Yoga is said to be as old as civilization, there is no physical evidence to support this claim. Earliest archaeological evidence of Yoga's existence could be found in stone seals which depict figures of Yoga Poses. The stone seals place Yoga's existence around 3000 B.C.
Scholars, however, have a reason to believe that Yoga existed long before that and traced its beginnings in Stone Age Shamanism. Both Shamanism and Yoga have similar characteristics particularly in their efforts to improve the human condition at that time. Also, they aim to heal community members and the practitioners act as religious mediators. Though we know Yoga as focusing more on the self, it started out as community-oriented before it turned inward.
For a better discussion of the history of Yoga, we could divide it into four periods: the Vedic Period, Pre-Classical Period, Classical Period, and Post-Classical Period.