Our genes are among the most intimate little bits of information that exist, passed down from our parents, and determining the unique traits that make us ourselves.
But what if our social partners' genes, too, exert some sort of influence on who we are? That's the startling implication of a new study in mice, published in PLOS Genetics. Scientists in the UK found that many health traits in lab mice—such as anxiety, body weight, the immune system, and the rate at which the body heals from injury—all seem to be, in part, affected by the genes of other mice who share their cage.
It's well-known that peer pressure can influence our health, through bad habits like smoking. But how genes in one individual may affect another is far less understood. While there's evidence from other animal studies that a mother's genes influence the wellbeing of her babies, the idea that social partner's genes could affect not just one's behavior but also their body may seem bewildering. How could this even work?
An attentive cage mate could have promoted the healing by licking the wound
It's far from clear. The study shows that partners' genes work indirectly through what's known as social genetic effects (SGEs), whereby the genes in one individual impact the health of another.
"It was eye opening to see that social genetic effects can affect a wide variety of health traits. It's easy to see why some behavioral traits, like anxiety for example, are affected. But we also found that SGE affect immune function and the rate of wound healing. This was quite surprising," said Amelie Baud, a postdoctoral researcher at the European Bioinformatics Institute (EBI) in Cambridge UK, who did the bulk of the work.
Baud and her colleagues measured how more than 100 health traits change in response to the cage mates' genetic makeup. By combining data from some 2,500 mice, she was able to calculate how much of the difference in mouse health can be explained not by their own genes, but by those of their cage mates.
For anxiety, this was around 12 percent, whereas the rate of skin wound closure came up to 18 percent. And for immune response, measured by the body's readiness to fight infections, the partners' genes carried even more weight than those in the measured animals.
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The effects on the immune system and wound healing in particular are puzzling. It's hard to see how this can be orchestrated by someone else's genes. There are several possible explanations, according to Oliver Stegle, a geneticist at the EBI and the head of the team that carried out the work.
One way, he said, is through direct contact between mice—an attentive cage mate could have promoted the healing by licking the wound, whereas a scrappy partner would have made it worse. Or, the effect might have been indirect, triggered by stress, which is known to impede the body's immune defense and healing processes.
Although such effects have not yet been explored in humans, it's easy to imagine how a stressful social life might take its toll on health.
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