It’s one of the biggest perks of being a dog owner: Your pooch is thrilled when you come home, wagging its tail, wiggling its body, and licking you with its tongue. Now, scientists say they have pinned down the genetic basis of this affection. Using clues from humans with a genetic disorder that makes them unusually friendly, the team found variations in several genes that make dogs more affable than wolves and some dogs friendlier than others.
The study shows that the genetics of dog behavior “might be even more relevant for understanding genetics of human behavior than we once thought,” says Per Jensen, a behavioral geneticist from Linköping University in Sweden who was not involved with the research.
Over the past decade, geneticists have discovered the DNA involved in key dog traits, such as size and coat variation. Some DNA seems linked to personality, and one study showed that dogs and humans enforce their bonds by gazing at each other. But few studies have pinned particular behaviors to specific genes. “There’s been a remarkable explosion of studies, with the exception of behavioral studies,” says Robert Wayne, an evolutionary biologist at the University of California, Los Angeles, who was not involved with the work.
Seven years ago, Monique Udell, an animal behaviorist at Oregon State University in Corvallis, and Princeton University geneticist Bridgett vonHoldt joined forces to link genes to a behavioral trait they think was pivotal to dog domestication: hypersociability. Researchers already know that dogs are hypersocial compared with wolves, and the team confirmed this by comparing the behavior of 18 dogs—some purebreds, others mixed breeds—with 10 captive, hand-raised wolves at a research and education institute in Indiana. As others had shown, the dogs were much friendlier than the wolves, even though the wolves had been raised by people. Both hand-raised wolves and dogs greet human visitors, but dogs continue to interact with people much longer than wolves do, even when visited by a stranger.
The researchers then turned to humans with Williams-Beuren syndrome, a developmental disorder that leads to mental disability and an “elfin” appearance, but also often makes a person very trusting and friendly. The syndrome results from the loss of part of chromosome 7. VonHoldt focused on this stretch of DNA because she previously had found that this region, which is on dog chromosome 6, seemed to have been important in canine evolution. “It was a long shot,” says Wayne, but VonHoldt decided to see whether this DNA was responsible for dogs’ friendliness.
The DNA varied widely in both dogs, and to a lesser degree, wolves, with parts inserted, deleted, or duplicated. “Almost every dog and wolf we sequenced had a different change,” VonHoldt says. People with Williams-Beuren also show great variation in this region, and the variation is thought to affect the severity of the disease and people’s personalities.
The same seems true in the wolves and dogs. Hypersocial dogs had more DNA disruptions than the more aloof wolves, the team reports today in Science Advances. Disruption on a gene for a protein called GTF21, which regulates the activity of other genes, was associated with the most social dogs. A relative lack of changes in that gene seems to lead to aloof, wolflike behavior, VonHoldt says. Changes in that gene in mice cause that species to be hypersocial as well. Two other genes also were linked to sociality in dogs.
“We’re almost describing variation in personality,” in the animals, VonHoldt explains. She and Ubell did not study enough purebred dogs to draw any conclusions about how these variations might influence breed personalities, however.
“The study is exciting because it provides such strong support for the ‘survival of the friendliest’” hypothesis of dog domestication, says Brian Hare, an evolutionary anthropologist at Duke University in Durham, North Carolina, who was not involved in the work. In ancient wolves with these gene disruptions “fear was replaced by friendliness and a new social partner [was] created.”
“In a sense, this is the first paper discovering the genes related to the high sociability of dogs,” says Takefumi Kikusui, an animal behaviorist at Azabu University in Sagamihara, Japan, also not involved with the work. Humans too have high sociability relative to other primates. “Probably, these two species, namely human and dogs, use the same genes for these social behaviors.”
However, some experts think the study needs to be expanded to more dogs and wolves to be sure of the conclusions. With so few individuals “the associations are at most suggestive at this point,” Jensen says. Kikusui suggests they look for this gene-behavior connection in other populations of dogs and more individuals.