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is the only source of variation and that all dogs are descended from a single pair of wolves. A similar degree of diversity could occur if, say, several wolves had been domesticated, each of which had distinctive DNA. But this is likely to be the case only if each of those wolves had lived in a different part of the world—a supposition that, in turn, implies several domestication events.
    The apparent contradictions between the archaeological evidence and the DNA evidence can be reconciled if we posit not just one domestication event but several, in different parts of the world. It is now becoming possible to examine the DNA of fossilized dog teeth taken from Neolithic burial sites. While only a few dozen individuals have been sequenced so far, the results tend to confirm that wolves were indeed domesticated at several, possibly many, different locations.
    Scientists have also begun to find proof for multiple domestications by looking at a different type of DNA, extracted from living dogs. The DNA that codes for the immune system is inherited from both parents, not just the mother, as mtDNA is. The much greater diversity in theDNA for the immune system suggests that dogs have far more forefathers than foremothers; in other words, dogs overall seem to have many male wolf ancestors between them, but only a few female wolf ancestors. Thus the genetic material from the “extra” males must have been introduced after domestication had started. The early domestic dog bitches would presumably have been attractive to, and so occasionally mated by, wild male wolves. Moreover, their puppies would have been born in close proximity to humans. And provided that the genetic contribution of their wolf father did not make them too intractable, they could have survived to contribute to the dog genome. There is no reason why a mating between a male dog and a female wolf should not also produce puppies, but they would be born in the wild and, hence, would be more likely to contribute to the wolf’s genome than to the dog’s.
    Thanks to recent scientific developments, we now know that the diversity of the modern dog’s genome is not hopelessly incompatible with the archaeological evidence surrounding the dog’s domestication. Nevertheless, there is still a discrepancy—possibly as large as five thousand to ten thousand years—between the most likely date suggested by the DNA (twenty thousand or more years ago) and the oldest date that most archaeologists will agree to (fourteen thousand years). The reason for this discrepancy probably lies in the type of evidence that archaeologists will accept as evidence for domestication. Human remains and the bones of wolves have been found together at sites going back a half-million years, long before modern humans evolved, but archaeologists do not accept these joint burials alone as signs of domestication. Rather, they look for evidence of domestication either in the remains of animals that are clearly distinguishable from wolves (e.g., those with a wider skull, a shorter muzzle, or smaller teeth) or in signs that the animals, even if otherwise indistinguishable from wolves, had a special place in human society—preferably both.
    Probably the earliest well-established archaeological example of a dog that is both biologically distinct from wolves and specially connected to humans is the burial, about twelve thousand years ago in what is now northern Israel, of a human with one hand resting on the body of a puppy. Not only does the position of the puppy show that it had a close relationship with that person, but its teeth are also significantlysmaller than those of any wolf that lived nearby at that time, indicating that it must have come from domestic stock.
    Neither the physical signs of domestication in this puppy, so distinct from its wild counterpart, nor the evident bond between the animal and its owner, can have arisen overnight. Rather, the puppy must have