Researchers examining data from more than one million people identified over 1,200 genetic variants associated with personality traits. However, the effects of these genes are very small and cannot be said to determine individuals' personalities on their own. Personality, like many other human traits, arises from a complex interaction of genetics and environment.
Some people are more social, some worry more, and others are more conscientious or more open to new experiences. The reasons for these differences are not solely found in environment, upbringing, or life experiences, and one of the largest genetic studies conducted on personality shows that genetics also plays a role in shaping some personality differences, albeit a small one.
By analyzing information from over one million people, researchers identified 1,260 common genetic variants associated with one or more traits of the well-known "Big Five" personality pattern. These five traits are extraversion, agreeableness, conscientiousness, neuroticism, and openness to experience, and for years they have been used as one of the main models for studying personality in psychology.
The results of this study, published September 2 in the journal Nature, indicate that common genetic variants can explain only part of the personality differences observed within a population. In other words, the new findings do not mean that a person's personality can be read or predicted from their genes.
Michelle Neyward, a genetic epidemiologist at the University of Bristol in the UK and the study's lead author, says personality is related to many aspects of human life, but it still cannot be said that personality traits are the direct cause of differences observed in people's health or behavior.
She adds that the study's goal is above all to show how genomic data can be used to study more precisely the relationship between personality and other aspects of human life.
Personality's links to health and lifestyle
Identifying these genetic variants allowed researchers to also examine the relationships between personality traits and a range of behaviors, habits, and health indicators. For example, higher conscientiousness was associated with greater daily activity. In contrast, openness to experience was linked to more activity at night.
Genetic variants associated with openness to experience were linked to a greater tendency toward certain tastes that people typically develop a liking for over time - including coffee, wine, strong cheeses, and pickles.
In another part of the study, variants linked to extraversion were associated with the likelihood of contracting COVID-19. Researchers speculate that the more social behavior of extraverted individuals could be one possible explanation for this association, but such a finding alone does not prove that extraversion directly increases infection risk.
Conscientiousness was also associated with lower body mass index, a lower likelihood of starting smoking, and a reduced rate of hospitalization.
How much does family matter?
Another important section of the study addressed whether the observed associations between genes and personality might actually stem from a shared family environment. To investigate this, researchers separately analyzed data from people who were biologically related, including twins and family members.
They found little evidence that a shared family environment could explain a large portion of the genetic associations observed with personality.
Neyward says she expected to observe a kind of "indirect genetic effect." For example, parents' genes might alter the childhood environment in ways that ultimately influence the child's personality, but the researchers did not find substantial evidence for such an association in this study. There was also little evidence that people typically choose partners with very similar personality traits to their own.
The largest genetic survey of personality
Personality genetic studies long faced a major problem: many large genomic databases lacked accurate and reliable personality data. To overcome this, data from 46 different groups were collected through an international collaboration. Depending on the traits examined, the number of participants ranged from about 611,000 to more than 1.14 million.
Participants completed psychological questionnaires related to the Big Five personality traits. These tests are not the only method of assessing personality and there is still debate about their capacity to capture all the complexities of human personality, but they are widely used in psychological research.
In total, researchers found 1,260 common genetic variants associated with at least one of the five personality traits, more than 800 of which had not been identified before.
The study increased the number of known genetic variants associated with conscientiousness from only three to 131, and the number associated with neuroticism from 224 to 706.
The set of common genetic variants, depending on the personality trait and analysis method, explained about 5 to 16 percent of the differences observed among individuals.
Genes do not determine your personality
Researchers emphasized that the effect of each of these genetic variants is very small on its own. For example, the effect of a typical genetic variant associated with extraversion was so tiny that it could change a person's position on the trait scale from the 50th percentile to about 50.35.
Therefore, one cannot look at an individual's genome and say they will be extraverted, anxious, conscientious, or open to new experiences. Neyward also says that attempting to predict people's personalities from their genetic makeup has little practical use, because if a researcher wants to know a person's personality, it can be measured directly with psychological tools.
The study's findings are more important for understanding biological mechanisms and examining relationships between personality and other human traits than for predicting a specific individual's personality.
Caution about causal conclusions
Some findings were obtained using a method called Mendelian randomization; an epidemiological approach that uses genetic differences to investigate the likelihood of causal relationships between a trait and health outcomes. Nevertheless, Neyward warns against overinterpreting such results.
She even expresses concern that the release of this large genetic dataset could spawn a wave of weak studies that misuse this method to draw causal conclusions about personality's relationship with diseases and behaviors. For this reason, the researchers provided recommendations alongside their published findings to better evaluate such studies.
Andrea Ganna, a statistical geneticist at the University of Helsinki who did not participate in the research, calls the study important. According to her, the genetic associations identified for personality are less affected by confounding factors compared to some other behavioral traits and can form a solid basis for future studies in behavioral and social genetics.
Still, the main message of the research is simpler than the notion of a "personality gene": traits like extraversion, anxiety, conscientiousness, or openness to experience are not the result of one or a few specific genes. Human personality is shaped by a highly complex network of genetic and environmental factors, each contributing only part of the larger picture.