Sizing Up Kinship: Larger Groups Win

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 (such as the lack of archaeological evidence for proto-religion and 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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8 thoughts on “Sizing Up Kinship: Larger Groups Win

  1. John

    How do people come to treat non-kin as kin?
    We know from Shepher’s work on incest avoidance that children who see a lot of each other will treat each other as kin. Wouldn’t ‘dancing, singing, and worshipping together’ release this inbuilt kin recognition mechanism?
    Religions are great enhancers of ‘fictive kin’. They use the language of brothers and sisters, God the father, the Earth mother etc (as do nationalisms of all sorts). Religions also bring people into regular face to face contact.
    I think your emphasis on fictive kin is very important…..but ‘proto-religion’ is not an alternative thesis.

  2. admin Post author

    I agree with you; my point is simply that many scholars assert that the evolutionary explanation for religion, or the origin of religion, is to be found in the group enhancing rituals of religion. Of course such rituals would bring people together and further enable fictive kinship (“What’s up soul brother?”), but this is probably a later development, occurring after supernaturalism matured or became systematic enough to allow for singing, dancing, and worshiping together.

    My favorite example of extended and fictive kinship comes from the Plains Indians and I wanted to include them in the post but did not for reasons of space. The Sioux, for example, number 7 distinct bands (and huge numbers of bands within bands) among the Lakota, but also include the Santee Sioux and the Yanktonais (together, the Dakota). At one point, the combined Sioux probably numbered 35,000 and all of these people recognized one another as kin of on sort or another. This is a truly impressive feat, made possible by language, abstraction, and kinship fictions. Their religious beliefs surely provided an assist, but these were quite variable and not much different from their enemies, such as the sun dancing Crow, Blackfeet, and Shoshoni.

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  5. Al West

    Fictive kinship is not necessarily about language – people who are not genealogically related or considered to be consanguines may form strong kin ties based purely on residence, this being the substance of the Westermarck effect (which likely does not depend on sharing any rituals other than living in the same place and probably eating together). Non-human primates are perfectly capable of this form of fictive kinship, even if they aren’t aware of it being fictive at all. Nor is any idea of ritual or the supernatural necessary. In fact, religion can hardly be invoked as a cause of group cohesion when groups already existed at fairly high levels of complexity prior to the development of modern humans. I agree with the post, therefore, but I would take it even further. It is necessary only to invoke non-human primate kinship to explain this! Although, of course, a capacity for language does rather help things along.

  6. admin Post author

    Nice points, especially on the Westermarck effect, which I had not previously considered (and will duly note in future posts). I think we agree that a little primate kinship can go quite a long way, and that as a matter of parsimony we need to fully exhaust the possibilities and effects of kinship before we begin telling stories about group bonding based on proto-religion.

    Postscript — I just read Karen Strier’s piece (2008) in the Annual Review of Anthropology on primate kinship/life history, and it really drives your points home!

  7. Al West

    Well, they’re not really my points! They come mostly from Robin Fox and Bernard Chapais. The latter produced an incredibly good book, “Primeval Kinship”, which came out rather recently. I found it rather revolutionary, and it has the capability, almost on its own, to put kinship studies on a firmer scientific basis. I’m a social anthropologist, not a primatologist, but I’m far from hostile to the inclusion of this incredible primatological data in attempts to understand human beings (who are, after all, primates). So that book comes highly recommended – spread the word!

  8. admin Post author

    I just ordered the Chapais book and must say that his recent comment on the Kim Hill hunter-gatherer kinship study that appeared in Science was powerful. He is really on to something, and I agree with you that this is one of this cases in which primatology is truly informative in a cultural (or social) sense.

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