Genes and personality: what a million-person study found

Genes and personality are genuinely connected, but not in anything resembling a genetic “personality test.” An analysis of data from more than a million people identified 1,260 genetic variants associated with personality traits, yet even this enormous dataset captures only a limited fraction of the differences between individuals.

The study focused on the Big Five: extraversion, agreeableness, conscientiousness, neuroticism and openness to experience. These are not five personality types. Instead, each describes a broad dimension along which people vary.

The researchers combined data from 46 cohorts. Depending on the personality trait being analysed, sample sizes ranged from 611,037 to 1,136,711 participants. They then conducted genome-wide association studies, or GWAS. Rather than looking for an “extraversion gene” or an “anxiety gene,” GWAS scans millions of common genetic variants to find variants that occur slightly more often in people scoring higher or lower on a trait.

Thousands of variants, not a personality gene

The analysis identified 1,260 approximately independent lead genetic variants associated with the Big Five traits. Of these, 824 were located in regions not previously associated with variation in the corresponding personality trait.

That pattern illustrates how genetically complex behavioural traits work. Personality is not controlled by a handful of switches with large effects. Its genetic component is distributed across many variants, each contributing only a very small effect on its own.

Some of the signals implicated genes active in the nervous system and prefrontal cortex. But the results did not support a simple model in which one neurotransmitter system maps neatly onto one personality trait. Instead, the biological follow-up pointed towards a much more complex set of molecular and cellular systems.

One set of numbers is particularly important. Common genetic variants detectable by these analyses accounted for roughly 4.8–9.3% of the observed variation in individual personality traits. After accounting for the typical reliability of personality questionnaires, the estimates rose to about 9.3–13.3%.

That does not mean that genes determine only around ten percent of personality. GWAS mainly captures the additive contribution tagged by common variants. It does not fully capture rare variants, genetic interactions or every other source of inherited variation. Twin and family studies have typically produced substantially higher estimates of personality heritability, in the range of roughly 40–60%.

The genetic signal survives a family test

A particularly informative part of the study involved within-family analyses using data from up to 50,725 participants. Comparing relatives helps reduce several sources of confounding that can affect ordinary population studies, including population structure, family background and correlations between parents’ characteristics and the environment they provide.

Most of the genetic signal remained after this test. In other words, the associations between DNA variants and personality cannot simply be explained by people with similar genomes also growing up in similar families.

This finding should not be interpreted as evidence that family or environment does not matter. The within-family analysis addresses a narrower question: whether shared family factors are creating the genetic associations detected by population-level GWAS. The results suggest that, for personality, this form of confounding is relatively small.

Genetic effects were also broadly consistent across geographic groups, ages, different personality questionnaires and whether personality was rated by the participants themselves or by someone who knew them.

Why DNA still cannot read your personality

Despite the huge sample size, polygenic indices remained limited predictors of personality. This distinction between population-level association and individual prediction is crucial.

A DNA variant being slightly more common among highly extraverted people tells us almost nothing about the personality of a particular person who carries it. Complex traits emerge from thousands of genetic differences, their combinations, development, social environments and life experiences.

The study also has important limits. Most of the statistical power came from participants with European-like genetic ancestry. African-like cohorts were substantially smaller, and polygenic prediction became weaker when discovery and target populations differed in ancestry. Personality was also measured with questionnaires of varying reliability.

The significance of the study, then, is not that scientists have discovered more than a thousand “personality genes.” There are no such genes in that simple sense. Instead, the work shows that the genetic component of personality is real, highly polygenic and remarkably reproducible — while the genome remains a poor instruction manual for reading the personality of an individual person.