Evolutionary Ecology of Human Pair-Bonds: Cross-Cultural Tests of Alternative Hypotheses

Human pair-bonds may have multiple evolved functions. One long-standing hypothesis suggests that pairbonds evolved for male provisioning. Alternatively pair-bonds may occur as a response to male mating competition when benefits of staying with a current mate outweigh costs of seeking new mates. A third hypothesis suggests that pair-bonds function to protect against infanticide by aggressive males. Tests of these hypotheses used data from the Standard Cross-Cultural Sample on divorce, alloparenting, polygyny, male contribution to subsistence, and male aggression. Results were not consistent with the infanticide/aggression hypothesis, but parental investment and male mating competition both accounted for significant cross-cultural variance in conjugal stability, suggesting that human pairing has multiple functions. Pair-bonds tended to be stable when men and women contributed equally to subsistence, and unstable when either sex contributed the majority to subsistence. We use the ethnographic record to explore relations among pair-bonds, mating competition, showing off, and conjugal complementarity.