Scientists Probe a Million Genomes to See How Genes Influence Personality

Are you a social butterfly, or keep to yourself? Do you prefer fight over flight when in stress or danger? All of these responses can be compiled into scores across five traits, also known as the Big Five personality traits— openness, conscientiousness, extraversion, agreeableness, and neuroticism– or the “OCEAN” model as an acronym. People often base someone’s personality on the events or environment they have been brought up in, but a new study reveals that around 1,200 genes influence the five personality traits. However, unlike eye color or curly hair, personality and genetics do not share a simple relationship.

Only 5-15% of Personality is Heritable

Researchers have been studying the link between genes and behavior long before sequencing techniques were developed. Early studies worked with identical twins, knowing that they share nearly 100% of their genetic material. Scientists compared their traits with those of fraternal or non-identical twins, and other siblings. Some studies went a step further, comparing twins raised in the same home with those raised in different homes to negate the influence of upbringing on genetics. The scientists concluded that genes could explain roughly 50% of personality variances, or 50% heritability.

With the rise of gene sequencing, scientists did not have to rely on twins anymore. Geneticists were able to study the influence of genes with greater precision than the earlier twin studies. The most powerful of such technologies, genome-wide association study (GWAS), can link traits to gene variants in detail, but it requires sample sizes in the millions for a statistical analysis with reasonable output. As geneticists have leveraged larger and more powerful GWAS, many of the Big Five traits have shown increased heritability due to the large sample size revealing subtler genetic links.

The new study was a large collaborative project called the Revived Genomics of Personality Consortium, bringing together 46 cohorts of participants whose genomes were sequenced. Each person answered questions related to one of the Big Five personality traits. The team collected data about the first four traits from 600,000 people, and for the last one, neuroticism, which determines emotional stability in a person, data was gathered from over 1.1 million people.

Earlier GWAS quashed the idea of half our personality being heritable, and the new work confirmed the same. Only 5 to 15 percent of personality is heritable, far lower than what the twin studies had implied. Twins might also be more likely to rate their personalities as similar for reasons unrelated to genetics, so the study may have overestimated the heritability of personality.

Genes and Environment Work Together

Controlling factors that can give a false connection between cause and effect is a major hurdle in GWAS, also known as confounders. For example, if a study finds that people who carry matches are more likely to develop cancer, we can start forming a relationship between carrying matches and lung cancer. However, carrying matches itself isn’t a cause of lung cancer; rather, smoking leads to it. Here, smoking is a confounder linked to carrying matches and is a direct cause of lung cancer. For a non-smoker, matches and cancer get incorrectly linked in a cause-and-effect system.

However, study co-author Michel Nivard, a genetic epidemiologist at the University of Bristol in the U.K., and his colleagues found no confounders while measuring personality. Genetic effects on personality among unrelated individuals tracked similarly within individuals from the same family. “We’ve basically been able to rule out that there’s any straightforward, simple social processes by which your parents directly influence your personality,” Nivard said.

A key takeaway from the study is to go easy on the different contributions of genes versus environmental factors when studying a feature as complex as personality. Genes and environment collaborate to design our mind and determine our moods, rather than partake in a tug-of-war. A study to properly study this interplay would not only be very expensive, but also require following participants for decades in a longitudinal study.

Although our DNA sequence is fixed, genes are like switches— detecting which genes are turned on and when is a variable factor. The environment influences this aspect of the genome, the study of which is known as epigenetics. Basing personality only on the DNA code we are born with is like trying to predict every move in a game of soccer before it starts by looking at the line-up.

However, Nivard and his team have a robust database to learn more about personalities within groups of people. GWAS doesn’t capture extremely rare variants that might link personality traits in certain families, making the procedure prone to slightly underestimating the effect of genes. Even if geneticists mapped all the rare gene variants that may influence personality, the chances of accounting for all of the genetic influence on personality are impossible. Epigenetics is a growing field with very little understanding, even less if we are trying to understand personality and behavior through it. Nivard calls such influences the “unknown unknowns.” To him, the next frontier for the genetics of personality lies in bringing these factors to the spotlight.