How DNA shapes who we are: More than 1,200 genetic variants help determine personality

Is a person’s character innate or acquired? Is biology or upbringing more important in shaping personality? For centuries, this debate has divided both the scientific community and society at large. Curiosity, ambition, conscientiousness and agreeableness all seem like traits that are shaped over the course of a lifetime. Yet science has long known that personality has a genetic component, thanks to a simple trick: comparing identical twins with fraternal twins. If identical twins resemble each other more closely in their personalities than fraternal twins do, then part of the explanation must lie in their DNA.

What remained unknown was where that part was located. A large-scale study published on Wednesday in Nature by an international consortium of researchers provides an answer for the first time: they identified 1,260 distinct genetic variants spread across the genome, 824 of which had never previously been linked to personality.

The study analyzed data from 1.14 million people, grouped into 46 cohorts, to identify which DNA variants are associated with the five major personality traits recognized in the scientific literature, known as the Big Five: extraversion, agreeableness, conscientiousness, neuroticism and openness to experience.

The findings do not suggest that personality can be predicted directly from a person’s DNA. Rather, they indicate that certain genetic variants may influence certain behaviors. They also confirm that upbringing and social experience ultimately play a greater role in shaping personality than genetics.

The international consortium behind this landmark study identified those 1,260 genetic variants as being “statistically robustly” associated with personality. Depending on the trait, that represents an increase of between threefold and forty-threefold over previous studies. Taken together, the variants account for between 4.8% and 9.3% of the variation in each personality trait across individuals. That is well below the 40% to 60% suggested by classic twin studies. In other words, environmental factors play a decisive role in shaping personality.

However, somewhat surprisingly, family has less influence than one might expect. Unlike other social traits, such as educational attainment, income or intelligence, personality is barely shaped by the family environment. When the researchers compared siblings with one another, or children with their parents, the genetic effects remained virtually identical to those observed in the population as a whole.

“It’s one of the things that surprised me most,” admits Michel Nivard, professor of genetic epidemiology at the University of Bristol and one of the study’s lead authors. “For educational attainment we see a clear correlation between the genes that influence education and the environments that favor it: children of more-educated parents inherit certain alleles but also attend better schools because their parents have more resources and invest in them. For personality, that effect almost doesn’t exist.”

Another important finding of the study is that there is no such thing as a “personality gene.” Unlike diseases such as Alzheimer’s, in which certain genetic variants dramatically increase risk, each of the 1,260 variants identified here contributes only a microscopic nudge. The average effect of the most influential variant, linked to extraversion, is equivalent to the difference between being at the 50th percentile of the population and the 50.35th percentile, a minuscule distinction.

The authors stress that even by combining hundreds of thousands of these variants, it is not possible to reliably predict the personality of a specific individual. Such genetic scores are useful only when averaged across large population groups. Nivard puts it this way: “If you want to know your personality, the easiest option is to take a 20-minute test [which you can take here]: the reliability is extremely high, and if you repeat it a year later you’ll get almost the same result.”

For that reason, he does not believe a genetic test capable of determining what personality someone will have is ever likely to exist.

Conscientiousness linked to lower smoking rates

The study goes beyond the genome, linking those genetic variants to dozens of real-world behaviors. Some of the findings are striking. People with a greater number of variants associated with openness to experience are more likely, by middle age, to move to urban, cosmopolitan neighborhoods, while those who score higher for conscientiousness tend to relocate to affluent residential areas. Openness is associated with greater nighttime activity, whereas conscientiousness is linked to greater daytime activity. Conscientiousness is also associated with lower rates of smoking and a lower body mass index.

Of the five major personality traits, agreeableness proved the most difficult to analyze. Researchers found weaker genetic correlations across countries and evidence that the trait is less heritable than the others. Nivard offers one possible explanation: “agreeable” may not mean the same thing everywhere. “I’m Dutch, and we’re very direct. In other cultures, that same frankness could be perceived as a lack of agreeableness,” he says. According to Nivard, this is the first time genetics has made it possible to assess objectively whether two cultures are measuring the same thing when they use the same word.

Another finding challenges much of the previous research: genetic profiles associated with openness to experience were correlated with a greater overall risk of psychopathology, something earlier clinical studies had not detected so clearly. Nivard does not yet have a definitive explanation. “It’s fascinating, but I don’t know what it means yet,” he says. One possibility, he suggests, is that people who are more open to new experiences may be more likely to participate in studies of this kind, even when they have a mental health condition, which could slightly bias the sample. He stresses, however, that this remains a hypothesis that has yet to be tested.

Because the study’s biggest discovery is not, in fact, what was published on Wednesday, but everything that remains to be published. The dataset is so vast — one million people organized into 46 research groups, or cohorts, offering countless opportunities for cross-analysis — that its findings are likely to shape the future of genetics, sociology, psychology and psychiatry.

And this is only the tip of the iceberg. The human genome contains between four and five million genetic variants, opening the door for further research. For geneticist Miguel Pita, who was not involved in the study, the achievement lies less in the findings themselves, “that genetics plays an important role in personality is almost self-evident,” he says, than in demonstrating it with such an enormous amount of data. “It’s a milestone in experimental and technical design. Sometimes, the obvious is the hardest thing to prove.”

The study stresses that the old question of “nature versus nurture” no longer makes sense as an either-or proposition. Nivard offers an analogy: in genetic studies of lung cancer, the variant most strongly associated with the disease is found in the nicotine receptor gene, even though no one disputes that smoking, an environmental factor, is the cause.

According to Pita, “in anything related to personality both factors will always play a role; talking about only one or the other is an outdated debate.”

Nivard agrees and argues that continuing to pit genes against environment is “old-fashioned, although it’s understandable that many people still find it intuitive: it’s what we learned in school.”

Sign up for our weekly newsletter to get more English-language news coverage from EL PAÍS USA Edition