Kin terms and fitness interdependence

Although genetic relatedness has been shown to be an important determinant of helping and other forms of cooperation among kin, it does not correspond well to the different types of kin designated by the kin terminologies used in human societies. This mismatch between genetic relatedness and kin terms has led some anthropologists to reject the idea that kin terms have anything to do with genetic relatedness or anything else biological. The evolutionary and cultural anthropological approaches can be reconciled through an appreciation of the concept of fitness interdependence, defined as the degree to which two or more organisms positively or negatively influence each other's success in replicating their genes. Fitness interdependence may arise for a variety of reasons, including not only genetic relatedness but also mating and marriage, risk-pooling, mutual aid, and common group membership. The major kin term systems correspond to cross-culturally variable but recurrent patterns of fitness interdependence among different types of kin. In addition, changes from one kin term system to another are associated with corresponding changes in recurrent patterns of fitness interdependence among kin, and kin terms are often used metaphorically in situations in which fitness interdependence has arisen among non-kin.