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!
to pre-Vedic Indian traditions; it is mentioned in the Rigveda, but most likely developed around the sixth and fifth centuries BCE, in ancient India's ascetic and śramaṇa movements. The chronology of earliest texts describing yoga-practices is unclear, varyingly credited to Upanishads. The "Yoga Sutras of Patanjali" date from the first half of the 1st millennium CE, but only gained prominence in the West in the 20th century. Hatha yoga texts emerged sometimes between the 9th and 11th century with origins in tantra.
Yoga
not with the rest of the record.' I was really being a bull about it. I remember being told, 'This was the song that they wrote for you had you won the show.' And I was like, 'Well now I definitely don’t want to do it!' Anyway, I appeased them and I recorded it and then I remember hearing it back and going 'OK, you were right, this was definitely a good idea.' And it became one of our bigger songs.