today's factoid

One theory to explain how human altruism evolved involves the way we interacted as groups early in our evolution. Towards the end of the Pleistocene period – about 12,000 years ago – humans foraged for food as hunter-gatherers. These groups competed against each other for survival.

The archaeological and ethnographic data [Bowles] used showed that 13% to 15% of foragers died from wars, which were common between groups.

source:
Why altruism paid off for our ancestors

I find this oddly comforting.