Personality and Genetics: Nature vs Nurture

Nature vs Nurture

Have you ever heard of the TV series Mindhunter? It follows two FBI agents who track down serial killers by using innovative methods and, in doing so, create a new profession: ‘Criminal Behavioral Analysts.’ They study notorious serial killers across the US, interviewing them to understand what drives them to commit such crimes. Are they shaped by their upbringing, or is something within them responsible? This question has puzzled scientists since the beginning of psychology and philosophy. Now, genetics—a relatively new field—is also trying to answer this question, giving rise to a branch known as Behavioral Genetics, which is dedicated to exploring it.

While I’m not an expert in any of these fields, I’ve been fascinated by this question for a long time. Ever since I started reading non-fiction in high school, I’ve found psychology captivating. I wanted to understand the human mind better, and, in a way, understand myself better too. As I continued reading books and articles on psychology, I came across some interesting insights into the nature vs. nurture debate.

On one side is the “nature” perspective. It holds that children inherit certain personality traits just as they inherit physical features from their parents. According to this view, personality is something inherent and unchangeable, unaffected by upbringing. On the other side, there’s the “nurture” perspective. Advocates of this view argue that the human mind starts as a blank slate and is shaped by the environment, experiences, and learning. So, which one is true? Let’s dive in a little deeper to explore both sides.

The Big Five

When it comes to understanding how people behave and see the world, psychologists have identified five important traits that can help us make sense of it all. These traits are known as the Big Five personality traits, or simply OCEAN, and they have been studied since the 1980s as a way to understand different personality types.

Let’s break it down:

• Openness to Experience: Some people are very curious and love trying new things, while others prefer to stick to what they know and are cautious about new experiences.
• Conscientiousness: This trait refers to how organized and efficient someone is. Some individuals are very methodical and careful, while others might be more carefree and spontaneous.
• Extraversion: This trait looks at how outgoing and energetic someone is. Some people thrive in social situations and love being around others, while others prefer solitude and enjoy their own company.
• Agreeableness: Here, we consider how friendly and compassionate a person is. Some individuals are naturally warm and kind, while others tend to be more critical and rational.
• Neuroticism: This trait relates to how sensitive and nervous someone can be. Some people are more resilient and confident in the face of challenges, while others may feel anxious or stressed more easily.

These traits play a significant role in Behavioral Science studies. So, understanding them is essential before delving into any research on human behavior.

Statistical Approach

Longitudinal Studies

A longitudinal study is a type of research design where scientists observe the same group of people or variables over a period of time, either short or long. These studies are important in understanding how genes influence human behavior. One type of longitudinal study is the Twin Study, which focuses on identical or fraternal twins. The Minnesota Twin Family Study, for example, began in 1989 and involved 1,300 sets of same-gendered twin pairs aged 11 or 17, with an additional 500 pairs recruited later. They were born between 1972 and 2000.

Another variation of the study involved twins who were separated at birth and raised in different families, called “The Minnesota Study of Twins Reared Apart,” which started in 1979. There’s also The Sibling Interaction and Behavior Study (SIBS), involving over 600 adoptive and non-adoptive families. The adoption study design helps separate the impact of environment and genetics on various traits, including psychological traits. Scientists have used various research methods over the years to answer these questions, and I’ll discuss some of their findings.

Twin Study

In a twin study, researchers collect data from many pairs of twins and compare the rates of similarity between identical and fraternal twins. The goal is to figure out whether the similarity is more due to genetic factors or environmental influences. If identical twins, who share all their genes, are more similar in a trait compared to fraternal twins, who share only half of their genes, it suggests that genetics play a significant role.

To measure this, scientists calculate something called a correlation coefficient, which tells us how much one twin’s trait is associated with the same trait in the other twin. The higher the correlation coefficient, the more likely it is that genetics have a strong influence on that particular trait.

Types of Influence

In understanding how nature (genetics) and nurture (environment) shape our personalities, researchers use twin studies to separate these influences into three parts:

• Heritability: This refers to the influence of our genes on our personality traits. When identical twins (who share all their genes) show more similarity in personality compared to fraternal twins (who share only about half their genes), it suggests that genes play an important role in shaping who we are.
• Shared Environment: This refers to the influence of the environment that both twins share, typically within the family. When both identical and fraternal twins show similar traits because they have had similar experiences in their family, it indicates that the shared environment has affected their personalities.
• Non-Shared Environment: This refers to the experiences that make twins within the same family different from each other. These influences are not determined by genes or the shared environment. For example, if one child in a family receives more affection from a parent, and as a result, develops higher self-esteem, this difference in parenting becomes 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

Key takeaways from the table:

• Nature has a stronger influence on personality than parents. Even identical twins raised in different households have similar personalities compared to fraternal twins raised separately.
• Genetics play a significant role in personality, but they don’t determine everything. Identical twins’ personality correlations and heritability estimates are less than 1.00, showing the environment’s importance. For example, heritability estimates for sexual orientation vary from 18% to 39%, indicating that 61% to 82% is due to environmental factors.
• The influence of shared environment on adult personality is minimal. While it does impact young children, this influence decreases as they grow older.
• Parents cannot solely shape their children into specific roles, such as geniuses, athletes, or criminals, through environmental influences alone. The last column represents other factors that make us unique and have a significant impact on personality.

To sum up, genetics is essential, but not the only factor shaping personality. Non-shared environmental influences play a bigger role, making us distinct individuals. Even identical twins have different personalities as they grow due to unique experiences.

Influence on Big Five

Scientists have conducted studies on twins to understand the impact of genetics and environment on personality traits. These studies revealed that for most of the traits they measured, more than half of the differences between twins were due to genetic factors. This means that our genes play a significant role in shaping our personalities.

Among the personality traits studied, some were strongly determined by our genes. These traits include ambition, vulnerability to stress (neuroticism), leadership qualities, risk-seeking behavior, a sense of well-being, and surprisingly, respect for authority. Approximately 40-50 percent of these traits can be attributed to genetic factors. However, it’s essential to remember that family influence also matters.

Recent studies have shown that the personality trait of conscientiousness has a lower genetic correlation compared to other traits. This suggests that parents or educators can have a considerable impact on a child’s development. For example, they can help a naturally spontaneous child develop qualities like duty and self-discipline, shaping their personality positively.

Moreover, the environment also plays a significant role in our personality. In a study in Britain, it was found that about 60 percent of a child’s unruly behavior at school is influenced by genetics. However, in places like London and other busy cities, environmental factors have a more substantial influence. Things like deprivation, housing conditions, education, and pollution levels can affect how our DNA expresses itself as personality traits.

Another interesting finding from the Minnesota twin studies is that identical twins raised apart are often more similar than those raised together. This is because twins raised together may consciously try to be different from their sibling, which can “turn off” certain genetic influences. This suggests that even though we inherit some parts of our personalities, we are not bound by them forever. Changing our environment or even having a strong determination to change can alter our disposition and personality over time. So, it’s not just about our genes; we have the potential to shape our own personalities through our actions and surroundings.

The Jim Twins

So far, we have discussed longitudinal studies and some of the major findings. These studies take place over many years and are usually based on surveys and statistical analysis. They don’t look at individual genes and instead gather information from family members who are related genetically. Now, let’s move on to the topic of Genetics and studies related to it. But before that, I want to share an intriguing story about famous twins known as the “Jim twins.”

These twins were adopted when they were just four weeks old. What’s amazing is that both of their adopting families, without knowing each other, named their sons James. When Jim and Jim finally reunited at the age of 39, they discovered some astonishing similarities:

• Both twins were married to women named Betty and had been divorced from women named Linda.
• One named his first son James Alan, while the other named his first son James Allan.
• Both twins had an adopted brother named Larry.
• They both named their pet dog Toy.
• Both had some law-enforcement training and had worked part-time as deputy sheriffs in Ohio.
• They both struggled with spelling but excelled in math.
• They both had skills in carpentry, mechanical drawing, and block lettering.
• They both used to go on vacation to the same three-block-long beach area in Florida.
• Both twins began experiencing tension headaches at the age of eighteen, gained ten pounds at the same time, and are six feet tall, weighing 180 pounds.

It’s quite spooky, isn’t it? Some of these similarities, like being a deputy sheriff in Ohio or vacationing in Florida, might be due to statistical bias. However, the rest of the similarities make us wonder how such a remarkable coincidence could happen.

Genetic Approach

Genetic Approach

What is a Gene?

Every cell in our body has a center called the Nucleus, and inside it are 23 pairs of Chromosomes. We get one chromosome of each pair from our father and the other from our mother. These chromosomes are made up of a molecule called DNA (deoxyribonucleic acid), and the DNA is grouped into segments called genes. Think of a gene as the basic building block that passes on characteristics from one generation to the next. In humans, we have about 25,000 genes. The genes of individuals within the same species are almost the same. For example, the DNA in your genes is about 99.9% identical to the DNA in my genes and in the DNA of every other human.

These genes are responsible for the various natural behaviors we have, and they define the traits of our species. We call these natural behaviors instincts. Different animals have different instincts: birds build nests, dogs are loyal to their human caretakers, and humans naturally learn to walk, speak, and understand language. However, the strength of these traits and behaviors can vary within the species. Some rabbits are more fearful than others, some dogs are more loyal, and some humans may be better at speaking or writing. These variations are partly due to the small differences (about 0.1%) in the genes among individuals within the species.

How Does it Affect Personality

Our personality is not determined by just one gene; rather, it is influenced by many genes working together. There is no single “IQ gene” that solely decides intelligence, and there are no “criminal genes” that force someone to commit crimes. Personality is a complex interplay of multiple genes. Some genes may increase certain traits, while others may decrease the same traits. This complex relationship, along with various random factors, ultimately shapes our personality.

Moreover, genes always work alongside the environment to create our personality. Having a specific set of genes doesn’t guarantee the development of a particular trait, as some traits may only emerge in specific environments. So, although genes do play a role in shaping our personalities, it’s essential to understand the extent to which they do so. The environment also plays a crucial part in how our personality develops.

How DNA Makes Us Who We Are

In the book Blueprint: How DNA Makes Us Who We Are, written by psychologist and geneticist Robert Plomin, he shares the culmination of over 30 years of research. The book presents some remarkable discoveries about how our DNA influences who we become, and I’ll highlight a couple of key ideas here.

Traditionally, mental health has been approached through the medical model, diagnosing specific disorders and addressing their causes. However, genetic research suggests that mental disorders are not clear-cut categories but rather a spectrum where each of us falls genetically. Let’s take depression as an example: if we compared the DNA of 1,000 depressed and non-depressed individuals, we might find around 1,000 genetic differences between the two groups. In the general population, the average person might have about 500 of these depression-related genetic differences. Some people may have even fewer, while others could have more. The likelihood of experiencing depression depends on how many of these genetic differences a person has, combined with unpredictable life events that could trigger it.

This groundbreaking genetic research leads to a significant realization: there are no distinct disorders; instead, there are varying degrees of traits. This means that curing a disorder is not possible because there is no discrete disorder to cure. However, we can alleviate symptoms, as seen with schizophrenia, where therapies like Cognitive Behavioral Therapy (CBT) can help people manage their behaviors and lead a better life. These disorders are simply extreme points on a continuous scale of traits.

Genome-wide Association Studies (GWAS)

Now, let’s delve into Genome-wide Association Studies (GWAS), which have shed light on how genes relate to personality traits. Although personality traits have a heritable component, no single gene has a direct impact on a specific trait. Rather, multiple genes work together to shape a particular trait. Additionally, personality traits are not absolute; they exist on a quantitative spectrum.

For GWAS, researchers like Chi-Hua Chen from the University of California, San Diego, have analyzed vast amounts of genetic data. They looked at around 60,000 genetic samples from a private firm called 23andMe and approximately 80,000 samples from the Genetics of Personality Consortium to identify genetic variants associated with personality traits.

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.

However, it’s essential to understand that our genes do not entirely determine our personalities or make psychiatric problems inevitable. The research has shown correlations between certain genes and traits but not a direct cause-and-effect relationship. It’s still early in the research, and more investigation is needed to better understand these connections. With further study, researchers hope to predict and treat psychological disorders more effectively in the future.

On a positive note, the research did not find any genetic overlap between mental illnesses and traits like agreeableness (being cooperative and compassionate) or conscientiousness (being responsible and self-disciplined). These traits seem to be more dependent on environmental factors rather than genetics.

Genetic personality traits (inherited from parents)

Distractability

Specific learning disabilities resulting from high levels of distractibility, such as ADHD, have been found to be linked to inherited genes. Although there are no genetic tests to determine ADHD, studies have shown that genes associated with ADHD tend to run in families.

​​​​Leadership

In a recent study, certain inherited DNA sequences were found to correlate with leadership abilities. It suggests that leadership skills may be passed down through generations through a specific genotype.

Neuroticism

During the Minnesota twin studies, scientists discovered that certain traits, including neuroticism, are heritable. People with neuroticism are more prone to stress and often appear more nervous and sensitive to stimuli. In contrast, those without this trait may have a more positive and calm demeanor.

Environmental influences on personality traits

Patience

The environment in which a child grows up can affect how patient they are and how they handle stress. A study looked at children from different places, some living in remote rural areas, while others lived in busy cities. The study found that kids from rural areas tended to be more patient. This suggests that the environment plays a big role in shaping our patience.

Intimacy

Intimacy, or how close we feel to others, seems to be influenced more by our environment than our genes. Researchers discovered that about two-thirds of this trait depends on our past experiences. If someone grows up in a family or community where love and emotional closeness are lacking, they might struggle with intimacy later in life. On the other hand, when kids have loving and emotionally connected experiences during their adolescence, their ability to form close relationships can become stronger.

Etiquette

Different communities and cultures have their own manners and etiquette rules. If you meet a polite and well-mannered person, chances are they were raised in a different environment than someone who behaves rudely. The standards of behavior, acceptable actions, and values we learn from our upbringing shape how we behave in various situations. Since etiquette varies across cultures, it can have different effects on our personality development.

Verdict

I firmly reject the idea that our personality is entirely predetermined by our genes. We always have choices in life. Every day, we make many small decisions that gradually form our habits and shape our personality. While our genes play a role in who we are, they don’t determine our personality in a fixed way. Instead, our behavior is heavily influenced by the everyday context of our lives. The largest impact on our personality comes from the environmental factors that are unique to us, known as non-shared environmental effects. These factors are often random or accidental, making it difficult to predict how a child will grow up. So, it’s safe to say that both nature and nurture matter, but in the end, our environment and our own willpower have the most significant influence on our personality.

---

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.