Dogs (Latin Canis lupus familiaris) belong to the notochord phylum, vertebrate subphylum, mammals, true beast subclasses, carnivores, clefts, and canines. Chinese is also called "dog", and dogs are distributed all over the world. Dogs and horses, cows, sheep, pigs, and chickens are also called "six animals". Some scientists believe that dogs were domesticated from gray wolves by early humans. The domestication time was 40,000 years ago to 15,000 years ago. Known as "human's most loyal friend", it is the pet with the highest breeding rate, and its life span is about 12-18 years . In Chinese culture, dogs are one of the zodiac signs, and they are 11th in the zodiac signs.