Dog domestication why

And already, they have yielded a surprising discovery that could radically reframe the debate around dog domestication, so that the big question is no longer when it happened, or where, but how many times. On the eastern edge of Ireland lies Newgrange, a 4,year-old monument that predates Stonehenge and the pyramids of Giza. Beneath its large circular mound and within its underground chambers lie many fragments of animal bones.

Press your finger behind your ear. And indeed, Bradley found DNA galore within the bone, enough to sequence the full genome of the long-dead dog. Larson and his colleague Laurent Frantz then compared the Newgrange sequences with those of almost modern dogs, and built a family tree that revealed the relationships between these individuals.

To their surprise, that tree had an obvious fork in its trunk—a deep divide between two doggie dynasties. One includes all the dogs from eastern Eurasia, such as Shar Peis and Tibetan mastiffs. The other includes all the western Eurasian breeds, and the Newgrange dog. The genomes of the dogs from the western branch suggest that they went through a population bottleneck—a dramatic dwindling of numbers.

Larson interprets this as evidence of a long migration. He thinks that the two dog lineages began as a single population in the east, before one branch broke off and headed west. This supports the idea that dogs were domesticated somewhere in China. The team calculated that the two dog dynasties split from each other between 6, and 14, years ago. But the oldest dog fossils in both western and eastern Eurasia are older than that.

Which means that when those eastern dogs migrated west into Europe, there were already dogs there. To Larson, these details only make sense if dogs were domesticated twice. Many thousands of years ago, somewhere in western Eurasia, humans domesticated grey wolves. The same thing happened independently, far away in the east. So, at this time, there were two distinct and geographically separated groups of dogs.

Along their travels, these migrants encountered the indigenous Ancient Western dogs, mated with them doggy style, presumably , and effectively replaced them.

Less than 10 percent comes from the Ancient Western dogs, which have since gone extinct. This is a bold story for Larson to endorse, not least because he himself has come down hard on other papers suggesting that cows, sheep, or other species were domesticated twice. Everything else is once. They concluded that dogs were domesticated somewhere in Europe or western Siberia, between 18, and 32, years ago.

By comparing the full genomes of 58 modern wolves and dogs, his team has shown that dogs in southern China are the most genetically diverse in the world. They must have originated there around 33, years ago, he says, before a subset of them migrated west 18, years later. Those Ancient Western dogs might have just been wolves, he says.

Or perhaps they were an even earlier group of migrants from the east. It must have happened in southern East Asia. Except, you totally can. Adam Boyko from Cornell University does, too: After studying the genes of village dogs—free-ranging mutts that live near human settlements—he argued for a single domestication in Central Asia, somewhere near India or Nepal.

And clearly, Larson does as well. Larson adds that his gene-focused peers are ignoring one crucial line of evidence—bones. If dogs originated just once, there should be a neat gradient of fossils with the oldest ones at the center of domestication and the youngest ones far away from it. The physical differences between a basset hound and wolf are obvious, but dogs have also changed in ways that are more than skin or fur deep.

One recent study shows how by bonding with us and learning to work together with humans, dogs may have actually become worse at working together as a species. Their pack lifestyle and mentality appear to be reduced and is far less prevalent even in wild dogs than it is in wolves. But at the first sign of trouble, dogs do something different. They look back to their human companion for help. This work hints that dogs may have lost some of their physical problem-solving abilities in favor of more social strategies, ones that rely on the unique sort of cooperation domesticated dogs have with humans.

This also matches the work showing that dogs are especially good at using human social cues. The relationship has become so close that even our brains are in sync. The intimacy of this relationship means that, by studying dogs, we may also learn much about human cognition.

We may never know the exact story of how the first dogs and humans joined forces, but dogs have undoubtedly helped us in countless ways over the years. Still, only now may we be realizing that by studying them, they can help us to better understand ourselves.

Brian Handwerk is a science correspondent based in Amherst, New Hampshire. Sonja Pauen via Flickr Long ago, before your four-legged best friend learned to fetch tennis balls or watch football from the couch, his ancestors were purely wild animals in competition—sometimes violent—with our own.

Just how many nuggets of fact might be sprinkled throughout this prehistoric fiction? When and where were dogs domesticated? Not even close. How did dogs become man's best friend? How have dogs changed since becoming our best friends? Dr Greger Larson of the University of Oxford said it was great to see more ancient dog genomes being published. Follow Helen on Twitter.

Image source, Getty Images. Image source, Amelie Scheu. DNA was obtained from the skull of an ancient dog. Image source, Timo Seregely. The dog skull inside an ancient burial chamber.