1 million people's genes reveal the heritability of the Big Five personality traits — and it's complicated

A family photo album can reflect how physical traits, such as blue eyes or lanky limbs, have been passed down — but a new analysis suggests that the way personality emerges across generations is far more complicated.

The meta-analysis, published Sept. 2 in the journal Nature , is the largest of its kind ever attempted. The work identified over 1,200 genes linked to five personality traits : extraversion, agreeableness, conscientiousness, openness to experience and neuroticism.

However, the scientists behind the study said its most important conclusion is that no single gene determines whether an individual will have a particular personality trait. Instead, thousands of genes exert tiny effects that are likely impossible to disentangle from environmental factors that shape our behavior.

Researchers have studied the link between genes and behavior for decades. Before the ability to analyze the genome in detail, many early studies looked to identical twins.

Knowing that identical twins share nearly 100% of their genetic material, scientists compared their traits with those of nonidentical twins and other siblings. Some studies compared twins raised in the same home with those raised in different homes in an attempt to separate the influence of upbringing from genetics. These efforts concluded that personality was roughly 50% heritable. ("Heritability" measures how much of the variance seen in a given trait can be explained by genes.)

The advent of gene sequencing enabled geneticists to calculate the influence of genes with greater precision than twin studies did. The most powerful tool in this arsenal is the genome-wide association study (GWAS), which can link traits to gene variants in detail. These statistical analyses require sample sizes in the millions, though.

The new study was a large collaborative project called the Revived Genomics of Personality Consortium, which brought together 46 cohorts of participants who'd had their genomes sequenced. Each person had been asked something related to one of the Big Five personality traits. The team had data from roughly 600,000 people about the first four traits — extraversion, agreeableness, conscientiousness, openness to experiences — and data from over 1.1 million people about their levels of neuroticism.

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