All dogs are descended from wolves, by domestication and artificial selection. This is known because DNA genome analysis has been done to discover this. They have been bred by humans. The earliest known fossil of a domestic dog is from 31,700 years ago in Belgium. Dogs have lived with people for at least 30,000 years. In 2013, a study was published that showed that the skull and teeth of a canid, dated to 33,000 years ago, had characteristics closer to a dog than to a wolf, and the authors conclude that "this specimen may represent a dog in the very early stages of domestication, i.e. an “incipient” dog." The researchers go on to suggest that it was, however, a line that did not lead to modern dogs. Genetically, this material is closer to that of a modern dog than to that of a wolf. Other signs of domestication are that sometimes, dogs were buried together with humans. Evidence of this is a tomb in Bonn, where a man of about 50 years of age, a woman of about 25 years of age, the remains of a dog, plus other artifacts were found. Radiocarbon dating showed that the human bones were between 13.300 and 14.000 years old.