In 2009, a lawyer from Trieste, Italy, successfully argued that his client’s possession of the so-called “warrior gene,” a variant of the MAOA gene linked to aggressive behavior, could reduce a murder sentence by a full year. The argument worked. It turns out the science didn’t hold up nearly as well.
After the 1990s, researchers linked the MAOA gene variant to violent behavior, which was subsequently reported in the media. But Aysu Okbay, assistant professor of psychiatry and genetics of complex traits at Amsterdam UMC in the Netherlands, says the whole premise of single-gene explanations for behavior has since collapsed.
“People believed that behavior comes from a few genes that have major consequences,” she says. “The whole concept has been proven to be wrong.”
Current research shows that personality develops through multiple genetic factors, including thousands of genetic variants, each causing unnoticeable effects. A 2015 meta-analysis of more than 2,500 twin studies covering nearly 18,000 human traits found that genetic differences account for about 47% of personality variation.
The Big Five personality traits of openness, conscientiousness, extraversion, agreeableness and neuroticism show only 9 to 18% heritability according to genome-wide association studies that analyze millions of small genetic variations across the genome.
The research shows that people have less genetic potential than scientists initially thought. Therefore, scientists must now investigate which environmental elements, including life events and social interactions and life situations, create the missing genetic potential.
The research repeatedly produces unexpected results for professor Brent Roberts, who teaches psychology at the University of Illinois at Urbana-Champaign.
He explains that major traumatic events in adults cause only mild psychological effects, which will not have significant long-term consequences. People do not experience significant personality changes as a result of marriage, divorce, or financial windfalls because these events act as individual elements that influence their core personality traits.
