Co-Residence Patterns in Hunter-Gatherer Societies Show Unique Human Social Structure

Human social structure and grouping are unique and may have a lot to do with our success as a species. This social structure appears to be based on cooperation with unrelated individuals and a reliance on cultural transmission. The ancestral form of human patterning has been argued to be either female philopatry with maternal grandmother provisioning, or male philopatry with adult male provisioning. Both of these hypotheses suggest grouping by kin and inclusive fitness as the primary reason for any cooperation.

An alternative model, proposed by Bernard Chapais suggests that partnerships of males revolving around a single related female could bridge relationships between different lineal groups. One way of achieving this is marriage of daughters to an unrelated but local group, creating a familial bond between the two groups. This would allow for greater interaction and visitation between groups and a high number of co-resident adults who are not genetically related. Between groups of large enough size, social networks will also be large and can lead to increased observation of rare innovations. The rate of social and cultural evolution would increase and lead to more complex social structure.

Hill et al. analyzed data of band composition from a worldwide sample of 32 hunter-gatherer societies. In the majority of the societies (19) there was no difference between parents living with adult sons versus daughters. In general the total number of co-residing male primary kin is higher than the number of co-residing female primary kin. There is also a pattern of frequent brother-sister co-residence that can be seen across all ages, not just for during ritual bride service.

Hill et al. more specifically analyzed 58 precontact Ache bands and 6 bands of Ju/’hoansi. Smaller Ju/’hoansi bands contain a greater proportion of primary kin, whereas larger Ache bands contain a higher proportion of distant kin. Kin of a family unit only make up about 40% of the co-resident adult members of a band. “Distant affines” or kin of kin make up about half of the co-resident adult members of a band. Finally about 25% of all the individuals in a band are not linked by family ties.

In general, the bands of the 32 societies are composed of distantly related or unrelated individuals. Primary kin generally make up less than 10% of these residential bands, although not much other information of these 32 societies is given. Given the large amount of movement of individuals and cooperation between groups, there would be a pressure for the evolution of positive social mechanisms. The large the populations of the two groups, the more frequent the interactions would be and the faster any cultural innovations may be transmitted and adopted. This is one possible explanation for why humans evolved social learning mechanisms that resulted in cumulative evolution.

Kim R. Hill, et al. 2011 Co-Residence Patterns in Hunter-Gatherer Societies Show Unique Human Social Structure. Science 331: 1286-1289.