Socio-ecologically adaptive slaving institutions

Slavery has taken strikingly different forms across human history. One of the sharpest contrasts concerns the fate of the enslaved: some societies were open to the integration of enslaved persons as full members, whereas others held them in permanent bondage. Existing ecological accounts try to explain slavery as a response to conditions favoring surplus production. They predict when slavery may appear, but not whether the enslaved are integrated. We argue that inter-societal conflict closes this gap. We develop a model of institutional adaptation in which societies raid one another for captives, produce a surplus, and then fight to loot that surplus. Three institutions compete: raiding for loot but not for captives, enslaving captives for maximal extraction, and exploiting captives but later integrating them as free members who help defend the surplus. Integration proves adaptive precisely where conflict is intense, because additional defenders are then worth more than the extra surplus that harsher treatment would have yielded; as theproductivity of unfree labor rises, exploitation without integration prevails instead. We assess these ideas against ethnographic data onslaving and conflict available for the Indigenous Peoples of the Pacific Coast of North America. Measuring conflict exposure by the raiding frequency of a society’s neighbors, we indeed observe that greater exposure predicts a higher probability of integrating enslaved persons, a pattern that neither ecology nor cultural affiliation alone can account for.