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

How much you groom somebody else is more important than who grooms you.

To out-group-members, oxytocin makes you crappier - less cooperative and more preemptively aggressive. It's not the luv hormone. It's the in-group parochialism/xenophobia hormone.

There's the complex categorization of low warmth/high competence. This is the hostile stereotype of Asian Americans by white America, of Jews in Europe, of Indo-Pakistanis in East Africa, of Lebanese in West Africa, of ethnic Chinese in Indonesia, and of the rich by the poor most everywhere. It's the same low-high derogation: They're cold, greedy, clannish - -but, dang, they're sure good at making money and you should go to one who is a doctor if you're seriously sick.

We all seek out stress. We hate the wrong kinds of stress but when it's the right kind, we love it - we pay good money to be stressed by a scary movie, a roller coaster ride, a challenging puzzle.

Genes are rarely about inevitability, especially when it comes to humans, the brain, or behavior. They're about vulnerability, propensities, tendencies.

Most of us don't collapse into puddles of stress-related disease.