A sociobiological interpretation of the structures and functions of the human family

Abstract

Altruism probably had a paramount importance in the development of human societies as a prominent basis of solidarity and social co-operation. Therefore, its evolution may be invoked to explain many aspects of human social organization, especially in simple societies. Evolutionary biology has made it clear that altruism evolves much more easily when directed towards close relatives. The average coefficient of relationship is much higher in a polygamous family than in a promiscuous group, and in a monogamous family than in a polygamous one. This suggests that polygamy must have prevailed over promiscuity, and monogamy over polygamy, by interdemic selection, except where the environment was particularly propitious to the latter. Many forms of preferential and prescriptive marriage, as well as incest taboo and exogamy, may be usefully analysed in this light. The levirate and the sororate raise the coefficient of relationship in the following generation to the highest degree possible in the given situation. The different marriage rules for parallel and cross-cousins discriminate between relatives of the same formal degree, but with different average biological relationship depending on paternity uncertainty. Incest taboo strengthens the avoidance of the closest forms of inbreeding that are already uncommon among lower primates. Exogamy institutionalizes the genetic exchange among groups, allowing for a continual expansion of altruism and the forms of solidarity and co-operation that are based on it. The shift from matrilineal to patrilineal organization profoundly affects the women's social condition by promoting forms of stricter control on their behaviour able to enhance paternity probability.