All dogs (Canis lupus familiaris) are descendants of the wolf (Canis lupus). By only breeding those males and females with the traits desired (size, herding ability, protective instinct, etc.), humans have created more than 170 dog breeds.

Wolf: © DaddyBit/iStockphoto; St. Bernards: © GlobalP/Eric Isselée/iStockphoto; Border collies: © GlobalP/Eric Isselée/iStockphoto; Yorkshire terriers: © jimmyjamesbond/iStockphoto