Humans are social mammals. In many important respects, it makes no sense to even think of us as individuals.

I suspect that in the past people with higher levels of social anxiety probably just spoke a little less than average, and noticably less on the much less frequent times they met strangers.

But i think it's its probably very inaccurate to imagine anyone who we'd recognize as an "introvert" in the much more collectivist cultures that dominate history.