If you live in a baboon troop in the Serengeti, you only have to work three hours a day for your calories, and predators don't mess with you much. What that means is you've got nine hours of free time every day to devote to generating psychological stress toward other animals in your troop. So the baboon is a wonderful model for living well enough and long enough to pay the price for all the social-stressor nonsense that they create for each other. They're just like us: They're not getting done in by predators and famines, they're getting done in by each other.

Importantly, rather than promoting aggression, testosterone promotes whatever is needed to maintain status when challenged.

It's great to have a buff frontal cortex to do that harder thing - for example, help a person in need rather buy some useless, shiny gee-gaw.

The problem isn't testosterone and aggression; it's how often we reward aggression. And we do: We give medals to masters of the "right" kinds of aggression. We preferentially mate with them. We select them as our leaders.

We're getting along so well; I trust you so much for this one second that I'm going to let you yank on me.

Individual differences in testosterone level predict very little about differences in aggression.

It's probably even the case that if you stoked up some Buddhist monks with tons of testosterone, they'd become wildly competitive as to who can do the most acts of random kindness.