Evolution of kinship structures driven by marriage tie and competition

Abstract

In indigenous societies, people are categorized into several cultural groups, so-called clans. The clan attribution governs the mating and descent relationships by certain rules. Such rules form various kinship structures. Anthropologists have revealed several classes of kinship structures and corresponding cultural characteristics. Here, we introduce an agent-based model of indigenous societies adopting the multi-level evolution of families and societies. A family is a unit of dynamics and society is an ensemble of families within which the interaction of families can take place. We assign each family a trait and a mate preference as an optimal trait of the bridegroom. Marriage takes place according to the mating preference. Families with similar traits cooperate with each other as well as with mates, whereas those with similar preferences compete for mates. The population of families is increased by such cooperation and declined by competition. With numerical simulations, families were found to form clusters in trait-preference space under a certain condition. Families in the same cluster are united by cultural similarity. Marriage occurs only between families from different clusters. Such clusters can be regarded as clans. Kinship structures emerge as the marriage and descent relationships of such clans. The emergent structures depend on environmental conditions such as the necessity of cooperation and strength of mating competition. Finally, by analyzing the global ethnographic database, called Standard Cross-Cultural Sample, we empirically verify the theoretical results on the environmental dependence of kinship structures.