A study of roughly 1 million people has found that personality is shaped by thousands of genes, each with a tiny effect — and that the link between DNA and character is far more complicated than the inheritance of a physical trait like eye color.
The meta-analysis, published Sept. 2 in the journal Nature, is the largest of its kind ever attempted. It identified over 1,200 genes linked to the Big Five personality traits: extraversion, agreeableness, conscientiousness, openness to experience and neuroticism.
But the scientists behind the work say the key conclusion is simpler: no single gene decides whether you are outgoing, anxious or organized. Instead, thousands of gene variants each nudge personality in small ways, and those effects are nearly impossible to separate from the environment that shapes behavior.
Assembling a million genomes
The project, called the Revived Genomics of Personality Consortium, brought together 46 separate groups of participants who had their genomes sequenced. Each person had been asked something related to one of the Big Five traits.
The team had data from roughly 600,000 people on the first four traits — extraversion, agreeableness, conscientiousness and openness to experience — and data from over 1.1 million people on neuroticism.
That scale matters. Genome-wide association studies, known as GWAS, link traits to gene variants in detail. They require sample sizes in the millions to work. This study had them.
What twin studies missed
For decades, researchers studied personality by looking at identical twins. Because identical twins share nearly 100% of their genetic material, scientists compared them with nonidentical twins and other siblings to estimate how much of personality comes from genes.
Some studies compared twins raised together with twins raised apart, trying to separate upbringing from genetics. Those efforts concluded that personality was roughly 50% heritable. Heritability measures how much of the variation in a trait can be explained by genes.
Gene sequencing changed the math. Modern GWAS suggested that the heritability of personality from common gene variants was roughly 5% to 15% — far lower than the twin studies claimed.
The gap between 50% and 15%
The new work confirms those low numbers, said study co-author Michel Nivard, a genetic epidemiologist at the University of Bristol in the U.K.
There are likely two reasons for the gap, Nivard said. GWAS may miss extremely rare gene variants that link personality traits within certain families, which would make heritability slightly underestimated. And twins may rate their own personalities as more similar than they really are for reasons unrelated to genetics, which would mean the twin studies overestimated heritability.
Ruling out parental influence
The study also tackled a thorny problem: confounding factors. In a GWAS on academic achievement, for example, genetics only tells part of the story. A person’s socioeconomic status, access to books and quality of tutoring also shape the outcome.
Nivard and his colleagues did not find such confounders in personality. The genetic effects on personality were the same within families as they were among unrelated individuals.
“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.
Brent Roberts on why personality is different
Brent Roberts, a psychologist at the University of Illinois at Urbana-Champaign who was not involved in the study, said the new work confirms a pattern researchers had suspected for years.
Generally, bigger GWAS studies reveal more subtle genetic links, and heritability estimates rise as sample sizes grow. But “with personality, it was really clear from the get-go that it was different,” Roberts said.
The study’s takeaway should not be to obsess over the exact split between genes and environment, Roberts argued. Our moods and minds are a collaboration between the two factors, not a tug-of-war.
What the numbers actually show
- Genes contribute to personality, but each one has a tiny effect.
- Twin studies may have overestimated heritability; GWAS puts it at 5% to 15%.
- No simple social process passes personality directly from parent to child.
- Rare gene variants may explain some of the missing heritability.
- The interaction between environment and gene expression remains largely unknown.
The cost of a better study
A proper study of how genes and environment interact would be vastly expensive and would require following participants for decades. “This is where the limitation of human genetics research is really profound,” Roberts said.
Part of the problem is that while DNA sequence is fixed, how the body accesses and reads DNA varies depending on the environment. Which genes get turned on, and when, are variable factors.
Assessing that relationship using only the DNA code is like trying to predict every move of a couple’s dance by looking at how they hold each other before the music starts.
The unknown unknowns
Nivard and his team can now use the consortium’s data to learn more about personality within groups of people. But he predicted that even once geneticists map all the rare variants that influence personality, some genetic influence will remain unaccounted for.
He called these the “unknown unknowns” — processes like the interaction between environment and gene expression that are not yet fully understood. Nivard said identifying these factors is where the field is headed.
Identifying those factors is the next frontier for the genetics of personality. The new study does not close the question. It sharpens it.
Source: livescience.com
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