For thousands of years, people have kept animals for many different reasons. They have kept sheep for wool, cows for milk, and dogs for work or companionship. When people tame and breed animals, this is called domestication. Every domestic animal we know today descended from a wild animal. Animals are easier to domesticate when they have certain physical traits and behaviors.

Image credits: main image, courtesy of AMNH; Sandra Olsen: courtesy of Sandra Olsen.