Largest study yet reveals over 1,200 genes linked to human personality

Psychologists and behavioural scientists have long used the so-called “Big Five” framework to describe the broad dimensions of human personality, grouping individual differences into five traits: extraversion, agreeableness, conscientiousness, openness to experience and neuroticism.

One of the largest studies of its kind has now examined how genetic variation is associated with those traits, offering new insight into the biological factors that may help shape human behaviour and influence the choices people make throughout their lives, as highlighted in an article by LiveScience.

The study identified more than 1,200 genes associated with the five personality traits, with broadly consistent genetic links appearing across different groups of participants, Western geographical settings, age ranges, reporting perspectives and methods used to measure personality. The findings suggest that differences in genetic makeup can account for at least some of the variation seen in people’s personalities.

The researchers were also able to examine how those genetic associations corresponded with patterns in people's lives, including where they tend to live, their career choices, relationships and aspects of their physical health.

For instance, people with genetic variants associated with greater openness to experience were more likely to live in cities during midlife, while those with variants linked to higher levels of neuroticism were more likely to live in suburban areas.

The researchers stressed that genetics can predict only a relatively small part of an individual's personality, with upbringing, social circumstances and other environmental influences also playing major roles. Even so, the effects associated with personality-related genetic variation appeared across a wide range of outcomes over the course of people's lives.

People with stronger genetic associations with conscientiousness, for example, were less likely to abuse substances, made fewer visits to hospital and tended to experience healthier ageing, according to the study.

The research also found genetic links between the Big Five traits and a number of mental health and neurodevelopmental disorders, including depression, anxiety, bipolar disorder, schizophrenia, attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder, borderline personality disorder, anorexia nervosa and obsessive-compulsive disorder (OCD).

Neuroticism showed the broadest pattern of association, with a genetic predisposition toward the trait linked to an increased risk of all the disorders examined in the study. The association was particularly pronounced for so-called internalising disorders, including anxiety, depression and anorexia.

Conscientiousness, meanwhile, was associated with a lower risk of neurodevelopmental disorders, although the trait showed an opposite relationship with compulsive disorders such as OCD.

Extraversion was linked to a lower risk of internalising disorders, but researchers also found an association with a higher risk of certain neurodevelopmental conditions, including autism spectrum disorder and ADHD.

“Personality seems to be relevant nearly everywhere you look,” lead author Ted Schwaba said in a news release. “We hope this study will encourage many other scientists to incorporate personality traits into their fields of study.”

“For example, genetic variants associated with neuroticism predict more time spent in the hospital,” Schwaba continued, “which is relevant to physicians and health researchers, and variants associated with openness to experience may help explain other patterns in people's lives.”

Despite the large number of genetic associations identified, however, the researchers said the study's most important finding may be what it does not show. There is no single gene that determines whether a person will be outgoing, conscientious, neurotic or possess any other particular personality characteristic.

Instead, thousands of genetic variants appear to have very small individual effects, with those effects interacting with one another and with environmental factors in ways that are extremely difficult to separate.

Long path paved by previous research

Scientists have been examining the relationship between genetics and behaviour for decades, long before modern genetic sequencing made it possible to analyse individual genomes in such detail. One of the earliest and most influential approaches involved studying identical twins, who share almost all of their genetic material.

Researchers compared identical twins with non-identical twins and other siblings to determine how closely particular traits were linked to genetic similarity. Some studies also examined twins who had been raised in different homes, allowing scientists to investigate whether similarities between them could be attributed more strongly to genetics than to a shared upbringing.

Those studies generally concluded that personality is approximately 50% heritable, although heritability does not mean that half of an individual's personality is genetically determined. Rather, it describes how much of the variation in a trait within a particular population can be statistically attributed to genetic differences.

The development of genome sequencing and large-scale genetic databases has since allowed researchers to examine those relationships with much greater precision. One of the most powerful tools is the genome-wide association study, or GWAS, which can identify statistical associations between particular genetic variants and traits across the genome.

Such studies become more reliable as sample sizes grow, however, often requiring hundreds of thousands or even millions of participants to detect the relatively small effects associated with complex human characteristics.

The new research was carried out as a large international collaboration known as the Revived Genomics of Personality Consortium. The project brought together 46 cohorts of participants whose genomes had been sequenced and who had completed assessments relating to at least one of the Big Five personality traits.

The researchers analysed data from roughly 600,000 people for four of the traits — extraversion, agreeableness, conscientiousness and openness to experience — while information from more than 1.1 million participants was available for neuroticism.

The scale of the study allowed the researchers to identify genetic patterns that would have been difficult to detect in smaller samples, while comparisons across different populations and measurement methods provided further evidence that at least some of the genetic associations with personality are broadly consistent.

The findings nevertheless reinforce the idea that personality is not the product of genes alone. Instead, human behaviour appears to emerge from a complicated interaction between thousands of genetic differences and the environments in which people grow up and live, making any simple attempt to explain personality through biology alone unlikely to capture the full picture.

By Nazrin Sadigova