosophical ideas about innatism. However, personality isn't set in stone. Environmental "nurture" factors can change someone's predominant personality traits over time. For example, exposure to the chemical lead during childhood may alter personality.

In 2014, a meta-analysis of genetic and environmental influences on personality development across the human lifespan found that people change with age. Personality traits are relatively stable during early childhood but often change dramatically during adolescence and young adulthood.

It's impossible to know exactly how much "nurture" changes personality as people get older. In 2019, a study of how stable personality traits are from age 16 to 66 found that people's Big 5 traits are both stable and malleable (able to be molded). During the 50-year span from high school to retirement, some traits like agreeableness and conscientiousness tend to increase, while others appear to be set in stone.

Nurture refers to all of the external or environmental factors that affect human development such as how someone is raised, socioeconomic status, early childhood experiences, education, and daily habits.

Although the word "nurture" may conjure up images of babies and young children being cared for by loving parents, environmental factors and life experiences have an impact on our psychological and physical well-being across the human life span. In adulthood, "nurturing" oneself by making healthy lifestyle choices can offset certain genetic predispositions.

For example, a May 2022 study found that people with a high genetic risk of developing the brain disorder Alzheimer's disease can lower their odds of developing dementia (a group of symptoms that affect memory, thinking, and social abilities enough to affect daily life) by adopting these seven healthy habits in midlife:

• Staying active
• Healthy eating
• Losing weight
• Not smoking
• Reducing blood sugar
• Controlling cholesterol
• Maintaining healthy blood pressure

The nature vs. nurture debate centers around whether individual differences in behavioral traits and personality are caused primarily by nature or nurture. Early philosophers believed the genetic traits passed from parents to their children influence individual differences and traits. Other well-known philosophers believed the mind begins as a blank slate and that everything we are is determined by our experiences.

While early theories favored one factor over the other, experts today recognize there is a complex interaction between genetics and the environment and that both nature and nurture play a critical role in shaping who we are.

Eye color and skin pigmentation are examples of "nature" because they are present at birth and determined by inherited genes. Developmental delays due to toxins (such as exposure to lead as a child or exposure to drugs in utero) are examples of "nurture" because the environment can negatively impact learning and intelligence.

In Child Development

The nature vs. nurture debate in child development is apparent when studying language development. Nature theorists believe genetics plays a significant role in language development and that children are born with an instinctive ability that allows them to both learn and produce language.

Nurture theorists would argue that language develops by listening and imitating adults and other children.

In addition, nurture theorists believe people learn by observing the behavior of others. For example, contemporary psychologist Albert Bandura's social learning theory suggests that aggression is learned through observation and imitation.

In Psychology

In psychology, the nature vs. nurture beliefs vary depending on the branch of psychology.

• Biopsychology:  Researchers analyze how the brain, neurotransmitters, and other aspects of our biology influence our behaviors, thoughts, and feelings. emphasizing the role of nature.
• Social psychology: Researchers study how external factors such as peer pressure and social media influence behaviors, emphasizing the importance of nurture.
• Behaviorism: This theory of learning is based on the idea that our actions are shaped by our interactions with our environment.

In Personality Development

Whether nature or nurture plays a bigger role in personality development depends on different personality development theories.

• Behavioral theories: Our personality is a result of the interactions we have with our environment, such as parenting styles, cultural influences, and life experiences.
• Biological theories: Personality is mostly inherited which is demonstrated by a study in the 1990s that concluded identical twins reared apart tend to have more similar personalities than fraternal twins.
• Psychodynamic theories: Personality development involves both genetic predispositions and environmental factors and their interaction is complex.

In Mental Illness

Both nature and nurture can contribute to mental illness development.

For example, at least five mental health disorders are associated with some type of genetic component ( autism ,  attention-deficit hyperactivity disorder (ADHD) ,  bipolar disorder , major depression, and  schizophrenia ).

Other explanations for mental illness are environmental, such as:

• Being exposed to drugs or alcohol in utero 
• Witnessing a traumatic event, leading to post-traumatic stress disorder (PTSD)
• Adverse life events and chronic stress during childhood

In Mental Health Therapy

Mental health treatment can involve both nature and nurture. For example, a therapist may explore life experiences that may have contributed to mental illness development (nurture) as well as family history of mental illness (nature).

At the same time, research indicates that a person's genetic makeup may impact how their body responds to antidepressants. Taking this into consideration is important for finding the right treatment for each individual.

 What Is Nativism (Extreme Nature Position)?

Innatism emphasizes nature's role in shaping our minds and personality traits before birth. Nativism takes this one step further and proposes that all of people's mental and physical characteristics are inherited and predetermined at birth.

In its extreme form, concepts of nativism gave way to the early 20th century's racially-biased eugenics movement. Thankfully, "selective breeding," which is the idea that only certain people should reproduce in order to create chosen characteristics in offspring, and eugenics, arranged breeding, lost momentum during World War II. At that time, the Nazis' ethnic cleansing (killing people based on their ethnic or religious associations) atrocities were exposed.

Philosopher John Locke's tabula rasa theory from 1689 directly opposes the idea that we are born with innate knowledge. "Tabula rasa" means "blank slate" and implies that our minds do not have innate knowledge at birth.

Locke was an empiricist who believed that all the knowledge we gain in life comes from sensory experiences (using their senses to understand the world), education, and day-to-day encounters after being born.

Today, looking at nature vs. nature in black-and-white terms is considered a misguided dichotomy (two-part system). There are so many shades of gray where nature and nurture overlap. It's impossible to tease out how inherited traits and learned behaviors shape someone's unique characteristics or influence how their mind works.

The influences of nature and nurture in psychology are impossible to unravel. For example, imagine someone growing up in a household with an alcoholic parent who has frequent rage attacks. If that child goes on to develop a substance use disorder and has trouble with emotion regulation in adulthood, it's impossible to know precisely how much genetics (nature) or adverse childhood experiences (nurture) affected that individual's personality traits or issues with alcoholism.

Epigenetics Blurs the Line Between Nature and Nurture

"Epigenetics " means "on top of" genetics. It refers to external factors and experiences that turn genes "on" or "off." Epigenetic mechanisms alter DNA's physical structure in utero (in the womb) and across the human lifespan.

Epigenetics blurs the line between nature and nurture because it says that even after birth, our genetic material isn't set in stone; environmental factors can modify genes during one's lifetime. For example, cannabis exposure during critical windows of development can increase someone's risk of neuropsychiatric disease via epigenetic mechanisms.

Nature vs. nurture is a framework used to examine how genetics (nature) and environmental factors (nurture) influence human development and personality traits.

However, nature vs. nurture isn't a black-and-white issue; there are many shades of gray where the influence of nature and nurture overlap. It's impossible to disentangle how nature and nurture overlap; they are inextricably intertwined. In most cases, nature and nurture combine to make us who we are. 

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By Christopher Bergland Christopher Bergland is a retired ultra-endurance athlete turned medical writer and science reporter. 

Nature vs. Nurture

Reviewed by Psychology Today Staff

The expression “nature vs. nurture” describes the question of how much a person's characteristics are formed by either “nature” or “nurture.” “Nature” means innate biological factors (namely genetics ), while “nurture” can refer to upbringing or life experience more generally.

Traditionally, “nature vs. nurture” has been framed as a debate between those who argue for the dominance of one source of influence or the other, but contemporary experts acknowledge that both “nature” and “nurture” play a role in psychological development and interact in complex ways.

• The Meaning of Nature vs. Nurture
• The Nature-vs.-Nurture Debate
• Identifying Genetic and Environmental Factors

The wording of the phrase “nature vs. nurture” makes it seem as though human individuality— personality traits, intelligence , preferences, and other characteristics—must be based on either the genes people are born with or the environment in which they grew up. The reality, as scientists have shown, is more complicated, and both these and other factors can help account for the many ways in which individuals differ from each other.

The words “nature” and “nurture” themselves can be misleading. Today, “ genetics ” and “environment” are frequently used in their place—with one’s environment including a broader range of experiences than just the nurturing received from parents or caregivers. Further, nature and nurture (or genetics and environment) do not simply compete to influence a person, but often interact with each other; “nature and nurture” work together. Finally, individual differences do not entirely come down to a person’s genetic code or developmental environment—to some extent, they emerge due to messiness in the process of development as well.

A person’s biological nature can affect a person’s experience of the environment. For example, a person with a genetic disposition toward a particular trait, such as aggressiveness, may be more likely to have particular life experiences (including, perhaps, receiving negative reactions from parents or others). Or, a person who grows up with an inclination toward warmth and sociability may seek out and elicit more positive social responses from peers. These life experiences could, in turn, reinforce an individual’s initial tendencies. Nurture or life experience more generally may also modify the effects of nature—for example, by expanding or limiting the extent to which a naturally bright child receives encouragement, access to quality education , and opportunities for achievement.

Epigenetics—the science of modifications in how genes are expressed— illustrates the complex interplay between “nature” and “nurture.” An individual’s environment, including factors such as early-life adversity, may result in changes in the way that parts of a person’s genetic code are “read.” While these epigenetic changes do not override the important influence of genes in general, they do constitute additional ways in which that influence is filtered through “nurture” or the environment.

Theorists and researchers have long battled over whether individual traits and abilities are inborn or are instead forged by experiences after birth. The debate has had broad implications: The real or perceived sources of a person’s strengths and vulnerabilities matter for fields such as education, philosophy , psychiatry , and clinical psychology. Today’s consensus—that individual differences result from a combination of inherited and non-genetic factors—strikes a more nuanced middle path between nature- or nurture-focused extremes.

The debate about nature and nurture has roots that stretch back at least thousands of years, to Ancient Greek theorizing about the causes of personality. During the modern era, theories emphasizing the role of either learning and experience or biological nature have risen and fallen in prominence—with genetics gaining increasing acknowledgment as an important (though not exclusive) influence on individual differences in the later 20th century and beyond.

“Nature versus nurture” was used by English scientist Francis Galton. In 1874, he published the book English Men of Science: Their Nature and Nurture , arguing that inherited factors were responsible for intelligence and other characteristics.

Genetic determinism emphasizes the importance of an individual’s nature in development. It is the view that genetics is largely or totally responsible for an individual’s psychological characteristics and behavior. The term “biological determinism” is often used synonymously.

The blank slate (or “tabula rasa”) view of the mind emphasizes the importance of nurture and the environment. Notably described by English philosopher John Locke in the 1600s, it proposed that individuals are born with a mind like an unmarked chalkboard and that its contents are based on experience and learning. In the 20th century, major branches of psychology proposed a primary role for nurture and experience , rather than nature, in development, including Freudian psychoanalysis and behaviorism.

Modern scientific methods have allowed researchers to advance further in understanding the complex relationships between genetics, life experience, and psychological characteristics, including mental health conditions and personality traits. Overall, the findings of contemporary studies underscore that with some exceptions—such as rare diseases caused by mutations in a single gene—no one factor, genetic or environmental, solely determines how a characteristic develops.

Scientists use multiple approaches to estimate how important genetics are for any given trait, but one of the most influential is the twin study. While identical (or monozygotic) twins share the same genetic code, fraternal (or dizygotic) twins share about 50 percent of the same genes, like typical siblings. Scientists are able to estimate the degree to which the variation in a particular trait, like extraversion , is explained by genetics in part by analyzing how similar identical twins are on that trait, compared to fraternal twins. ( These studies do have limitations, and estimates based on one population may not closely reflect all other populations.) 

It’s hard to call either “nature” or “nurture,” genes or the environment, more important to human psychology. The impact of one set of factors or the other depends on the characteristic, with some being more strongly related to one’s genes —for instance, autism appears to be more heritable than depression . But in general, psychological traits are shaped by a balance of interacting genetic and non-genetic influences.

Both genes and environmental factors can contribute to a person developing mental illness. Research finds that a major part of the variation in the risk for psychiatric conditions such as autism spectrum disorder, anxiety disorders, depression, and schizophrenia can be attributed to genetic differences. But not all of that risk is genetic, and life experiences, such as early-life abuse or neglect, may also affect risk of mental illness (and some individuals, based on their genetics, are likely more susceptible to environmental effects than others).

Like other psychological characteristics, personality is partly heritable. Research suggests less than half of the difference between people on measures of personality traits can be attributed to genes (one recent overall estimate is 40 percent). Non-genetic factors appear to be responsible for an equal or greater portion of personality differences between individuals. Some theorize that the social roles people adopt and invest in as they mature are among the more important non-genetic factors in personality development.

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Our cultures shape us in profound ways. The latest research from cultural psychology offers fascinating insights into the nature-nurture interaction.

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Nature and nurture as an enduring tension in the history of psychology.

• Hunter Honeycutt Hunter Honeycutt Bridgewater College, Department of Psychology
• https://doi.org/10.1093/acrefore/9780190236557.013.518
• Published online: 30 September 2019

Nature–nurture is a dichotomous way of thinking about the origins of human (and animal) behavior and development, where “nature” refers to native, inborn, causal factors that function independently of, or prior to, the experiences (“nurture”) of the organism. In psychology during the 19th century, nature-nurture debates were voiced in the language of instinct versus learning. In the first decades of the 20th century, it was widely assumed that that humans and animals entered the world with a fixed set of inborn instincts. But in the 1920s and again in the 1950s, the validity of instinct as a scientific construct was challenged on conceptual and empirical grounds. As a result, most psychologists abandoned using the term instinct but they did not abandon the validity of distinguishing between nature versus nurture. In place of instinct, many psychologists made a semantic shift to using terms like innate knowledge, biological maturation, and/or hereditary/genetic effects on development, all of which extend well into the 21st century. Still, for some psychologists, the earlier critiques of the instinct concept remain just as relevant to these more modern usages.

The tension in nature-nurture debates is commonly eased by claiming that explanations of behavior must involve reference to both nature-based and nurture-based causes. However, for some psychologists there is a growing pressure to see the nature–nurture dichotomy as oversimplifying the development of behavior patterns. The division is seen as both arbitrary and counterproductive. Rather than treat nature and nurture as separable causal factors operating on development, they treat nature-nurture as a distinction between product (nature) versus process (nurture). Thus there has been a longstanding tension about how to define, separate, and balance the effects of nature and nurture.

• nature–nurture
• development
• nativism–empiricism
• innate–learned
• behavioral genetics
• epigenetics

Nature and Nurture in Development

The oldest and most persistent ways to frame explanations about the behavioral and mental development of individuals is to distinguish between two separate sources of developmental causation: (a) intrinsic, preformed, or predetermined causes (“nature”) versus (b) extrinsic, experiential, or environmental causes (“nurture”). Inputs from these two sources are thought to add their own contribution to development (see Figure 1 ).

Figure 1. The traditional view of nature and nurture as separate causes of development. In the traditional view, nature and nurture are treated as independent causal influences that combine during development to generate outcomes. Note that, during development, the effects of nature and nurture (shown in horizontal crossing lines) remain independent so that their effects on outcomes are theoretically separable.

Because some traits seem to derive more from one source than the other, much of the tension associated with the nature–nurture division deals with disagreements about how to balance the roles of nature and nurture in the development of a trait.

Evidence of Nature in Development

Evidence to support the nature–nurture division usually derives from patterns of behavior that suggest a limited role of environmental causation, thus implying some effect of nature by default. Table 1 depicts some common descriptors and conditions used to infer that some preference, knowledge, or skill is nature based.

Table 1. Common Descriptors and Associated Conditions for Inferring the Effects of Nature on Development

It is important to reiterate that nature-based causation (e.g., genetic determination) is inferred from these observations. Such inferences can generate tension because each of the observations listed here can be explained by nurture-based (environmental) factors. Confusion can also arise when evidence of one descriptor (e.g., being hereditary) is erroneously used to justify a different usage (e.g., that the trait is unlearned).

The Origins of Nature Versus Nurture

For much of recorded history, the distinction between nature and nurture was a temporal divide between what a person is innately endowed with at birth, prior to experience (nature), and what happens thereafter (nurture). It was not until the 19th century that the temporal division was transformed into a material division of causal influences (Keller, 2010 ). New views about heredity and Darwinian evolution justified distinguishing between native traits and genetic causes from acquired traits and environmental causes. More so than before, the terms nature and nurture were often juxtaposed in an opposition famously described by Sir Francis Galton ( 1869 ) as that between “nature versus nurture.”

Galton began writing about heredity in the mid-1860s. He believed we would discover laws governing the transmission of mental as well as physical qualities. Galton’s take on mental heredity, however, was forged by his desire to improve the human race in a science he would later call “eugenics.” In the mid- 19th century , British liberals assumed humans were equivalent at birth. Their social reform efforts were geared to enhancing educational opportunities and improving living conditions. Galton, a political conservative, opposed the notion of natural equality, arguing instead that people were inherently different at birth (Cowan, 2016 ), and that these inherited mental and behavioral inequalities were transmitted through lineages like physical qualities. Because Galton opposed the widely held Lamarckian idea that the qualities acquired in one’s lifetime could modify the inherited potential of subsequent generations, he believed long-lasting improvement of the human stock would only come by controlling breeding practices.

To explain the biological mechanisms of inheritance, Galton joined a growing trend in the 1870s to understand inheritance as involving the transmission of (hypothetical) determinative, germinal substances across generations. Foreshadowing a view that would later become scientific orthodoxy, Galton believed these germinal substances to be uninfluenced by the experiences of the organism. His theory of inheritance, however, was speculative. Realizing he was not equipped to fully explicate his theory of biological inheritance, Galton abandoned this line of inquiry by the end of that decade and refocused his efforts on identifying statistical laws of heredity of individual differences (Renwick, 2011 ).

Historians generally agree that Galton was the first to treat nature (as heredity) and nurture (everything else) as separate causal forces (Keller, 2010 ), but the schism gained biological legitimacy through the work of the German cytologist Auguste Weismann in the 1880s. Whereas Galton’s theory was motivated by his political agenda, Weismann was motivated by a scientific, theoretical agenda. Namely, Weismann opposed Lamarckian inheritance and promoted a view of evolution driven almost entirely by natural selection.

Drawing upon contemporary cytological and embryological research, Weismann made the case that the determinative substances found in the germ cells of plants and animals (called the “germ-plasm”) that are transmitted across generations were physically sequestered very early in embryogenesis and remained buffered from the other cells of the body (“somato-plasm”). This so-called, Weismann’s barrier meant that alterations in the soma that develop in the lifetime of the organism through the use or disuse of body parts would not affect the germinal substances transmitted during reproduction (see Winther, 2001 , for review). On this view, Lamarckian-style inheritance of acquired characteristics was not biologically possible.

Galton and Weismann’s influence on the life sciences cannot be overstated. Their work convinced many to draw unusually sharp distinctions between the inherited (nature) and the acquired (nurture). Although their theories were met with much resistance and generated significant tension in the life sciences from cytology to psychology, their efforts helped stage a new epistemic space through which to appreciate Mendel’s soon to be rediscovered breeding studies and usher in genetics (Muller-Wille & Rheinberger, 2012 ).

Ever since, psychology has teetered between nature-biased and nurture-biased positions. With the rise of genetics, the wedge between nature–nurture was deepened in the early to mid- 20th century , creating fields of study that focused exclusively on the effects of either nature or nurture.

The “Middle Ground” Perspective on Nature–Nurture

Twenty-first-century psychology textbooks often state that the nature–nurture debates have been resolved, and the tension relaxed, because we have moved on from emphasizing nature or nurture to appreciating that development necessarily involves both nature and nurture. In this middle-ground position, one asks how nature and nurture interact. For example, how do biological (or genetic) predispositions for behaviors or innate knowledge bias early learning experiences? Or how might environmental factors influence the biologically determined (maturational) unfolding of bodily form and behaviors?

Rejection of the Nature–Nurture Divide

For some, the “middle-ground” resolution is as problematic as “either/or” views and does not resolve a deeper source of tension inherent in the dichotomy. On this view, the nature–nurture divide is neither a legitimate nor a constructive way of thinking about development. Instead, developmental analysis reveals that the terms commonly associated with nature (e.g., innate, genetic, hereditary, or instinctual) and nurture (environmental or learned) are so entwined and confounded (and often arbitrary) that their independent effects cannot be meaningfully discussed. The nature–nurture division oversimplifies developmental processes, takes too much for granted, and ultimately hinders scientific progress. Thus not only is there a lingering tension about how to balance the effects of nature and nurture in the middle-ground view, but there is also a growing tension to move beyond the dichotomous nature–nurture framework.

Nativism in Behavior: Instincts

Definitions of instinct can vary tremendously, but many contrast (a) instinct with reason (or intellect, thought, will), which is related to but separable from contrasting (b) instinct with learning (or experience or habit).

Instinct in the Age of Enlightenment

Early usages of the instinct concept, following Aristotle, treated instinct as a mental, estimative faculty ( vis aestimativa or aestimativa naturalis ) in humans and animals that allowed for the judgments of objects in the world (e.g., seeing a predator) to be deemed beneficial or harmful in a way that transcends immediate sensory experience but does not involve the use of reason (Diamond, 1971 ). In many of the early usages, the “natural instinct” of animals even included subrational forms of learning.

The modern usage of instincts as unlearned behaviors took shape in the 17th century . By that point it was widely believed that nature or God had implanted in animals and humans innate behaviors and predispositions (“instincts”) to promote the survival of the individual and the propagation of the species. Disagreements arose as to whether instincts derived from innate mental images or were mindlessly and mechanically (physiologically) generated from innately specified bodily organization (Richards, 1987 ).

Anti-Instinct Movement in the Age of Enlightenment

Challenges to the instinct concept can be found in the 16th century (see Diamond, 1971 ), but they were most fully developed by empiricist philosophers of the French Sensationalist tradition in the 18th century (Richards, 1987 ). Sensationalists asserted that animals behaved rationally and all of the so-called instincts displayed by animals could be seen as intelligently acquired habits.

For Sensationalists, instincts, as traditionally understood, did not exist. Species-specificity in behavior patterns could be explained by commonalities in physiological organization, needs, and environmental conditions. Even those instinctual behaviors seen at birth (e.g., that newly hatched chicks peck and eat grain) might eventually be explained by the animal’s prenatal experiences. Erasmus Darwin ( 1731–1802 ), for example, speculated that the movements and swallowing experiences in ovo could account for the pecking and eating of grain by young chicks. The anti-instinct sentiment was clearly expressed by the Sensationalist Jean Antoine Guer ( 1713–1764 ), who warned that instinct was an “infantile idea” that could only be held by those who are ignorant of philosophy, that traditional appeals to instincts in animals not only explained nothing but served to hinder scientific explanations, and that nothing could be more superficial than to explain behavior than appealing to so-called instincts (Richards, 1987 ).

The traditional instinct concept survived. For most people, the complex, adaptive, species-specific behaviors displayed by naïve animals (e.g., caterpillars building cocoons; infant suckling behaviors) appeared to be predetermined and unlearned. Arguably as important, however, was the resistance to the theological implications of Sensationalist philosophy.

One of the strongest reactions to Sensationalism was put forward in Germany by Herman Samuel Reimarus ( 1694–1768 ). As a natural theologian, Reimarus, sought evidence of a God in the natural world, and the species-specific, complex, and adaptive instincts of animals seemed to stand as the best evidence of God’s work. More so than any other, Reimarus extensively catalogued instincts in humans and animals. Rather than treat instincts as behaviors, he defined instincts as natural impulses (inner drives) to act that were expressed perfectly, without reflection or practice, and served adaptive goals (Richards, 1987 ). He even proposed instincts for learning, a proposal that would resurface in the mid- 20th century , as would his drive theory of instinct (Jaynes & Woodward, 1974 ).

Partly as a result of Reimarus’ efforts, the instinct concept survived going into the 19th century . But many issues surrounding the instinct concept were left unsettled. How do instincts differ from reflexive behaviors? What role does learning play in the expression of instincts, if any? Do humans have more or fewer instincts than animals? These questions would persist well into the first decades of the 20th century and ultimately fuel another anti-instinct movement.

Instinct in the 19th Century

In the 19th century , the tension about the nature and nurture of instincts in the lifetime of animals led to debates about the nature and nurture of instincts across generations . These debates dealt with whether instincts should be viewed as “inherited habits” from previous generations or whether they result from the natural selection. Debating the relative roles of neo-Lamarckian use-inheritance versus neo-Darwinian natural selection in the transmutation of species became a significant source of tension in the latter half of the 19th century . Although the neo-Lamarckian notion of instincts as being inherited habits was rejected in the 20th century , it has resurged in recent years (e.g., see Robinson & Barron, 2017 ).

Darwinian evolutionary theory required drawing distinctions between native and acquired behaviors, and, perhaps more so than before, behaviors were categorized along a continuum from the purely instinctive (unlearned), to the partially instinctive (requiring some learning), to the purely learned. Still, it was widely assumed that a purely instinctive response would be modified by experience after its first occurrence. As a result, instinct and habit were very much entangled in the lifetime of the organism. The notion of instincts as fixed and unmodifiable would not be widely advanced until after the rise of Weismann’s germ-plasm theory in the late 19thcentury .

Given their importance in evolutionary theory, there was greater interest in more objectively identifying pure instincts beyond anecdotal reports. Some of the most compelling evidence was reported by Douglas Spalding ( 1844–1877 ) in the early 1870s (see Gray, 1967 ). Spalding documented numerous instances of how naïve animals showed coordinated, seemingly adaptive responses (e.g., hiding) to objects (e.g., sight of predators) upon their first encounter, and he helped pioneer the use of the deprivation experiment to identify instinctive behaviors. This technique involved selectively depriving young animals of seemingly critical learning experiences or sensory stimulation. Should animals display some species-typical action following deprivation, then, presumably, the behavior could be labeled as unlearned or innate. In all, these studies seemed to show that animals displayed numerous adaptive responses at the very start, prior to any relevant experience. In a variety of ways, Spalding’s work anticipated 20th-century studies of innate behavior. Not only would the deprivation experiment be used as the primary means of detecting native tendencies by European zoologists and ethologists, but Spalding also showed evidence of what would later be called imprinting, critical period effects and evidence of behavioral maturation.

Reports of pure instinct did not go unchallenged. Lloyd Morgan ( 1896 ) questioned the accuracy of these reports in his own experimental work with young animals. In some cases, he failed to replicate the results and in other cases he found that instinctive behaviors were not as finely tuned to objects in the environment as had been claimed. Morgan’s research pointed to taking greater precision in identifying learned and instinctive components of behavior, but, like most at the turn of the 20th century , he did not question that animal behavior involved both learned and instinctive elements.

A focus on instinctive behaviors intensified in the 1890s as Weismann’s germ-plasm theory grew in popularity. More so than before, a sharp distinction was drawn between native and acquired characteristics, including behavior (Johnston, 1995 ). Although some psychologists continued to maintain neo-Lamarckian notions, most German (Burnham, 1972 ) and American (Cravens & Burnham, 1971 ) psychologists were quick to adopt Weismann’s theory. They envisioned a new natural science of psychology that would experimentally identify the germinally determined, invariable set of native psychological traits in species and their underlying physiological (neural) basis. However, whereas English-speaking psychologists tended to focus on how this view impacted our understanding of social institutions and its social implications, German psychologists were more interested in the longstanding philosophical implications of Weismann’s doctrine as it related to the differences (if any) between man and beast (Burnham, 1972 ).

Some anthropologists and sociologists, however, interpreted Weismann’s theory quite differently and used it elevate sociology as its own scientific discipline. In the 1890s, the French sociologist Emil Durkheim, for example, interpreted Weismann’s germinal determinants as a generic force on human behavior that influenced the development of general predispositions that are molded by the circumstances of life (Meloni, 2016 ). American anthropologists reached similar conclusions in the early 20th century (Cravens & Burnham, 1971 ). Because Weismann’s theory divorced biological inheritance from social inheritance, and because heredity was treated as a generic force, sociologists felt free to study social (eventually, “cultural”) phenomena without reference to biological or psychological concerns.

Anti-Instinct Movement in the 1920s

Despite their differences, in the first two decades of the 20th century both psychologists and sociologists generally assumed that humans and animals had some native tendencies or instincts. Concerns were even voiced that instinct had not received enough attention in psychology. Disagreements about instincts continued to focus on (the now centuries old debates of) how to conceptualize them. Were they complex reflexes, impulses, or motives to act, or should instinct be a mental faculty (like intuition), separate from reasoning and reflex (Herrnstein, 1972 )?

In America, the instinct concept came under fire following a brief paper in 1919 by Knight Dunlap titled “Are There Any Instincts?” His primary concern dealt with teleological definitions of instincts in which an instinct referred to all the activities involved in obtaining some end-state (e.g., instincts of crying, playing, feeding, reproduction, war, curiosity, or pugnacity). Defined in this way, human instincts were simply labels for human activities, but how these activities were defined was arbitrarily imposed by the researchers. Is feeding, for instance, an instinct, or is it composed of more basic instincts (like chewing and swallowing)? The arbitrariness of classifying human behavior had led to tremendous inconsistencies and confusion among psychologists.

Not all of the challenges to instinct dealt with its teleological usage. Some of the strongest criticisms were voiced by Zing-Yang Kuo throughout the 1920s. Kuo was a Chinese animal psychologist who studied under Charles Tolman at the University of California, Berkeley. Although Kuo’s attacks on instinct changed throughout the 1920s (see Honeycutt, 2011 ), he ultimately argued that all behaviors develop in experience-dependent ways and that appeals to instinct were statements of ignorance about how behaviors develop. Like Dunlap, he warned that instincts were labels with no explanatory value. To illustrate, after returning to China, he showed how the so-called rodent-killing instinct in cats often cited by instinct theorists is not found in kittens that are reared with rodents (Kuo, 1930 ). These kittens, instead, became attached to the rodents, and they resisted attempts to train rodent-killing. Echoing the point made by Guer, Kuo claimed that appeals to instinct served to stunt scientific inquiry into the developmental origins of behavior.

But Kuo did not just challenge the instinct concept. He also argued against labeling behaviors as “learned.” After all, whether an animal “learns” depends on the surrounding environmental conditions, the physiological and developmental status of the animal, and, especially, the developmental (or experiential) history of that animal. Understanding learning also required developmental analysis. Thus Kuo targeted the basic distinction between nature and nurture, and he was not alone in doing so (e.g., see Carmichael, 1925 ), but his call to reject it did not spread to mainstream American psychologists.

By the 1930s, the term instinct had fallen into disrepute in psychology, but experimental psychologists (including behaviorists) remained committed to a separation of native from acquired traits. If anything, the dividing line between native and acquired behaviors became more sharply drawn than before (Logan & Johnston, 2007 ). For some psychologists, instinct was simply rebranded in the less contentious (but still problematic) language of biological drives or motives (Herrnstein, 1972 ). Many other psychologists simply turned to describing native traits as due to “maturation” and/or “heredity” rather than “instinct.”

Fixed Action Patterns

The hereditarian instinct concept received a reboot in Europe in the 1930s with the rise of ethology led by Konrad Lorenz, Niko Tinbergen, and others. Just as animals inherit organs that perform specific functions, ethologists believed animals inherit behaviors that evolved to serve adaptive functions as well. Instincts were described as unlearned (inherited), blind, stereotyped, adaptive, fixed action patterns, impervious to change that are initiated (released) by specific stimuli in the environment.

Ethologists in 1930s and 1940s were united under the banner of innateness. They were increasingly critical of the trend by American psychologists (i.e., behaviorists) to focus on studying on how a limited number of domesticated species (e.g., white rat) responded to training in artificial settings (Burkhardt, 2005 ). Ethologists instead began with rich descriptions of animal behavior in more natural environments along with detailed analyses of the stimulus conditions that released the fixed action patterns. To test whether behavioral components were innate, ethologists relied primarily on the deprivation experiment popularized by Spalding in the 19th century . Using these methods (and others), ethologists identified numerous fascinating examples of instinctive behaviors, which captured mainstream attention.

In the early 1950s, shortly after ethology had gained professional status (Burkhardt, 2005 ), a series of challenges regarding instinct and innateness were put forth by a small cadre of North American behavioral scientists (e.g., T. C. Schneirla, Donald Hebb, Frank Beach). Arguably the most influential critique was voiced by comparative psychologist Daniel Lehrman ( 1953 ), who presented a detailed and damning critique of deprivation experiments on empirical and logical grounds. Lehrman explained that deprivation experiments isolate the animal from some but not all experiences. Thus deprivation experiments simply change what an animal experiences rather than eliminating experience altogether, and so they cannot possibly determine whether a behavior is innate (independent of experience). Instead, these experiments show what environmental conditions do not matter in the development of a behavior but do not speak to what conditions do matter .

Lehrman went on to argue that the whole endeavor to identify instinctive or innate behavior was misguided from the start. All behavior, according to Lehrman, develops from a history of interactions between an organism and its environment. If a behavior is found to develop in the absence of certain experiences, the researcher should not stop and label it as innate. Rather, research should continue to identify the conditions under which the behavior comes about. In line with Kuo, Lehrman repeated the warning that to label something as instinctive (or inherited or maturational) is a statement of ignorance about how that behavior develops and does more to stunt than promote research.

Lehrman’s critique created significant turmoil among ethologists. As a result, ethologists took greater care in using the term innate , and it led to new attempts to synthesize or re-envision learning and instinct .

Some of these attempts focused on an increased role for learning and experience in the ontogeny of species-typical behaviors. These efforts spawned significant cross-talk between ethologists and comparative psychologists to more thoroughly investigate behavioral development under natural conditions. Traditional appeals to instinct and learning (as classical and operant conditioning) were both found to be inadequate for explaining animal behavior. In their stead, these researchers focused more closely on how anatomical, physiological, experiential, and environmental conditions influenced the development of species-typical behaviors.

Tinbergen ( 1963 ) was among those ethologists who urged for greater developmental analysis of species-typical behaviors, and he included it as one of his four problems in the biological study of organisms, along with causation (mechanism), survival value (function), and evolution. Of these four problems, Tinbergen believed ethologists were especially well suited to study survival value, which he felt had been seriously neglected (Burkhardt, 2005 ).

The questions of survival value coupled with models of population genetics would gain significant momentum in the 1960s and 1970s in England and the United States with the rise of behavioral ecology and sociobiology (Griffiths, 2008 ). But because these new fields seemed to promote some kind of genetic determinism in behavioral development, they were met with much resistance and reignited a new round of nature–nurture debates in the 1970s (see Segerstrale, 2000 ).

However, not all ethologists abandoned the instinct concept. Lorenz, in particular, continued to defend the division between nature and nurture. Rather than speaking of native and acquired behaviors, Lorenz later spoke of two different sources of information for behavior (innate/genetic vs. acquired/environmental), which was more a subtle shift in language than it was an actual change in theory, as Lehrman later pointed out.

Some ethologists followed Lorenz’s lead and continued to maintain more of a traditional delineation between instinct and learning. Their alternative synthesis viewed learning as instinctive (Gould & Marler, 1987 ). They proposed that animals have evolved domain-specific “instincts to learn” that result from the its genetic predispositions and innate knowledge. To support the idea of instincts for learning, ethologists pointed to traditional ethological findings (on imprinting and birdsong learning), but they also drew from the growing body of work in experimental psychology that seemed to indicate certain types of biological effects on learning.

Biological Constraints and Preparedness

While ethology was spreading in Europe in the 1930s–1950s, behaviorism reigned in the United States. Just as ethologists were confronted with including a greater role of nurture in their studies, behaviorists were challenged to consider a greater role of nature.

Behaviorists assumed there to be some behavioral innateness (e.g., fixed action patterns, unconditioned reflexes, primary reinforcers and drives). But because behaviorists focused on learning, they tended to study animals in laboratory settings using biologically (or ecologically) irrelevant stimuli and responses to minimize any role of instinct (Johnston, 1981 ). It was widely assumed that these studies would identify general laws of learning that applied to all species regardless of the specific cues, reinforcers, and responses involved.

Challenges to the generality assumption began to accumulate in the 1960s. Some studies pointed to failures that occurred during conditioning procedures. Breland and Breland ( 1961 ), for example, reported that some complex behaviors formed through operant conditioning would eventually become “displaced” by conditioned fixed action patterns in a phenomenon they called “instinctive drift.” Studies of taste-aversion learning (e.g., Garcia & Koelling, 1966 ) also reported the failure of rats to associate certain events (e.g., flavors with shock or audiovisual stimuli with toxicosis).

Other studies were pointing to enhanced learning. In particular, it was found that rats could form strong conditioned taste aversions after only a single pairing between a novel flavor and illness. (This rapid “one trial learning” was a major focus in the research from Niko Tinbergen’s ethological laboratory.) Animals, it seemed, had evolved innate predispositions to form (or not form) certain associations.

In humans, studies of biological constraints on learning were mostly limited to fear conditioning. Evidence indicated that humans conditioned differently to (biologically or evolutionarily) fear-relevant stimuli like pictures of spiders or snakes than to fear-irrelevant stimuli like pictures of mushrooms or flowers (Ohman, Fredrikson, Hugdahl, & Rimmö, 1976 ).

These findings and others were treated as a major problem in learning theory and led to calls for a new framework to study learning from a more biologically oriented perspective that integrated the evolutionary history and innate predispositions of the species. These predispositions were described as biological “constraints” on, “preparedness,” or “adaptive specializations” for learning, all of which were consistent with the “instincts to learn” framework proposed by ethologists.

By the 1980s it was becoming clear that the biological preparedness/constraint view of learning suffered some limitations. For example, what constraints count as “biological” was questioned. It was well established that there were general constraints on learning associated with the intensity, novelty, and timing of stimuli. But, arbitrarily it seemed, these constraints were not classified as “biological” (Domjan & Galef, 1983 ). Other studies of “biological constraints” found that 5- and 10-day old rats readily learned to associated a flavor with shock (unlike in adults), but (like in adults) such conditioning was not found in 15-day-old rats (Hoffman & Spear, 1988 ). In other words, the constraint on learning was not present in young rats but developed later in life, suggesting a possible role of experience in bringing about the adult-like pattern.

Attempts to synthesize these alternatives led to numerous calls for more ecologically oriented approaches to learning not unlike the synthesis between ethology and comparative psychology in the 1960s. All ecological approaches to learning proposed that learning should be studied in the context of “natural” (recurrent and species-typical) problems that animals encounter (and have evolved to encounter) using ecologically meaningful stimuli and responses. Some argued (e.g., Johnston, 1981 ) that studies of learning should take place within the larger context of studying how animals develop and adapt to their surround. Others (Domjan & Galef, 1983 ) pointed to more of a comparative approach in studying animal learning in line with behavioral ecology that takes into account how learning can be influenced by the possible selective pressures faced by each species. Still, how to synthesize biological constraints (and evolutionary explanations) on learning with a general process approach remains a source of tension in experimental psychology.

Nativism in Mind: Innate Ideas

Nativism and empiricism in philosophy.

In the philosophy of mind, nature–nurture debates are voiced as debates between nativists and empiricists. Nativism is a philosophical position that holds that our minds have some innate (a priori to experience) knowledge, concepts, or structure at the very start of life. Empiricism, in contrast, holds that all knowledge derives from our experiences in the world.

However, rarely (if ever) were there pure nativist or empiricist positions, but the positions bespeak a persistent tension. Empiricists tended to eschew innateness and promote a view of the mental content that is built by general mechanisms (e.g., association) operating on sensory experiences, whereas nativists tend to promote a view of mind that contains domain-specific, innate processes and/or content (Simpson, Carruthers, Laurence, & Stich, 2005 ). Although the tension about mental innateness would loosen as empiricism gained prominence in philosophy and science, the strain never went away and would intensify again in the 20th century .

Nativism in 20th Century Psychology: The Case of Language Development

In the first half of the 20th century , psychologists generally assumed that knowledge was gained or constructed through experience with the world. This is not to say that psychologists did not assume some innate knowledge. The Swiss psychologist Jean Piaget, for example, believed infants enter the world with some innate knowledge structures, particularly as they relate to early sensory and motor functioning (see Piaget, 1971 ). But the bulk of his work dealt with the construction of conceptual knowledge as children adapt to their worlds. By and large, there were no research programs in psychology that sought to identify innate factors in human knowledge and cognition until the 1950s (Samet & Zaitchick, 2017 )

An interest in psychological nativism was instigated in large part by Noam Chomsky’s ( 1959 ) critique of B. F. Skinner’s book on language. To explain the complexity of language, he argued, we must view language as the knowledge and application of grammatical rules. He went on to claim that the acquisition of these rules could not be attributed to any general-purpose, learning process (e.g., reinforcement). Indeed, language acquisition occurs despite very little explicit instruction. Moreover, language is special in terms of its complexity, ease, and speed of acquisition by children and in its uniqueness to humans. Instead, he claimed that our minds innately contain some language-specific knowledge that kick-starts and promotes language acquisition. He later claimed this knowledge can be considered some sort of specialized mental faculty or module he called the “language acquisition device” (Chomsky, 1965 ) or what Pinker ( 1995 ) later called the “language instinct.”

To support the idea of linguistic nativism, Chomsky and others appealed to the poverty of the stimulus argument. In short, this argument holds that our experiences in life are insufficient to explain our knowledge and abilities. When applied to language acquisition, this argument holds children’s knowledge of language (grammar) goes far beyond the limited, and sometimes broken, linguistic events that children directly encounter. Additional evidence for nativism drew upon the apparent maturational quality of language development. Despite wide variations in languages and child-rearing practices across the world, the major milestones in language development appear to unfold in children in a universal sequence and timeline, and some evidence suggested a critical period for language acquisition.

Nativist claims about language sparked intense rebuttals by empiricist-minded psychologists and philosophers. Some of these retorts tackled the logical limitations of the poverty of stimulus argument. Others pointed to the importance of learning and social interaction in driving language development, and still others showed that language (grammatical knowledge) may not be uniquely human (see Tomasello, 1995 , for review). Nativists, in due course, provided their own rebuttals to these challenges, creating a persistent tension in psychology.

Extending Nativism Beyond Language Development

In the decades that followed, nativist arguments expanded beyond language to include cognitive domains that dealt with understanding the physical, psychological, and social worlds. Developmental psychologists were finding that infants appeared to be much more knowledgeable in cognitive tasks (e.g., on understanding object permanence) and skillful (e.g., in imitating others) than had previously been thought, and at much younger ages. Infants also showed a variety of perceptual biases (e.g., preference for face-like stimuli over equally complex non-face-like stimuli) from very early on. Following the standard poverty of the stimulus argument, these findings were taken as evidence that infants enter the world with some sort of primitive, innate, representational knowledge (or domain-specific neural mechanisms) that constrains and promotes subsequent cognitive development. The nature of this knowledge (e.g., as theories or as core knowledge), however, continues to be debated (Spelke & Kinzler, 2007 ).

Empiricist-minded developmental psychologists responded by demonstrating shortcomings in the research used to support nativist claims. For example, in studies of infants’ object knowledge, the behavior of infants (looking time) in nativist studies could be attributed to relatively simple perceptual processes rather than to the infants’ conceptual knowledge (Heyes, 2014 ). Likewise, reports of human neonatal imitation not only suffered from failures to replicate but could be explained by simpler mechanisms (e.g., arousal) than true imitation (Jones, 2017 ). Finally, studies of perceptual preferences found in young infants, like newborn preferences for face-like stimuli, may not be specific preferences for faces per se but instead may reflect simpler, nonspecific perceptual biases (e.g., preferences for top-heavy visual configurations and congruency; Simion & Di Giorgio, 2015 ).

Other arguments from empiricist-minded developmental psychologists focused on the larger rationale for inferring innateness. Even if it is conceded that young infants, like two-month-olds, or even two-day-olds, display signs of conceptual knowledge, there is no good evidence to presume the knowledge is innate. Their knowledgeable behaviors could still be seen as resulting from their experiences (many of which may be nonobvious to researchers) leading up to the age of testing (Spencer et al., 2009 ).

In the 21st century , there is still no consensus about the reality, extensiveness, or quality of mental innateness. If there is innate knowledge, can experience add new knowledge or only expand the initial knowledge? Can the doctrine of innate knowledge be falsified? There are no agreed-upon answers to these questions. The recurring arguments for and against mental nativism continue to confound developmental psychologists.

Maturation Theory

The emergence of bodily changes and basic behavioral skills sometimes occurs in an invariant, predictable, and orderly sequence in a species despite wide variations in rearing conditions. These observations are often attributed to the operation of an inferred, internally driven, maturational process. Indeed, 21st-century textbooks in psychology commonly associate “nature” with “maturation,” where maturation is defined as the predetermined unfolding of the individual from a biological or genetic blueprint. Environmental factors play a necessary, but fundamentally supportive, role in the unfolding of form.

Preformationism Versus Epigenesis in the Generation of Form

The embryological generation of bodily form was debated in antiquity but received renewed interest in the 17th century . Following Aristotle, some claimed that embryological development involved “epigenesis,” defined as the successive emergence of form from a formless state. Epigenesists, however, struggled to explain what orchestrated development without appealing to Aristotelean souls. Attempts were made to invoke to natural causes like physical and chemical forces, but, despite their best efforts, the epigenesists were forced to appeal to the power of presumed, quasi-mystical, vitalistic forces (entelechies) that directed development.

The primary alternative to epigenesis was “preformationism,” which held that development involved the growth of pre-existing form from a tiny miniature (homunculus) that formed immediately after conception or was preformed in the egg or sperm. Although it seems reasonable to guess that the invention and widespread use of the microscope would immediately lay to rest any claim of homuncular preformationism, this was not the case. To the contrary, some early microscopists claimed to see signs of miniature organisms in sperm or eggs, and failures to find these miniatures were explained away (e.g., the homunculus was transparent or deflated to the point of being unrecognizable). But as microscopes improved and more detailed observations of embryological development were reported in the late 18th and 19th centuries , homuncular preformationism was finally refuted.

From Preformationism to Predeterminism

Despite the rejection of homuncular preformationism, preformationist appeals can be found throughout the 19th century . One of the most popular preformationist theories of embryological development was put forth by Ernst Haeckel in the 1860s (Gottlieb, 1992 ). He promoted a recapitulation theory (not original to Haeckel) that maintained that the development of the individual embryo passes through all the ancestral forms of its species. Ontogeny was thought to be a rapid, condensed replay of phylogeny. Indeed, for Haeckel, phylogenesis was the mechanical cause of ontogenesis. The phylogenetic evolution of the species created the maturational unfolding of embryonic form. Exactly how this unfolding takes place was less important than its phylogenetic basis.

Most embryologists were not impressed with recapitulation theory. After all, the great embryologist Karl Ernst von Baer ( 1792–1876 ) had refuted strict recapitulation decades earlier. Instead, there was greater interest in how best to explain the mechanical causes of development ushering in a new “experimental embryology.” Many experimental embryologists followed the earlier epigenesists by discussing vitalistic forces operating on the unorganized zygote. But it soon became clear that the zygote was structured, and many people believed the zygote contained special (unknown) substances that specified development. Epigenesis-minded experimental embryologists soon warned that the old homuncular preformationism was being transformed into a new predetermined preformationism.

As a result, the debates between preformationism and epigenesis were reignited in experimental embryology, but the focus of these debates shifted to the various roles of nature and nurture during development. More specifically, research focused on the extent to which early cellular differentiation was predetermined by factors internal to cells like chromosomes or cytoplasm (preformationism, nature) or involved factors (e.g., location) outside of the cell (epigenesis, nurture). The former emphasized reductionism and developmental programming, whereas the latter emphasized some sort of holistic, regulatory system responsive to internal and external conditions. The tension between viewing development as predetermined or “epigenetic” persists into the 21st century .

Preformationism gained momentum in the 20th century following the rediscovery of Mendel’s studies of heredity and the rapid rise of genetics, but not because of embryological research on the causes of early differentiation. Instead, preformationism prevailed because it seemed embryological research on the mechanisms of development could be ignored in studies of hereditary patterns.

The initial split between heredity and development can be found in Galton’s speculations but is usually attributed to Weismann’s germ-plasm theory. Weismann’s barrier seemed to posit that the germinal determinants present at conception would be the same, unaltered determinants transmitted during reproduction. This position, later dubbed as “Weismannism,” was ironically not one promoted by Weismann. Like nearly all theorists in the 19th century , he viewed the origins of variation and heredity as developmental phenomena (Amundson, 2005 ), and he claimed that the germ-plasm could be directly modified in the lifetime of the organism by environmental (e.g., climactic and dietary) conditions (Winther, 2001 ). Still, Weismann’s theory treated development as a largely predetermined affair driven by inherited, germinal determinants buffered from most developmental events. As such, it helped set the stage for a more formal divorce between heredity and development with the rise of Mendelism in the early 20th century .

Mendel’s theory of heredity was exceptional in how it split development from heredity (Amundson, 2005 ). More so than in Weismann’s theory, Mendel’s theory assumed that the internal factors that determine form and are transmitted across generations remain unaltered in the lifetime of the organism. To predict offspring outcomes, one need only know the combination of internal factors present at conception and their dominance relations. Exactly how these internal factors determined form could be disregarded. The laws of hereditary transmission of the internal factors (e.g., segregation) did not depend on the development or experiences of the organism or the experiences the organism’s ancestors. Thus the experimental study of heredity (i.e., breeding) could proceed without reference to ancestral records or embryological concerns (Amundson, 2000 ). By the mid-1920s, the Mendelian factors (now commonly called “genes”) were found to be structurally arranged on chromosomes, and the empirical study of heredity (transmission genetics) was officially divorced from studies of development.

The splitting of heredity and development found in Mendel’s and Weismann’s work met with much resistance. Neo-Lamarckian scientists, especially in the United States (Cook, 1999 ) and France (Loison, 2011 ), sought unsuccessfully to experimentally demonstrate the inheritance of acquired characteristics into the 1930s.

In Germany during the 1920s and 1930s, resistance to Mendelism dealt with the chromosomal view of Mendelian heredity championed by American geneticists who were narrowly focused on studying transmission genetics at the expense of developmental genetics. German biologists, in contrast, were much more interested in the broader roles of genes in development (and evolution). In trying to understand how genes influence development, particularly of traits of interest to embryologists, they found the Mendelian theory to be lacking. In the decades between the world wars, German biologists proposed various expanded views of heredity that included some form of cytoplasmic inheritance (Harwood, 1985 ).

Embryologists resisted the preformationist view of development throughout the early to mid- 20th century , often maintaining no divide between heredity and development, but their objections were overshadowed by genetics and its eventual synthesis with evolutionary theory. Consequently, embryological development was treated by geneticists and evolutionary biologists as a predetermined, maturational process driven by internal, “genetic” factors buffered from environmental influence.

Maturation Theory in Psychology

Maturation theory was applied to behavioral development in the 19th century in the application of Haeckel’s recapitulation theory. Some psychologists believed that the mental growth of children recapitulated the history of the human race (from savage brute to civilized human). With this in mind, many people began to more carefully document child development. Recapitulationist notions were found in the ideas of many notable psychologists in the 19th and early 20th centuries (e.g., G. S. Hall), and, as such, the concept played an important role in the origins of developmental psychology (Koops, 2015 ). But for present purposes what is most important is that children’s mental and behavioral development was thought to unfold via a predetermined, maturational process.

With the growth of genetics, maturational explanations were increasingly invoked to explain nearly all native and hereditary traits. As the instinct concept lost value in the 1920s, maturation theory gained currency, although the shift was largely a matter of semantics. For many psychologists, the language simply shifted from “instinct versus learning” to “maturation versus practice/experience” (Witty & Lehman, 1933 ).

Initial lines of evidence for maturational explanations of behavior were often the same as those that justified instinct and native traits, but new embryological research presented in the mid-1920s converged to show support for strict maturational explanations of behavioral development. In these experiments (see Wyman, 2005 , for review), spanning multiple laboratories, amphibians (salamanders and frogs) were exposed to drugs that acted as anesthetics and/or paralytics throughout the early stages of development, thus reducing sensory experience and/or motor practice. Despite the reduced sensory experiences and being unable to move, these animals showed no delays in the onset of motor development once the drugs wore off.

This maturational account of motor development in amphibians fit well with contemporaneous studies of motor development in humans. The orderly, invariant, and predictable (age-related) sequential appearance of motor skills documented in infants reared under different circumstances (in different countries and across different decades) was seen as strong evidence for a maturational account. Additional evidence was reported by Arnold Gessell and Myrtle McGraw, who independently presented evidence in the 1920s to show that the pace and sequence of motor development in infancy were not altered by special training experiences. Although the theories of these maturation theorists were more sophisticated when applied to cognitive development, their work promoted a view in which development was primarily driven by neural maturation rather than experience (Thelen, 2000 ).

Critical and Sensitive Periods

As the maturation account of behavioral development gained ground, it became clear that environmental input played a more informative role than had previously been thought. Environmental factors were found to either disrupt or induce maturational changes at specific times during development. Embryological research suggested that there were well-delineated time periods of heightened sensitivity in which specific experimental manipulations (e.g., tissue transplantations) could induce irreversible developmental changes, but the same manipulation would have no effect outside of that critical period.

In the 1950s–1960s a flurry of critical period effects were reported in birds and mammals across a range of behaviors including imprinting, attachment, socialization, sensory development, bird song learning, and language development (Michel & Tyler, 2005 ). Even though these findings highlighted an important role of experience in behavioral development, evidence of critical periods was usually taken to imply some rigid form of biological determinism (Oyama, 1979 ).

As additional studies were conducted on critical period effects, it became clear that many of the reported effects were more gradual, variable, experience-dependent, and not necessarily as reversible as was previously assumed. In light of these reports, there was a push in the 1970s (e.g., Connolly, 1972 ) to substitute “sensitive period” for “critical period” to avoid the predeterminist connotations associated with the latter and to better appreciate that these periods simply describe (not explain) certain temporal aspects of behavioral development. As a result, a consensus emerged that behaviors should not be attributed to “time” or “age” but to the developmental history and status of the animal under investigation (Michel & Tyler, 2005 ).

Heredity and Genetics

In the decades leading up to and following the start of the 20th century , it was widely assumed that many psychological traits (not just instincts) were inherited or “due to heredity,” although the underlying mechanisms were unknown. Differences in intelligence, personality, and criminality within and between races and sexes were largely assumed to be hereditary and unalterable by environmental intervention (Gould, 1996 ). The evidence to support these views in humans was often derived from statistical analyses of how various traits tended to run in families. But all too frequently, explanations of data were clouded by pre-existing, hereditarian assumptions.

Human Behavioral Genetics

The statistical study of inherited human (physical, mental, and behavioral) differences was pioneered by Galton ( 1869 ). Although at times Galton wrote that nature and nurture were so intertwined as to be inseparable, he nevertheless devised statistical methods to separate their effects. In the 1860s and 1870s, Galton published reports purporting to show how similarities in intellect (genius, talent, character, and eminence) in European lineages appeared to be a function of degree of relatedness. Galton considered, but dismissed, environmental explanations of his data, leading him to confirm his belief that nature was stronger than nurture.

Galton also introduced the use of twin studies to tease apart the relative impact of nature versus nurture, but the twin method he used was markedly different from later twin studies used by behavioral geneticists. Galton tracked the life history of twins who were judged to be very similar or very dissimilar near birth (i.e., by nature) to test the power of various postnatal environments (nurture) that might make them more or less similar over time. Here again, Galton concluded that nature overpowers nurture.

Similar pedigree (e.g., the Kallikak study; see Zenderland, 2001 ) and twin studies appeared in the early 1900s, but the first adoption study and the modern twin method (which compares monozygotic to dizygotic twin pairs) did not appear until the 1920s (Rende, Plomin, & Vandenberg, 1990 ). These reports led to a flurry of additional work on the inheritance of mental and behavioral traits over the next decade.

Behavioral genetic research peaked in the 1930s but rapidly lost prominence due in large part to its association with the eugenics movement (spearheaded by Galton) but also because of the rise and eventual hegemony of behaviorism and the social sciences in the United States. Behavioral genetics resurged in the 1960s with the rising tide of nativism in psychology, and returned to its 1930s-level prominence in the 1970s (McGue & Gottesman, 2015 ).

The resurgence brought with a new statistical tool: the heritability statistic. The origins of heritability trace back to early attempts to synthesize Mendelian genetics with biometrics by Ronald Fisher and others. This synthesis ushered in a new field of quantitative genetics and it marked a new way of thinking about nature and nurture. The shift was to no longer think about nature and nurture as causes of traits in individuals but as causes of variation in traits between populations of individuals. Eventually, heritability came to refer to the amount of variance in a population sample that could be statistically attributed to genetic variation in that sample. Kinship (especially twin) studies provided seemingly straightforward ways of partitioning variation in population trait attributes into genetic versus environmental sources.

Into the early 21st century , hundreds of behavioral genetic studies of personality, intelligence, and psychopathology were reported. With rare exceptions, these studies converge to argue for a pervasive influence of genetics on human psychological variation.

These studies have also fueled much controversy. Citing in part behavioral genetic research, the educational psychologist Arthur Jensen ( 1969 ) claimed that the differences in intelligence and educational achievement in the United States between black and white students appeared to have a strong genetic basis. He went on to assume that because these racial differences appeared hereditary, they were likely impervious to environmental (educational) intervention. His article fanned the embers of past eugenics practices and ignited fiery responses (e.g., Hirsch, 1975 ). The ensuing debates not only spawned a rethinking of intelligence and how to measure it, but they ushered in a more critical look at the methods and assumptions of behavioral genetics.

Challenges to Behavioral Genetics

Many of the early critiques of behavioral genetics centered on interpreting the heritability statistic commonly calculated in kinship (family, twin, and adoption) studies. Perhaps more so than any other statistic, heritability has been persistently misinterpreted by academics and laypersons alike (Lerner, 2002 ). Contrary to popular belief, heritability tells us nothing about the relative impact of genetic and environmental factors on the development of traits in individuals. It deals with accounting for trait variation between people, not the causes of traits within people. As a result, a high heritability does not indicate anything about the fixity of traits or their imperviousness to environmental influence (contra Jensen), and a low heritability does not indicate an absence of genetic influence on trait development. Worse still, heritability does not even indicate anything about the role of genetics in generating the differences between people.

Other challenges to heritability focused not on its interpretation but on its underlying computational assumptions. Most notably, heritability analyses assume that genetic and environmental contributions to trait differences are independent and additive. The interaction between genetic and environmental factors were dismissed a priori in these analyses. Studies of development, however, show that no factor (genes, hormones, parenting, schooling) operates independently, making it impossible to quantify how much of a given trait in a person is due to any causal factor. Thus heritability analyses are bound to be misleading because they are based on biologically implausible and logically indefensible assumptions about development (Gottlieb, 2003 ).

Aside from heritability, kinship studies have been criticized for not being able to disentangle genetic and environmental effects on variation. It had long been known that that in family (pedigree) studies, environmental and genetic factors are confounded. Twin and adoption studies seemed to provide unique opportunities to statistically disentangle these effects, but these studies are also deeply problematic in assumptions and methodology. There are numerous plausible environmental reasons for why monozygotic twin pairs could resemble each other more than dizygotic twin pairs or why adoptive children might more closely resemble their biological than their adoptive parents (Joseph & Ratner, 2013 ).

A more recent challenge to behavioral genetics came from an unlikely source. Advances in genomic scanning in the 21st century made it possible in a single study to correlate thousands of genetic polymorphisms with variation in the psychological profiles (e.g., intelligence, memory, temperament, psychopathology) of thousands of people. These “genome-wide association” studies seemed to have the power and precision to finally identify genetic contributions to heritability at the level of single nucleotides. Yet, these studies consistently found only very small effects.

The failure to find large effects came to be known as the “missing heritability” problem (Maher, 2008 ). To account for the missing heritability, some behavioral geneticists and molecular biologists asserted that important genetic polymorphisms remain unknown, they may be too rare to detect, and/or that current studies are just not well equipped to handle gene–gene interactions. These studies were also insensitive to epigenetic profiles (see the section on Behavioral Epigenetics), which deal with differences in gene expression. Even when people share genes, they may differ in whether those genes get expressed in their lifetimes.

But genome-wide association studies faced an even more problematic issue: Many of these studies failed to replicate (Lickliter & Honeycutt, 2015 ). For those who viewed heritability analyses as biologically implausible, the small effect sizes and failures to replicate in genome-wide association studies were not that surprising. The search for independent genetic effects was bound to fail, because genes simply do not operate independently during development.

Behavioral Epigenetics

Epigenetics was a term coined in the 1940s by the developmental biologist Conrad Waddington to refer to a new field of study that would examine how genetic factors interact with local environmental conditions to bring about the embryological development of traits. By the end of the 20th century , epigenetics came to refer to the study of how nongenetic, molecular mechanisms physically regulate gene expression patterns in cells and across cell lineages. The most-studied mechanisms involve organic compounds (e.g., methyl-groups) that physically bind to DNA or the surrounding proteins that package DNA. The addition or removal of these compounds can activate or silence gene transcription. Different cell types have different, stable epigenetic markings, and these markings are recreated during cell division so that cells so marked give rise to similar types of cells. Epigenetic changes were known to occur during developmental periods of cellular differentiation (e.g., during embryogenesis), but not until 2004 was it discovered that these changes can occur at other periods in the life, including after birth (Roth, 2013 )

Of interest to psychologists were reports that different behavioral and physiological profiles (e.g., stress reactivity) of animals were associated with different epigenetic patterns in the nervous system (Moore, 2015 ). Furthermore, these different epigenetic patterns could be established or modified by environmental factors (e.g., caregiving practices, training regimes, or environmental enrichment), and, under certain conditions, they remain stable over long periods of time (from infancy to adulthood).

Because epigenetic research investigates the physical interface between genes and environment, it represents an exciting advance in understanding the interaction of nature and nurture. Despite some warnings that the excitement over behavioral epigenetic research may be premature (e.g., Miller, 2010 ), for many psychologists, epigenetics underscores how development involves both nature and nurture.

For others, what is equally exciting is the additional evidence epigenetics provides to show that the genome is an interactive and regulated system. Once viewed as the static director of development buffered from environment influence, the genome is better described as a developing resource of the cell (Moore, 2015 ). More broadly, epigenetics also points to how development is not a genetically (or biologically) predetermined affair. Instead, epigenetics provides additional evidence that development is a probabilistic process, contingent upon factors internal and external to the organism. In this sense, epigenetics is well positioned to help dissolve the nature–nurture dichotomy.

Beyond Nature–Nurture

In the final decades of the 20th century , a position was articulated to move beyond the dichotomous nature–nurture framework. The middle-ground position on nature–nurture did not seem up to the task of explaining the origins of form, and it brought about more confusion than clarity. The back-and-forth (or balanced) pendulum between nature- and nurture-based positions throughout history had only gone in circles. Moving forward would require moving beyond such dichotomous thinking (Johnston, 1987 ).

The anti-dichotomy position, referred to as the Developmentalist tradition, was expressed in a variety of systems-based, metatheoretical approaches to studying development, all of which extended the arguments against nature–nurture expressed earlier by Kuo and Lehrman. The central problem with all nativist claims according to Developmentalists is a reliance on preformationism (or predeterminism).

The problem with preformationism, they argue, besides issues of evidence, is that it is an anti-developmental mindset. It presumes the existence of the very thing(s) one wishes to explain and, consequently, discourages developmental analyses. To claim that some knowledge is innate effectively shuts down research on the developmental origins of that knowledge. After all, why look for the origins of conceptual knowledge if that knowledge is there all along? Or why search for any experiential contributions to innate behaviors if those behaviors by definition develop independently of experience? In the words of Developmentalists Thelen and Adolph ( 1992 ), nativism “leads to a static science, with no principles for understanding change or for confronting the ultimate challenge of development, the source of new forms in structure and function” (p. 378).

A commitment to maturational theory is likely one of the reasons why studies of motor development remained relatively dormant for decades following its heyday in the 1930–1940s (Thelen, 2000 ). Likewise, a commitment to maturational theory also helps explain the delay in neuroscience to examine how the brain physically changes in response to environmental conditions, a line of inquiry that only began in the 1960s.

In addition to the theoretical pitfalls of nativism, Developmentalists point to numerous studies that show how some seemingly native behaviors and innate constraints on learning are driven by the experiences of animals. For example, the comparative psychologist Gilbert Gottlieb ( 1971 ) showed that newly hatched ducklings display a naïve preference for a duck maternal call over a (similarly novel) chicken maternal call (Gottlieb, 1971 ), even when duck embryos were repeatedly exposed to the chicken call prior to hatching (Gottlieb, 1991 ). It would be easy to conclude that ducklings have an innate preference to approach their own species call and that they are biologically constrained (contraprepared) in learning a chicken call. However, Gottlieb found that the naïve preference for the duck call stemmed from exposure to the duck embryos’ own (or other) vocalizations in the days before hatching (Gottlieb, 1971 ). Exposure to these vocalizations not only made duck maternal calls more attractive, but it hindered the establishment of a preference for heterospecific calls. When duck embryos were reared in the absence of the embryonic vocalizations (by devocalizing embryos in ovo ) and exposed instead to chicken maternal calls, the newly hatched ducklings preferred chicken over duck calls (Gottlieb, 1991 ). These studies clearly showed how seemingly innate, biologically based preferences and constraints on learning derived from prenatal sensory experiences.

For Developmentalists, findings like these suggest that nativist explanations of any given behavior are statements of ignorance about how that behavior actually develops. As Kuo and Lehrman made clear, nativist terms are labels, not explanations. Although such appeals are couched in respectable, scientific language (e.g., “X is due to maturation, genes, or heredity”), they argue it would be more accurate simply to say that “We don’t know what causes X” or that “X is not due to A, B, or C.” Indeed, for Developmentalists, the more we unpack the complex dynamics about how traits develop, the less likely we are to use labels like nature or nurture (Blumberg, 2005 ).

On the other hand, Developmentalists recognize that labeling a behavior as “learned” also falls short as an explanatory construct. The empiricist position that knowledge or behavior is learned does not adequately take into account that what is learned and how easily something is learned depends on (a) the physiological and developmental status of the person, (b) the nature of the surrounding physical and social context in which learning takes place, and the (c) experiential history of the person. The empiricist tendency to say “X is learned or acquired through experience” can also short-circuit developmental analyses in the same way as nativist claims.

Still, Developmentalists appreciate that classifying behaviors can be useful. For example, the development of some behaviors may be more robust, reliably emerging across a range of environments and/or remaining relatively resistant to change, whereas others are more context-specific and malleable. Some preferences for stimuli require direct experience with those stimuli. Other preferences require less obvious (indirect) types of experiences. Likewise, it can still be useful to describe some behaviors in the ways shown in Table 1 . Developmentalists simply urge psychologists to resist the temptation to treat these behavioral classifications as implying different kinds of explanations (Johnston, 1987 ).

Rather than treat nature and nurture as separate developmental sources of causation (see Figure 1 ), Developmentalists argue that a more productive way of thinking about nature–nurture is to reframe the division as that between product and process (Lickliter & Honeycutt, 2015 ). The phenotype or structure (one’s genetic, epigenetic, anatomical, physiological, behavioral, and mental profile) of an individual at any given time can be considered one’s “nature.” “Nurture” then refers to the set of processes that generate, maintain, and transform one’s nature (Figure 2 ). These processes involve the dynamic interplay between phenotypes and environments.

Figure 2. The developmentalist alternative view of nature–nurture as product–process. Developmentalists view nature and nurture not as separate sources of causation in development (see Figure 1 ) but as a distinction between process (nurture) and product (nature).

It is hard to imagine any set of findings that will end debates about the roles of nature and nurture in human development. Why? First, more so than other assumptions about human development, the nature–nurture dichotomy is deeply entrenched in popular culture and the life sciences. Second, throughout history, the differing positions on nature and nurture were often driven by other ideological, philosophical, and sociopolitical commitments. Thus the essential source of tension in debates about nature–nurture is not as much about research agendas or evidence as about basic differences in metatheoretical positions (epistemological and ontological assumptions) about human behavior and development (Overton, 2006 ).

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In This Article Expand or collapse the "in this article" section Nature versus Nurture Debate in Psychology

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Nature versus Nurture Debate in Psychology by Hunter Honeycutt LAST MODIFIED: 12 January 2023 DOI: 10.1093/obo/9780199828340-0305

The nature-nurture dichotomy is a long-standing and pervasive framework for thinking about the causal influences believed to be operating during individual development. In this dichotomy, nature refers to factors (e.g., genes, genetic programs, and/or biological blueprints) or forces (e.g., heredity and/or maturation) inherent to the individual that predetermine the development of form and function. Nurture generally refers to all the remaining, typically “external,” causal factors (e.g., physical and social conditions) and processes (e.g., learning and experience) that influence development. The nature versus nurture debate in psychology deals with disagreements about the extent to which the development of traits in humans and animals reflects the relative influence of nature and nurture. It is commonly stated that psychologists have moved on from asking whether traits (or variation in traits) develop from nature or nurture, to recognize instead that both nature and nurture work together or “interact” to produce outcomes, although exactly how to view the interaction is a matter of much debate. While acknowledging the interaction of nature and nurture, one’s theoretical models and research focus might emphasize the prominence of one over the other. Thus, nativists focus more on the importance of innate factors or forces operating on development, whereas empiricists focus more on experiential or environmental factors. However, not everyone finds value in thinking about development in terms of nature and nurture. By the middle of the twentieth century, some psychologists, biologists, and philosophers began to view nature-nurture as a conceptually deficient and biologically implausible dichotomy that oversimplifies the dynamics of behavior and development. Such people espouse some variant of “developmental systems theory” and seek to eliminate or otherwise fuse the nature-nurture division.

The works in this section are mostly trade books that provide general introductions to the nature-nurture debate across a variety of topical areas in psychology, all of which would be suitable for use in classes with undergraduate students at all levels. Goldhaber 2012 contrasts four popular perspectives on the nature-nurture issue and would be a good place to start for anyone unfamiliar with the nature-nurture debate in psychology. Nativist perspectives are represented by Pinker 2002 , Plomin 2018 , and Vallortigara 2021 . An empiricist-leaning position on behavior development is put forth in Schneider 2012 . Developmental systems theory is promoted in Blumberg 2005 and Moore 2002 . Two edited books are included and both are better suited for advanced undergraduate- or graduate-level students. The first edited book, Coll, et al. 2013 , focuses on the nature-nurture issue across a range of topics and perspectives in psychology. The other, Mayes and Lewis 2012 , presents empiricist (or environmentalist) perspectives on child development.

Bateson, P. 2017. Behaviour, development and evolution . Cambridge, UK: OpenBook Publishers.

DOI: 10.11647/OBP.0097

Written by a distinguished ethologist who draws extensively from his work on animal behavior, this book argues that the nature-nurture division is neither valid nor helpful in capturing the complex system of factors that influence behavioral development. Topics include imprinting and attachment, parent-offspring relations, the influence of early-life experiences on later-life outcomes, problems with genetic determinism, and the role of behavior in evolutionary change.

Blumberg, M. S. 2005. Basic instinct: The genesis of novel behavior . New York: Thunder’s Mouth Press.

Consistent with developmental systems theory, Blumberg presents an overview of the conceptual and empirical limitations of nativism in explanations of behavioral and neural development in animals and cognitive development in humans.

Coll, C. G., E. L. Bearer, and R. M. Lerner, eds. 2013. Nature-nurture: The complex interplay of genetic and environmental influences on human behavior and development . New York: Psychology Press.

The contents of this edited volume are almost entirely original works with commentary that span multiple disciplines (psychology, biology, economics, philosophy) and multiple perspectives (behavioral genetics and developmental systems theory) on the nature-nurture issue.

Goldhaber, D. 2012. The nature-nurture debates: Bridging the gap . Cambridge, UK: Cambridge Univ. Press.

DOI: 10.1017/CBO9781139022583

Goldhaber reviews four major perspectives (behavior genetics, environmentalism, evolutionary psychology, and developmental systems theory) on the nature-nurture issue. He argues we should reject reductionist views based on either genetic determinism or environmental determinism in favor of more holistic, interactionist approaches.

Mayes, L. C., and M. Lewis, eds. 2012. The Cambridge handbook of environment in human development . Cambridge, UK: Cambridge Univ. Press.

This handbook explores a wide variety of ways in which the environment influences child development. Chapters cover conceptual frameworks and methodological issues in thinking about and studying environmental influences as well reviewing ways in which environmental contexts and systems influence specific aspects of child development.

Moore, D. S. 2002. The dependent gene: The fallacy of nature vs. nurture . New York: Henry Holt.

This book provides an introduction to the developmental systems theory take on the nature-nurture issue particularly as it relates to genetic determinism, heritability and heredity.

Pinker, S. 2002. The blank slate: The modern denial of human nature . New York: Viking.

In this best-selling book, Pinker draws on evidence from behavioral genetics, evolutionary psychology, and cognitive psychology to argue for a nativist position concerning human nature.

Plomin, R. 2018. Blueprint: How DNA makes us who we are . Cambridge, MA: MIT Press.

Plomin reviews traditional and more modern evidence from behavioral genetics to argue that genes are the primary factor in bringing about psychological differences between people. Moreover, he argues that many “environmental” factors operating on development are themselves strongly influenced by genetic differences.

Schneider, S. M. 2012. The science of consequences: How they affect genes, change the brain, and impact our world . Amherst, NY: Prometheus Books.

Schneider presents a view grounded in behavior analysis to argue for the critical role that the consequences of genetic activity, neural activity, and behavioral activity play in individual development. While emphasizing environmental (or experiential) factors influencing development, this book also highlights the systemic and interactive nature of developmental systems across multiple levels of analysis.

Vallortigara, G. 2021. Born knowing: Imprinting and the origins of knowledge . Cambridge, MA: MIT Press.

DOI: 10.7551/mitpress/14091.001.0001

Drawing upon research in comparative cognition and comparative neuroscience, much of it his own, Vallortigara argues that animals, including humans, enter the world with a set of unlearned, innate or instinctive behaviors and neural circuits that bias or predispose subsequent learning and development.

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Human development, nature and nurture: Working beyond the divide

• Thinking on the Edge
• Published: 03 September 2012
• Volume 7 , pages 308–321, ( 2012 )

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• Ilina Singh 1  

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In this essay, I explore what social science might contribute to building a better understanding of relations between ‘nature’ and ‘nurture’ in human development. I first outline changing scientific perspectives on the role of the environment in the developmental and behavioural sciences, beginning with a general historical view of the developmental science of human potentials in the twentieth century, and then reflecting on a call to arms against ‘toxic stress’ issued in 2012 by the American Academy of Pediatrics. I suggest that such post-genomic programmes of early intervention, which draw on emerging scientific theories of organismic plasticity and developmental malleability, raise significant social and ethical concerns. At the same time, such programmes challenge social scientists to move beyond critique and to contribute to new developmental models that deconstruct the old divide between nature and nurture. I conclude by describing efforts that posit new terms of reference and, simultaneously, new kinds of research interests and questions that are not founded upon, and are not efforts to resolve, the nature–nurture debate.

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Singh, I. Human development, nature and nurture: Working beyond the divide. BioSocieties 7 , 308–321 (2012). https://doi.org/10.1057/biosoc.2012.20

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8 Nature and Nurture

Chris Allen

People have a deep intuition about what has been called the “nature–nurture question.” Some aspects of our behavior feel as though they originate in our genetic makeup, while others feel like the result of our upbringing or our own hard work. The scientific field of behavior genetics attempts to study these differences empirically, either by examining similarities among family members with different degrees of genetic relatedness, or, more recently, by studying differences in the DNA of people with different behavioral traits. The scientific methods that have been developed are ingenious, but often inconclusive. Many of the difficulties encountered in the empirical science of behavior genetics turn out to be conceptual, and our intuitions about nature and nurture get more complicated the harder we think about them. In the end, it is an oversimplification to ask how “genetic” some particular behavior is. Genes and environments always combine to produce behavior, and the real science is in the discovery of how they combine for a given behavior.

Learning Objectives

• Understand what the nature–nurture debate is and why the problem fascinates us.
• Understand why nature–nurture questions are difficult to study empirically.
• Know the major research designs that can be used to study nature–nurture questions.
• Appreciate the complexities of nature–nurture and why questions that seem simple turn out not to have simple answers.

Introduction

There are three related problems at the intersection of philosophy and science that are fundamental to our understanding of our relationship to the natural world: the mind–body problem, the free will problem, and the nature–nurture problem. These great questions have a lot in common. Everyone, even those without much knowledge of science or philosophy, has opinions about the answers to these questions that come simply from observing the world we live in. Our feelings about our relationship with the physical and biological world often seem incomplete. We are in control of our actions in some ways, but at the mercy of our bodies in others; it feels obvious that our consciousness is some kind of creation of our physical brains, at the same time we sense that our awareness must go beyond just the physical. This incomplete knowledge of our relationship with nature leaves us fascinated and a little obsessed, like a cat that climbs into a paper bag and then out again, over and over, mystified every time by a relationship between inner and outer that it can see but can’t quite understand.

It may seem obvious that we are born with certain characteristics while others are acquired, and yet of the three great questions about humans’ relationship with the natural world, only nature–nurture gets referred to as a “debate.” In the history of psychology, no other question has caused so much controversy and offense: We are so concerned with nature–nurture because our very sense of moral character seems to depend on it. While we may admire the athletic skills of a great basketball player, we think of his height as simply a gift, a payoff in the “genetic lottery.” For the same reason, no one blames a short person for his height or someone’s congenital disability on poor decisions: To state the obvious, it’s “not their fault.” But we do praise the concert violinist (and perhaps her parents and teachers as well) for her dedication, just as we condemn cheaters, slackers, and bullies for their bad behavior.

The problem is, most human characteristics aren’t usually as clear-cut as height or instrument-mastery, affirming our nature–nurture expectations strongly one way or the other. In fact, even the great violinist might have some inborn qualities—perfect pitch, or long, nimble fingers—that support and reward her hard work. And the basketball player might have eaten a diet while growing up that promoted his genetic tendency for being tall. When we think about our own qualities, they seem under our control in some respects, yet beyond our control in others. And often the traits that don’t seem to have an obvious cause are the ones that concern us the most and are far more personally significant. What about how much we drink or worry? What about our honesty, or religiosity, or sexual orientation? They all come from that uncertain zone, neither fixed by nature nor totally under our own control.

One major problem with answering nature-nurture questions about people is, how do you set up an experiment? In nonhuman animals, there are relatively straightforward experiments for tackling nature–nurture questions. Say, for example, you are interested in aggressiveness in dogs. You want to test for the more important determinant of aggression: being born to aggressive dogs or being raised by them. You could mate two aggressive dogs—angry Chihuahuas—together, and mate two nonaggressive dogs—happy beagles—together, then switch half the puppies from each litter between the different sets of parents to raise. You would then have puppies born to aggressive parents (the Chihuahuas) but being raised by nonaggressive parents (the Beagles), and vice versa, in litters that mirror each other in puppy distribution. The big questions are: Would the Chihuahua parents raise aggressive beagle puppies? Would the beagle parents raise  non aggressive Chihuahua puppies? Would the puppies’  nature  win out, regardless of who raised them? Or… would the result be a combination of nature  and  nurture? Much of the most significant nature–nurture research has been done in this way (Scott & Fuller, 1998), and animal breeders have been doing it successfully for thousands of years. In fact, it is fairly easy to breed animals for behavioral traits.

With people, however, we can’t assign babies to parents at random, or select parents with certain behavioral characteristics to mate, merely in the interest of science (though history does include horrific examples of such practices, in misguided attempts at “eugenics,” the shaping of human characteristics through intentional breeding). In typical human families, children’s biological parents raise them, so it is very difficult to know whether children act like their parents due to genetic (nature) or environmental (nurture) reasons. Nevertheless, despite our restrictions on setting up human-based experiments, we do see real-world examples of nature-nurture at work in the human sphere—though they only provide partial answers to our many questions.

The science of how genes and environments work together to influence behavior is called  behavioral genetics . The easiest opportunity we have to observe this is the  adoption study . When children are put up for adoption, the parents who give birth to them are no longer the parents who raise them. This setup isn’t quite the same as the experiments with dogs (children aren’t assigned to random adoptive parents in order to suit the particular interests of a scientist) but adoption still tells us some interesting things, or at least confirms some basic expectations. For instance, if the biological child of tall parents were adopted into a family of short people, do you suppose the child’s growth would be affected? What about the biological child of a Spanish-speaking family adopted at birth into an English-speaking family? What language would you expect the child to speak? And what might these outcomes tell you about the difference between height and language in terms of nature-nurture?

Another option for observing nature-nurture in humans involves  twin studies . There are two types of twins: monozygotic (MZ) and dizygotic (DZ). Monozygotic twins, also called “identical” twins, result from a single zygote (fertilized egg) and have the same DNA. They are essentially clones. Dizygotic twins, also known as “fraternal” twins, develop from two zygotes and share 50% of their DNA. Fraternal twins are ordinary siblings who happen to have been born at the same time. To analyze nature–nurture using twins, we compare the similarity of MZ and DZ pairs. Sticking with the features of height and spoken language, let’s take a look at how nature and nurture apply: Identical twins, unsurprisingly, are almost perfectly similar for height. The heights of fraternal twins, however, are like any other sibling pairs: more similar to each other than to people from other families, but hardly identical. This contrast between twin types gives us a clue about the role genetics plays in determining height. Now consider spoken language. If one identical twin speaks Spanish at home, the co-twin with whom she is raised almost certainly does too. But the same would be true for a pair of fraternal twins raised together. In terms of spoken language, fraternal twins are just as similar as identical twins, so it appears that the genetic match of identical twins doesn’t make much difference.

Twin and adoption studies are two instances of a much broader class of methods for observing nature-nurture called quantitative genetics, the scientific discipline in which similarities among individuals are analyzed based on how biologically related they are. We can do these studies with siblings and half-siblings, cousins, twins who have been separated at birth and raised separately (Bouchard, Lykken, McGue, & Segal, 1990; such twins are very rare and play a smaller role than is commonly believed in the science of nature–nurture), or with entire extended families (see Plomin, DeFries, Knopik, & Neiderhiser, 2012, for a complete introduction to research methods relevant to nature–nurture).

For better or for worse, contentions about nature–nurture have intensified because quantitative genetics produces a number called a  heritability coefficient , varying from 0 to 1, that is meant to provide a single measure of genetics’ influence of a trait. In a general way, a heritability coefficient measures how strongly differences among individuals are related to differences among their genes. But beware: Heritability coefficients, although simple to compute, are deceptively difficult to interpret. Nevertheless, numbers that provide simple answers to complicated questions tend to have a strong influence on the human imagination, and a great deal of time has been spent discussing whether the heritability of intelligence or personality or depression is equal to one number or another.

One reason nature–nurture continues to fascinate us so much is that we live in an era of great scientific discovery in genetics, comparable to the times of Copernicus, Galileo, and Newton, with regard to astronomy and physics. Every day, it seems, new discoveries are made, new possibilities proposed. When Francis Galton first started thinking about nature–nurture in the late-19th century he was very influenced by his cousin, Charles Darwin, but genetics  per se  was unknown. Mendel’s famous work with peas, conducted at about the same time, went undiscovered for 20 years; quantitative genetics was developed in the 1920s; DNA was discovered by Watson and Crick in the 1950s; the human genome was completely sequenced at the turn of the 21st century; and we are now on the verge of being able to obtain the specific DNA sequence of anyone at a relatively low cost. No one knows what this new genetic knowledge will mean for the study of nature–nurture, but as we will see in the next section, answers to nature–nurture questions have turned out to be far more difficult and mysterious than anyone imagined.

What Have We Learned About Nature–Nurture?

It would be satisfying to be able to say that nature–nurture studies have given us conclusive and complete evidence about where traits come from, with some traits clearly resulting from genetics and others almost entirely from environmental factors, such as childrearing practices and personal will; but that is not the case. Instead,  everything  has turned out to have some footing in genetics. The more genetically-related people are, the more similar they are—for  everything : height, weight, intelligence, personality, mental illness, etc. Sure, it seems like common sense that some traits have a genetic bias. For example, adopted children resemble their biological parents even if they have never met them, and identical twins are more similar to each other than are fraternal twins. And while certain psychological traits, such as personality or mental illness (e.g., schizophrenia), seem reasonably influenced by genetics, it turns out that the same is true for political attitudes, how much television people watch (Plomin, Corley, DeFries, & Fulker, 1990), and whether or not they get divorced (McGue & Lykken, 1992).

It may seem surprising, but genetic influence on behavior is a relatively recent discovery. In the middle of the 20th century, psychology was dominated by the doctrine of behaviorism, which held that behavior could only be explained in terms of environmental factors. Psychiatry concentrated on psychoanalysis, which probed for roots of behavior in individuals’ early life-histories. The truth is, neither behaviorism nor psychoanalysis is incompatible with genetic influences on behavior, and neither Freud nor Skinner was naive about the importance of organic processes in behavior. Nevertheless, in their day it was widely thought that children’s personalities were shaped entirely by imitating their parents’ behavior, and that schizophrenia was caused by certain kinds of “pathological mothering.” Whatever the outcome of our broader discussion of nature–nurture, the basic fact that the best predictors of an adopted child’s personality or mental health are found in the biological parents he or she has never met, rather than in the adoptive parents who raised him or her, presents a significant challenge to purely environmental explanations of personality or psychopathology. The message is clear: You can’t leave genes out of the equation. But keep in mind, no behavioral traits are completely inherited, so you can’t leave the environment out altogether, either.

Trying to untangle the various ways nature-nurture influences human behavior can be messy, and often common-sense notions can get in the way of good science. One very significant contribution of behavioral genetics that has changed psychology for good can be very helpful to keep in mind: When your subjects are biologically-related, no matter how clearly a situation may seem to point to environmental influence, it is never safe to interpret a behavior as wholly the result of nurture without further evidence. For example, when presented with data showing that children whose mothers read to them often are likely to have better reading scores in third grade, it is tempting to conclude that reading to your kids out loud is important to success in school; this may well be true, but the study as described is inconclusive, because there are genetic  as well as  environmental pathways between the parenting practices of mothers and the abilities of their children. This is a case where “correlation does not imply causation,” as they say. To establish that reading aloud causes success, a scientist can either study the problem in adoptive families (in which the genetic pathway is absent) or by finding a way to randomly assign children to oral reading conditions.

The outcomes of nature–nurture studies have fallen short of our expectations (of establishing clear-cut bases for traits) in many ways. The most disappointing outcome has been the inability to organize traits from  more – to  less -genetic. As noted earlier, everything has turned out to be at least  somewhat  heritable (passed down), yet nothing has turned out to be  absolutely  heritable, and there hasn’t been much consistency as to which traits are  more  heritable and which are  less  heritable once other considerations (such as how accurately the trait can be measured) are taken into account (Turkheimer, 2000). The problem is conceptual: The heritability coefficient, and, in fact, the whole quantitative structure that underlies it, does not match up with our nature–nurture intuitions. We want to know how “important” the roles of genes and environment are to the development of a trait, but in focusing on “important” maybe we’re emphasizing the wrong thing. First of all, genes and environment are both crucial to  every  trait; without genes the environment would have nothing to work on, and too, genes cannot develop in a vacuum. Even more important, because nature–nurture questions look at the differences among people, the cause of a given trait depends not only on the trait itself, but also on the differences in that trait between members of the group being studied.

The classic example of the heritability coefficient defying intuition is the trait of having two arms. No one would argue against the development of arms being a biological, genetic process. But fraternal twins are just as similar for “two-armedness” as identical twins, resulting in a heritability coefficient of zero for the trait of having two arms. Normally, according to the heritability model, this result (coefficient of zero) would suggest all nurture, no nature, but we know that’s not the case. The reason this result is not a tip-off that arm development is less genetic than we imagine is because people  do not vary  in the genes related to arm development—which essentially upends the heritability formula. In fact, in this instance, the opposite is likely true: the extent that people differ in arm number is likely the result of accidents and, therefore, environmental. For reasons like these, we always have to be very careful when asking nature–nurture questions, especially when we try to express the answer in terms of a single number. The heritability of a trait is not simply a property of that trait, but a property of the trait in a particular context of relevant genes and environmental factors.

Another issue with the heritability coefficient is that it divides traits’ determinants into two portions—genes and environment—which are then calculated together for the total variability. This is a little like asking how much of the experience of a symphony comes from the horns and how much from the strings; the ways instruments or genes integrate is more complex than that. It turns out to be the case that, for many traits, genetic differences affect behavior under some environmental circumstances but not others—a phenomenon called gene-environment interaction , or G x E. In one well-known example, Caspi et al. (2002) showed that among maltreated children, those who carried a particular allele of the MAOA gene showed a predisposition to violence and antisocial behavior, while those with other alleles did not. Whereas, in children who had not been maltreated, the gene had no effect. Making matters even more complicated are very recent studies of what is known as epigenetics, a process in which the DNA itself is modified by environmental events, and those genetic changes transmitted to children.

Several studies have attempted to determine to what extent the findings from model animals are transferable to humans. Examination of post-mortem brain tissue from healthy human subjects found that the human equivalent of the glucocorticoid receptor gene promoter (NR3C1 exon 1F promoter) is also unique to the individual (Turner, Pelascini, Macedo, & Muller, 2008). A similar study examining newborns showed that methylation of the glucocorticoid receptor gene promoter maybe an early epigenetic marker of maternal mood and risk of increased hormonal responses to stress in infants 3 months of age (Oberlander et al., 2008). Although further studies are required to examine the functional consequence of this DNA methylation, these findings are consistent with our studies in the neonate and adult offspring of low licking and grooming mothers that show increased DNA methylation of the promoter of the glucocorticoid receptor gene, decreased glucocorticoid receptor gene expression, and increased hormonal responses to stress (Weaver et al., 2004). Examination of brain tissue from suicide victims found that the human glucocorticoid receptor gene promoter is also more methylated in the brains of individuals who had experienced maltreatment during childhood (McGowan et al., 2009). These finding suggests that DNA methylation mediates the effects of early environment in both rodents and humans and points to the possibility of new therapeutic approaches stemming from translational epigenetic research. Indeed, similar processes at comparable epigenetic labile regions could explain why the adult offspring of high and low licking/grooming mothers exhibit widespread differences in hippocampal gene expression and cognitive function (Weaver, Meaney, & Szyf, 2006).

However, this type of research is limited by the inaccessibility of human brain samples. The translational potential of this finding would be greatly enhanced if the relevant epigenetic modification can be measured in an accessible tissue. Examination of blood samples from adult patients with bipolar disorder, who also retrospectively reported on their experiences of childhood abuse and neglect, found that the degree of DNA methylation of the human glucocorticoid receptor gene promoter was strongly positively related to the reported experience of childhood maltreatment decades earlier. For a relationship between a molecular measure and reported historical exposure, the effects size is extraordinarily large. This opens a range of new possibilities: given the large effect size and consistency of this association, measurement of the GR promoter methylation may effectively become a blood test measuring the physiological traces left on the genome by early experiences. Although this blood test cannot replace current methods of diagnosis, this unique and addition information adds to our knowledge of how disease may arise and be manifested throughout life. Near-future research will examine whether this measure adds value over and above simple reporting of early adversities when it comes to predicting important outcomes, such as response to treatment or suicide.

Epigenetic strategy to understanding gene-environment interactions

Some common questions about nature–nurture are, how susceptible is a trait to change, how malleable is it, and do we “have a choice” about it? These questions are much more complex than they may seem at first glance. For example, phenylketonuria is an inborn error of metabolism caused by a single gene; it prevents the body from metabolizing phenylalanine. Untreated, it causes mental retardation and death. But it can be treated effectively by a straightforward environmental intervention: avoiding foods containing phenylalanine. Height seems like a trait firmly rooted in our nature and unchangeable, but the average height of many populations in Asia and Europe has increased significantly in the past 100 years, due to changes in diet and the alleviation of poverty. Even the most modern genetics has not provided definitive answers to nature–nurture questions. When it was first becoming possible to measure the DNA sequences of individual people, it was widely thought that we would quickly progress to finding the specific genes that account for behavioral characteristics, but that hasn’t happened. There are a few rare genes that have been found to have significant (almost always negative) effects, such as the single gene that causes Huntington’s disease, or the Apolipoprotein gene that causes early onset dementia in a small percentage of Alzheimer’s cases. Aside from these rare genes of great effect, however, the genetic impact on behavior is broken up over many genes, each with very small effects. For most behavioral traits, the effects are so small and distributed across so many genes that we have not been able to catalog them in a meaningful way. In fact, the same is true of environmental effects. We know that extreme environmental hardship causes catastrophic effects for many behavioral outcomes, but fortunately extreme environmental hardship is very rare. Within the normal range of environmental events, those responsible for differences (e.g., why some children in a suburban third-grade classroom perform better than others) are much more difficult to grasp.

The difficulties with finding clear-cut solutions to nature–nurture problems bring us back to the other great questions about our relationship with the natural world: the mind-body problem and free will. Investigations into what we mean when we say we are aware of something reveal that consciousness is not simply the product of a particular area of the brain, nor does choice turn out to be an orderly activity that we can apply to some behaviors but not others. So it is with nature and nurture: What at first may seem to be a straightforward matter, able to be indexed with a single number, becomes more and more complicated the closer we look. The many questions we can ask about the intersection among genes, environments, and human traits—how sensitive are traits to environmental change, and how common are those influential environments; are parents or culture more relevant; how sensitive are traits to differences in genes, and how much do the relevant genes vary in a particular population; does the trait involve a single gene or a great many genes; is the trait more easily described in genetic or more-complex behavioral terms?—may have different answers, and the answer to one tells us little about the answers to the others.

It is tempting to predict that the more we understand the wide-ranging effects of genetic differences on all human characteristics—especially behavioral ones—our cultural, ethical, legal, and personal ways of thinking about ourselves will have to undergo profound changes in response. Perhaps criminal proceedings will consider genetic background. Parents, presented with the genetic sequence of their children, will be faced with difficult decisions about reproduction. These hopes or fears are often exaggerated. In some ways, our thinking may need to change—for example, when we consider the meaning behind the fundamental American principle that all men are created equal. Human beings differ, and like all evolved organisms they differ genetically. The Declaration of Independence predates Darwin and Mendel, but it is hard to imagine that Jefferson—whose genius encompassed botany as well as moral philosophy—would have been alarmed to learn about the genetic diversity of organisms. One of the most important things modern genetics has taught us is that almost all human behavior is too complex to be nailed down, even from the most complete genetic information, unless we’re looking at identical twins. The science of nature and nurture has demonstrated that genetic differences among people are vital to human moral equality, freedom, and self-determination, not opposed to them. As Mordecai Kaplan said about the role of the past in Jewish theology, genetics gets a vote, not a veto, in the determination of human behavior. We should indulge our fascination with nature–nurture while resisting the temptation to oversimplify it.

Epigenetics  is the study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself.  Epigenetics looks at all events that occur in the absence of changes in DNA sequence. Epigenetics is looking at changes of the gene expression, rather than changes in the DNA code itself.

Epigenome: epigenome refers to the genetic patterns and information made up of chemical compounds and proteins that can attach to DNA, and direct such actions as turning genes on or off, controlling the production of proteins in particular cells and changing the expression of a gene. These changes in the epigenome may be passed down through heritance, or may be changed by environmental experiences.

Genotype: is an organism’s full hereditary information. … The genes that contribute to a trait”. Genotype is an organism’s full hereditary information.

Phenotype: is an organism’s actual observed properties, such as morphology, development, or behavior.

• Bouchard, T. J., Lykken, D. T., McGue, M., & Segal, N. L. (1990). Sources of human psychological differences: The Minnesota study of twins reared apart. Science, 250(4978), 223–228.
• Caspi, A., McClay, J., Moffitt, T. E., Mill, J., Martin, J., Craig, I. W., Taylor, A. & Poulton, R. (2002). Role of genotype in the cycle of violence in maltreated children. Science, 297(5582), 851–854.
• McGue, M., & Lykken, D. T. (1992). Genetic influence on risk of divorce. Psychological Science, 3(6), 368–373.
• Plomin, R., Corley, R., DeFries, J. C., & Fulker, D. W. (1990). Individual differences in television viewing in early childhood: Nature as well as nurture. Psychological Science, 1(6), 371–377.
• Plomin, R., DeFries, J. C., Knopik, V. S., & Neiderhiser, J. M. (2012). Behavioral genetics. New York, NY: Worth Publishers.
• Scott, J. P., & Fuller, J. L. (1998). Genetics and the social behavior of the dog. Chicago, IL: University of Chicago Press.
• Turkheimer, E. (2000). Three laws of behavior genetics and what they mean. Current Directions in Psychological Science, 9(5), 160–164.

This is an edited and adapted chapter from a chapter by Eric Turkheimer PhD, contributed to the NOBA project. The original authors bear no responsibility for this chapter. The original chapter can be found here:

Turkheimer, E. (2019). The nature-nurture question. In R. Biswas-Diener & E. Diener (Eds),  Noba textbook series: Psychology.  Champaign, IL: DEF publishers. Retrieved from  http://noba.to/tvz92edh

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3.1: Nature vs. Nurture

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Developmental psychology seeks to understand the influence of genetics (nature) and environment (nurture) on human development.

Learning objective.

• Evaluate the reciprocal impacts between genes and the environment and the nature vs. nurture debate
• A significant issue in developmental psychology has been the relationship between the innateness of an attribute (whether it is part of our nature) and the environmental effects on that attribute (whether it is derived from or influenced by our environment, or nurture).
• Today, developmental psychologists rarely take polarized positions with regard to most aspects of development; instead, they investigate the relationship between innate and environmental influences.
• The biopsychosocial model states that biological, psychological, and social factors all play a significant role in human development.
• Environmental inputs can affect the expression of genes , a relationship called gene-environment interaction. An individual’s genes and their environment work together, communicating back and forth to create traits .
• The diathesis– stress model serves to explore how biological or genetic traits (diatheses) interact with environmental influences (stressors) to produce disorders, such as depression, anxiety , or schizophrenia .
• genotype That part (DNA sequence) of the genetic makeup of a cell, and therefore of an organism or individual, which determines a specific characteristic (phenotype) of that cell/organism/individual.
• heritability The ratio of the genetic variance of a population to its phenotypic variance; i.e., the proportion of variability that is genetic in origin.
• gene A unit of heredity; a segment of DNA or RNA that is transmitted from one generation to the next and carries genetic information such as the sequence of amino acids for a protein.
• trait An identifying characteristic, habit, or trend.
• innate Inborn; native; natural.

Developmental Psychology

Developmental psychology is the scientific study of changes that occur in human beings over the course of their lives. This field examines change and development across a broad range of topics, such as motor skills and other psycho-physiological processes; cognitive development involving areas like problem solving, moral and conceptual understanding; language acquisition; social, personality , and emotional development; and self- concept and identity formation. Developmental psychology explores the extent to which development is a result of gradual accumulation of knowledge or stage-like development, as well as the extent to which children are born with innate mental structures as opposed to learning through experience.

Nature Versus Nurture

A significant issue in developmental psychology is the relationship between the innateness of an attribute (whether it is part of our nature ) and the environmental effects on that attribute (whether it is influenced by our environment, or nurture ). This is often referred to as the nature vs. nurture debate, or nativism vs. empiricism.

• A nativist (“nature”) account of development would argue that the processes in question are innate and influenced by an organism’s genes. Natural human behavior is seen as the result of already-present biological factors, such as genetic code.
• An empiricist (“nurture”) perspective would argue that these processes are acquired through interaction with the environment. Nurtured human behavior is seen as the result of environmental interaction, which can provoke changes in brain structure and chemistry. For example, situations of extreme stress can cause problems like depression.

The nature vs. nurture debate seeks to understand how our personalities and traits are produced by our genetic makeup and biological factors, and how they are shaped by our environment, including our parents, peers, and culture . For instance, why do biological children sometimes act like their parents? Is it because of genetic similarity, or the result of the early childhood environment and what children learn from their parents?

Interaction of Genes and the Environment

Today, developmental psychologists rarely take such polarized positions (either/or) with regard to most aspects of development; instead, they investigate the relationship between innate and environmental influences (both/and). Developmental psychologists will often use the biopsychosocial model to frame their research: this model states that biological, psychological, and social (socio-economical, socio-environmental, and cultural) factors all play a significant role in human development.

We are all born with specific genetic traits inherited from our parents, such as eye color, height, and certain personality traits. Beyond our basic genotype , however, there is a deep interaction between our genes and our environment: our unique experiences in our environment influence whether and how particular traits are expressed, and at the same time, our genes influence how we interact with our environment (Diamond, 2009; Lobo, 2008). There is a reciprocal interaction between nature and nurture as they both shape who we become, but the debate continues as to the relative contributions of each.

Heritability refers to the origin of differences among people; it is a concept in biology that describes how much of the variation of a trait in a population is due to genetic differences in that population. Individual development, even of highly heritable traits such as eye color, depends not only on heritability but on a range of environmental factors, such as the other genes present in the organism and the temperature and oxygen levels during development. Environmental inputs can affect the expression of genes, a relationship called gene-environment interaction. Genes and the environment work together, communicating back and forth to create traits.

Some concrete behavioral traits are dependent upon one’s environment, home, or culture, such as the language one speaks, the religion one practices, and the political party one supports. However, some traits which reflect underlying talents and temperaments—such as how proficient at a language, how religious, or how liberal or conservative—can be partially heritable.

This chart illustrates three patterns one might see when studying the influence of genes and environment on individual traits. Each of these traits is measured and compared between monozygotic (identical) twins, biological siblings who are not twins, and adopted siblings who are not genetically related. Trait A shows a high sibling correlation but little heritability (illustrating the importance of environment). Trait B shows a high heritability, since the correlation of the trait rises sharply with the degree of genetic similarity. Trait C shows low heritability as well as low correlation generally, suggesting that the degree to which individuals display trait C has little to do with either genes or predictable environmental factors.

Heritability Estimates

This chart illustrates three patterns one might see when studying the influence of genes and environment on individual traits. Typically, monozygotic twins will have a high correlation of sibling traits, while biological siblings will have less in common, and adoptive siblings will have less than that. However, this can vary widely by trait.

Diathesis-Stress Model

The diathesis–stress model is a psychological theory that attempts to explain behavior as a predispositional vulnerability together with stress from life experiences. The term diathesis derives from the Greek term for disposition, or vulnerability, and it can take the form of genetic, psychological, biological, or situational factors. The diathesis, or predisposition , interacts with the subsequent stress response of an individual. Stress refers to a life event or series of events that disrupt a person’s psychological equilibrium and potentially serve as a catalyst to the development of a disorder. Thus, the diathesis–stress model serves to explore how biological or genetic traits (diatheses) interact with environmental influences (stressors) to produce disorders, such as depression, anxiety, or schizophrenia.

• Nature vs. Nurture. Provided by : Boundless. Located at : https://www.boundless.com/psychology/textbooks/boundless-psychology-textbook/human-development-14/introduction-to-human-development-69/nature-vs-nurture-265-12800/ . Project : Boundless Psychology. License : CC BY-SA: Attribution-ShareAlike

Nature vs Nurture: Genes or Environment

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The nature versus nurture debate focuses on the question of whether genetic or environmental factors matter most in the course of human development.

What is it that makes you who you are? Some might say that it is your genes that have the greatest influence in controlling your personality and preferences. Others might say that it is your environment and the unique experiences you have had over the course of your life that have a greater role.

In this article, learn more about the nature vs. nurture debate and what research has found about the contributions of genetic and environmental factors.

Table of Contents

What Is the Nature vs Nurture Debate?

The nature vs. nurture debate is often described as one of the big philosophical and scientific questions facing psychologists. So what exactly does this debate mean? Why is it important for understanding the human mind and behavior?  

Let’s start by learning more about each of these factors.

• Nature: This side of the debate argues that genes have the greatest influence over who we are, from the way we look to the way we behave. Genes determine physical traits such as height, eye color, hair color, and face shape, but they can also contribute to other attributes such as your personality traits and cognitive abilities.
• Nurture: This side of the debate argues that environmental variables such as how we were raised, individual experience, and other social relationships play a more important role. Your upbringing, your early social interactions, school, and peers all play a role in shaping who you are and how you behave.

Let’s consider an example. If a student excels at math, is it because they inherited that ability from their parents or is it because they work hard to learn the subject?

Nature would suggest that they do well because they are genetically inclined to do so, while nature argues that their talent stems from their upbringing and educational background.

History of Nature vs. Nurture

The debate over nature and nurture predates psychology and goes back to the days of the ancient philosophers. In philosophy, this is often referred to as the nativism versus empiricism debate. What do these two terms mean and how do they relate to nature and nurture.

The nativist approach suggests that inheritance plays the greatest role in determining characteristics. Nativism proposes that people’s characteristics, both physical and mental, are innate. These are things that are passed down genetically from our ancestors. The nativist approach essentially espouses the nature side of the argument.

Noam Chomsky’s theory of language acquisition is one of the best-known examples of nativism in psychology.  Chomsky suggested that language develops as a result of an innate language acquisition device. He believed that people are able to learn language because they have an innate, hard-wired capacity for what he referred to as universal grammar.

Empiricism represents the nurture side of the debate. The empiricist approach suggests that all learning is the result of experience and environmental factors.

The philosopher John Locke took an empiricist approach and proposed a concept known as tabula rasa, which means “blank slate.” This approach that the mind is essentially that —a blank slate—and that it is through learning and experience that all knowledge, skill, and behavioral patterns are acquired.

Behaviorism is one example of an empirical approach to understanding human behavior. Behaviorists such as John B. Watson and B.F. Skinner believed that all human behavior was the result of conditioning, either classical (associative) or operant ( reinforcement and punishment ).

Watson was famously known for proclaiming that he could train anyone to be anything using the principles of conditioning, regardless of that individual’s genetics and background.

Approaches to Psychology

While few contemporary psychologists take an extreme, hard-lined empiricist or nativist approach, different branches of psychology do sometimes tend to emphasize one influence over the other.

Biological Psychology

Biological psychology, for example, tends to focus more on the nature side of the debate. This area of psychology focuses on how biological factors influence human behavior, so things such as the brain, neurons, and neurotransmitters are of greater interest than external factors.

Behavioral Psychology

Behavioral psychology tends to take the nurture side of the debate, focusing on how environmental factors and learned associations contribute to how people think and act.

Health Psychology

Health psychology is an example of an approach that tends to lie somewhere in the middle. Health psychologists are focused on understanding how both biological and environmental factors contribute and interact to affect an individual’s health.

Examples of Nature vs. Nurture

Looking at examples can be helpful to understand why the nature vs nurture debate has been so crucial throughout psychology’s history. The topic is not just an important philosophical debate. It has been critical for understanding what factors influence different aspects of human behavior and has been the source of considerable controversy at times.

Consider the long debate over the factors that influence intelligence. Those on the nature side of the debate suggest that the greatest influence on IQ is inheritance. Some early thinkers such as Francis Galton believed that intelligence could largely be attributed to genetic factors.

Such views have been used to justify discriminatory social policies and attitudes. When some research suggested that some groups of people had lower IQ scores, for example, some researchers interpreted such results to suggest that these individuals scored lower as a result of genetics.

Those taking the nurture side of the debate point out that other factors such as biased test construction, racism, and systemic discrimination impacting educational access and quality play a more important role.

Inequality, discrimination, and lack of access play a role in shaping how well people perform on intelligence tests and other assessments of educational outcomes.

Gender Differences and Education

Sex differences in school performance and attainment is another area where the debate between the contributions of nature vs nurture comes into play. Girls often perform better on verbal tests but less well on math. As they advance in school, girls also become less likely to enter STEM courses and STEM fields.

Those taking a nature perspective might suggest that girls are inherently less capable in these subjects. Nature advocates, however, would point out that social variables including gender stereotypes and discrimination have a greater influence.

Many researchers today believe that human behavior is influenced by both nature and nurture, and that it is often the interaction of the two variables that is even more important.

Impact of the Nature and Nurture Debate

Few modern psychologists would take an extreme nature or nurture position. Rather than asking which one controls specific variables, researchers are more likely to wonder about the degree to which each of these forces plays a role. So what exactly are the relative contributions of nature and nurture?

According to the research, the answer is about 50/50. Researchers collected the results of nearly every twin study conducted over the last half-century. Doing this allowed them to determine which factors played a role in determining certain characteristics.

Twin studies examine similarities and differences by looking at twins who are either raised together or raised apart. This allows researchers to determine the impact of genes versus the environment.

Researchers analyzed more than 2,700 twin studies involving a whopping 14.5 million pairs of twins from 39 different countries and discovered that genes and environment share a roughly equal role in determining who we are.

Variations in personality traits and disease were determined to be 49% due to genetics and 51% due to environment.

One important thing to note is that while the research suggests a 50/50 split, the findings did reveal that genes do play a greater role in the risk of certain diseases. Bipolar disorder, for example, was found to be approximately 70% heritable.

How Nature and Nurture Interact

Today, many experts suggest that we should be more concerned with how nature and nurture interact to determine how we develop. We might be genetically inclined toward a certain trait, for example, but our experiences can determine to what degree that trait is expressed.

Height is a good example of how genes and the environment can interact to make you who you are. Even if you inherit genes for tallness, proper nourishment is important for reaching that height. Kids who come from tall families might not become tall if they do not receive proper nutrition during their childhood.

So while we know that both factors are equally important, the question we are left to ponder is just how much of a role each factor plays in the development of certain characteristics. As the research suggests, some diseases are more strongly linked to genetics than to the environment.

As researchers continue to explore how nature and nurture interact, we will continue to gain a deeper understanding of the factors that contribute to who we are.

Haworth CM, Davis OS, Plomin R. Twins Early Development Study (TEDS): a genetically sensitive investigation of cognitive and behavioral development from childhood to young adulthood .  Twin Res Hum Genet . 2013;16(1):117-125. doi:10.1017/thg.2012.91

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11.3 Is Personality More Nature or More Nurture? Behavioral and Molecular Genetics

Learning objectives.

• Explain how genes transmit personality from one generation to the next.
• Outline the methods of behavioral genetics studies and the conclusions that we can draw from them about the determinants of personality.
• Explain how molecular genetics research helps us understand the role of genetics in personality.

One question that is exceedingly important for the study of personality concerns the extent to which it is the result of nature or nurture. If nature is more important, then our personalities will form early in our lives and will be difficult to change later. If nurture is more important, however, then our experiences are likely to be particularly important, and we may be able to flexibly alter our personalities over time. In this section we will see that the personality traits of humans and animals are determined in large part by their genetic makeup, and thus it is no surprise that identical twins Paula Bernstein and Elyse Schein turned out to be very similar even though they had been raised separately. But we will also see that genetics does not determine everything.

In the nucleus of each cell in your body are 23 pairs of chromosomes . One of each pair comes from your father, and the other comes from your mother. The chromosomes are made up of strands of the molecule DNA (deoxyribonucleic acid), and the DNA is grouped into segments known as genes . A gene is the basic biological unit that transmits characteristics from one generation to the next . Human cells have about 25,000 genes.

The genes of different members of the same species are almost identical. The DNA in your genes, for instance, is about 99.9% the same as the DNA in my genes and in the DNA of every other human being. These common genetic structures lead members of the same species to be born with a variety of behaviors that come naturally to them and that define the characteristics of the species. These abilities and characteristics are known as instincts — complex inborn patterns of behaviors that help ensure survival and reproduction (Tinbergen, 1951). Different animals have different instincts. Birds naturally build nests, dogs are naturally loyal to their human caretakers, and humans instinctively learn to walk and to speak and understand language.

But the strength of different traits and behaviors also varies within species. Rabbits are naturally fearful, but some are more fearful than others; some dogs are more loyal than others to their caretakers; and some humans learn to speak and write better than others do. These differences are determined in part by the small amount (in humans, the 0.1%) of the differences in genes among the members of the species.

Personality is not determined by any single gene, but rather by the actions of many genes working together. There is no “IQ gene” that determines intelligence and there is no “good marriage partner gene” that makes a person a particularly good marriage bet. Furthermore, even working together, genes are not so powerful that they can control or create our personality. Some genes tend to increase a given characteristic and others work to decrease that same characteristic—the complex relationship among the various genes, as well as a variety of random factors, produces the final outcome. Furthermore, genetic factors always work with environmental factors to create personality. Having a given pattern of genes doesn’t necessarily mean that a particular trait will develop, because some traits might occur only in some environments. For example, a person may have a genetic variant that is known to increase his or her risk for developing emphysema from smoking. But if that person never smokes, then emphysema most likely will not develop.

Studying Personality Using Behavioral Genetics

Perhaps the most direct way to study the role of genetics in personality is to selectively breed animals for the trait of interest. In this approach the scientist chooses the animals that most strongly express the personality characteristics of interest and breeds these animals with each other. If the selective breeding creates offspring with even stronger traits, then we can assume that the trait has genetic origins. In this manner, scientists have studied the role of genetics in how worms respond to stimuli, how fish develop courtship rituals, how rats differ in play, and how pigs differ in their responses to stress.

Although selective breeding studies can be informative, they are clearly not useful for studying humans. For this psychologists rely on behavioral genetics — a variety of research techniques that scientists use to learn about the genetic and environmental influences on human behavior by comparing the traits of biologically and nonbiologically related family members (Baker, 2010). Behavioral genetics is based on the results of family studies , twin studies , and adoptive studies .

A family study starts with one person who has a trait of interest—for instance, a developmental disorder such as autism—and examines the individual’s family tree to determine the extent to which other members of the family also have the trait . The presence of the trait in first-degree relatives (parents, siblings, and children) is compared to the prevalence of the trait in second-degree relatives (aunts, uncles, grandchildren, grandparents, and nephews or nieces) and in more distant family members. The scientists then analyze the patterns of the trait in the family members to see the extent to which it is shared by closer and more distant relatives.

Although family studies can reveal whether a trait runs in a family, it cannot explain why. In a twin study , researchers study the personality characteristics of twins . Twin studies rely on the fact that identical (or monozygotic) twins have essentially the same set of genes, while fraternal (or dizygotic) twins have, on average, a half-identical set. The idea is that if the twins are raised in the same household, then the twins will be influenced by their environments to an equal degree, and this influence will be pretty much equal for identical and fraternal twins. In other words, if environmental factors are the same, then the only factor that can make identical twins more similar than fraternal twins is their greater genetic similarity.

In a twin study, the data from many pairs of twins are collected and the rates of similarity for identical and fraternal pairs are compared . A correlation coefficient is calculated that assesses the extent to which the trait for one twin is associated with the trait in the other twin. Twin studies divide the influence of nature and nurture into three parts:

• Heritability (i.e., genetic influence) is indicated when the correlation coefficient for identical twins exceeds that for fraternal twins, indicating that shared DNA is an important determinant of personality.
• Shared environment determinants are indicated when the correlation coefficients for identical and fraternal twins are greater than zero and also very similar. These correlations indicate that both twins are having experiences in the family that make them alike.
• Nonshared environment is indicated when identical twins do not have similar traits. These influences refer to experiences that are not accounted for either by heritability or by shared environmental factors. Nonshared environmental factors are the experiences that make individuals within the same family less alike. If a parent treats one child more affectionately than another, and as a consequence this child ends up with higher self-esteem, the parenting in this case is a nonshared environmental factor.

In the typical twin study, all three sources of influence are operating simultaneously, and it is possible to determine the relative importance of each type.

An adoption study compares biologically related people, including twins, who have been reared either separately or apart . Evidence for genetic influence on a trait is found when children who have been adopted show traits that are more similar to those of their biological parents than to those of their adoptive parents. Evidence for environmental influence is found when the adoptee is more like his or her adoptive parents than the biological parents.

The results of family, twin, and adoption studies are combined to get a better idea of the influence of genetics and environment on traits of interest. Table 11.6 “Data From Twin and Adoption Studies on the Heritability of Various Characteristics” presents data on the correlations and heritability estimates for a variety of traits based on the results of behavioral genetics studies (Bouchard, Lykken, McGue, Segal, & Tellegen, 1990).

Table 11.6 Data From Twin and Adoption Studies on the Heritability of Various Characteristics

Sources: Långström, N., Rahman, Q., Carlström, E., & Lichtenstein, P. (2008). Genetic and environmental effects on same-sex sexual behavior: A population study of twins in Sweden. Archives of Sexual Behavior , doi:10.1007/s10508-008-9386-1; Loehlin, J. C. (1992). Genes and environment in personality development . Thousand Oaks, CA: Sage Publications, Inc; McGue, M., & Lykken, D. T. (1992). Genetic influence on risk of divorce. Psychological Science, 3 (6), 368–373; Plomin, R., Fulker, D. W., Corley, R., & DeFries, J. C. (1997). Nature, nurture, and cognitive development from 1 to 16 years: A parent-offspring adoption study. Psychological Science, 8 (6), 442–447; Tellegen, A., Lykken, D. T., Bouchard, T. J., Wilcox, K. J., Segal, N. L., & Rich, S. (1988). Personality similarity in twins reared apart and together. Journal of Personality and Social Psychology, 54 (6), 1031–1039.

If you look in the second column of Table 11.6 “Data From Twin and Adoption Studies on the Heritability of Various Characteristics” , you will see the observed correlations for the traits between identical twins who have been raised together in the same house by the same parents. This column represents the pure effects of genetics, in the sense that environmental differences have been controlled to be a small as possible. You can see that these correlations are higher for some traits than for others. Fingerprint patterns are very highly determined by our genetics ( r = .96), whereas the Big Five trait dimensions have a heritability of 40–50%.

You can also see from the table that, overall, there is more influence of nature than of parents. Identical twins, even when they are raised in separate households by different parents (column 4), turn out to be quite similar in personality, and are more similar than fraternal twins who are raised in separate households (column 5). These results show that genetics has a strong influence on personality, and helps explain why Elyse and Paula were so similar when they finally met.

Despite the overall role of genetics, you can see in Table 11.6 “Data From Twin and Adoption Studies on the Heritability of Various Characteristics” that the correlations between identical twins (column 2) and heritability estimates for most traits (column 6) are substantially less than 1.00, showing that the environment also plays an important role in personality (Turkheimer & Waldron, 2000). For instance, for sexual orientation the estimates of heritability vary from 18% to 39% of the total across studies, suggesting that 61% to 82% of the total influence is due to environment.

You might at first think that parents would have a strong influence on the personalities of their children, but this would be incorrect. As you can see by looking in column 7 of Table 11.6 “Data From Twin and Adoption Studies on the Heritability of Various Characteristics” , research finds that the influence of shared environment (i.e., the effects of parents or other caretakers) plays little or no role in adult personality (Harris, 2006). Shared environment does influence the personality and behavior of young children, but this influence decreases rapidly as the child grows older. By the time we reach adulthood, the impact of shared environment on our personalities is weak at best (Roberts & DelVecchio, 2000). What this means is that, although parents must provide a nourishing and stimulating environment for children, no matter how hard they try they are not likely to be able to turn their children into geniuses or into professional athletes, nor will they be able to turn them into criminals.

If parents are not providing the environmental influences on the child, then what is? The last column in Table 11.6 “Data From Twin and Adoption Studies on the Heritability of Various Characteristics” , the influence of nonshared environment, represents whatever is “left over” after removing the effects of genetics and parents. You can see that these factors—the largely unknown things that happen to us that make us different from other people—often have the largest influence on personality.

Studying Personality Using Molecular Genetics

In addition to the use of behavioral genetics, our understanding of the role of biology in personality recently has been dramatically increased through the use of molecular genetics , which is the study of which genes are associated with which personality traits (Goldsmith et al., 2003 Strachan & Read, 1999). These advances have occured as a result of new knowledge about the structure of human DNA made possible through the Human Genome Project and related work that has identified the genes in the human body (Human Genome Project, 2010) 1 . Molecular genetics researchers have also developed new techniques that allow them to find the locations of genes within chromosomes and to identify the effects those genes have when activated or deactivated.

Figure 11.13

These “knockout” mice are participating in studies in which some of their genes have been deactivated to determine the influence of the genes on behavior.

Tatiana Bulyonkova – New rats – CC BY-SA 2.0.

One approach that can be used in animals, usually in laboratory mice, is the knockout study . In this approach the researchers use specialized techniques to remove or modify the influence of a gene in a line of “knockout” mice (Crusio, Goldowitz, Holmes, & Wolfer, 2009). The researchers harvest embryonic stem cells from mouse embryos and then modify the DNA of the cells. The DNA is created such that the action of certain genes will be eliminated or “knocked out.” The cells are then injected into the embryos of other mice that are implanted into the uteruses of living female mice. When these animals are born, they are studied to see whether their behavior differs from a control group of normal animals. Research has found that removing or changing genes in mice can affect their anxiety, aggression, learning, and socialization patterns.

In humans, a molecular genetics study normally begins with the collection of a DNA sample from the participants in the study, usually by taking some cells from the inner surface of the cheek. In the lab, the DNA is extracted from the sampled cells and is combined with a solution containing a marker for the particular genes of interest as well as a fluorescent dye. If the gene is present in the DNA of the individual, then the solution will bind to that gene and activate the dye. The more the gene is expressed, the stronger the reaction.

Figure 11.14

Researchers use dyes, such as these in a sample of stem cells, to determine the action of genes from DNA samples.

UCL News – A nascent retina, generated from a 3D embryonic stem cell culture – CC BY-NC 2.0.

In one common approach, DNA is collected from people who have a particular personality characteristic and also from people who do not. The DNA of the two groups is compared to see which genes differ between them. These studies are now able to compare thousands of genes at the same time. Research using molecular genetics has found genes associated with a variety of personality traits including novelty-seeking (Ekelund, Lichtermann, Järvelin, & Peltonen, 1999), attention-deficit/hyperactivity disorder (Waldman & Gizer, 2006), and smoking behavior (Thorgeirsson et al., 2008).

Reviewing the Literature: Is Our Genetics Our Destiny?

Over the past two decades scientists have made substantial progress in understanding the important role of genetics in behavior. Behavioral genetics studies have found that, for most traits, genetics is more important than parental influence. And molecular genetics studies have begun to pinpoint the particular genes that are causing these differences. The results of these studies might lead you to believe that your destiny is determined by your genes, but this would be a mistaken assumption.

For one, the results of all research must be interpreted carefully. Over time we will learn even more about the role of genetics, and our conclusions about its influence will likely change. Current research in the area of behavioral genetics is often criticized for making assumptions about how researchers categorize identical and fraternal twins, about whether twins are in fact treated in the same way by their parents, about whether twins are representative of children more generally, and about many other issues. Although these critiques may not change the overall conclusions, it must be kept in mind that these findings are relatively new and will certainly be updated with time (Plomin, 2000).

Furthermore, it is important to reiterate that although genetics is important, and although we are learning more every day about its role in many personality variables, genetics does not determine everything. In fact, the major influence on personality is nonshared environmental influences, which include all the things that occur to us that make us unique individuals. These differences include variability in brain structure, nutrition, education, upbringing, and even interactions among the genes themselves.

The genetic differences that exist at birth may be either amplified or diminished over time through environmental factors. The brains and bodies of identical twins are not exactly the same, and they become even more different as they grow up. As a result, even genetically identical twins have distinct personalities, resulting in large part from environmental effects.

Because these nonshared environmental differences are nonsystematic and largely accidental or random, it will be difficult to ever determine exactly what will happen to a child as he or she grows up. Although we do inherit our genes, we do not inherit personality in any fixed sense. The effect of our genes on our behavior is entirely dependent upon the context of our life as it unfolds day to day. Based on your genes, no one can say what kind of human being you will turn out to be or what you will do in life.

Key Takeaways

• Genes are the basic biological units that transmit characteristics from one generation to the next.
• Personality is not determined by any single gene, but rather by the actions of many genes working together.
• Behavioral genetics refers to a variety of research techniques that scientists use to learn about the genetic and environmental influences on human behavior.
• Behavioral genetics is based on the results of family studies, twin studies, and adoptive studies.
• Overall, genetics has more influence than do parents on shaping our personality.
• Molecular genetics is the study of which genes are associated with which personality traits.
• The largely unknown environmental influences, known as the nonshared environmental effects, have the largest impact on personality. Because these differences are nonsystematic and largely accidental or random, we do not inherit our personality in any fixed sense.

Exercises and Critical Thinking

• Think about the twins you know. Do they seem to be very similar to each other, or does it seem that their differences outweigh their similarities?
• Describe the implications of the effects of genetics on personality, overall. What does it mean to say that genetics “determines” or “does not determine” our personality?

1 Human Genome Project. (2010). Information. Retrieved from http://www.ornl.gov/sci/techresources/Human_Genome/home.shtml

Baker, C. (2004). Behavioral genetics: An introduction to how genes and environments interact through development to shape differences in mood, personality, and intelligence. Retrieved from http://www.aaas.org/spp/bgenes/Intro.pdf

Bouchard, T. J., Lykken, D. T., McGue, M., Segal, N. L., & Tellegen, A. (1990). Sources of human psychological differences: The Minnesota study of twins reared apart. Science, 250 (4978), 223–228. Retrieved from http://www.sciencemag.org/cgi/content/abstract/250/4978/223

Crusio, W. E., Goldowitz, D., Holmes, A., & Wolfer, D. (2009). Standards for the publication of mouse mutant studies. Genes, Brain & Behavior, 8 (1), 1–4.

Ekelund, J., Lichtermann, D., Järvelin, M. R., & Peltonen, L. (1999). Association between novelty seeking and the type 4 dopamine receptor gene in a large Finnish cohort sample. American Journal of Psychiatry, 156 , 1453–1455.

Goldsmith, H., Gernsbacher, M. A., Crabbe, J., Dawson, G., Gottesman, I. I., Hewitt, J.,…Swanson, J. (2003). Research psychologists’ roles in the genetic revolution. American Psychologist, 58 (4), 318–319.

Harris, J. R. (2006). No two alike: Human nature and human individuality . New York, NY: Norton.

Plomin, R. (2000). Behavioural genetics in the 21st century. International Journal of Behavioral Development, 24 (1), 30–34.

Roberts, B. W., & DelVecchio, W. F. (2000). The rank-order consistency of personality traits from childhood to old age: A quantitative review of longitudinal studies. Psychological Bulletin, 126 (1), 3–25.

Strachan, T., & Read, A. P. (1999). Human molecular genetics (2nd ed.). Retrieved from http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=hmg&part=A2858

Thorgeirsson, T. E., Geller, F., Sulem, P., Rafnar, T., Wiste, A., Magnusson, K. P.,…Stefansson, K. (2008). A variant associated with nicotine dependence, lung cancer and peripheral arterial disease. Nature, 452 (7187), 638–641.

Tinbergen, N. (1951). The study of instinct (1st ed.). Oxford, England: Clarendon Press.

Turkheimer, E., & Waldron, M. (2000). Nonshared environment: A theoretical, methodological, and quantitative review. Psychological Bulletin, 126 (1), 78–108.

Waldman, I. D., & Gizer, I. R. (2006). The genetics of attention deficit hyperactivity disorder. Clinical Psychology Review, 26 (4), 396–432.

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• v.9; 2013 Dec

Perceptions of nature, nurture and behaviour

Mairi levitt.

Department of Politics, Philosophy and Religious Studies, Lancaster University, County South, Lancaster, LA1 4YL UK

Trying to separate out nature and nurture as explanations for behaviour, as in classic genetic studies of twins and families, is now said to be both impossible and unproductive. In practice the nature-nurture model persists as a way of framing discussion on the causes of behaviour in genetic research papers, as well as in the media and lay debate. Social and environmental theories of crime have been dominant in criminology and in public policy while biological theories have been seen as outdated and discredited. Recently, research into genetic variations associated with aggressive and antisocial behaviour has received more attention in the media. This paper explores ideas on the role of nature and nurture in violent and antisocial behaviour through interviews and open-ended questionnaires among lay publics. There was general agreement that everybody’s behaviour is influenced to varying degrees by both genetic and environmental factors but deterministic accounts of causation, except in exceptional circumstances, were rejected. Only an emphasis on nature was seen as dangerous in its consequences, for society and for individuals themselves. Whereas academic researchers approach the debate from their disciplinary perspectives which may or may not engage with practical and policy issues, the key issue for the public was what sort of explanations of behaviour will lead to the best outcomes for all concerned.

Trying to separate out nature and nurture as explanations for behaviour, as in classic genetic studies of twins and families, is now said to be both impossible and unproductive. The nature-nurture debate is declared to be officially redundant by social scientists and scientists, ‘outdated, naive and unhelpful’ (Craddock, 2011 , p.637), ‘a false dichotomy’ (Traynor 2010 , p.196). Geneticists argue that nature and nurture interact to affect behaviour through complex and not yet fully understood ways, but, in practice, the debate continues 1 . Research papers by psychologists and geneticists still use the terms nature and nurture, or genes and environment, to consider their relative influences on, for example, temperament and personality, childhood obesity and toddler sleep patterns (McCrae et al., 2000 ; Anderson et al., 2007 ; Brescianini, 2011 ). These papers separate out and quantify the relative influences of nature/genes and nurture/environment. These papers might be taken to indicate how individuals acquire their personality traits or toddlers acquire their sleep patterns; part is innate or there at birth and part is acquired after birth due to environmental influences. The findings actually refer to technical heritability which is, ‘the proportion of phenotypic variation attributable to genetic differences between individuals’ (Keller, 2010 , p.57). In practice, as Keller illustrates, there is ‘slippage’ between heritability, meaning a trait being biologically transmissible, and technical heritability. This is not simply a mistake made by the media or ‘media hype’ but is, she argues, ‘almost impossible to avoid’ (ibid, p.71).

While researchers are aware of the complexity of gene-environment interaction, the ‘nature and nurture’ model persists as a simple way of framing discussion on the causes of behaviours. It is also a site of struggle between (and within) academic disciplines and, through influence on policy, has consequences for those whose behaviours are investigated. There is general agreement between social scientists and geneticists about the past abuses of genetics but disagreement over whether it will be possible for the new behavioural genetics to avoid discrimination and eugenic practices, and about the likely benefits that society will gain from this research (Parens et al. 2006 , xxi). In a special issue of the American Journal of Sociology ‘Exploring genetics and social structure’, Bearman considers the reasons why sociologists are concerned about genetic effects on behaviour; first they see it as legitimating existing societal arrangements, which assumes that ‘genetic’ is unchangeable. Second, if sociologists draw on genetic research it contaminates the sociological enterprise and, third, whatever claims are made to the contrary, it is a eugenicist project (Bearman, 2008 , vi). As we will see all these concerns were expressed by the publics in this study. Policy makers and publics are interested in explaining problem behaviour in order to change/control it, not in respecting disciplinary boundaries, and will expect the role of genetics to be considered alongside social factors. 2

Social and environmental theories of criminal behaviour have been dominant in criminology, and in public policy (Walsh, 2009 , p.7). Genetic disorders and mental illness have provided explanations for a small minority of offenders with specific conditions. A 2007 survey of American criminologists found that ‘criminologists of all ideological persuasions view alleged biosocial causes of crime (hormonal, genetic, and evolutionary factors and possibly low intelligence) as relatively unimportant’ compared with environmental causes (Cooper et al., 2010 ). Sociology textbooks have typically discussed biological theories of criminality only as discredited (Haralambos and Holborn, 2004 , Giddens, 2009 ). Biosocial theories are seen as attractive to ‘agents of social control’ and to be more likely to lead to abusive treatment of offenders. However, with increasing research and public interest in genetics more attention has been paid to biological aspects of crime and to genetic variations within the normal range. Research has focussed on violent and antisocial behaviours which are criminal or may be seen as a precursor to criminal behaviour, for example, antisocial behaviour in young people. Media reports have headlined ‘warrior genes’, ‘the aggressive gene’ and the ‘get out of jail free gene’, all referring to levels of monoamine oxidase A (MAOA) (Lea and Chambers, 2007 ; Levitt and Pieri, 2009 ) 3 . Think tanks and ethics groups have considered the ethics and practicalities of genetic testing for behavioural traits (Campbell and Ross, 2004 ; Dixon, 2005 Nuffield Council on Bioethics, 2002 ).

An attraction of research into genes and behaviour is the hope that identifying a genetic factor that is correlated with an increased incidence of, say, violent and antisocial behaviour, will point to a way of reducing such behaviour. Fotaki discusses the attraction of biological explanations of inequalities in health based on the assumption that genetic interventions ‘would succeed in addressing the causes of ill health that public health policies cannot.’ (Fotaki, 2011 , p.641). The danger is that biological explanations ‘are once more employed for political purposes to explain away the social roots of health inequalities.’ (ibid). Social scientists, and criminologists, have presented biological/genetic explanations of behaviour as dangerous in terms of their potential effect on the individuals or groups identified as genetically at risk. There are obvious dangers of discrimination against, and the stigmatisation of, already vulnerable groups who would be the first to be tested i.e. ‘problem’ families or minority ethnic groups. Discrimination could affect education, employment and family life. The effect of an individual being told s/he has a risk based on a genetic test has been much discussed in relation to health risks (Claassen et al., 2010 . While such information could be motivating, because it is personalised, it can also induce a fatalistic attitude that discourages the person from taking preventative measures. Claasen et al. conclude that it is important to identify those vulnerable to the fatalistic impact and to tailor health risk information (ibid p.194). Identifying risk for behaviour, rather than for disease, is likely to be more problematic because of the difficulty of finding preventative measures that are within the individuals’ own control.

..using DNA to assess risk, make a diagnosis or tailor treatments, may weaken beliefs in the efficacy of preventive behaviour and reinforce biological ways of reducing risk, resulting in a preference for medication as opposed to behavioural means to control or reduce risk (ibid, xiv).

Claasen et al.’s comment on genetic tests for health conditions could apply equally to parents given a behavioural risk for their young child from a genetic test, perhaps before any problem behaviour was evident. The test result could weaken parents’ belief that they could take action to prevent/reduce the risk of the behaviour developing in their child and pharmaceutical solutions, as posited by Caspi et al. might not be available (Caspi et al., 2002 , xvii). However, it is not necessarily the case that evidence of genetic or biological influence on behaviour leads to more punitive treatment. DeLisi et al. give the example of the use of findings from adolescent brain science in the case of Roper v. Simmons in the US which abolished the death penalty for adolescents. On the basis of the research it was stated that young people under the age of 18 ‘are more vulnerable or susceptible to negative influences and outside pressures including peer pressure’ (DeLisa et al., 2010 , p.25) When evidence on genetic traits associated with criminal behaviour has been allowed by courts, mainly in the US, it has so far more often been accepted as a mitigating rather than an aggravating factor in the offenders’ behaviour (Denno, 2009 , Farahany and Coleman, 2006 ).

Environmental explanations of behaviour can, of course, also be presented as deterministic, claiming a closed future for those experiencing poverty and disadvantage. However, it is biological explanations that have caused more concern not only because of the history of eugenics but also because they may be seen as more fundamental, being there from birth, and as harder to change. The public in surveys are reported to see the greatest role for genetic factors in physical features, a lesser role in health conditions and a smaller role still in human behaviour (Condit, 2010 , p.619).

Public perceptions

The model of nature/genes and nurture/environment is still used in behavioural genetics, as well as in popular culture, and has implications for public policy, including the treatment of offenders who claim that a genetic trait has influenced their criminal behaviour. The aim of this research was to explore ideas on the causes of behaviour, particularly violent and antisocial behaviour and examine how respondents use the nature/nurture model. This qualitative research looks at the ways in which lay publics in different age groups conceptualise the factors and influences that made them who they are and their explanations for the behaviour of other people; especially violent behaviour. It was hypothesised that the increased research and media emphasis on the role of genetic factors in health and behaviour might result in an increasing interest in ‘nature’, biology and genes as explanations for behaviour particularly among the young, but, when explaining their own behaviour people might prefer to see themselves as agents with control over their lives. By exploring explanations of behaviour with respondents from different generations, age differences should be apparent.

The views of 78 respondents from 3 generations were gathered by individual interview and questionnaires, using the same open ended questions and responses to two real-life criminal court case studies where environmental or genetic factors had been used by the defence team. Respondents were drawn from a group of retired people participating in an informal ‘senior learners’ programme at Lancaster University, a group of their mainly younger relatives and, in order to recruit more third generation respondents, a group of first year students taking a criminology module. The senior learners group had a programme of talks and discussions and could attend undergraduate lectures. They had, by definition, shown an interest in current issues in a range of fields. There were no educational or age requirements for the group but all the volunteers were retired from paid work and were aged from around 65 years to over 80 years.. They had had similar careers to those popular with social science students; social work, probation, teaching and administrative positions. The senior learners were asked to pass on questionnaires to younger relatives to investigate age differences in attitudes. The first 13 senior learners who responded were interviewed but as only 15 questionnaires were received from their relatives ethical approval was obtained to distribute the same questionnaire to Lancaster University students taking the criminology first year module. Most students were enrolled on social science degrees, including psychology and sociology, and age 18 or 19. While the sample of senior learners and relatives had only a few more women than men, 78 per cent of the students were female reflecting the gender balance on the module as a whole. This makes it difficult to comment on any gender differences in responses. No claims to generalisability are made for this exploratory study. Responses were coded and entered on SPSS and also analysed thematically using Atlas-ti.

The introduction to the interviews and questionnaire was ‘I am interested in your views and ideas on what makes us the people we are; what makes people behave the way they do? What is the influence of nature and nurture?’ The terms, nature and nurture were not used again until the final question. Although the terms were not defined all respondents readily used them with consistent meanings. They identified ‘nature’ with biology, ‘what you are born with’ and genes or DNA and nurture with all aspects of the environment including parenting, socio-economic conditions, the food you eat, culture and other people. Their understanding of environment was therefore similar to that used by genetic researchers; environment as everything that is external to the individual, although they tended to refer more to the social than the biological environment.

A general warm-up question asked whether, in their own family, there was anything they thought of as a ‘family trait’. Then respondents were asked; ‘Imagine a baby swapped at birth and brought up in a completely different family– which influences do you think would be most important – the influence of the birth parents or the influences of the new family- and why?’ 4 The rest of the interview schedule, and the subsequent questionnaire, consisted of open-ended questions.

Respondents were asked how they would explain different kinds of behaviour if they came across a child who is kind and considerate; a young person who displays antisocial and aggressive behaviour adult and an adult with criminal convictions for violence. This was to tap into any differences in general explanations of good and bad behaviour in young people and adults. A quotation about the child killers in the Bulger case being ‘unreformable’ was used to ascertain whether they saw some types of violent behavior, and the actors concerned, as immutable. In order to see how respondents conceptualized the influences of nature/biology/genes and environment/people/experiences in their own lives, respondents were asked to write down ‘what or who made you what you are today’ and any explanation of their responses. Comments were gathered on the introduction of an environmental factor (childhood neglect) by the defence in a violent attack by two young boys in England, and on a genetic factor (MAOA levels) introduced by the defence in an criminal court in Italy. Respondents were asked how they thought such evidence should be dealt with; whether it should affect the degree of blame and whether it should affect criminal responsibility. The final question asked if it mattered ‘for individuals or society’ whether nature or nurture was seen as most important in explaining problem behaviour. Those interviewed were asked if they had any further comments and there was a space for any additional comments on the questionnaire.

This paper focuses on the ways in which respondents employed nature/genes and nurture/environment in their responses as a whole and what other concepts they drew on when explaining behaviour.

Respondents’ explanations of what makes people behave the way they do are discussed through three themes.

• Nurture is more influential than nature
• Nature and nurture interact
• Emphasising nature (but never nurture) can be dangerous

Theme 1: Nurture is more influential than nature

Whether asked about influences on a baby adopted at birth, on their own lives, on an aggressive child or a violent young person, almost all respondents emphasised nurture. Parents and family were seen as the most important influences for babies and young children, moving to peer group and other relationships and experiences for a young person. The explanation for the violent behaviour of an adult had more to do with the individual and the importance of nurture/environment in explaining behaviour weakened. The quotations below explaining behaviour in a child adopted at birth, a young person and an adult illustrate the widening of influences from infancy through childhood and the onus on adults to take responsibility for themselves.

[a child] The environment in which a child grows up in, particularly the influence and role of the parents shapes how a child will grow up and what sort of adult they will be (77 Student). [a young person] I believe that upbringing shapes a person’s personality. Provisions of education, lifestyle opportunities and friendship groups all determine ….outlook. You can see evidence in young people at the school I teach at (20 Relative). Once adult they have to take responsibility for themselves and address whatever has been in their background. An adult can’t turn round and say it’s not my fault (5 Senior Learner).

Participants also saw themselves as shaped by the people surrounding them, starting with their parents, or those who brought them up. Several mentioned the illness and/or death of a parent during their childhood and older respondents talked about separation due to the second world war. Students were especially likely to mention the influence of morals instilled in them by their parents, the core values and discipline that they were taught at home. Educational experiences were important to all. For the senior learners the school leaving age had been age 15, so whether or not they stayed on at school and took public examinations was crucial for their future, and, this decision depended largely on their parents and environment. For the student respondents who had come to university from school, life so far has been ‘kind of set-out’ (41 Student), in the sense that they had progressed through the education system to gain qualifications for university. For their peer group it was normal still to be in education or training at the age of 18.

The lasting effects of early influences were particularly striking among the senior learners, because they were much further removed in years from their childhood. Many related stories about parental influence and also about teachers who taught them at least 50 years ago and had affected them for better or worse. For example a senior learner recalled one of her teachers;

I hated primary school – the teacher in 3rd or 4th year juniors [for ages 9–11] I hated her she was not a nice woman….. I passed to go to the grammar school and it shocked her. She made a derogatory comment – may not have been directed at me but felt it was- about some who should have passed and didn’t and some passing who should not have done…… I always vowed I would never be like that when I was teaching….(11 Senior Learner).

Those who related negative influences presented themselves as active in response, not necessarily at the time but later in their lives. For example a student whose mother had died wrote that ‘it made me more independent’ and another student who was bullied at school wrote that ‘it made me stronger’. The adult had to deal with all the influences (negative or positive) and take control.

Theme 2: Nature and nurture interact

While respondents’ view of themselves and of a child adopted at birth assigned greater influence to environment this did not mean that they held a simplistic model of, for example 60:40 nurture to nature. In this one question when they were asked to choose one or other as the major influence, almost all chose nurture, as many social scientists might do. However, in open questions and comments more complex interactive models were expressed. Environment/nurture can affect genes/nature and vice versa. No one used the term epigenetics but responses referred to the possibility of environmental influences affecting gene expression, for example;

People with certain predispositions (e.g. to violence) are affected by society, and society affects how their genes are expressed (40 Student).

An older respondent reflects on personal experience of child rearing and asks whether nurture is influenced by nature;

I think the nature nurture debate is very interesting. In my family I can see where my children have their own natures that have developed despite being brought up in the same family with the same boundaries etc. However, as a parent did I alter how I nurture them to take into account their nature? (14 Senior Learner).

This quotation illustrates the inseparability of nature and nurture. The child is developing within the family and the parent is developing parenting strategies informed by previous experiences and by other influences including the reactions of the children.

It was obvious to respondents that both genetic and environmental factors impact on everyone (although the role of genes is not yet understood) and it will be harder for some than for others to behave well because of their genes and environment. These people may need different treatment or extra help if they have committed violent and aggressive crimes but that does not excuse their behaviour. Only in exceptional cases, like insanity, can a young person or adult be said to have no choice but to act in a particular way. It is important that people are seen as responsible while also giving them the help they need. In these two comments the treatment for environmental problems and ‘biology’ are similar; the individual can be helped to modify his/her behaviour.

No, [nature and nurture] both play a part, but they can’t be the explanation for everything. Some people grow up in broken homes and get treated appallingly- yet they seem to understand right + wrong and accept responsibility for their actions. There are too many excuses and we never solve any problems, just make them harder to resolve.......I think if you are sane and you know right from wrong you need to suffer the consequences if you’ve committed a crime, but I do appreciate you may need help psychologically if you have anger issues, for example. If we constantly find reasons to diminish blame from people who have committed heinous acts of crime more people will think they can get away with it and it will cause more harm than good (78 Student). Some say you can’t fight your biology, but there are social factors that can stop bad behaviour like learned restraint (72 Student).

The desire to leave a space for individual agency may be linked to the finding that emphasising nature, but never nurture, could be dangerous. It is clear that as children grow up they can exercise more control over their environment, although some have more control and choices than others. On the other hand, whatever the individual is born with (genes and nature) is, or seems to be, less malleable which could lead to different criminal justice policies and different social perceptions of the criminal.

Theme 3: Emphasising nature (but never nurture) can be dangerous for society as a whole as well as for the criminal and victims

The question asked was whether it mattered ‘for individuals or society’ if either nature or nurture was seen as most important in explaining problem behavior. The two most popular answers were that both nature and nurture were needed to explain behaviour, or, that nurture was more important and that there were dangers in emphasising nature. No one in the sample regarded an emphasis on nurture as dangerous or detrimental to the individual or society. On the contrary, emphasising nurture was thought more likely to lead to non-punitive treatment of offenders. There would be attempts to alter future behaviour through improved education and parenting and spreading of knowledge in society about the impact nurture has on young people. Society as a whole would share the blame rather than the individual. As a student put it; ‘society as a whole [would be] open for criticism’ (55 S). An emphasis on nurture was therefore seen as more likely to lead to understanding of problem behaviours and effective treatment, however, the individuals were still to be held responsible for their behaviour.

In contrast there was a mistrust of nature/genetic explanations that again centred on the practical consequences for individuals. It would affect the way criminals were treated by others but could also change their view of themselves. Behaviour would be seen as unchangeable, out of the control of the individual or social action. As a consequence, individual accountability might be removed. The idea that individuals must normally be held responsible for their actions was constantly emphasised (Levitt, 2013 ).

It does [matter] because [if nurture is emphasised] people will care, parent and look after and raise people with more care. However if it’s proven it is nature, then people may lose the will to live (60 Student).

Several SLs referred to the examination at the end of primary education (the ‘eleven plus’) when explaining why they emphasised environment/nurture rather than nature, or, in this case, innate intelligence. The ‘eleven plus’ examination was used to decide which children would be offered a place at an academically selective grammar school and was based on the idea that intelligence, and future academic achievement, could be accurately measured and predicted at the age of 10 or 11.

‘The 11+ was a nature thing. I did the 11+ − it had an effect. Saying children not going to improve or change. Very embedded in the whole idea of nature – it can’t really be true’ (8 Senior Learner).

An emphasis on nature has practical detrimental consequences for individuals. Their status is fixed, for example as ‘not academic’ or ‘born evil’ and suggests, to them and to others, that their ‘nature’ is unchangeable or very difficult to change by individual or social action.

Yes, [it matters] hugely as position of blame is dependent on whether a person chose to do what they did .....nature suggests no control (35 Student).

Those who thought an emphasis on nature meant people were irredeemable either gave that as a reason not to emphasise nature or to suggest that in fact ‘defects’ of nature could be overcome, as in this comment by a student emphasising the power of education;

Yes it is very important because it helps to understand if people are reformable (nurture) or irredeemable (nature). I believe we are determined by our education and thus with the proper help we can change. In the case of people with major biological defects, education is still a way to get over these obstacles and society should be ready to help these people (38 Student).

It might be thought that offenders themselves would embrace a genetic explanation of their behaviour if this was interpreted, as the respondents feared, as meaning they were not responsible for their crimes. However, a small study of juvenile offenders in the Netherlands found that they gave social explanations of their crimes and most rejected the idea that biology might be a factor. They committed a crime for a specific purpose like to get money or to impress others or they gave environmental reasons such as a deprived background or peer pressure or explained their offences were due to psychological conditions brought on by the use of alcohol and soft drugs (Horstkötter et al., 2012 , p.291). Whether they gave goal directed or environmental reasons ‘most of them also state that they had a choice and that it was their choice to commit the crime’ (ibid p.292). As one young offender said in interview;

In the end the person makes the choice himself… The choices I have made also had a share in my past. But in the end I am the one who has made these choices (ibid).

Genes and environment

Respondents were at ease with the language of nature and nurture which was only used in the introduction to the questionnaire or interview. They readily equated genes with nature and nurture with all sorts of environmental influences. There was an acknowledgement that our understanding of environmental factors is greater than our understanding of genetics but that that would change. Older respondents were more likely to be concerned about such a change.

They're going to be doing a lot more with genetics. Influences policy profoundly and people have to be very careful. It worries me that seen to be [more determining]. The complexities don’t get looked at. If you emphasise environment it is safer from a policy point of view because given that most people don’t know what they are talking about it is safer to see the person as redeemable than to come down on the side of genetics and write people off (3 Senior Learner).

This quotation is typical in its view that nature/genes are seen as determining even though the influences on behaviour are, in reality, complex. Like the studies quoted at the beginning of the article respondents often acknowledged the complexities as nature and nurture interact but separated them when explaining the causes of specific behaviours. Students were less likely to be fearful of genetic explanations of behaviour despite their academic interest in social science. However, the hypothesis that young people might be more likely to be interested in genetic explanations for behaviour was not shown in this small study. The senior learners were more likely to refer to reading on genes and display knowledge of genetics. Older respondents and their relatives more often echoed the sociologists’ concerns about behavioural genetics discussed by Bearman earlier (Bearman, 2008 ). For those who feared the practical consequences of genetic explanations, like the respondent quoted above, ‘it is safer’ to keep away from them.

Some respondents in all age groups were prepared for advances in genetics to change their understanding of behaviour and prepared for current views of genes/nature as more basic, fixed and unchanging to change too. One of the youngest relatives, in her 20s, emphasised our incomplete knowledge of genetic influences on behaviour as a reason for focussing on nurture ‘at present’;

It is very tricky as we cannot see genes and I am not sure that I totally trust the idea of blaming genes for violent behaviour- maybe the person has a gene for passive behaviour as well. …….In any case we can change nurture but at present we cannot change nature so let’s do one thing at a time (20 Relative).

As respondents in this small study grappled with explanations for their own and others’ behaviour they focussed on the practical consequences leading to a greater concern over explanations based on nature than the more familiar ones based on a complex web of environmental factors. Whereas academic researchers approach the debate from their disciplinary perspectives which may or may not engage with practical and policy issues, the key issue for the public was what sort of explanations of behaviour will lead to the best outcomes for all concerned.

1 Behavioural epigenetic research has indicated that life experiences can affect gene expression. While controversial the research suggests the possibility of further complications for the nature-nurture relationship as nurture may be said to shape nature (Buchen, 2010 Powledge, 2011 ). 2 Bearman op cit iv. The ESRC Cambridge Network Social Contexts of Pathways into Crime (SCoPiC) promoted multidisciplinary research into the causes of crime and included the E risk longitudinal twin study led by Terri Moffitt which investigated how genetic and environmental factors shape children's disruptive behaviour http://www.scopic.ac.uk Accessed 3 Sep 2013. 3 Violent and antisocial behaviour in this longitudinal study was correlated with a common genetic trait (low expression of MAOA) only where the person was severely maltreated in childhood. Behaviour was measured on 4 outcomes; diagnoses of conduct disorder, psychological tests of aggression and anti-social personality disorder and convictions for violent crime. Caspi et al. 2002 (supplementary material). 4 This initial warm-up question implied that the influences of nature and nurture could be separated and quantified as in common usage both in academic and popular discourses. As discussed respondents were able to express their views more fully (and with more complexity) in the subsequent open questions.

Acknowledgement

The support of the Economic and Social Research Council (ESRC) is gratefully acknowledged. This work was part of the Research Programme of the ESRC Genomics Network at Cesagen (ESRC Centre for Economic and Social Aspects of Genomics).

Competing interests

The author declares that she has no competing interests.

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• Published: 08 January 2021

Nurture might be nature: cautionary tales and proposed solutions

• Sara A. Hart   ORCID: orcid.org/0000-0001-9793-0420 1 , 2 ,
• Callie Little 2 , 3 &
• Elsje van Bergen   ORCID: orcid.org/0000-0002-5860-5745 4  

npj Science of Learning volume  6 , Article number:  2 ( 2021 ) Cite this article

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• Human behaviour

Across a wide range of studies, researchers often conclude that the home environment and children’s outcomes are causally linked. In contrast, behavioral genetic studies show that parents influence their children by providing them with both environment and genes, meaning the environment that parents provide should not be considered in the absence of genetic influences, because that can lead to erroneous conclusions on causation. This article seeks to provide behavioral scientists with a synopsis of numerous methods to estimate the direct effect of the environment, controlling for the potential of genetic confounding. Ideally, using genetically sensitive designs can fully disentangle this genetic confound, but these require specialized samples. In the near future, researchers will likely have access to measured DNA variants (summarized in a polygenic scores), which could serve as a partial genetic control, but that is currently not an option that is ideal or widely available. We also propose a work around for when genetically sensitive data are not readily available: the Familial Control Method. In this method, one measures the same trait in the parents as the child, and the parents’ trait is then used as a covariate (e.g., a genetic proxy). When these options are all not possible, we plead with our colleagues to clearly mention genetic confound as a limitation, and to be cautious with any environmental causal statements which could lead to unnecessary parent blaming.

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Most parents spend hours fretting over decisions about the environment they provide to their children. The scientific literature mirrors this idea. Across a wide range of studies from many psychological domains, researchers often conclude that the environment parents provide and children’s outcomes are causally linked, through environmental transmission (see Box 1 ). For example, a study examining the association of having a home library as an adolescent and later adult literacy, numeracy and technology skills drew our attention because of in-depth coverage in the Guardian ( https://www.theguardian.com/books/2018/oct/10/growing-up-in-a-house-full-of-books-is-major-boost-to-literacy-and-numeracy-study-finds ). This study used a very rich and well-powered dataset, and found a correlation between the number of books in adolescents’ homes and literacy performance in adulthood. They conclude that “growing up with home libraries boosts adult skills”, inferring a causal connection 1 . This is depicted in Fig. 1 . Here we discuss how the correlation between the environments parents provide, the “rearing environment”, and their children’s outcomes can indeed be fully due to a causal association, or importantly, can also be partly or fully due to a genetic confounding, illustrated in Fig. 2 (see Footnote 1 in the Supplementary Notes ). After highlighting the problem, we suggest ways that psychological scientists can examine research questions related to the rearing environment and children’s outcomes in ways that account for, or at least acknowledge, genetic confounding.

Number of books in the home is thought to be an environmental causal effect on children’s reading ability. Figure by ref. 66 available at https://bit.ly/3gl8MVk under a CC BY 4.0 license.

Parents share genes related to reading ability with their children, and also control the number of books in their home. This creates gene–environment interplay. It is important to note that the environmental effect may still have a causal role, even with gene–environment interplay. If genes play a role but are not modeled (as in Fig. 1 ), the correlation between the environmental measure and the child’s trait is genetically confounded. Here, the role of genes is modeled, allowing for an estimation of the genetic effect and the environmental effect. Figure by ref. 66 available at https://bit.ly/31c52z9 under a CC BY 4.0 license.

Genetic control of exposure to the environment

Decades of work from behavioral genetics show that children’s traits are influenced by both genetic and environmental effects 2 , 3 . Likely more surprising to hear for most is that genetic influences are often seen on measures of the “environment”, suggesting that the contexts surrounding children are partly under genetic control 4 . For example, a meta-analysis found cumulative support for genetic influences on the parenting children received 5 . This idea, that there is genetic influence on exposure to environments, is called a gene–environment correlation. A gene–environment correlation describes the process by which a person’s genotype influences their exposure to the environment 6 . It is certainly not the case that genes are doing this directly, but instead genotypes matter for aspects of our personality, behaviors and cognitions, which then influence how we interact with our environment and how others interact with us 7 . This concept of an individual purposely and dynamically interacting with their surrounding environment is not limited to behavioral genetics; similar processes have been described in other literatures, for example person-centered interactions 8 and the Selective Optimization with Compensation 9 .

Specifically, there are three types of gene–environment correlations that can result in genetic confounds 6 . First, a “passive gene–environment correlation” describes the association between the genotype a child inherits from their parents and the environment the child is raised in. Another way to think of it is that genes are a third variable which influence both the rearing environment a child receives as well as the child’s own traits, via genetic transmission from parents to child. This means it is not possible to draw causal conclusions between the rearing environment and children’s traits. For example, home environments have been found to be less chaotic for children with high effortful control, with results indicating that the same genes in parents which contribute to the levels of structure in their home (i.e., factors such as absence of noise and crowding, as well as presence of structure and routine) are also transmitted to their children and contribute to effortful control 10 . Second, an “evocative gene–environment correlation” is when a person’s genetically influenced trait elicits, or evokes, a specific response from others in the environment. For example, it has been found that a person’s genes are associated with being rated as “more likeable” by others, meaning how others perceive you as a social partner, and then likely interact with you, is influenced by your genes 11 . Third, an “active gene–environment correlation” describes the association of a person’s genetically influenced traits and the environments they select. For example, the genetically influenced personality trait of socialization, measured in childhood, was associated with exposure to risky environments related to substance abuse in adolescence, in that children with low socialization were exposed to more risky environments 12 . All three have the potential to cloud the true combination of genetic and environmental influences transmitted between parents and children (i.e., genetic confounding), but it is theorized that passive gene–environment correlations have a greater effect in childhood 13 , and as such passive gene–environment correlations are the focus of our review.

To give an example of how (passive) gene–environment correlations can result in genetic confounding in studies focused on the rearing environment, a high impact finding reported that parents with higher math anxiety have children with higher math anxiety, solely due to the home environment 14 . The authors attribute helping with math homework as the causal environmental factor, concluding that parents with high math anxiety should not help with their children’s math homework. This causal connection could exist, but equally parents with math anxiety also pass on genetic (and environmental) risks related to both lower math cognition and higher math anxiety 15 . Because this genetic transmission was not controlled for, causal claims and associated parenting advice are not justified.

Another example, this time from the medical literature, examined the intergenerational transmission of smoking behavior from parents to adolescents, concluding that “the attitudes, beliefs, and behaviors toward [adolescent] cigarette use are learned through [parent] modeling” 16 . Again, this study focused on the environmental transmission from parents to offspring without accounting for the transmission of genes related to smoking behaviors and risk-taking behaviors 17 . Furthermore, the authors conclude that smoking cessation interventions in adults can reduce smoking in subsequent generations. Parent-centered interventions might help to reduce adolescent smoking, but what is overlooked is that children carry their own genetic risks for smoking, and direct intervention with the adolescents 18 could more strongly influence their smoking behaviors.

We are certainly not the first to point out this familial transmission confound within the ecological literature. Indeed, nearly 40 years ago, Scarr and McCartney proposed that “the human experience and its effects on development depend primarily on the evolved nature of the human genome” 13 , and nearly 30 years ago Plomin and Bergeman 19 addressed the prevalence of genetic confounding by illustrating that genetic influences are found on most if not all environmental measures. Since then, several reviews have pointed to multiple examples from parental warmth to alcohol use to depression where causal pathways from parent behavior to child outcomes are reported, without accounting for genetic confounding 20 , 21 , 22 . These reviews have called for researchers to use caution with causal statements, and to address genetic confounding in their limitations. Further, they have asked for journal editors and reviewers to be better watch-dogs in this endeavor; to insist that manuscripts adhere to these standards. However, based on our experience listening to conference presentations and reading press releases and newspaper articles, we believe these guidelines are not yet being met.

We believe a reason why these previous reviews have not successfully changed minds and methods is because they have not given actionable correlational design solutions to researchers outside of behavior genetics. Therefore, when faced with not doing the work or publishing work with only a potential genetic confound, researchers have chosen the latter. Therefore, in the following section we will give many possible solutions, from genetically sensitive designs to design solutions that work in lieu of genetically sensitive data, and finally, a renewed call for changes in reporting standards.

Box 1 A glossary of some key terms

What researchers can do.

The designs that we discuss below present a not all-encompassing but global overview of genetically sensitive designs and polygenic-scores (PGS) designs, and include a genetic-proxy control design (the “Familial Control Method”), which we recommend when genetically sensitive data are not available, as well as several other proxy control designs. These designs vary in how well they disentangle the genetic confound and in how challenging they are in terms of obtaining and analyzing the data.

Genetically sensitive designs

Genetically sensitive designs are ideal for studying genetic and environmental influences and their interplay. These designs take advantage of samples of related individuals that differ in genetic relatedness (e.g., monozygotic and dizygotic twins; Fig. 3 ) or differ in environmental exposure (e.g., monozygotic twins reared apart). By far the most commonly used genetically sensitive design is the classical twin design. This design works because twins share either all (identical or monozygotic twins) or half (non-identical or dizygotic twins) of their genes 23 . Both types of twins share some parts of their environment such as their home, school, and neighborhood (referred to as common or shared environmental influences), and experience some aspects of their environments separately from each other such as peer groups, hobbies, or illness (referred to as unique or non-shared environmental influences). By comparing the average correlation between the two twins in a twin pair on a trait for monozygotic versus dizygotic twins, variance can be partitioned into additive genetic influences or heritability, shared environmental influences, and non-shared environmental influences (see Footnote 2 in the Supplementary Notes ) (Fig. 4 ). Heritability of a trait is indicated if the correlation between monozygotic twins is higher than that of dizygotic twins. Shared environmental influences are estimated by subtracting the heritability estimate from the monozygotic twin correlation, and the estimated shared environmental influences is larger when the correlation coefficient between monozygotic versus dizygotic twins are close in magnitude. Finally, non-shared environmental influences are estimated by subtracting the monozygotic twin correlation from one.

The scatter plots depict how much the two types of (reared-together) twins resemble their co-twin on reading ability. Each dot represents the reading scores of both children within a pair. It can be seen that monozygotic twins are much more alike. From this, it can be concluded that differences between children are largely due to genetic differences. The data come from van Bergen et al. 34 and represent word-reading fluency test scores in Grade 2 of twin pairs with complete data. The score is the number of words read correctly within 1 min. In this sample, the monozygotic and dizygotic twin correlations were 0.84 and 0.46, respectively, which yield estimates using the Falconer formulas 67 of A  = 0.76, C  = 0.08, and E  = 0.16 (see Fig. 4 ). Figure by ref. 66 available at https://bit.ly/3k4w2Ji under a CC BY 4.0 license.

In behavioral-genetic models, the three sources of influences on individual differences are commonly labeled by the letters A, C, and E, respectively, stemming from A dditive genetic influences (also known as heritability, and sometimes represented by an h 2 instead on an A), C ommon environmental influences (also known as shared environmental influences), and non-shared E nvironmental influences (and measurement E rror). Note that the latter are by definition uncorrelated between twins. See for a detailed representation of the classical twin model, for example, Figure A.9 in ref. 23 ; r MZ  = monozygotic twin correlation; r DZ  = dizygotic twin correlation. Figure by ref. 66 available at https://bit.ly/2Xkr29P under a CC BY 4.0 license.

With regard to disentangling possible genetic confounds and instead studying the direct effect of specific aspects of the rearing environment, classical twin studies are limited because both type of twins commonly share their rearing environments. For example, twin children growing up together are exposed to the same home library or household income, so monozygotic and dizygotic twin resemblance cannot be compared for these types of environmental measures. However, a classical twin study can begin to separate the direct effect of the home environment in two cases. First, child twins can be asked to individually rate their own rearing environment (Fig. 4 ). Since individual experiences are correlated with genetic predisposition, monozygotic twins often rate their experiences of the home environment more similarly with each other than dizygotic twins do. Therefore, when child twins can report their own ratings of their rearing environment, these estimates can serve to differentiate monozygotic and dizygotic twins. Twins who are children might not differ in how many books they have in the home, but they will likely differ in how much their parents read to them, or how much their parents monitor their reading. In these cases, the extent to which aspects of children’s rating of their rearing environment do not show entirely environmental influences, in other words, some heritability is measured on the “rearing environment”, this infers that there is a genetic confound, via a passive gene–environment correlation 4 , 19 . Using child twin ratings of their rearing environment, Hanscombe et al. 24 found that 22% of the variance of chaos in the home was attributable to genetic factors, and moreover, 37% of association between chaos in the home and school achievement was due to shared genes. This suggests that this “environmental” variable of chaos in the home, measuring noise and lack of structure in the home, is partially genetically confounded. This means that chaos in the home does not have a completely direct, or causal role, on children’s school achievement.

The second way that the classical twin model can be used to identify the direct effect of the home environment, free of genetic confounding, is by focusing on the environment that adult twins create (see Fig. 4 , but replace “reading ability” with “books in their home” or the like). When twins are adults they can differ in how many books they own and the income of their household, so genetic and environmental influences on their home environments can be studied. These studies quantify genetic and environmental influences on the home environment that twins create 4 , but they do not quantify the influence of these home characteristics on outcomes in their offspring.

Other genetically sensitive designs that can address the direct effect of the rearing environment, after accounting for genetic confounding, are adoption studies, within-family sibling studies, and twin-family studies 25 . In an adoption design, resemblance between adopted children and their biological parents is due to heritability (plus the prenatal environment). In contrast, resemblance between adopted children and their adoptive parents is fully due to the environment that the parents have provided. Another way to examine the rearing environment while partially controlling for genetic confounding is to use non-twin biological siblings within a family 26 , 27 . Because biological siblings, like dizygotic twins, share half of their genes, sibling resemblance on a trait suggests the influence of genetic factors along with some shared environmental influences. However, non-twin siblings can differ on several aspects of the rearing environment such as family size or parental health and age at birth, therefore, any dissimilarity between siblings can help to determine the influences of these non-shared aspects of the rearing environments on a given trait. Sibling designs have also recently incorporated the use of genome-wide PGS which strengthen their ability to control for confounding by disentangling direct genetic influences from gene–environment correlations 28 , 29 . PGS designs are discussed in more detail, below.

Twin-family studies include twins and their family members, like young twins and their parents, or adult twins and their children. The latter, referred to as children-of-twins design (Fig. 5 ), is particularly suitable to study the effect of children’s rearing environment, free of genetic confounding 21 . Put simply, consider a mother who has an identical twin sister. The mother’s son shares half of his genetic variants with his mother, but also with his aunt. If for a given trait he resembles his mother as much as his aunt, this suggests that the resemblance is fully due to shared genes. Conversely, if he is more like his mother than aunt, this demonstrates that the resemblance between mother and son is at least partially due to the environment provided by his mother (see Footnote 3 in the Supplementary Notes ). There are even more complex extended twin family designs, described well in Keller et al. 30 and McAdams et al. 31 .

In the given example, the (adult) twins are sisters. The genetic transmission (left hand side) is fixed at 0.50 because parents and children share 50% of their genome. The other set of genes that influence the child trait (bottom left) are genetic influences that explain variance in the child trait but not the parent trait. The crucial test for presence of environmental transmission is whether the p-path is significant. Note that ‘child’ can refer to child or adult offspring. See, for the full and detailed model, ref. 31 . Figure by ref. 66 available at https://bit.ly/2D0aNYJ under a CC BY 4.0 license.

In sum, genetically sensitive designs can assess whether the rearing environment is influencing children’s outcomes, outside of genetic confounds. Although they are observational and hence cannot establish causality, or the absence thereof, they can strongly infer causality above and beyond the majority of typical observational studies. An important point to make is if a genetically sensitive study suggests no direct causality of the rearing environment on children’s outcomes, it does not imply that intervening is pointless. Successful parenting interventions are able to experimentally induce changes in parents’ skills or behaviors, which then causally improve child outcomes. Thus, observational studies, such as all the genetically sensitive designs described here, and experimental studies (preferably randomized controlled trials 32 ) answer related but different questions: the first on “what is”, so causality in the natural situation, and the second on “what could be”, so causality due to intervening 33 , 34 .

Returning to genetically sensitive designs, the disadvantage is that they require access to such data, which are challenging to collect and analyze. We note for a reader interested in using twin data to better answer their questions about the direct role of the rearing environment, twin datasets are increasingly becoming publically available. For example, TwinLife ( https://www.twin-life.de/en ), TEDS ( http://www.teds.ac.uk/researchers ), NLSY kinship links ( http://nlsy-links.github.io/NlsyLinks/ ), Netherlands Twin Register ( http://tweelingenregister.vu.nl/research ), and others are available online or via application. In addition, there is a data sharing culture in the behavioral genetics community, and most will likely share when asked. We suggest that researchers consider using these resources to better test their research questions.

PGS designs

A new avenue to study intertwined genetic and environmental effects employs genome-wide PGS. This method relies on genome-wide association studies (GWASs) which pinpoint genetic variants (i.e., single nucleotide polymorphisms (SNPs)) that are linked to a trait (Fig. 6 ). The most powerful GWAS to date ( N  > 1 million) has identified 1271 genetic variants associated with educational attainment 35 . Each of them has a tiny effect, but these tiny effects can be summed in a PGS. The PGS, calculated for all (unrelated) individuals in an independent sample, explains 12% of the variance in educational attainment. Note that twin studies estimate the heritability of educational attainment at 40% 36 , so the PGS currently captures less than one-third of this; the remainder is the “missing heritability” 37 .

Left panel: A published genome-wide association study (GWAS) serves as an external database. In an extremely large sample, a GWAS estimates tiny associations ( \({\hat{\mathrm b}}\) ) between the trait of interest and millions of genetic variants. Specifically, the genetic variants studied are single-nucleotide polymorphisms (SNPs), located across the genome. Middle panel: Polygenic scoring can be done in a sample that was not part of the GWAS. For each individual in this sample, the SNP effects ( \({\hat{\mathrm b}}\) ) are multiplied by the number of trait-associated alleles (0, 1, or 2) the person carries. These values are summed across all SNPs to arrive at the individual’s PGS. Right panel: The resulting PGSs across individuals in that sample are normally distributed. If the trait of interest is a disorder, like ADHD, the individuals in the right tail have the highest genetic risk for developing ADHD. PGSs are not yet strong enough for predictions at the individual level, but see the main text for examples of how PGSs advance science at the group level. Figure adapted from ref. 69 . Figure by ref. 66 available at https://bit.ly/2BPcCXP under a CC BY 4.0 license.

As we speak, novel methods are being designed to disentangle nature and nurture that draw on PGS. Below, we list some examples of recent developments. First, Dolan et al. 38 bring PGS into the classical twin design. By doing so, one can estimate the gene–environment correlation, rather than assume it is absent. Second, Lee et al. 35 and Selzam et al. 29 found that for cognitive traits, the predictive power of a PGS within a family was about 50% lower than across unrelated individuals. The attenuation of the PGS’ predictive power within families suggests that passive gene–environment correlations (as captured by the PGS) contribute to children’s cognitive development. As a third example, both Kong et al. 39 and Bates et al. 40 separately proposed the same design incorporating parental and offspring PGS to disentangle environmental transmission from genetic transmission (i.e., account for the genetic confound between the home environment and child outcomes). In both cases, the researchers split the genetic variants of the parents in half—those that the parent had and had not transmitted to the offspring—and calculated for each half the PGS for educational attainment (Fig. 7 ). The researchers do this because of the biological fact that a parent only transmits a random half of their genes to their child. And for this design to work, both parents and their child must be included (but see ref. 41 for a work around). Amazingly, what the researchers found was both sets of parent PGS predicted adult offspring’s educational attainment. The predictive value of the transmitted PGS was unsurprising, as this captures directly transmitted genetic effects. But the predictive value of the non-transmitted PGS was not certain. If non-transmitted PGS influence children’s traits, this effect must be environmental, likely acting through rearing behaviors that affect the child’s development. Kong et al. 39 aptly coined this genetic effect through the rearing environment “genetic nurturing”. Belsky et al. 42 did a similar analysis but with an updated PGS score. Interestingly, when this design is expanded to include grandparents, there is little evidence for genetic nurturing from the grandparent generation 43 . Fourth, Wertz et al. 44 incorporated both PGS of mothers and children, as well as direct measures of parenting. They showed that mothers’ cognitive stimulation explained the relation of the maternal non-transmitted PGS to child educational attainment. This indicated that there is a direct environmental transmission of parenting on children’s outcomes, unconfounded by correlated genetic transmission. Finally, de Zeeuw et al. 45 and Willoughby et al. 46 both used the full genetic-nurturing design (employing DNA of children and both parents) and found (thereby replicated) genetic-nurturing effects on adults’ educational attainment. Crucially, for outcomes in childhood, academic achievement and ADHD-symptoms, Zeeuw et al. 45 only found direct genetic effects; no genetic nurturing. They concluded that a large contributor to why the rearing environment predicts child outcomes may well be intergenerational transmission of genetic effects.

In this design, one needs genotypes of parents and offspring, and a measured trait in the offspring generation only. The trait in the parents, for example educational attainment, is unobserved and indexed by a polygenic score of, in this example, educational attainment. The child receives half of the genotypes of father (top left) and mother (top right) and these transmitted alleles influence the child trait directly. The parental alleles that the child does not receive can still influence the child trait indirectly, via genetically influenced behaviors in the parents (denoted by the dotted genetic-nurturing paths). Genetic nurturing is present if the polygenic score of the untransmitted alleles explains a significant proportion of the variance in the child trait. The proportion of variance explained by the polygenic score of the transmitted alleles include both genetic nurturing and direct effects. Note that ‘child’ can refer to child or adult offspring. T = transmitted, NT = non-transmitted. Figure adapted from ref. 39 . Figure by ref. 66 available at https://bit.ly/2PjpkRu under a CC BY 4.0 license.

At the moment, measured genetic variants only explain small proportions of variance and the papers mentioned above may be seen by behavioral researchers as only a proof-of-principle. Nevertheless, these exciting developments will gain in strength when increasingly larger GWASs of all sorts of traits yield more refined PGS. By this we mean that PGSs will begin to explain more and more portions of the variance in outcomes we are interested in, with the hope that eventually they will reach the theoretical upper limit of SNP heritability. Even then, using them as a genetic control (i.e., as a covariate) will continue to underestimate the total genetic effects we are looking to control. PGSs account for only one type of genetic effect, namely common variants. There is increasing evidence that traits such as educational attainment are influenced by not only common variants, but also rare variants 47 , 48 . Another concern is that new work is indicting that a PGS is not a measure of only genetic variance. Instead, it likely represents not only causal genetic effects, but genetic ancestry, assortative mating, gene x environment interactions, direct environmental influences (i.e., genetic nurture), and environmental confounds from, for example, SES 49 , 50 . Therefore, a measure of genes (i.e., a PGS) can predict trait variance via environmental routes. This parallels our earlier notion that a measure of the environment can predict trait variance via genetic routes.

In summary, at the moment the PGS is not a perfect “genetic control”, as it does not account for all of the genetic effects and also accounts for other effects, including the very environment we are interested in. But, we believe that next to no control, using a PGS as a statistical control is still better. Costs of genotyping are falling and the number of cohorts with genotype data is growing 51 . We predict that in the not-so-far future, using simply and cheaply collected genotypic information will become a regular part of the behavioral researchers’ data collection protocol, especially as the predictive validity of the PGSs increases. This means that PGSs will allow researchers to partly control for genetic confounds in their models. We foresee that it will be easier to use PGSs than rely on genetically sensitive designs.

Genetic-proxy control designs: the Familial Control Method

The designs discussed above are the current gold-standards. However, as these types of samples discussed above are not currently easy to collect and analyze, we propose here a useful work around 52 , 53 . Our colleagues can measure the same trait in both the parents as the child, and use the paternal and maternal traits as covariates. We advise to assess the traits in both parents (but acknowledge the challenge that brings), because the child shares only 50% of their genes with one parent, but all of their genes with both parents. Hence, both parents are needed to best tag the child’s genetic liability. The parental traits, included as two covariates, then serve as a proxy for the familial transmission, including genetic transmission. In doing so, you have a proxy control for the familial effect. Hence, we term this method the Familial Control Method.

The Familial Control Method is designed for traits that are mostly transmitted from parent to child through genes rather than the environment, like reading ability 54 , 55 (see Footnote 4 in the Supplementary Notes ). Van Bergen et al. 53 capitalized on this in studying whether children’s reading ability is influenced by the home literacy environment, like reading habits of the parents and the number of books in the home. Analyses consisted of straight-forward step-wise regression analyses, illustrated in Fig. 8 . The home literacy environment correlated with children’s reading ability, but for most home-literacy indicators the effect was no longer significant after accounting for the reading ability of the parents. This suggests genetic confound rather than a genuine environmental effect. The one exception was the number of books children grow up with, which did explain variance over and beyond parents’ reading skills (Fig. 8 ). This suggests a genuine environmental effect on children’s reading by the number of books itself, or something related, like the value that the family places on reading 45 .

The findings that are depicted here come from van Bergen et al. 53 . The key question is whether the environmental measure explains variance beyond the familial effect, as this indicates a genuine environmental effect. In the example given, this was 5% and significant. This was negligible and non-significant for the other environmental measures reported in ref. 53 . Figure by ref. 66 available at https://bit.ly/2Pfjelh under a CC BY 4.0 license.

A similar approach was taken by Hart et al. 52 in studying the effect of the home numeracy environment on children’s math ability. When a parent’s math ability was included in the model, some effects of aspects of the home numeracy environment on children’s math ability were attenuated, but most held up. A note of caution is that the skills of only one parent could be obtained and controlled for, so the study lacked a proxy for the genetic liability passed on by the other parent. The authors concluded that doing more math-related activities with your children does seem to directly boost their math.

We advise researchers who are interested in applying the Familial Control Method to search first in the literature for adoption and twin-family studies. Such studies with the outcome trait of interest (e.g., reading ability) assessed in both the parent and the offspring generation, test whether parent to offspring transmission is mainly genetic or environmental in nature 54 , 55 . However, such studies are scarce. If such studies for the trait of interest do not exist, a good starting point are classical twin studies. Traits with no or a small influence of the shared environment (referred to as C), like neurological traits, are more likely to be transmitted just genetically compared to traits with large shared-environment influences, like social values. Results of meta-analyses of twin studies on a very large number of traits can be found in Polderman et al. 2 and the accompanying webtool ( http://match.ctglab.nl/ ).

The Familial Control Method, using a parental trait as genetic proxy, is not watertight, and certain assumptions must be made for it to be effective for your research question (see Footnote 5 in the Supplementary Notes ). First, if, for a certain trait, parent–child resemblance is not only due to genetic transmission but also environmental transmission, the Familial Control Method can be too conservative, as it also takes away some of the variance due to true environmental effects. However, one could argue that for many situations, being slightly too cautious in causal claims about environmental influences is less harmful than being too lax. However, this might not be the case for all researchers, and we encourage behavioral researchers to consider if being too conservative is actual harmful (e.g., for the effect of an unsafe home environment on child psychopathology) Second, as mentioned earlier, the trait measured in the parents should be the same or highly similar as the trait measured in the child. This means that traits which are not at least reasonably the same in childhood as adulthood (i.e., across birth cohorts and across the lifespan) would not work in this design. So the trait should be at least reasonably measurement invariant and relatedly, show reasonable genetic stability. Fortunately, for many phenotypes, children’s phenotypes are simply developmental precursors to the adult phenotypes (e.g., for reading ability 56 , and for ADHD 57 ). A researcher must decide if the mentioned assumptions are appropriate for their trait of interest, but fortunately we do believe that these assumptions are reasonable for most to make. Third, correlations among the parent and child trait and the environmental measure of interest will be attenuated by measurement error. To reduce measurement error, one can do regressions according to the Familial Control Method in a structural equation modeling framework, with multiple indicators per construct. One can fit a model with as the outcome the latent child trait of interest, and as (correlated) predictors, the latent traits of both parents and the environmental measure of interest. If dropping the regression path ‘environmental measure → child outcome’ leads to a significantly worse model fit, this implies that the environmental measure is associated with the outcome above and beyond the familial effect. If the trait of interest is genetically transmitted, this equates to above and beyond genetic confounding, so suggests a direct environmental influence. The effect size here is given by the difference in explained variance in the child outcome of the models with and without the ‘environmental measure → child outcome’ path. Adopting a structural equation modeling framework with latent variables is especially advisable for constructs that are notoriously hard to measure reliably. Another advantage of this framework, compared to stepwise regressions, is that families with missing data can be retained.

It is likely the case that for most behavioral researchers interested in the direct role of the rearing environment, the Familial Control Method is currently the most feasible proxy genetic control. It does not require data of twin or adoption families, nor collecting DNA samples. In terms of prediction, parental traits capture more of the variance in children’s outcome than polygenic scores, so likely also capture more of the genetic confound. For the example of reading ability, it has been found that the abilities of both of the parents explain 21% of the ability of children 58 . In comparison, polygenic scores (based on the educational-attainment GWAS) have been found to explain only 2–5% of reading ability in children 59 , and more recently 5–14% of “educational achievement” (including reading, writing, speaking, listening, and mathematics) in ages 7 to 16 years 60 . Certainly this proportion of variance explained from simple polygenic scores is not trivial, and the predictive ability of polygenic scores is anticipated to increase in the coming years. However, for most behavioral scientists the trait in the parents is not only easier to measure, but currently also a better predictor. On a related note, the value of parental traits as predictors of child outcomes has been used for decades in studying precursors of developmental disorders. In such family-risk studies, children with a family history of say dyslexia, attention-deficit/hyperactivity disorder or autism are followed from an early age, before the disorder manifests itself. These children have an increased risk to develop the disorder 61 , 62 .

Other proxy control designs

Other proxy controls such as sociodemographic factors (e.g., SES) have been used ubiquitously, but these statistical adjustments are not capable of accounting for genetic confounding as adequately as the Familial Control Method, for several reasons. First, although sociodemographic factors such as educational attainment have been significantly associated with genetic factors through twin studies (40% 36 ) and GWAS (~14% 35 ), the estimates are less than unity which indicates that genetic influences are not entirely responsible for individual differences in SES. Indeed, work examining the intergenerational transmission of SES has suggested that both genetic and environmental transmission occurs 63 . In this scenario where SES is transmitted through genetic and environmental pathways, when controlling for SES in data analyses, a proportion of variance attributable to other background or environmental factors is also being controlled for in the model, unintentionally leading to reduced associations between potentially important family-level predictors and child outcomes. In other words, you’d be throwing the baby out with the bathwater.

On the other hand, controlling for SES does not actually control for all of the genetic confounding. Say a researcher is interested in controlling for genetic confounding when examining the direct influence of books in the home on children’s reading. Parental SES is a proxy for parental reading skill, but not a perfect correlate (average correlation is 0.26 64 ). Controlling for parental SES would not control for all of the potential genetic confounds on the association between books in the home and children’s reading ability. In conclusion, when controlling for SES, other potential sources of environmental variance are also being removed from the prospective models, and at the same time would not capture the extent of genetic confounding. We believe this would happen with other proxy control measures as well, outside of the Familial Control Method described above.

Here we have laid out numerous ways that genetic confounding can be controlled for when examining the rearing environment, summarized in a decision flowchart (Fig. 9 ). We can certainly foresee times that none of these options are possible. Therefore, we conclude that in those instances, our colleagues need to clearly mention the possible genetic confounding as a limitation, and to be cautious with any environmental causal statements which could lead to unnecessary parent blaming or to interventions that are a waste of time and resources. To return to our first example, expecting all homes to have plenty of books is an idealistic goal, as it would surround all children with the opportunity to read if they wished. But unfortunately, having the opportunity to read as one wishes does not unlock the code of reading for all children. Reading is a skill that requires direct instruction and practice, and children with a family history of dyslexia themselves have a 45% chance of dyslexia despite adequate instruction and practice 61 . Simply having books around the home is not enough 65 , yet the message that parents are getting is that it is. The take home messages from that are that either parents who do not have the resources for a home library are hurting their children, or parents with children struggling to read are at blame because they did not have quite enough books in the home. This is unfair and inaccurate. In the end, we believe that it is important to discover true environmental effects as well as how genes and environments interplay, especially when malleable, because then we can focus as a field on creating and testing interventions that have a greater chance of directly improving children’s outcomes.

DK = don’t know. Figure by ref. 66 available at https://bit.ly/3gkM6Et under a CC BY 4.0 license.

Reporting summary

Further information on experimental design is available in the Nature Research Reporting Summary linked to this paper.

Data availability

Data sharing not applicable to this article as no datasets were generated or analyzed during the current study.

Code availability

Code sharing not applicable to this article as no codes were generated during the current study.

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S.A.H. is supported by Eunice Kennedy Shriver National Institute of Child Health & Human Development Grants HD052120 and HD095193. Views expressed herein are those of the authors and have neither been reviewed nor approved by the granting agencies. E.vB. is supported by NWO VENI fellowship 451-15-017 (“Decoding the gene-environment interplay of reading ability”) and ZonMw grant 531003014 (“Genetics as a research tool: A natural experiment to elucidate the causal effects of social mobility on health”). She is a member of the Consortium on Individual Development (CID; NWO Gravitation grant 024.001.003) and of Research Institute LEARN!.

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Hart, S.A., Little, C. & van Bergen, E. Nurture might be nature: cautionary tales and proposed solutions. npj Sci. Learn. 6 , 2 (2021). https://doi.org/10.1038/s41539-020-00079-z

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Perceptions of nature, nurture and behaviour

• Mairi Levitt 1  

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Trying to separate out nature and nurture as explanations for behaviour, as in classic genetic studies of twins and families, is now said to be both impossible and unproductive. In practice the nature-nurture model persists as a way of framing discussion on the causes of behaviour in genetic research papers, as well as in the media and lay debate. Social and environmental theories of crime have been dominant in criminology and in public policy while biological theories have been seen as outdated and discredited. Recently, research into genetic variations associated with aggressive and antisocial behaviour has received more attention in the media. This paper explores ideas on the role of nature and nurture in violent and antisocial behaviour through interviews and open-ended questionnaires among lay publics. There was general agreement that everybody’s behaviour is influenced to varying degrees by both genetic and environmental factors but deterministic accounts of causation, except in exceptional circumstances, were rejected. Only an emphasis on nature was seen as dangerous in its consequences, for society and for individuals themselves. Whereas academic researchers approach the debate from their disciplinary perspectives which may or may not engage with practical and policy issues, the key issue for the public was what sort of explanations of behaviour will lead to the best outcomes for all concerned.

Trying to separate out nature and nurture as explanations for behaviour, as in classic genetic studies of twins and families, is now said to be both impossible and unproductive. The nature-nurture debate is declared to be officially redundant by social scientists and scientists, ‘outdated, naive and unhelpful’ (Craddock, 2011 , p.637), ‘a false dichotomy’ (Traynor 2010 , p.196). Geneticists argue that nature and nurture interact to affect behaviour through complex and not yet fully understood ways, but, in practice, the debate continues 1 . Research papers by psychologists and geneticists still use the terms nature and nurture, or genes and environment, to consider their relative influences on, for example, temperament and personality, childhood obesity and toddler sleep patterns (McCrae et al., 2000 ; Anderson et al., 2007 ; Brescianini, 2011 ). These papers separate out and quantify the relative influences of nature/genes and nurture/environment. These papers might be taken to indicate how individuals acquire their personality traits or toddlers acquire their sleep patterns; part is innate or there at birth and part is acquired after birth due to environmental influences. The findings actually refer to technical heritability which is, ‘the proportion of phenotypic variation attributable to genetic differences between individuals’ (Keller, 2010 , p.57). In practice, as Keller illustrates, there is ‘slippage’ between heritability, meaning a trait being biologically transmissible, and technical heritability. This is not simply a mistake made by the media or ‘media hype’ but is, she argues, ‘almost impossible to avoid’ (ibid, p.71).

While researchers are aware of the complexity of gene-environment interaction, the ‘nature and nurture’ model persists as a simple way of framing discussion on the causes of behaviours. It is also a site of struggle between (and within) academic disciplines and, through influence on policy, has consequences for those whose behaviours are investigated. There is general agreement between social scientists and geneticists about the past abuses of genetics but disagreement over whether it will be possible for the new behavioural genetics to avoid discrimination and eugenic practices, and about the likely benefits that society will gain from this research (Parens et al. 2006 , xxi). In a special issue of the American Journal of Sociology ‘Exploring genetics and social structure’, Bearman considers the reasons why sociologists are concerned about genetic effects on behaviour; first they see it as legitimating existing societal arrangements, which assumes that ‘genetic’ is unchangeable. Second, if sociologists draw on genetic research it contaminates the sociological enterprise and, third, whatever claims are made to the contrary, it is a eugenicist project (Bearman, 2008 , vi). As we will see all these concerns were expressed by the publics in this study. Policy makers and publics are interested in explaining problem behaviour in order to change/control it, not in respecting disciplinary boundaries, and will expect the role of genetics to be considered alongside social factors. 2

Social and environmental theories of criminal behaviour have been dominant in criminology, and in public policy (Walsh, 2009 , p.7). Genetic disorders and mental illness have provided explanations for a small minority of offenders with specific conditions. A 2007 survey of American criminologists found that ‘criminologists of all ideological persuasions view alleged biosocial causes of crime (hormonal, genetic, and evolutionary factors and possibly low intelligence) as relatively unimportant’ compared with environmental causes (Cooper et al., 2010 ). Sociology textbooks have typically discussed biological theories of criminality only as discredited (Haralambos and Holborn, 2004 , Giddens, 2009 ). Biosocial theories are seen as attractive to ‘agents of social control’ and to be more likely to lead to abusive treatment of offenders. However, with increasing research and public interest in genetics more attention has been paid to biological aspects of crime and to genetic variations within the normal range. Research has focussed on violent and antisocial behaviours which are criminal or may be seen as a precursor to criminal behaviour, for example, antisocial behaviour in young people. Media reports have headlined ‘warrior genes’, ‘the aggressive gene’ and the ‘get out of jail free gene’, all referring to levels of monoamine oxidase A (MAOA) (Lea and Chambers, 2007 ; Levitt and Pieri, 2009 ) 3 . Think tanks and ethics groups have considered the ethics and practicalities of genetic testing for behavioural traits (Campbell and Ross, 2004 ; Dixon, 2005 Nuffield Council on Bioethics, 2002 ).

An attraction of research into genes and behaviour is the hope that identifying a genetic factor that is correlated with an increased incidence of, say, violent and antisocial behaviour, will point to a way of reducing such behaviour. Fotaki discusses the attraction of biological explanations of inequalities in health based on the assumption that genetic interventions ‘would succeed in addressing the causes of ill health that public health policies cannot.’ (Fotaki, 2011 , p.641). The danger is that biological explanations ‘are once more employed for political purposes to explain away the social roots of health inequalities.’ (ibid). Social scientists, and criminologists, have presented biological/genetic explanations of behaviour as dangerous in terms of their potential effect on the individuals or groups identified as genetically at risk. There are obvious dangers of discrimination against, and the stigmatisation of, already vulnerable groups who would be the first to be tested i.e. ‘problem’ families or minority ethnic groups. Discrimination could affect education, employment and family life. The effect of an individual being told s/he has a risk based on a genetic test has been much discussed in relation to health risks (Claassen et al., 2010 . While such information could be motivating, because it is personalised, it can also induce a fatalistic attitude that discourages the person from taking preventative measures. Claasen et al. conclude that it is important to identify those vulnerable to the fatalistic impact and to tailor health risk information (ibid p.194). Identifying risk for behaviour, rather than for disease, is likely to be more problematic because of the difficulty of finding preventative measures that are within the individuals’ own control.

..using DNA to assess risk, make a diagnosis or tailor treatments, may weaken beliefs in the efficacy of preventive behaviour and reinforce biological ways of reducing risk, resulting in a preference for medication as opposed to behavioural means to control or reduce risk (ibid, xiv).

Claasen et al.’s comment on genetic tests for health conditions could apply equally to parents given a behavioural risk for their young child from a genetic test, perhaps before any problem behaviour was evident. The test result could weaken parents’ belief that they could take action to prevent/reduce the risk of the behaviour developing in their child and pharmaceutical solutions, as posited by Caspi et al. might not be available (Caspi et al., 2002 , xvii). However, it is not necessarily the case that evidence of genetic or biological influence on behaviour leads to more punitive treatment. DeLisi et al. give the example of the use of findings from adolescent brain science in the case of Roper v. Simmons in the US which abolished the death penalty for adolescents. On the basis of the research it was stated that young people under the age of 18 ‘are more vulnerable or susceptible to negative influences and outside pressures including peer pressure’ (DeLisa et al., 2010 , p.25) When evidence on genetic traits associated with criminal behaviour has been allowed by courts, mainly in the US, it has so far more often been accepted as a mitigating rather than an aggravating factor in the offenders’ behaviour (Denno, 2009 , Farahany and Coleman, 2006 ).

Environmental explanations of behaviour can, of course, also be presented as deterministic, claiming a closed future for those experiencing poverty and disadvantage. However, it is biological explanations that have caused more concern not only because of the history of eugenics but also because they may be seen as more fundamental, being there from birth, and as harder to change. The public in surveys are reported to see the greatest role for genetic factors in physical features, a lesser role in health conditions and a smaller role still in human behaviour (Condit, 2010 , p.619).

Public perceptions

The model of nature/genes and nurture/environment is still used in behavioural genetics, as well as in popular culture, and has implications for public policy, including the treatment of offenders who claim that a genetic trait has influenced their criminal behaviour. The aim of this research was to explore ideas on the causes of behaviour, particularly violent and antisocial behaviour and examine how respondents use the nature/nurture model. This qualitative research looks at the ways in which lay publics in different age groups conceptualise the factors and influences that made them who they are and their explanations for the behaviour of other people; especially violent behaviour. It was hypothesised that the increased research and media emphasis on the role of genetic factors in health and behaviour might result in an increasing interest in ‘nature’, biology and genes as explanations for behaviour particularly among the young, but, when explaining their own behaviour people might prefer to see themselves as agents with control over their lives. By exploring explanations of behaviour with respondents from different generations, age differences should be apparent.

The views of 78 respondents from 3 generations were gathered by individual interview and questionnaires, using the same open ended questions and responses to two real-life criminal court case studies where environmental or genetic factors had been used by the defence team. Respondents were drawn from a group of retired people participating in an informal ‘senior learners’ programme at Lancaster University, a group of their mainly younger relatives and, in order to recruit more third generation respondents, a group of first year students taking a criminology module. The senior learners group had a programme of talks and discussions and could attend undergraduate lectures. They had, by definition, shown an interest in current issues in a range of fields. There were no educational or age requirements for the group but all the volunteers were retired from paid work and were aged from around 65 years to over 80 years.. They had had similar careers to those popular with social science students; social work, probation, teaching and administrative positions. The senior learners were asked to pass on questionnaires to younger relatives to investigate age differences in attitudes. The first 13 senior learners who responded were interviewed but as only 15 questionnaires were received from their relatives ethical approval was obtained to distribute the same questionnaire to Lancaster University students taking the criminology first year module. Most students were enrolled on social science degrees, including psychology and sociology, and age 18 or 19. While the sample of senior learners and relatives had only a few more women than men, 78 per cent of the students were female reflecting the gender balance on the module as a whole. This makes it difficult to comment on any gender differences in responses. No claims to generalisability are made for this exploratory study. Responses were coded and entered on SPSS and also analysed thematically using Atlas-ti.

The introduction to the interviews and questionnaire was ‘I am interested in your views and ideas on what makes us the people we are; what makes people behave the way they do? What is the influence of nature and nurture?’ The terms, nature and nurture were not used again until the final question. Although the terms were not defined all respondents readily used them with consistent meanings. They identified ‘nature’ with biology, ‘what you are born with’ and genes or DNA and nurture with all aspects of the environment including parenting, socio-economic conditions, the food you eat, culture and other people. Their understanding of environment was therefore similar to that used by genetic researchers; environment as everything that is external to the individual, although they tended to refer more to the social than the biological environment.

A general warm-up question asked whether, in their own family, there was anything they thought of as a ‘family trait’. Then respondents were asked; ‘Imagine a baby swapped at birth and brought up in a completely different family– which influences do you think would be most important – the influence of the birth parents or the influences of the new family- and why?’ 4 The rest of the interview schedule, and the subsequent questionnaire, consisted of open-ended questions.

Respondents were asked how they would explain different kinds of behaviour if they came across a child who is kind and considerate; a young person who displays antisocial and aggressive behaviour adult and an adult with criminal convictions for violence. This was to tap into any differences in general explanations of good and bad behaviour in young people and adults. A quotation about the child killers in the Bulger case being ‘unreformable’ was used to ascertain whether they saw some types of violent behavior, and the actors concerned, as immutable. In order to see how respondents conceptualized the influences of nature/biology/genes and environment/people/experiences in their own lives, respondents were asked to write down ‘what or who made you what you are today’ and any explanation of their responses. Comments were gathered on the introduction of an environmental factor (childhood neglect) by the defence in a violent attack by two young boys in England, and on a genetic factor (MAOA levels) introduced by the defence in an criminal court in Italy. Respondents were asked how they thought such evidence should be dealt with; whether it should affect the degree of blame and whether it should affect criminal responsibility. The final question asked if it mattered ‘for individuals or society’ whether nature or nurture was seen as most important in explaining problem behaviour. Those interviewed were asked if they had any further comments and there was a space for any additional comments on the questionnaire.

This paper focuses on the ways in which respondents employed nature/genes and nurture/environment in their responses as a whole and what other concepts they drew on when explaining behaviour.

Respondents’ explanations of what makes people behave the way they do are discussed through three themes.

Nurture is more influential than nature

Nature and nurture interact

Emphasising nature (but never nurture) can be dangerous

Theme 1: Nurture is more influential than nature

Whether asked about influences on a baby adopted at birth, on their own lives, on an aggressive child or a violent young person, almost all respondents emphasised nurture. Parents and family were seen as the most important influences for babies and young children, moving to peer group and other relationships and experiences for a young person. The explanation for the violent behaviour of an adult had more to do with the individual and the importance of nurture/environment in explaining behaviour weakened. The quotations below explaining behaviour in a child adopted at birth, a young person and an adult illustrate the widening of influences from infancy through childhood and the onus on adults to take responsibility for themselves.

[a child] The environment in which a child grows up in, particularly the influence and role of the parents shapes how a child will grow up and what sort of adult they will be (77 Student).

[a young person] I believe that upbringing shapes a person’s personality. Provisions of education, lifestyle opportunities and friendship groups all determine ….outlook. You can see evidence in young people at the school I teach at (20 Relative).

Once adult they have to take responsibility for themselves and address whatever has been in their background. An adult can’t turn round and say it’s not my fault (5 Senior Learner).

Participants also saw themselves as shaped by the people surrounding them, starting with their parents, or those who brought them up. Several mentioned the illness and/or death of a parent during their childhood and older respondents talked about separation due to the second world war. Students were especially likely to mention the influence of morals instilled in them by their parents, the core values and discipline that they were taught at home. Educational experiences were important to all. For the senior learners the school leaving age had been age 15, so whether or not they stayed on at school and took public examinations was crucial for their future, and, this decision depended largely on their parents and environment. For the student respondents who had come to university from school, life so far has been ‘kind of set-out’ (41 Student), in the sense that they had progressed through the education system to gain qualifications for university. For their peer group it was normal still to be in education or training at the age of 18.

The lasting effects of early influences were particularly striking among the senior learners, because they were much further removed in years from their childhood. Many related stories about parental influence and also about teachers who taught them at least 50 years ago and had affected them for better or worse. For example a senior learner recalled one of her teachers;

I hated primary school – the teacher in 3rd or 4th year juniors [for ages 9–11] I hated her she was not a nice woman….. I passed to go to the grammar school and it shocked her. She made a derogatory comment – may not have been directed at me but felt it was- about some who should have passed and didn’t and some passing who should not have done…… I always vowed I would never be like that when I was teaching….(11 Senior Learner).

Those who related negative influences presented themselves as active in response, not necessarily at the time but later in their lives. For example a student whose mother had died wrote that ‘it made me more independent’ and another student who was bullied at school wrote that ‘it made me stronger’. The adult had to deal with all the influences (negative or positive) and take control.

Theme 2: Nature and nurture interact

While respondents’ view of themselves and of a child adopted at birth assigned greater influence to environment this did not mean that they held a simplistic model of, for example 60:40 nurture to nature. In this one question when they were asked to choose one or other as the major influence, almost all chose nurture, as many social scientists might do. However, in open questions and comments more complex interactive models were expressed. Environment/nurture can affect genes/nature and vice versa. No one used the term epigenetics but responses referred to the possibility of environmental influences affecting gene expression, for example;

People with certain predispositions (e.g. to violence) are affected by society, and society affects how their genes are expressed (40 Student).

An older respondent reflects on personal experience of child rearing and asks whether nurture is influenced by nature;

I think the nature nurture debate is very interesting. In my family I can see where my children have their own natures that have developed despite being brought up in the same family with the same boundaries etc. However, as a parent did I alter how I nurture them to take into account their nature? (14 Senior Learner).

This quotation illustrates the inseparability of nature and nurture. The child is developing within the family and the parent is developing parenting strategies informed by previous experiences and by other influences including the reactions of the children.

It was obvious to respondents that both genetic and environmental factors impact on everyone (although the role of genes is not yet understood) and it will be harder for some than for others to behave well because of their genes and environment. These people may need different treatment or extra help if they have committed violent and aggressive crimes but that does not excuse their behaviour. Only in exceptional cases, like insanity, can a young person or adult be said to have no choice but to act in a particular way. It is important that people are seen as responsible while also giving them the help they need. In these two comments the treatment for environmental problems and ‘biology’ are similar; the individual can be helped to modify his/her behaviour.

No, [nature and nurture] both play a part, but they can’t be the explanation for everything. Some people grow up in broken homes and get treated appallingly- yet they seem to understand right + wrong and accept responsibility for their actions. There are too many excuses and we never solve any problems, just make them harder to resolve.......I think if you are sane and you know right from wrong you need to suffer the consequences if you’ve committed a crime, but I do appreciate you may need help psychologically if you have anger issues, for example. If we constantly find reasons to diminish blame from people who have committed heinous acts of crime more people will think they can get away with it and it will cause more harm than good (78 Student).

Some say you can’t fight your biology, but there are social factors that can stop bad behaviour like learned restraint (72 Student).

The desire to leave a space for individual agency may be linked to the finding that emphasising nature, but never nurture, could be dangerous. It is clear that as children grow up they can exercise more control over their environment, although some have more control and choices than others. On the other hand, whatever the individual is born with (genes and nature) is, or seems to be, less malleable which could lead to different criminal justice policies and different social perceptions of the criminal.

Theme 3: Emphasising nature (but never nurture) can be dangerous for society as a whole as well as for the criminal and victims

The question asked was whether it mattered ‘for individuals or society’ if either nature or nurture was seen as most important in explaining problem behavior. The two most popular answers were that both nature and nurture were needed to explain behaviour, or, that nurture was more important and that there were dangers in emphasising nature. No one in the sample regarded an emphasis on nurture as dangerous or detrimental to the individual or society. On the contrary, emphasising nurture was thought more likely to lead to non-punitive treatment of offenders. There would be attempts to alter future behaviour through improved education and parenting and spreading of knowledge in society about the impact nurture has on young people. Society as a whole would share the blame rather than the individual. As a student put it; ‘society as a whole [would be] open for criticism’ (55 S). An emphasis on nurture was therefore seen as more likely to lead to understanding of problem behaviours and effective treatment, however, the individuals were still to be held responsible for their behaviour.

In contrast there was a mistrust of nature/genetic explanations that again centred on the practical consequences for individuals. It would affect the way criminals were treated by others but could also change their view of themselves. Behaviour would be seen as unchangeable, out of the control of the individual or social action. As a consequence, individual accountability might be removed. The idea that individuals must normally be held responsible for their actions was constantly emphasised (Levitt, 2013 ).

It does [matter] because [if nurture is emphasised] people will care, parent and look after and raise people with more care. However if it’s proven it is nature, then people may lose the will to live (60 Student).

Several SLs referred to the examination at the end of primary education (the ‘eleven plus’) when explaining why they emphasised environment/nurture rather than nature, or, in this case, innate intelligence. The ‘eleven plus’ examination was used to decide which children would be offered a place at an academically selective grammar school and was based on the idea that intelligence, and future academic achievement, could be accurately measured and predicted at the age of 10 or 11.

‘The 11+ was a nature thing. I did the 11+ − it had an effect. Saying children not going to improve or change. Very embedded in the whole idea of nature – it can’t really be true’ (8 Senior Learner).

An emphasis on nature has practical detrimental consequences for individuals. Their status is fixed, for example as ‘not academic’ or ‘born evil’ and suggests, to them and to others, that their ‘nature’ is unchangeable or very difficult to change by individual or social action.

Yes, [it matters] hugely as position of blame is dependent on whether a person chose to do what they did .....nature suggests no control (35 Student).

Those who thought an emphasis on nature meant people were irredeemable either gave that as a reason not to emphasise nature or to suggest that in fact ‘defects’ of nature could be overcome, as in this comment by a student emphasising the power of education;

Yes it is very important because it helps to understand if people are reformable (nurture) or irredeemable (nature). I believe we are determined by our education and thus with the proper help we can change. In the case of people with major biological defects, education is still a way to get over these obstacles and society should be ready to help these people (38 Student).

It might be thought that offenders themselves would embrace a genetic explanation of their behaviour if this was interpreted, as the respondents feared, as meaning they were not responsible for their crimes. However, a small study of juvenile offenders in the Netherlands found that they gave social explanations of their crimes and most rejected the idea that biology might be a factor. They committed a crime for a specific purpose like to get money or to impress others or they gave environmental reasons such as a deprived background or peer pressure or explained their offences were due to psychological conditions brought on by the use of alcohol and soft drugs (Horstkötter et al., 2012 , p.291). Whether they gave goal directed or environmental reasons ‘most of them also state that they had a choice and that it was their choice to commit the crime’ (ibid p.292). As one young offender said in interview;

In the end the person makes the choice himself… The choices I have made also had a share in my past. But in the end I am the one who has made these choices (ibid).

• Genes and environment

Respondents were at ease with the language of nature and nurture which was only used in the introduction to the questionnaire or interview. They readily equated genes with nature and nurture with all sorts of environmental influences. There was an acknowledgement that our understanding of environmental factors is greater than our understanding of genetics but that that would change. Older respondents were more likely to be concerned about such a change.

They're going to be doing a lot more with genetics. Influences policy profoundly and people have to be very careful. It worries me that seen to be [more determining]. The complexities don’t get looked at. If you emphasise environment it is safer from a policy point of view because given that most people don’t know what they are talking about it is safer to see the person as redeemable than to come down on the side of genetics and write people off (3 Senior Learner).

This quotation is typical in its view that nature/genes are seen as determining even though the influences on behaviour are, in reality, complex. Like the studies quoted at the beginning of the article respondents often acknowledged the complexities as nature and nurture interact but separated them when explaining the causes of specific behaviours. Students were less likely to be fearful of genetic explanations of behaviour despite their academic interest in social science. However, the hypothesis that young people might be more likely to be interested in genetic explanations for behaviour was not shown in this small study. The senior learners were more likely to refer to reading on genes and display knowledge of genetics. Older respondents and their relatives more often echoed the sociologists’ concerns about behavioural genetics discussed by Bearman earlier (Bearman, 2008 ). For those who feared the practical consequences of genetic explanations, like the respondent quoted above, ‘it is safer’ to keep away from them.

Some respondents in all age groups were prepared for advances in genetics to change their understanding of behaviour and prepared for current views of genes/nature as more basic, fixed and unchanging to change too. One of the youngest relatives, in her 20s, emphasised our incomplete knowledge of genetic influences on behaviour as a reason for focussing on nurture ‘at present’;

It is very tricky as we cannot see genes and I am not sure that I totally trust the idea of blaming genes for violent behaviour- maybe the person has a gene for passive behaviour as well. …….In any case we can change nurture but at present we cannot change nature so let’s do one thing at a time (20 Relative).

As respondents in this small study grappled with explanations for their own and others’ behaviour they focussed on the practical consequences leading to a greater concern over explanations based on nature than the more familiar ones based on a complex web of environmental factors. Whereas academic researchers approach the debate from their disciplinary perspectives which may or may not engage with practical and policy issues, the key issue for the public was what sort of explanations of behaviour will lead to the best outcomes for all concerned.

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The support of the Economic and Social Research Council (ESRC) is gratefully acknowledged. This work was part of the Research Programme of the ESRC Genomics Network at Cesagen (ESRC Centre for Economic and Social Aspects of Genomics).

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Levitt, M. Perceptions of nature, nurture and behaviour. Life Sci Soc Policy 9 , 13 (2013). https://doi.org/10.1186/2195-7819-9-13

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Received : 18 September 2013

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DOI : https://doi.org/10.1186/2195-7819-9-13

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