Last week I wrote in my “Matter” column at the New York Times about how wolves became dogs. I described two new studies on the genetic transformation that produced our canine pets, starting about 32,000 years ago. The scientists who did the research discovered that certain genes in the dog genome have experienced strong natural selection.
Some of those evolving genes are especially intriguing, because they’re known to be important in the brain. One of these genes, for example, makes a protein that’s involved in controlling the level of a neurotransmitter called serotonin. Serotonin influences behaviors like aggression–not just in dogs, but in humans. And in humans, that same gene has experienced strong natural selection, too. For humans and dogs, alike, a key step in our recent evolution may have involved becoming more sociable.
I got a surprising email yesterday from Pat Levitt, the director of the Program in Developmental Neurogenetics of the Institute for the Developing Mind at the Keck School of Medicine of USC in Los Angeles. Although Levitt wasn’t involved in the dog research, it hit home for him. This table is the reason why. It lists a dozen genes that experienced strong selection in both dogs and humans. Two of those genes have been shown to be involved in the brain, four in digestion, and six in the cell cycle. (When those last six mutate, they can cause cancer.)
There’s a mistake on that list–but a mistake of the good kind. One of the six cancer genes is called MET. “However,” Levitt wrote to me, “in 2006, my laboratory published a paper in the Proceedings of the National Academy of Science on a mutation in the MET gene that increases risk for autism.” (Here’s the paper.) In fact, a variant of the MET gene is now recognized as one of the strongest genetic risks for autism.
Levitt and his colleagues have continued to study the gene to understand how it plays a role in autism. My fellow Phenomena blogger Virginia Hughes wrote last year about how Levitt and his colleagues discovered that it shapes the wiring connections between neurons. Not just any neurons, however. It’s most active in circuits in the brain that are involved in social and emotional behavior.
“I don’t believe it is a coincidence that both the serotonin transporter and MET are on the list,” says Levitt.
It’s not exceptional for a gene to be active in different parts of the body and to have different functions. Natural selection can spread a gene because one of those functions boosts survival and offspring, while the other function gets carried along for the ride. So scientists who want to know why MET evolved in both us and dogs will need to figure out how its protein changed in each species, and how that change affected its different incarnations. It’s conceivable that MET evolved as a defense against early cancers in both humans and dogs. It’s also conceivable that its transformation was crucial for the emergence of sociable people and dogs alike.
I contacted one of the dog gene scientists, Ya-Ping Zhang, to see what he thought of Levitt’s correction. Zhang is excited to discover MET is moonlighting in the brain. He and his colleagues are now studying MET, along with the other fast-evolving genes, to get a better sense of what they’re up to in dogs and wolves. It’ll take a few years, at least, before they get some answers. But I think it will be worth the wait.