Computer simulations uncover universality in cultural anthropology observations

What rules shaped humanity's original social networks? The earliest social networks were tightly knit cultural groups made of multiple biologically related families. That single group would then develop relationships with other cultural groups in their local area. Researchers used statistical physics and computer models common in evolutionary biology to explain the origin of common community structures documented by cultural anthropologists around the world.

Graphical representations of simulated social networks
Graphical representations of simulated social networks © Kenji Itao, University of Tokyo, CC BY-SA 4.0 - Researchers used computer simulations based on principles of statistical physics and evolutionary biology to model how human societies would form under different conditions. Direct-exchange (left), generalized-exchange (center), and restricted-exchange (right) social structure models observed by cultural anthropologists in the 1960s are represented graphically. Credit:

Kenji Itao el al., "Evolution of kinship structures driven by marriage tie and competition," PNAS (2020). 


Significance:  Cultural anthropology has revealed kinship structures with certain rules of marriage and descent as the basis of social relationships in indigenous societies. However, it remains unanswered how they have emerged or what determines different structures. Here, we build a simple model of family groups, in which exchange of brides and resultant cooperation and competition are considered, by applying an agent-based model and multilevel evolution. The incest taboo and several kinship structures, consistent with field studies, spontaneously emerge. Different structures appear, depending on the strengths of cooperation and conflict, which can explain the distribution of kinship structures in indigenous societies. The theoretical studies by simple constitutive models, as presented here, will unveil universal features and formulate a general theory in anthropology.

Abstract: The family unit and kinship structures form the basis of social relationships in indigenous societies. Families constitute a cultural group, a so-called clan, within which marriage is prohibited by the incest taboo. The clan attribution governs the mating preference and descent relationships by certain rules. Such rules form various kinship structures, including generalized exchange, an indirect exchange of brides among more than two clans, and restricted exchange, a direct exchange of brides with the flow of children to different clans. These structures are distributed in different areas and show different cultural consequences. However, it is still unknown how they emerge or what conditions determine different structures. Here, we build a model of communities consisting of lineages and family groups and introduce social cooperation among kin and mates and conflict over mating. Each lineage has parameters characterizing the trait and mate preference, which determines the possibility of marriage and the degree of cooperation and conflict among lineages. Lineages can cooperate with those having similar traits to their own or mates’, whereas lineages with similar preferences compete for brides. In addition, we introduce community-level selection by eliminating communities with smaller fitness and follow the so-called hierarchical Moran process. We numerically demonstrate that lineages are clustered in the space of traits and preferences, resulting in the emergence of clans with the incest taboo. Generalized exchange emerges when cooperation is strongly needed, whereas restricted exchange emerges when the mating conflict is strict. This may explain the geographical distribution of kinship structures in indigenous societies.

Keywords: social physicskinship structureincest taboomultilevel selection