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 Origins concludes, 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, their survival 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.

Boehm says all surviving hunter-gatherers enforce law-like social rules to prevent excessive egoism, nepotism, and cronyism. They use rebukes, ridicule, shame, shunning, exile and execution (typically delegated to close male kin of the condemned, to avoid inter-family feuding). For example, meat isn’t distributed by the successful hunter but by neutral stakeholders. Excessively dominant alpha-male behavior—like hogging more than a fair share of meat—is punished by “counterdominant coalitions.” If the strong abused their power they were eliminated, in a sort of inverted eugenics. Resisting injustice and tyranny are universal traits in today’s hunter-gatherers. They likely run 10,000 generations deep in our prehistory.

Social punishment created powerful selection pressures. Self-control becomes the lowest-cost strategy for avoiding social penalties. Shame and guilt likely evolved as mechanisms for internalizing the logic of team rules—a social contract written into our biology. We intuitively recognize what is considered punishable. And often punish ourselves. Cultures configure shame and guilt system triggers differently. But rules balancing short term individual selfish gain with longer-term or team interests are more evolutionarily productive. Thinking of our evolved urges as irresistible is a deep error, since self-control, especially relative to social rules, has long been needed for survival (see “evo-irresistible error”)

Our ancestors bred themselves to be team players. They used intelligently directed artificial selection of good cooperators as mates (“auto-domestication”). Bad cooperators were less likely to be selected for, or successful at, the hugely costly and highly collaborative business of raising long helpless offspring.

Justice, wrote Hesiod, poet of the ancient Greek masses and Homer’s rival, was “Zeus's greatest gift” to us. Greatest or not, without it human nature wouldn’t be what it is. And we wouldn’t exist.

Illustration by Julia Suits, The New Yorker Cartoonist & author of The Extraordinary Catalog of Peculiar Inventions.

Previously in this series:

It Is in Our Nature to Be Self-Deficient

Inheriting Second Natures

Our Ruly Nature

It Is in Our Nature to Need Stories

Tools Are in Our Nature

We Fit Nature To Us: Evolutions two way street