Culture Magazine

Sizing Up Kinship: Larger Groups Win

By Cris

There are a number of scholars who claim that “religion” evolved as an adaptation. What kind of adaptation? A group level adaptation. The story usually goes like this: at some unknown time during the middle or upper Paleolithic, certain groups of hominins developed proto-religious beliefs. These beliefs supposedly caused group members to dance, sing, and worship together, thus making the group more cooperative, cohesive, and prosocial. Consequently, these groups were more successful than groups which were not proto-religious and did not dance, sing, and worship together. Or so the story goes.

Although there are several problems with this story, beginning with the lack of archaeological evidence for such beliefs-activities and continuing with simpler explanations for what little evidence there is, the primary flaw in the argument is that it says nothing about the primary variable — group size — which drives the outcome of group competition. What makes one group more successful than another? In nearly all cases involving competing groups of social mammals, larger groups out-compete smaller ones.

The reasons are fairly obvious and supported by the evidence: larger groups have lower predation risk and have greater success in agonistic encounters. They have larger ranges or territories, and when resources are depleted or disappear, migration – usually a hazardous undertaking, is less hazardous. When a larger group of social mammals encounters a smaller one, the larger nearly always prevails. Larger groups also have a greater store of collective knowledge with respect to nearly everything that matters – water, food, shelter, and predators.

In a previous post, I examined the primary variables affecting group competition in an ancestral setting. Aside from group size, these included tools and language. The latter, in particular, would have had a galvanizing effect: “In addition to the planning and coordination it would have enabled, language at some point made possible notions of extended and fictive kinship, further strengthening this most powerful form of social glue.”

In an important study recently published in Science, Kim Hill and colleagues examined 32 present-day hunting and gathering societies to determine their group structure and residence patterns. They found “that hunter-gatherers display a unique social structure where (i) either sex may disperse or remain in their natal group, (ii) adult brothers and sisters often co-reside, and (iii) most individuals in residential groups are genetically unrelated. These patterns produce large interaction networks of unrelated adults and suggest that inclusive fitness cannot explain extensive cooperation in hunter-gatherer bands.” Surprisingly, most residential bands were not composed of primary genetic kin:

The data demonstrate that primary kin associations are typical, but that most adult band members are not close kin in any of the societies in our sample….[P]rimary and distant kin of a family unit make up only about 40% of the co-resident adult members of a band….[A]bout one-quarter of the individuals in a band are not linked directly to ego by any known genealogical or marriage tie.

Stated another way, 40% of the adult members of a typical foraging band are genetic kin and 75% of them are linked by genes and/or marriage. That is a high percentage of genetic and affinal relatedness. But what about the other 25% who are not related by blood or marriage? Are they considered to be non-kin? Hardly.

All known hunter-gatherer societies have elaborate kinship systems that extend kinship to large numbers of people who are not related by genes or marriage. Indeed, these systems are so extensive and complicated that a good number of anthropologists have devoted entire careers to studying them. These studies began with Lewis Henry Morgan in 1871 (Systems of Consanguinity and Affinity of the Human Family) and culminated with Claude Levi-Straus’ classic, The Elementary Structures of Kinship (1949).

What is the point of all this kinship, whether genetic, affinal, or fictive? The most compelling explanation is that it enables larger residential groups and creates networks of allied groups. Larger groups with more allies would have had an obvious advantage competing against groups lacking such ties. We do not need proto-religion to explain enhanced group cohesion and cooperation. Kinship will do just fine.


Hill, K., Walker, R., Bozicevic, M., Eder, J., Headland, T., Hewlett, B., Hurtado, A., Marlowe, F., Wiessner, P., & Wood, B. (2011). Co-Residence Patterns in Hunter-Gatherer Societies Show Unique Human Social Structure Science, 331 (6022), 1286-1289 DOI: 10.1126/science.1199071

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