[mgh2]

The OP statement is very interesting, will need more resources to confirm. Related: https://news.ycombinator.com/item?id=30010119

As for introvert/extroversion: On Susan Cain's book "Quiet"

The "Galen’s Prophesy" reveals certain behavioral predispositions of children within four months old: https://www.youtube.com/watch?v=CVJBzvaylH8&ab_channel=JillB...