Shooting American Family, Kentucky, By Carl Kiilsgaard

Engels expanded Morgan's hypothesis that economical factors caused the transformation of primitive community into a class-divided society. Engels' theory of resource control, and later that of Karl Marx, was used to explain the cause and effect of change in family structure and function. The popularity of this theory was largely unmatched until the 1980s, when other sociological theories, most notably structural functionalism, gained acceptance.
Kinship terminology
Archaeologist Lewis Henry Morgan (1818–1881) performed the first survey of kinship terminologies in use around the world. Although much of his work is now considered dated, he argued that kinship terminologies reflect different sets of distinctions. For example, most kinship terminologies distinguish between sexes (the difference between a brother and a sister) and between generations (the difference between a child and a parent). Moreover, he argued, kinship terminologies distinguish between relatives by blood and marriage (although recently some anthropologists have argued that many societies define kinship in terms other than "blood").