the neo-Darwinists were practically driven to their conclusions by their initial assumption: that science demands a rational explanation, that this means attributing rational motives to all behavior, and that a truly rational motivation can only be one that, if observed in humans, would normally be described as selfishness or greed.

In other words, the palette of social organization was rich and diverse from the beginning: early humans, like us, were constantly in the business of shaping and reshaping their social arrangements, with evidence of conscious embracing and rejection of all sorts of social forms.