It is traditional in China, when a person is born, one animal is used to symbolize this born year. Twelve symbolic animals representing the Earthly Branches, is a traditional way in China to number the year and to recorded a person's age.

Ancient Chinese invented the method of designate the years by Heavenly Stems and Earthly Branches. Heavenly Stems consist of 10 characters: jia, yi, bing, ding, wu, ji, geng, xin, ren, gui. And Earthly Branches are composed of 12 characters. Combining each 10 Heavenly Stems with the 12 Earthly Branches in sequence creates 60 chronological symbols. These 60 symbols are used in circles and thus each year has a chronological symbol. Later, people used 12 animal signs to correspond to the 12 Earthly Branches, forming 12 Symbolic Animals, namely, Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Sheep, Monkey, Rooster, Dog, Pig. Thus when a person is born, there is an animal sign as symbolic animal. The year 2008 is year of Rat, so children born in this year are all Rat babies.

Even though Chinese now number the years and their age under the Gregorian calendar, they still continue to use symbolic animals. As long as people know a person's probable age and his symbolic animal, people can infer his exact age and year of birth.