We know dogs are our best animal friends, but have you ever thought about what that might mean? Fossils show we've shared our work and homes with dogs for tens of thousands of years. Now there's growing evidence that we influenced dogs' evolution—and they, in turn, changed ours. Even more than our closest relatives, the apes, dogs are the species with whom we communicate best. Combining history, paleontology, biology, and cutting-edge medical science, Kay Frydenborg paints a picture of how two different species became deeply entwined—and how we coevolved into the species we are today.