The bond between dog and man was forged at least 10,000 years ago; on that much, scientists can agree. But questions about precisely when and why dogs were domesticated remain unclear.
Did hunter-gatherers tiptoe into wolf dens, kidnap pups, and train them to guard and hunt? Or, was it a more opportunistic situation: once people began to settle down and start farming and generating waste, did wolves learn to coexist peacefully with garbage dumps and the people that filled them with scraps?
A new study led by scientists at the Broad Institute, a genomics research center in Cambridge, and Uppsala University in Sweden tries to begin to answer the question by looking at the DNA of wolves and dogs, finding that key genetic changes affected dogs’ ability to eat a starch-rich diet, as well as their brain development.
The research, published Wednesday in the journal Nature, didn’t determine when those genetic changes occurred, or whether the digestive changes occurred at the same time as domestication. But the genetic differences provide new clues about what separates dogs from wolves, and may even implicate genes that changed as both humans and dogs shifted to a different diet — mutations that might underlie modern diseases, such as diabetes.
“It’s quite intuitive that one of the things that really changed with dogs was what they eat; wolves are carnivores, and dogs are omnivores, eating everything like we do,’’ said Kerstin Lindblad-Toh, director of vertebrate genome biology at the Broad Institute and Uppsala University and the senior author of the study.
The reason the genes might be interesting ways to probe disease, including human disease, is a bit subtler.
The researchers see the 36 regions of the genome that popped out as different between dogs and wolves as areas that may have been changed as wolves adapted to a human lifestyle. Those areas might provide hints about the genes and biological underpinnings of modern diseases that have arisen with the shift from a peripatetic existence to a grain-based diet and life in settlements.
“Dogs get lots of the diseases humans get: cancer, diabetes, cardiomyopathy, and behavioral [syndromes], such as OCD and aggression,’’ Lindblad-Toh said.
Lindblad-Toh plans to keep studying the genes highlighted in the study, to learn more about what they do. For example, 19 regions of the genome that were different between dogs and wolves contain genes involved in brain function and development, and it would be interesting to see whether these could explain changes in behavior that would help transform a wolf into man’s best friend. She also hopes to look at DNA from ancient dog and wolf remains to better understand when those genetic changes emerged, which could provide clues about when and how domestication occurred.
Outside researchers said that the study was intriguing but that it can’t settle that fundamental question.
Yaroslav Kuzmin, a geoarcheaologist from the Institute of Geology and Mineralogy of the Siberian Branch of the Russian Academy of Sciences, in Novosibirsk, Russia, wrote in an e-mail that several early dog specimens have been found from before people began practicing agriculture, and before starchy food scraps would have been available.
For the earliest dog-like specimens, dating back to more than 30,000 years ago, Kuzmin said it was still unclear what forces could have caused their domestication.
Raymond Coppinger, an emeritus professor at Hampshire College, has advanced the theory that dogs — like pigeons, cockroaches, and other animals — were able to thrive alongside humans and human waste products, once the garbage dump became a facet of human life. He said the new study was well done, but added it is important to not take the conclusions too far: modern dogs would have been eating a more human-like diet for thousands of years, and the current study can’t answer the essential question of whether the digestion adaptations went hand-in-hand with domestication or came afterward.
Still, he said, the question of whether wolves were domesticated by hunters is testable in a different way: by trying to domesticate wolf pups, training them to act like dogs and not like wild animals.
“People who say they domesticated the dog by taking wolf pups out of a den — well, I’m sorry,’’ Coppinger said. “But all those people who said that never took a wolf pup out of a den. But I have.’’