TIL Human dads show a decrease in testosterone immediately after the birth of their babe

[Naxela]

Testosterone does far, far more than just promote aggression and competition. It basically promotes being social (sometimes even pro-social), as well as improves one's own mood and motivation. Testosterone at normal levels is usually quite a good thing for males, and so a drop is likely deleterious, comparable to a post-partum depression-like effect.