The Phylogenetic Roots of Human Kinship Systems

Abstract

Nonhuman primates don’t have formal kinship systems, but genetic relatedness shapes patterns of residence, behavior, mating preferences, and cognition in the primate order. The goal of this article is to provide insight about the ancestral foundations on which the first human kinship systems were built. In order for evolution to favor nepotistic biases in behavior, individuals need to have opportunities to interact with their relatives and to be able to identify them. Both these requirements impose constraints on the evolution of kinship bonds in primate species. For nonhuman primates and many other mammals, maternal care generates close ties between mothers and offspring and among littermates. For species in which mother–offspring bonds extend beyond weaning, associations with the mother also generate familiarity among siblings of different ages. For species with female philopatry, mother–offspring ties provide the foundation for lifelong relationships between mothers and daughters, and dense matrilineal kin networks. However, several factors constrain the development of kinship bonds in nonhuman primates. First, dispersal strategies, which are designed to reduce inbreeding, bias kinship networks in favor of the philopatric sex. Second, hostile relationships between groups mean that kin ties are usually severed when individuals move from one group to another. Third, in species with polygynandrous mating systems, uncertainty about paternity and restricted periods of male reproductive monopoly limit the scope for development of ties among fathers and offspring, paternal siblings, or extended paternal kin networks. In this article, I explore the impact of these factors on the evolution of ancestral human kinship systems.