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.
Twins and DNA sequencers
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.)
Genetic studies of personality traits previously relied on comparisons between twins. Now, genetic sequencing technologies have advanced the field. (Image credit: Johner Images via Getty Images)
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.
Generally, as geneticists have leveraged larger and more powerful GWAS, many traits have shown increased heritability because these bigger studies can identify more subtle genetic links, said Brent Roberts, a psychologist at the University of Illinois at Urbana-Champaign who was not involved in the new study. But "with personality, it was really clear from the get-go that it was different," Roberts said.
Earlier GWAS had suggested that the heritability of personality from common gene variants was roughly 5% to 15%, far lower than the estimate suggested by twin studies. The new work has confirmed those low numbers, said study co-author Michel Nivard, a genetic epidemiologist at the University of Bristol in the U.K.
It may be that GWAS do not capture extremely rare variants that might link personality traits in certain families, which means the heritability may be slightly underestimated, Nivard suggested. Additionally, twins are more likely to rate their personalities as similar for reasons unrelated to genetics, so the twin studies may have overestimated the heritability of personality, Nivard noted.
Cutting out confounders
It can be difficult to control for confounding factors in GWAS. For example, if scientists were investigating the influence of genes on academic achievement, genetics only tells part of the story; a person's socioeconomic status and access to books and tutoring also influence their education.
But in this case, Nivard and his colleagues did not find confounders in measuring personality. The researchers found that the genetic effects on personality are the same within families as they are 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.
A key takeaway from the study should be not to focus too much on the different contributions of genes versus environmental factors in a trait as complex as personality, Roberts said. Our moods and minds are a collaboration between the two factors, not a tug-of-war, he argued.
A study to properly measure this interplay 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, he added, is that while our DNA sequence is fixed, how the body accesses and reads DNA varies significantly depending on the environment a person finds themselves in. In other words, which genes get turned on and when are variable factors.
Assessing this enmeshed relationship using only the DNA code we are born with is like trying to predict every move of a couple's dance by looking at how they hold each other before the music starts up.
Nivard and his team can now use this powerful data source to learn more about personalities within groups of people, he said. Nivard predicted that, even once geneticists have mapped all the rare gene variants that may influence personality, some genetic influence will still go unaccounted for; processes such as the interaction between the environment and gene expression are still not fully understood. He called these the "unknown unknowns." Identifying these factors is the next frontier for the genetics of personality.
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A parrot missing half his beak has become top bird at New Zealand’s Willowbank Wildlife Reserve. Named Bruce, he wins every fight with other kea parrots. He also gets priority access to food.
This observation has made scientists question their ideas about disabilities in animal social groups. Bruce showed that a physical disadvantage doesn’t have to hold an animal back. Sometimes the right moves and a little creativity can make all the difference.
Researchers shared this finding April 20 in Current Biology.
Willowbank’s kea live in a large aviary with trees and a stream. Visitors who stop by often fail to notice the parrots snoozing among the leaves. But when they spot Bruce, they always make the same comment, says behavioral ecologist Alex Grabham: “Look at that poor bird.”
That pity is misguided, says Grabham. He’s part of a team studying kea at the University of Canterbury in Christchurch, New Zealand. That team tracked how Bruce interacted with his flock. (A group of kea is called a circus, reflecting the birds’ playful nature.) Like other parrots, kea have a social hierarchy. This is a ranking system where some birds are in charge; others follow the leader. Birds compete for the top spot by fighting, squawking or puffing up feathers.
Meet Bruce, the disabled kea parrot that managed to become the alpha male of his flock.
Grabham’s team spent four weeks recording 162 physical confrontations between the nine males in Bruce’s circus. Bruce won all 36 of his. Without a doubt, he was the top kea.
What’s more, he’s the first disabled animal to be recorded achieving top status within a group, at least without support from an able-bodied ally. (Faben was a dominant, or “alpha,” male chimpanzee living at Gombe National Park in Tanzania. He lost his top rank after polio paralyzed his arm. Faben’s brother took over his alpha status, but also became his ally. Faben then worked his way back to second place after perfecting a charging technique to bat away rivals.)
Parrot jousting
Also key to Bruce’s success: an unusual combat technique. Other kea tend to rely solely on kicking to repel other birds. Bruce supplemented his kicks with a unique jousting technique. He jabbed at rivals with his exposed lower beak.
Grabham’s team filmed 109 more confrontations between Bruce and the other birds. During these, Bruce kicked slightly more than he jousted. But jousting proved much more effective. Jousting drove off his opponent 73 percent of the time. When Bruce kicked, he drove them off just 48 percent of the time.
As another kea approaches, Bruce (seen here on the right) jabs with his half a beak. This fighting style has helped the disabled parrot win alpha status among his circus in New Zealand.Ximena Nelson
Bruce’s top spot comes with perks. Other male kea will preen Bruce, helping to clean parts of his beak that he cannot reach. This is highly unusual among kea. Normally, they only preen their mates. The lower another male’s rank, the more likely he was to preen Bruce. This behavior mimics hierarchical grooming seen in chimps.
Lower-ranked birds also gave Bruce first dibs on food. The birds’ food was spread mostly between four central feeders. Over the four weeks that Grabham’s team analyzed Bruce, he was the first to dine at those feeders 83 percent of the time. On four days, the other birds gave Bruce 15 minutes of alone time with all four feeders. Later, they ate his leftovers.
Another kea preens Bruce (left). This helps remove food that gets stuck in Bruce’s beak. Alex Grabham
In many animal societies, top status comes at a cost. “An animal that is high up in the dominance hierarchy has to defend that position constantly,” says Amalia Bastos. She’s a comparative psychologist at the University of St Andrews in Scotland who used to study Bruce. Alpha male baboons, for instance, show higher levels of stress hormones called glucocorticoids (Glu-ko-KOR-ti-koids).
Grabham’s team measured those hormones in the birds’ droppings. Bruce, it turns out, was the most chill kea in his circus. It isn’t yet clear why. But Grabham thinks that Bruce is so dominant that other kea don’t mount any serious challenges to his throne. “He isn’t going to be followed around and beaten up or bullied or chased,” Grabham says. And Bruce “knows that.”
It’s unclear whether Bruce would have thrived as well in a wild circus as he has at Willowbank. Bastos points out that with his damaged beak, Bruce might struggle with tougher foods during the winter. In the wild, most kea circuses don’t have a fixed hierarchy. Birds join and depart groups throughout the year, constantly changing the rankings. For now, in Willowbank’s strict hierarchy, Bruce is boss.
This isn’t the first study to show Bruce is capable of innovation. In 2021, researchers reported his self-preening technique. He uses pebbles to clean his feathers. “Bruce has now shown twice that being different is not necessarily disadvantageous,” Bastos says.
Bruce gained renown a few years ago for showing tool use. To groom himself, the parrot would select a pebble and hold it just so. This pebble “tool” overcame the lack of a part of his upper beak.
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