Morgan discovered that all around the world, the earlier and consanguine form of the family was common to Europeans, Indigenous people, and all “barbarians” in both the distant past and among those who maintained premodern traditions for many centuries afterward. Such families were based on a gens (plural form, gentes), or common ancestor, progressing through the maternal line since paternity was necessarily uncertain. Among the Iroquois, the roles of sachem (or chief) and war-leader were filled by men, the former coming from within the gens, passing to brothers or nephews but never from father to son. The tribe as a whole (consisting of eight gentes) had the power to both appoint and remove the sachem and war-chief, and marriage within the gens was forbidden, even as possessions remained firmly within the gens after death (thereby separating marriage from property). The gens allowed adoption, but loyalty to a bloodline served as the basis of law, so tribal councils would sit in judgment of disputes among members of different gentes.

A group of affiliated gentes formed a phratry, which similarly organized the conduct of its members and relations with other phratries, just as within gentes.