Abstract: Where do dogs come from? Where do human beings come from? Recent research suggests a single answer: domestication. The various characteristics of dogs, distinguishing them from wolves, appear to be byproducts of domestication and (as recently shown by Richard Wrangham) a reduction in “reactive aggression.” It has long been thought that human beings domesticated dogs, but it is more plausible to think that that dogs domesticated themselves. As dogs are to wolves, so is the less robust but more docile Homo sapiens to various other, now extinct human species, including Homo erectus, Neanderthals, and Denisovans. Homo sapiens can be seen as the dog of the various human species. Homo sapiens survived in part because a reduction in reactive aggression made it possible for us to display significant increases in social learning and cooperation.