They are indigenous to China, and are themselves Chinese characters, corresponding to words with no concrete meaning other than the associated branch's ordinal position in the list.

In addition to the calendar months, each branch has been associated with several distinct cultural categories, including animals and the hours of the day, with some regional variation.

Jonathan Smith has proposed that the first meanings of the earthly branches, predating the Shang, were phases of the moon, with the Heavenly Stems at that point referring to divisions of the ecliptic.

After being adopted as a calendar these would have lost their clear lunar reference, permitting their re-purposing for Jupiter stations.

[2] In the context of Chinese cosmology becoming increasingly sophisticated during the Warring States period (c. 475 – 221 BC), the 12-, 10-, and 60-cycles began to be applied to units of time other than days.