Most people who do a lot of exercise, particularly in the form of competitive athletics, have unneurotic, extraverted, optimistic personalities to begin with. (Marathon runners are exceptions to this.)

For example, most mammals are either monogamous or polygamous. But as every poet or divorce attorney will tell you, humans are confused - After all, we have monogamy, polygamy, polyandry, celibacy, and so on. In terms of the most unique thing we do socially, my vote goes to something we invented alongside cities - we have lots of anonymous interactions and interactions with strangers. That has shaped us enormously.

Naturally, things are more complicated - those groovy, pro-social effects of oxytocin apply to how we interact with in-group members.

The frontal cortex is an incredibly interesting part of the brain - ours is proportionately bigger and/or more complex than in any other species.

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.

Almost always, genes are about potentials and vulnerabilities rather than about determinism.

Get it wrong, and we call it a cult. Get it right, in the right time and the right place, and maybe, for the next few millennia, people won't have to go to work on your birthday.