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Genes play a greater role in determining key personality traits like social skills and learning ability than the way we are brought up by our parents, researchers claimed.

The findings contradict the existing belief among psychologists that the environment we grow up in plays a larger role than genetics in shaping our personality.

Researchers from Edinburgh University studied more than 800 sets of identical and non-identical twins to learn whether genetics or upbringing has a greater effect on how successful people are in life.

Twins are useful in such studies because almost all twins share the same home environment as each other, but only identical twins share exactly the same genetics.

Participants were asked a series of questions about how they perceive themselves and others, such as "are you influenced by people with strong opinions?"

By applying their answers to a well-established scale of psychological scale, researchers could assess and categorise different personality traits for each person.

Writing in the Journal of Personality, the researchers found that identical twins were twice as likely as non-identical twins to share the same personality traits, suggesting that their DNA was having the greatest impact.

Genetics were most influential on people's sense of self-control and also affected their social and learning abilities and their sense of purpose.

Prof Timothy Bates, who led the study, said: "Previously, the role of family and the environment around the home often dominated people's ideas about what affected psychological wellbeing. However, this work highlights a much more powerful influence from genetics."

The study was focused on personality traits which contribute to our chances of success in life by dictating whether, for example, how determined we are to overcome challenges.

Prof Bates said: "If you think of things that people are born with you think of social status or virtuoso talent, but this is looking at what we do with what we've got.

"The biggest factor we found was self control. There was a big genetic difference in [people's ability to] restrain themselves and persist with things when they got difficult and react to challenges in a positive way."

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It's nature, not nurture: personality lies in genes, twins study shows

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Genes play a greater role in determining key personality traits like social skills and learning ability than the way we are brought up by our parents, researchers claimed. The findings contradict the existing belief among psychologists that the environment we grow up in plays a larger role than genetics in shaping our personality.

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Is personality determined by nature or nurture? New research suggests environment is stronger than genes

Personality traits are inherited through observed behaviour, not genetics

Foster parents have greater influence on personality development than birth parents in zebra finches

Study raises questions about the inheritance of personality in humans

The debate over whether nature or nurture defines personality has taken a further twist after scientists found foster parents have a greater impact on personality than directly inherited genes from parents.

Researchers at the University of Exeter and the University of Hamburg used the zebra finches to investigate how personality is transferred between generations.

They found that foster parents have a greater influence on the personalities of fostered offspring than the genes inherited from birth parents.

' 'This research shows that personality variation can be more rapidly transmitted across generations than previously thought' - Dr Nick Royle

The research measured personality by placing the zebra finches in a new environment and counting the number of features they visited.

Some were shy, staying mainly in one place while others explored widely demonstrating a more outgoing personality. Male and female birds were then paired up and allowed to breed.

Each clutch of eggs was fostered by another pair just prior to hatching. Offspring personality was measured once they were adults.

Offspring size was also measured and was found to be primarily genetically inherited and not significantly influenced by foster parent size.

Dr Nick Royle from the University of Exeter said: 'This is one of the first experiments to show that behaviour can be non-genetically transmitted from parents to offspring.

NATURE OR NURTURE - WHAT IS IT?

Our study shows that in zebra finches, personality traits can be transmitted from one generation to another through behaviour, not just genetics.'

Speaking to MailOnline, Dr. Royle said, 'It's important to understand more about the mechanisms underlying the inheritance of personality.

'Most previous studies have found personality to be genetically heritable, but few studies have looked at the potential for personality to be non-genetically transmitted.

'Our research findings are therefore surprising because they show that, for zebra finches, personality is primarily determined by the environment they experience after hatching.

'We know this because we cross-fostered eggs just before hatching, so any genetic parent effects on personality were limited to the time before hatching.'

He added: 'Although this study considers personality inheritance in zebra finches, it raises questions about the inheritance of personality in other species, including humans.

'Do adopted children inherit the personality characteristics of their birth parents or their adoptive parents? Is the environment more important than genetic inheritance in the development of personality? '

The research was published in the journal Biology Letters.

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Is personality determined by nature or nurture? New research suggests environment is stronger than genes

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Personality traits are inherited through observed behaviour, not genetics Foster parents have greater influence on personality development than birth parents in zebra finches Study raises questions about the inheritance of personality in humans The debate over whether nature or nurture defines personality has taken a further twist after scientists found foster parents have a greater impact on personality than directly inherited genes from parents.

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A lot has changed in our understanding of the timeless nature-nurture debate. Find out where we are now.

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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.

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.

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:

1. 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.

2. 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.

3. 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.

References

Bandura, A. Ross, D., & Ross, S. A. (1961). Transmission of aggression through the imitation of aggressive models. Journal of Abnormal and Social Psychology, 63, 575-582

Bandura, A. (1977). Social learning theory. Englewood Cliffs, NJ: Prentice Hall.

Bouchard, T. J. (1994). Genes, Environment, and Personality. Science, 264(5166), 1700-1701.

Bowlby, J. (1969). Attachment. Attachment and loss: Vol. 1. Loss. New York: Basic Books.

Caspi, A., Sugden, K., Moffitt, T. E., Taylor, A., Craig, I. W., Harrington, H., ... & Poulton, R. (2003). Influence of life stress on depression: moderation by a polymorphism in the 5-HTT gene. Science, 301(5631), 386-389.

Chomsky, N. (1957). Syntactic structures. Mouton de Gruyter.

Chomsky, N. (1965). Aspects of the theory of syntax. MIT Press.

Dube, S. R., Anda, R. F., Felitti, V. J., Edwards, V. J., & Croft, J. B. (2002). Adverse childhood experiences and personal alcohol abuse as an adult. Addictive Behaviors, 27(5), 713-725.

Flynn, J. R. (1987). Massive IQ gains in 14 nations: What IQ tests really measure. Psychological Bulletin, 101(2), 171.

Freud, S. (1905). Three essays on the theory of sexuality. Se, 7.

Galton, F. (1883). Inquiries into human faculty and its development. London: J.M. Dent & Co.

Gottlieb, G. (2007). Probabilistic epigenesis. Developmental Science, 10, 1-11.

Haworth, C. M., Davis, O. S., & Plomin, R. (2013). Twins Early Development Study (TEDS): a genetically sensitive investigation of cognitive and behavioral development from childhood to young adulthood. Twin Research and Human Genetics, 16(1), 117-125.

Jensen, A. R. (1969). How much can we boost I.Q. and scholastic achievement? Harvard Educational Review, 33, 1-123.

Johnston, T. D., & Edwards, L. (2002). Genes, interactions, and the development of behavior. Psychological Review, 109, 26-34.

Keller, M. C., Neale, M. C., & Kendler, K. S. (2007). Association of different adverse life events with distinct patterns of depressive symptoms. American Journal of Psychiatry, 164(10), 1521-1529.

Monroe, S. M., & Simons, A. D. (1991). Diathesis-stress theories in the context of life stress research: implications for the depressive disorders. Psychological Bulletin, 110(3), 406.

Oliver, B. R., & Plomin, R. (2007). Twins" Early Development Study (TEDS): A multivariate, longitudinal genetic investigation of language, cognition and behavior problems from childhood through adolescence. Twin Research and Human Genetics, 10(1), 96-105.

Petrill, S. A., Plomin, R., Berg, S., Johansson, B., Pedersen, N. L., Ahern, F., & McClearn, G. E. (1998). The genetic and environmental relationship between general and specific cognitive abilities in twins age 80 and older. Psychological Science, 9(3), 183-189.

Plomin, R., & Petrill, S. A. (1997). Genetics and intelligence: What's new?. Intelligence, 24(1), 53-77.

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

Plomin, R., & Bergeman, C. S. (1991). The nature of nurture: Genetic influence on "environmental" measures. behavioral and Brain Sciences, 14(3), 373-386.

Plomin, R., & DeFries, J. C. (1983). The Colorado adoption project. Child Development, 276-289.

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.

Evidence for an Interaction

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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.

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If I were to ask you the simple question,"Do you think that genes influence your personality?"the first thing you might think is that I'm asking you a stupid question. After all, nearly all our lay beliefs about the world include beliefs that some of our genetic material influences who we become as people. And though we do believe, to varying degrees, that our experiences shape who are, I'm sure we can't think of all that many people who believe, like Aristotle, that we are a tabula rasa (blank slate). As well, if you believe in evolution then you must have an implicit belief that genes influence who we are. If evolution has taught us anything, it is that survival means passing on the fittest of our genes to the next generation.

So, you come to this post with the implicit belief that your personality is most certainly influenced by your genes. What if I told that this is not what the most recent research in behavioral genetics would suggest?

Genes and Personality: The Early Years
In the early years examining the links between genes and personality, it was typical for a study to examine self-reports of personality and compare the self-reports between fraternal twins -who share roughly 50% of their genes-to those of identical twins, who share 100% of their genes. In these early twin studies, very consistent effects emerged that suggested one thing: when it comes to personality, genes matter.

In that work, researchers calculated heritability estimates-in lay terms, the amount of variation in personality that is explained by genes-by examining personality similarity between twin pairs. For identical twins, heritability estimates hovered around 46%, and 23% for fraternal twins (a heritability of 1.00 means that all variance is genetic; Jang et al., 1996). Together, this early work was very clear in its suggestion that there are some genetic influences on personality. The next question, was of course, which genes would be the biggest players in the gene-to-personality pathways?

Candidate Genes
The early work in twins is suggestive of the possibility that eventually, with enough knowledge about human DNA, scientists will be able to discover a specific gene for, well, for anything related to personality, preferences, intelligence, or physical characteristics. That's a potentially exciting domain of future research, and one that researchers have examined very vigorously in the last 15 years or so. In this work, affectionately referred to as "gene for" studies by one of my colleagues, researchers looked for specific small repeating sections of genes (single nucleotide polymorphisms or SNPs) that identified a version of a specific gene. The SNPs usually were related to the specific production or reception of neuropeptides implicated in any number of social behaviors in non-humans. One really famous SNP is the APOE4 genetic polymorphism, which has been linked to increased risk for Alzheimer's Disease in humans. Another one is the GG variant of the oxytocin receptor gene rs53576, which is associated with increased oxytocin receptors in the brain.

The critical point in these "gene for" studies is that, if we know what parts of personality that a specific neuropeptide influences, then its genetic variants should predict behavior in a similar fashion. More specifically, knowing how oxytocin influences personality ( although oxytocin's influence on behavior is still in question) would suggest that knowing variations in specific SNPs on the oxytocin receptor gene should help us predict personality.

In the subsequent "gene for" research, many researchers were left disappointed Specifically, for every breakthrough finding linking a specific SNP to a personality characteristic, there was a null replication. Several of the most promising candidate genes, such as the MAOA gene which has been linked to antisocial behavior in past research (Caspi et al., 2002), have failed to replicate in subsequent work, according to several meta-analyses (De Moor et al., 2010).

So, then genes don't influence personality?

The current prevailing genetic evidence seems to suggest that we actually don't have genes for personality. And this conclusion doesn't come from a lack of trying: The US government has spent billions on genetic research. Billions. BILLIONS!!! When I think about all the money that went into this "gene for" research, I want to throw myself out the second floor window of the psychology building. The fall wouldn't kill me, but I imagine it would hurt just as bad as it does to realize that much of our research funding was flushed down the "gene for" toilet.

Of course, the conclusion that genes don't influence personality is most certainly wrong, after all, we have decades of twin research showing similarity in personality between identical twins. At least some of that similarity has to be genetic. Are we missing something that might help uncover the great mystery linking genes and personality?

Take a longer look at the genes.
One potentially promising approach involves examining many candidate genes that relate to a specific biological system associated with personality. In one such approach, Jamie Derringer led a consortium of researchers in an examination of a collection of SNPs associated with Dopamine in prior research, and then examined associations between this collection of SNPs and sensation seeking behavior. Sensation seeking is a personality trait that is linked to a number of behavioral disorders relating to substance use and addiction-and much of the human and non-human research indicates that dopamine plays a role in this behavior.

This work differs from the "gene for" research of the past because it doesn't rely on the association of a single SNP related to dopamine influencing sensation seeking. Rather, the study looks at a number of SNPs related to dopamine in prior research, to determine if these SNPs work in concert to influence dopamine levels, and sensation seeking more broadly. This approach is appealing because it involves conceiving of genes and personality not as simple one-to-one relationships, but instead, as complex systems of genes that work in concert to express a personality trait.

The findings of this research were promising: Taking into account all the SNPs associated with sensation-seeking behaviors as an aggregate, dopamine genes worked in concert to explain around 6.6% of variation in sensation-seeking behavior (Derringer et al., 2010).

We're still not there yet.
Remember that twin studies suggested that 40% of identical twin personality was genetic? Well 6.6% in the dopamine genes study is a far-cry from 40% in this twin research. Where does the rest of the heritability go?

One possible answer arises from understanding what happens to DNA before it is expressed as a personality characteristic. As your high school biology instructor will tell you, DNA is a code for building proteins, hormones, and neuropeptides that serve specific cellular functions within the body. One thing that early gene-personality work overlooked is that a lot has to happen to allow DNA to code for specific hormones/neuropeptides, that then have to act at the cellular level to subsequently influence personality. In short, genes need to be expressed at a cellular levelin order to influence personality, and so one place where a genetic researcher might want to look to examine gene influences on personality is at this expression-that is, what genes are being unzipped by RNA, so that specific hormones/proteins are produced?

Research in honey bees is suggestive of the potential of examining RNA to predict behavior. In this work, messenger RNA abundance was a significant predictor of behavioral transitions of honey bees from hive workers to foragers (Whitfield et al., 2003). Human work in this domain is an exciting area of future research.

If you've made it this far, you can appreciate (like I do), that the question: "Do genes influence personality?" cannot receive a simple answer. On the one hand, genes clearly seem to contribute to personality, but on the other, much of the genetic evidence has not supported this view. I'm cautiously optimistic about the future of gene work. Are you?

Whitfield, C. (2003). Gene Expression Profiles in the Brain Predict Behavior in Individual Honey Bees Science, 302 (5643), 296-299 DOI: 10.1126/science.1086807

Derringer, J., Krueger, R., Dick, D., Saccone, S., Grucza, R., Agrawal, A., Lin, P., Almasy, L., Edenberg, H., Foroud, T., Nurnberger, J., Hesselbrock, V., Kramer, J., Kuperman, S., Porjesz, B., Schuckit, M., Bierut, L., & , . (2010). Predicting Sensation Seeking From Dopamine Genes: A Candidate-System Approach Psychological Science, 21 (9), 1282-1290 DOI: 10.1177/0956797610380699

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If I were to ask you the simple question,"Do you think that genes influence your personality?"the first thing you might think is that I'm asking you a stupid question. After all, nearly all our lay beliefs about the world include beliefs that some of our genetic material influences who we become as people.

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Nature refers to the biological factors in a human. Essentially, it is the genetic or hereditary makeup of an individual. These are the genes that we are born with that cannot be altered with conditioning. Traits such as hair color and type, eye color, height, and physical makeup forms a part of what is called "nature". Disorders and diseases that are inherited genetically also forms a part of this view.

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Nature Vs. Nurture: What Affects Your Behavior Profoundly?

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You like social outings and spending time with your friends. So is this because you are genetically disposed to do so, or is it because of the environment you grew up in? And what is the reason for your fear of dogs? These are some of the things that form a part of the age-old nature vs.

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Learning Objectives

1. Explain how genes transmit personality from one generation to the next.

2. Outline the methods of behavioral genetics studies and the conclusions that we can draw from them about the determinants of personality.

3. 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 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 - 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 , 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

Correlation between children raised together

Correlation between children raised apart

Estimated percent of total due to

Identical twins

Fraternal twins

Identical twins

Fraternal twins

Heritability (%)

Shared environment (%)

Nonshared environment (%)

This table presents some of the observed correlations and heritability estimates for various characteristics.

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.

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.

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

1. 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?

2. 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?

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

References

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.

This is a derivative of Introduction to Psychology by a publisher who has requested that they and the original author not receive attribution, which was originally released and is used under CC BY-NC-SA. This work, unless otherwise expressly stated, is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

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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.