The authors predict that fitness outcomes will be negatively associated with spousal relatedness among foragers but positively associated among non-foragers, due to the greater social benefits of intensive kinship systems among non-foragers. Support is found for this hypothesis; however, an interaction effect is discovered with inbreeding, which appears to account for the variability in these relationships independent of subsistence activity. The authors qualify this support in order to explain why the incidence of cousin-marriage in non-foraging societies is not higher.

The authors examine degree of intensiveness (kin-relatedness) among foraging and agropastoralist societies, predicting that hunter-gatherers will pursue more extensive kinship networks in order to maximize residential options in the case of unpredictability or uneven geographic distribution of food resources. Support is found for the hypothesis, and it is suggested that while extensive fission-fusion dynamics are beneficial in foraging systems, the increase in cooperation in large-scale agricultural settlements is aided by norms which encourage kin marriage and relatedness.

Authors use genealogical data to investigate pair bond stability and reproductive skew across a sample of 80 small-scale societies. Results suggest that male reproductive skew and pair-bond stability are independent sources of cross-cultural variation in human mating patterns.