"Social contracts are written into our biology. As is the justice they need. The arc of our evolution has long bent towards the justice of “laws” fittest for team survival. We bred ourselves, by artificial selection, to internalize and feel strongly about social rules.
Christopher Boehm in Moral Originsconcludes, after intensive analysis of 50 representative hunter-gatherer cultures, that our ancestors likely experienced a “radical political change,” evolving from a hierarchic “apelike ‘might is right’…social order,” to become more egalitarian. About 250,000 years ago, theirsurvival became a team sport because chasing big-game toward teammates was much more productive than solo hunting. But only if profit-sharing was sustainable. Even with fit teammates hunting needs luck (e.g. 4% success today). Then, as now, the logic of social insurance solved team problems by sharing profits and risks. Productivity gains in interdependent teams radically changed our evolution. Cooperators thrived. As did teams with the best adapted sharing rules, provided they were well enforced."
Via Howard Rheingold