Chinese Astrology is said by some scholars to be the oldest horoscope system in the world. However if you trace Western Astrology back to its Middle East roots, both types are likely to have been born in their current recognizable form around 3000 years BC, however they stem from entirely different beginnings as well as traditions and parts of the world.
The 12 animals are further flavored by the pervading element of that particular year (elements also revolve as a separate cycle). It is said that Buddha is responsible for the 12 animals as they were the only ones who came to bid him farewell into the next life.
Chinese Astrology is concerned with nature and its traits, the signs progress year by year, whereas Western Astrology cycles monthly. The consideration of Yin and Yang is a very great influence upon this subject, Yin being passive, female and receptive while Yang is aggressive, male and exploratory. The various permutations of these 2 essential forces in nature, places, organizations, events and humanity and the quest to achieve balance so that both operate together in harmony rather than opposing or canceling each other out are an essentially Oriental viewpoint and quest, they form the basis of many Far Eastern traditions and other influences in Chinese Society such as Feng Shui.
The 12 Animal Signs are : Rat, Ox, Tiger, Rabbit (or Cat), Dragon, Snake, Horse, Goat (or Sheep), Monkey, Rooster, Dog and Pig. The animal ruling year in which you were born has a profound influence on your life.
As the Chinese say, This is the animal that hides in your heart.
There are 5 elements: Wood, Fire, Earth, Metal and Water, each adding a nuance of almost tactile character to the animal sign.Chinese astrology is based on the Chinese calendar year of your birth or the year of an event. There are also many more nuances involving the month and day.