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,