A great read by Venkatesh Rao, from Forbes:
There is a theory in evolutionary biology that reciprocal altruism and cooperation first appeared as a solution to the food storage problem. If you were an early hominid and you killed a large mammoth, you could not possibly eat it all before it rotted. So you shared it. The best bank for your excess capital was your friend’s stomach. That way, you could play banker when your friend killed the next mammoth.