Indeed, the zodiac division is represented by other Chinese characters which relate to the yin/yang of the five elements. Such division/ astronomy can be traced back to I Ching. The animal signs were used probably for the convenience of common people. And the 12 animal yearly signs indeed is about t...

The use of animal signs were found in ancient Chinese text in AD 1, as a way to represent the yin/yang five elements so people in general could remember easily.