Brief summary: Dawkins demonstrates a classic "Prisoner Dilemma AI tournament". No big surprise to us today, but at the time the revelation that Tit for Tat is one of -- if not *the* -- most effective strateg(y|ies) was a surprising result. He goes on to demonstrate animals employing the Tit for Tat strategy. Assumptions of generosity, with vengefulness, appear to be strongly selected for.
(Bug report: I was sent to this post via this link, and I see MAIN bolded above the title instead of DISCUSSION. The URL is misleading too, shouldn't urls of discussion posts contain "/r/discussion/" instead of "/lw"?)
(EDIT: Grognor just told me that "every discussion post has a main-style URL that bolds MAIN")