The friendship between humans and canines dates back millennia. The many breeds of dog we keep as pets today are descendants of wolves. Scientists believe that between 15,000 and 40,000 years ago, wolves were likely attracted to human settlements, where they could snack on food scraps and take shelter during the cold months. Humans, in turn, would have kept the friendliest wolves around as helpful companions.
Over time, humans bred these canines to pass on desirable traits, or characteristics, such as the ability to understand social cues from humans. After dozens of generations, the animals evolved into a different subspecies: Canis lupus familiaris, or the domestic dog.