I remember Yoga being really popular in the 1980's.
It was!  I remember that too.
Apparently it dates back to the 6th and 5th centuries BCE, coming from India during the pre-Vedic period.
Yes, I have researched India for a historical society I was in. 
Do you have any idea how it ties into the early history of India?
It's been awhile since I researched it, but I do know that it was developed that early in history.  It was interesting to read about it!
I guess the modern derivative of the ancient practice dates as far back as the first millennium CE, but has only real caught on around here this century.
Yoga is something that I haven't really tried, but I do like certain aspects of it.