Evolutionarily (assuming that's a word) this phenomenon makes perfect sense. Testosterone and aggression high so that fit male is able to mate with discerning

Evolutionarily (assuming that's a word) this phenomenon makes perfect sense. Testosterone and aggression high so that fit male is able to mate with discerning fit female. Couple have babies, but testosterone lowers for satisfied male, encouraging him to stay with mate. This mutation would raise the odds substantially that the offspring of the couple survive given the male presence and protection. Then, when said offspring and mate get older and testosterone goes up, all bets are off and the cycle repeats. In the modern era, this phenomenon can be bypassed by commuting via bike everyday in San Francisco up beyond category climbs, at least in my experience so far :)