Studying kinship helps Anthropologists see more larger picture items such as political organization, social organization, as well as economics. By studying the characteristics that are found in marriages, including but not limited to: exchanges between families (dowries, bridewealth, bride service, & more modern gift giving), partner selection, organization of the family unit (polygamy or monogamy), residential patterns, and the taboos common inside of marriage including (divorce, incest, adoption, etc.), anthropologists can piece together information that can be used to look at the entire culture as a whole. For example, while currently illegal in the United States, certain past and present cultures have practiced polygamy for multiple reasons; including lack of a certain sex within the marriage, or to increase (or decrease) genetic diversity, or simply because of economic pressures. For instance in the past a family of three brothers may all contribute a bridewealth (in the form of chickens, goats, etc.) to the bride’s family to all have her as their wife in a poor village.
Incest has been taboo in nearly every culture over time with a few notable exceptions (for example royal families, in an attempt to keep the blood lines pure). The main reason for this “universal” taboo in incest is that marriage is a social construct; it brings families together, and in turn communities. Incest creates isolation, and does not strengthen community ties, therefore anthropologically speaking incest became taboo because it was in direct opposition to community which advances civilization. Although in the lecture, natural revulsion is labeled a myth, there is, at a genetic level, the need for every species to have genetic diversity. In-breeding, a result of incest reproductively, goes counter to our basic genetic, evolutionary programming to diversify. Because siblings or parent/child pairings offers smaller genetic diversity, over time our species (as well as countless others) that favored or at least condoned incest, where out-competed by those that didn’t and had greater genetic diversity.