Language and language structures pre-date history. (One cannot have a hsitory to share without a way to communicate it).

And there are disaprate structures and rules that arose independently across the globe. Different cultures and groups and regions developed in isolation. Similarities only arose through trade and interaction with neighbors.

They developed in isolation, but didn’t all of these groups discover roughly the same things at roughly the same time? Language, fire, agriculture, building?

One of the earliest (if not the earliest) formal grammars is that of Panini, a Sanskrit grammarian of the 4th century B.C.

I’m sure people have been analyzing language for as long as they’ve been speaking it, but Panini was the first to write a comprehensive formal analysis of his language and his grammar inspired the traditional grammars of Latin and Greek, which continue to inspire grammatical analysis to this day.