This study proposes that extended family households are more common when a mother or father in a one-family household cannot meet activity requirements. Empirical analysis suggests that this trend occurs in both agricultural and non-agricultural societies.

This article tests some conditions that may lead to the emergence of unilineal descent, focusing on unilocality and warfare. Unilineal descent is thought to be likely in a unilocal society without a centralized political system that is experiencing intra- or inter-societal warfare. The authors also posit that a "clan" system usually develops prior to a "lineage" system.