Personality and Genetics

Nature vs Nurture

Have you watched the TV series called Mindhunter? It’s about two FBI agents who goes after serial killers using their unorthodox methods that eventually creates a new profession called ‘Criminal Behavioral Analyst’. They studied famous serial killers from all around the US and interviewed them and tried to understand what made them do the things they did. Was it their upbringing or are they simply wired that way? This question has been tormenting scientists ever since the inception of Psychology and Philosophy. Another branch of science that is fairly new, Genetics, is also now trying to answer this question. Scientists now have an entire branch dedicated to it, Behavioral Genetics. I am not an expert in any of the sectors mentioned above. But this question has been itching my mind for a long time as well. Ever since I started reading non-fiction books back in high school, I was drawn to Psychology. That curiosity to understand human mind and in turn, ‘Myself’, has led me to read tons of books and articles about Psychology. Today I want to share some interesting facts I found out during this journey that shine some light on the debate between Nature vs Nurture. On the one side, there’s the notion that the apple doesn’t fall far from the tree (“nature”). Children inherit specific personality traits in the same way they inherit physical features from parents. Personality is wired in, and no quirks of upbringing will change it. In the opposing corner stands the theory of nurture. This side argues that the human mind is a blank slate, and it’s the sum total of your environment, learning and experiences that shape you to be the person you are today. Which one is true? Let’s try to find out.

The Big Five

While there are endless possibilities for how a person behaves and perceives the world, five primary traits are often measured. The Big Five personality traits (OCEAN) is a suggested grouping for personality traits, developed from the 1980s onward in psychological trait theory. The theory identified five factors from which a personality type can be determined.

• O – Openness to experience (inventive/curious vs. consistent/cautious)
• C – Conscientiousness (efficient/organized vs. extravagant/careless)
• E – Extraversion (outgoing/energetic vs. solitary/reserved)
• A – Agreeableness (friendly/compassionate vs. critical/rational)
• N – Neuroticism (sensitive/nervous vs. resilient/confident)

This theory or taxonomy is used in most of the studies in Behavioral science and that’s why it’s important to get familiarized with them before jumping into the studies themselves.

Statistical Approach

Longitudinal Studies

A longitudinal study is a research design that involves repeated observations of the same variables (e.g., people) over short or long periods of time. There are many such studies designed in order to understand the influence of genes in human behavior. One of them is Twin Study. Twin studies are studies conducted on identical or fraternal twins. It is considered a key tool in behavioral genetics. Minnesota Twin Family Study is a twin study established in June 1989 with 1300 same-gendered twin pairs age 11 or 17, with an additional cohort of 500 such pairs recruited around 2004. They were born between 1972 and 2000. Another variation of this study was based on reared apart twins. Thomas J. Bouchard began to study twins who were separated at birth and reared in different families as “The Minnesota Study of Twins Reared Apart” in 1979. Another study called The Sibling Interaction and Behavior Study (SIBS) is a study of over 600 adoptive and non-adoptive families. The adoption study design allows one to disentangle the environmental and genetic influences on a phenotype, including psychological phenotypes. There are numerous other research methodologies that scientists have used over the decades to answer this questions. I am going to discuss some of the findings here.

Twin Study

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. The idea is that 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. 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.

Types of Influence

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.
• Non-shared 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. Non-shared 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 non-shared environmental factor.

Data from Twin and Adoption Studies

	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 (%)
Age of puberty					45	5	50
Aggression	0.43	0.14	0.46	0.06
Alzheimer disease	0.54	0.16
Fingerprint patterns	0.96	0.47	0.96	0.47	100	0	0
General cognitive ability					56	0	44
Likelihood of divorce	0.52	0.22
Sexual orientation	0.52	0.22			18–39	0–17	61–66
Big Five dimensions					40–50

table source

Some key takeaways from the table:

• 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).
• Despite the overall role of genetics, we can also see 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. 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.
• Column 7 shows us that the influence of shared environment (i.e., the effects of parents or other caretakers) plays little or no role in adult personality. Shared environment does influence the personality and behavior of young children, but this influence decreases rapidly as the child grows older.
• 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 the table represents whatever is “left over” after removing the effects of genetics and parents. We 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.

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 non-shared 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.

Influence on Big Five

For most of the traits measured, more than half the variation between the twins was shown to be genetic. Among the traits found, most strongly determined by heredity were ambition, vulnerability to stress (neuroticism), leadership, risk-seeking, a sense of well-being and, surprisingly, respect for authority. The genetic factor for these traits was found to run somewhere in the region of 40-50 percent. Even though the twin studies demonstrate the strong influence of nature, family influence still matters. More recent studies, for example, have shown that the personality trait of conscientiousness has a far lower genetic correlation than the other personality traits. This suggests that a parent or educator might equip an inherently spontaneous child with the tools he/she needs to show duty and self-discipline, and thus influence the development of his/her personality. It’s not just family influence that matters, either. In a British study, researchers found that, on average, 60 percent of the variation in a child’s unruly behavior in school was down to their genes. But in London and other global hotspots, environment played a far greater role. The researchers concluded that issues such as deprivation, housing, education and even pollution levels could all influence how your DNA expresses itself as personality.

This brings us to another fascinating conclusion drawn by the Minnesota twin studies. Researchers found that raised-apart identical twins are more similar than identical twins that are raised together. That’s because together-twins have the opportunity to recognize their similarities and deliberately change their behavior so they might be different from their sibling – effectively turning off their genes. All of which seems to suggest that, even if we do inherit certain parts of our personalities, we’re not forever stuck with them. There’s a strong possibility that we can change our disposition simply by changing our environment, or possibly even through sheer force of will.

So far I have just discussed about the longitudinal studies and some of the major findings. These studies are conducted over a long period of time and they are mostly based on surveys and statistical analysis. They do not take into consideration individual genes and directly collect data from family members who are by definition genetically related. Next I’ll dive into Genetics and studies based on that. Before going to that let me share the story of a famous twin called “Jim twins”. These twins were adopted at the age of four weeks. Both of the adopting couples, unknown to each other, named their son James. Upon reunion of the twins when they were 39 years old, Jim and Jim have learned that:

• Both twins are married to women named Betty and divorced from women named Linda.
• One has named his first son James Alan while the other named his first son James Allan.
• Both twins have an adopted brother whose name is Larry.
• Both named their pet dog Toy.
• Both had some law-enforcement training and had been a part-time deputy sheriff in Ohio.
• Each did poorly in spelling and well in math.
• Each did carpentry, mechanical drawing, and block lettering.
• Each went to vacation in Florida in the same three-block-long beach area.
• Both twins began suffering from tension headaches at eighteen, gained ten pounds at the same time, and are six feet tall and 180 pounds.

Spooky, huh? Some of these incidents such as being a deputy sheriff in Ohio or vacation in Florida might have been caused by statistical bias, but the rest of them definitely makes us wonder, how on earth such kind of coincidence is possible.

Genetic Approach

What is a Gene?

Each cell in our body has a Nucleus and there are 23 pairs of Chromosomes in each of them. One of each pair comes from our father, and the other comes from our 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. 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.

How Does it Affect Personality

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 “criminal genes” that makes a person commit crimes. 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. So despite the fact that genes do impact our personalities, it is crucial to understand, “to what extent?”.

How DNA Makes Us Who We Are

In his book, Blueprint: How DNA Makes Us Who We Are, American psychologist and geneticist Robert Plomin has put together his entire life’s work between the covers. It took him more than 30 years to conduct his studies and for the technology to evolve to a state where he could do the studies he wanted to do and finally after all these years, he brought this book to us along with some extraordinary findings. I am going to write a separate blog post just about this book. But I can share one or two key ideas here.

At the moment, mental health follows the classical medical model by diagnosing a disorder and then seeking to deal with its cause. But genetic research suggests there are no clear lines in mental disorders, rather a spectrum on which we are all genetically placed. The example that Plomin gives is depression. If, say, there were 1,000 DNA differences found between two control groups of depressed and non-depressed people, it might be that in the general population the average person would have 500 of these depression-causing differences. And many people far fewer. Those with the fewest would be at least risk of becoming depressed and those with the most, at the greatest risk. It’s a question of probability, not certainty – an underlying predisposition, as it were, that might be triggered by unpredictable events.

This genetic research leads to a momentous conclusion. There are no qualitative disorders, only quantitative dimensions. That means you can’t cure a disorder, because there is no disorder. You can ameliorate the symptoms, which is what they do now with schizophrenia. They don’t try and cure the underlying problem. They just say: ‘There are some behaviors, and CBT (Cognitive behavioral therapy) can help people change their behaviors so they rub along better in life. They are merely the quantitative extremes of continuous traits.

Robert Plomin

Genome-wide Association Studies (GWAS)

So far we have established that genes influence our personality, no single gene can influence any particular personality trait, multiple genes work together to form a trait and no personality trait is absolute, rather it’s all just a quantitative value in a spectrum. At this point let’s explore some of the findings from genome based studies to see which genes correlate to each other.

“Although personality traits are heritable, it has been difficult to characterize genetic variants associated with personality until recent, large-scale GWAS,” explains lead researcher Chi-Hua Chen from the University of California, San Diego. Chen and his team analyzed genetic data, including around 60,000 genetic samples collected by private firm 23andMe and some 80,000 samples provided by the Genetics of Personality Consortium.

Correlated Genes

• The genes WSCD2 and PCDH15 are connected to extraversion, while the gene L3MBTL2 and the chromosome 8p23.1 are tied to neuroticism.
• Genes related to neuroticism and openness to experience were clustered together in the same regions as genes linked to certain psychiatric disorders.
• Some genetic correlations showed connections between extraversion and attention deficit/hyperactivity disorder (ADHD).
• There are correlation between openness and schizophrenia and bipolar disorder.
• Neuroticism and depression and anxiety are correlated as well.

In other words, the same parts of DNA coding that help define our personalities could also affect our likelihood of developing mental health problems. That’s not to say the genes we’re born with fully define our personality and make psychiatric problems inevitable. It’s still early days for the research, and the study has only shown a correlation, not a causative link between personality traits and certain psychological disorders, but the team says with more investigation, they might be able to find a way to predict and treat these disorders in the future.

On another note, the research found no genetic overlap between mental illnesses and agreeableness (being cooperative and compassionate), or conscientiousness (being responsible and self-disciplined). Those are dependent on known or unknown environmental factors. Let’s summarize these in the next section a bit and see which traits actually come from parents and which are environmentally influenced based on all types of research findings.

Genetic personality traits (inherited from parents)

Distractability

Specific learning disabilities resulting from high levels of distractability, such as ADHD, have been found to be linked to numerous inherited genes. Unfortunately, there are no genetic tests to determine whether someone has ADHD; however, after nearly 2,000 studies, it has been found that the genes typically linked to ADHD often run in families.

​​​​Leadership

In a newer study, specific inherited DNA sequences were found to correlate with leadership abilities. In this study, a particular genotype was found associated with passing leadership abilities down through generations.

Neuroticism

During the Minnesota twin studies, scientists found that certain traits, including neuroticism, were inheritable. People with this trait are more vulnerable to stress and are often seen as more nervous and sensitive to stimuli, while those without may have a more positive and calm demeanor.

Environmental influences on personality traits

Patience

The environment in which a child is raised can influence their level of patience and reaction to stressors. A study measuring the patience of children abroad found that those residing in more remote and rural locations tended to be more patient than those living in more industrialized city locations. The ability to be patient and tolerant of uncertainty varied significantly based on the location, suggesting that the environment greatly influenced this trait.

Intimacy

Intimacy seems to be more based on the environment rather than genetics. Researchers found that two-thirds of this personality trait depended on past experiences. Someone raised in an unloving or individualistic environment may have low amounts of this trait- meaning they tend to keep to themselves and do not have a strong desire to be in emotionally intense relationships or situations. Doctors also stated that this gene, in particular, can be greatly strengthened through quality interactions with family; this trait will develop more in children exposed to emotional and physical intimacy during adolescence.

Etiquette

People within different communities or cultures will have contrasting practices when it comes to manners and etiquette. A polite person who practices good manners typically will have had a different upbringing than a person who acts oppositely. Certain standards of decorum, acceptable behaviors, and morality result in a learned expression of how a person behaves in different settings. Etiquette varies depending on culture and therefore has differing effects on personality development.

Verdict

The idea that my personality traits or my characteristics are predetermined and I have no other option but to follow my genetic coding is quite unacceptable to me. We always have a choice. Every single day we make hundreds of small choices and we live by those choices which eventually grow to become our habits or personality. 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 on the context of our life as it unfolds day to day. Based on my genes, no one can say what kind of human being I will turn out to be or what I will do in life. The largely unknown environmental influences, known as the non-shared environmental effects, have the largest impact on personality. Because these non-shared environmental differences are non-systematic 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. So it could be said that, Nature and Nurture both are important for sure, but end of the day the world we live in and our willpower will influence our Personality more than either of them.

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You can also go through the articles on Truity, ScienceAlert, CrystalKnows, University of Minnesota Website, The Guardian and the book Introduction to Psychology by Charles Stangor and Jennifer Walinga to dig deeper into this topic. There are numerous other resources but I found these to be very informative and easy to understand at the same time. If you find/know any other material to study more on Behavioral Genetics, feel free to share in the comments along with your opinion on this.