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our dogs, is their ability to bond with us and understand us, to an extent that no other animal can match. Understanding what has happened during domestication is therefore a key element in understanding the dog.
    To understand the domestic dog fully, we need to look beyond the process of domestication—beyond even the wolf—to examine the dog’s entire history. We need to know where the dog came from and what all its ancestors were like—not just its closest living relative, the wolf. Of course, it is ultimately impossible for us to know precisely how the domestic dog’s ancestors behaved, whether we are examining its immediate forebears (wolves that lived more than ten thousand years ago) or its more distant ancestors (social canids, the precursors of the wolf, in the Pliocene era several million years ago). They are all extinct. We can, however, get some idea of how they might have behaved by examining the range of behavior that is characteristic of today’s social canids. Indeed, a detailed examination of the behavior of those species would not only shed light onto the dog’s earliest ancestors but also help us work out why it was that, apart from the wolf, none of the canids were successfully and permanently domesticated.
    DNA analysis leaves no doubt that the dog is descended only (or at least almost entirely) from the grey wolf, Canis lupus. The first comprehensivesequencing of the maternal DNA of dogs, wolves, coyotes, and jackals, published in 1997, produced no evidence that dogs had ancestors in any species other than the grey wolf. 1 None of the dozens of investigations performed since then have contradicted this; however, there is still a relative lack of data on paternal DNA, which is more difficult to analyze, so it is still possible that a few types of dog could claim descent from other canids through their paternal line.
    Genetically, dogs and wolves have a great deal in common—but the mere fact that two species have considerable overlap in their DNA doesn’t mean that their behavior will be the same. Indeed, many animals with similar DNA are drastically different from one another, especially in terms of behavior. We know this thanks to the DNA “revolution,” which has led to the sequencing of the genomes of humans, canines, felines, and an increasing number of other species. Many of these sequences exhibit a remarkable degree of similarity. For example, your DNA and your dog’s are identical for about 25 percent of their length, which is perhaps not surprising given that you are both mammals; roughly the same 25 percent is also found in mice. The other 75 percent accounts for why dogs, mice, and people look—and behave—very differently from one another.
    Species that are much more closely related to one another than we are to dogs can share almost their entire DNA sequences, and it’s tempting to assume that they must therefore be restricted to the same range of behavior. But DNA doesn’t control behavior directly; rather, it specifies the structure of proteins and other constituents of cells, such that a tiny change in DNA can lead to a huge change in behavior. For example, there is no “blueprint” for the brain; each nerve cell in the brain emerges out of interactions between thousands of DNA sequences. A change in one “letter” in those sequences could have an enormous effect on the way the brain functions, or none at all—we simply don’t know enough yet about how DNA and behavior interact. Take two closely related apes: the chimpanzee and the bonobo. Common chimps share 99.6 percent of their DNA with bonobos, and yet the social behavior of these two kinds of great ape couldn’t be more different. Common chimps are omnivorous, often hunting other kinds of monkey, and their social groups are based on coalitions between males, who are highly aggressivetoward outsiders and may even murder them if they get the