Robin Dunbar, Human Evolution: Why so many social layers?
CHAPTER 8
How Kinship, Language and Culture Came to Be
[final section]
Why so many social layers?
I have argued that religion and story-telling became important because of the need to bond communities that were, by primate standards, very large. So let’s explore just what these entail in contemporary human societies in a little more detail. As I pointed out [earlier], our natural communities of 150 individuals are not socially homogeneous but rather consist of a series of layers made up of relationships of different emotional and social quality. We have much stronger relationships with some individuals in our 150 than with others, and we see them more often as a result. We have identified four such layers that consist, inclusively, of 5, 15, 50 and 150 individuals, but these layers also extend out beyond the 150 for at least two more layers (500 and 1,500). Social systems with hierarchically structured layers of this kind are, in fact, characteristic of primates, and hence in themselves are nothing especially novel in humans. What is novel in humans is the number of layers. What functions do these various layers subserve? …
The substructuring of primate groups owes its origins to the need to create coalitions or alliances that protect individuals against the costs of living in large groups. In effect, each layer provides the framework that supports the layer above, with the next layer being an emergent property of the layer below with the two held together in a complex tension. The substructuring of human communities will have arisen for the same reasons: at each level, the smaller grouping makes the existence of the next layer possible.
In some ways, the easiest to explain is the 15 layer, as this is specifically predicted as the natural coalition size based on a relationship between grooming clique size and neocortex volume in primates. In monkeys and apes, the grooming clique (i.e. one’s set of regular grooming partners) functions as a coalition to buffer the individual against the stresses of living in large social groups. As a result, clique size increases in a regular way with total group size. In effect, grooming cliques exist to keep everyone else off your back so as to defuse the stresses of living in groups: the bigger the group, the worse the stresses, and the bigger the grooming-clique-cum-coalition that you need to keep everyone else at bay. The size predicted for humans by the ape equation for this relationship is exactly the 15 layer, suggesting that this may be its principal function in humans. In effect, it is the basis for obtaining social support as well as economic and other forms of everyday social help; it is the set of individuals who will unhesitatingly come to your help when you need it.
The innermost 5 layer that exists within the 15 layer probably functions mainly to offer more intense emotional support. This layer may reflect the fact that humans’ more sophisticated mentalizing competences leave them vulnerable to forms of psychological fragility not found in our primate cousins. Theory of mind and higher order mentalizing allow us to imagine the future consequences of our behaviour and hence foresee the terrible things that might befall us in ways that other animals simply cannot do. Having a shoulder to cry on in these circumstances may be crucial to our mental wellbeing and hence our ability to cope with a social world that is much more complex than that in which any other primate lives.
The most obvious characteristic of the 50 layer in hunter-gatherers is that it is the group in which humans prefer to spend the night together, and this may be the key to its original function. Partly because of our poor night-time vision and partly because we have to sleep on the ground, this is the time at which humans are most vulnerable to predators. We are inevitably obliged to rely on group size as the only viable defence against nocturnal predators. While the smaller arboreal primates need to watch out only for day-hunting eagles (mainly hawk eagles or, in South America, harpy eagles), the larger, more terrestrial primates are more susceptible to nocturnal predators: the three most important predators of baboons are leopards (nocturnal), lions (hunt mostly at night) and hyenas (nocturnal). While it is true that the 50 layer also provides the basis for women’s foraging (women tend to forage in rather larger groups than the men), it seems unlikely that humans needed groups of this size just for digging up roots or collecting berries. On balance, their role seems to be protection against predators at night, and perhaps to provide a pool of people for safety while foraging during the day.
We have identified six plausible functions for the 50 and 150 layers: protection against predators, defence of territory or food resources, defence of reproductive mates, trading arrangements to minimize environmental risk, information exchange on the location of resources, and protection against raiding by neighbouring human communities (otherwise known as the warfare hypothesis). In a series of studies, we came to the conclusion that what has become known as the warfare hypothesis (defence against raiders) had by far the strongest support as an explanation. It may be no accident that the social brain equation predicts that the 150 layer appears for the first time in the archaeological record at more or less the time that we see the beginnings of the demographic explosion around 100,000 years ago.
Table 8.2 An assessment of the most likely functions for each of the six grouping levels in modern hunter-gatherer societies.
Of course, once you have a bonded community to act as protection, you can also use it for multiple other purposes. Trading arrangements that allow you to seek refuge elsewhere when things are bad in your local area are an obvious secondary benefit for large communities, and the same is surely true of the benefits that a large, more widely distributed community provides in terms of information about the distribution of food resources. Exchange networks have been described in many hunter-gatherer societies. Among the Ju/’hoansi of southwest Africa, for example, the exchange of ‘symbolic’ gifts known as hxaro creates a dispersed network of mutually supportive relationships. Hxaro partners provide help, often by allowing exchange partners to seek refuge with them when conditions deteriorate in their local area. The anthropologist Polly Wiessner has described cases in which half of one San population moved in with distant hxaro partners during a period of food shortage that would have resulted in certain death had they not done so. Similar exchange networks have been reported for other hunter-gatherers, and there is some suggestion that they might have existed in the European Upper Palaeolithic.
The important feature of hxaro partners is that they are not members of your own (50-level) band (the people you actually live with), but people who live elsewhere. In Wiessner’s San population, hxaro partners typically lived within 40 km of each other, which, as the anthropologists Bob Layton and Sean O’Hara have shown, just happens to be the average radius of a community territory in tropical hunter-gatherers. In other words, hxaro exchanges take place principally between people who belong to the same (150-level) community, reinforcing the suggestion that the community is the core unit for the exchange cooperation, not the band. …
… We should also consider the layers beyond 150 that we know, from our analyses of ethnographic societies, form a natural extension of the scaled series of grouping circles in the contemporary world. It has been suggested that the 500 layer is the minimum size to maintain genetic exchange without risk of excessive inbreeding: in many traditional societies, people generally avoid marrying members of their own (150 layer) community, and instead typically marry people from the adjacent community (the partners in their 500-layer extended community). It seems a perfectly sensible explanation for this layer, since it consists mostly of people we would consider to be acquaintances – those with whom we have semi-casual relationships that are not based on reciprocated, personal friendships but rather based on more formal, categorical relationships (which, of course, are wholly dependent on language). That is potentially important from a mating point of view because it means that our community knows them well enough for one of our network members to be able to vouch for their suitability as marriage partners.
That leaves only the 1,500 layer, conventionally identified in the ethnographic literature as the tribe or ethnolinguistic community, a community defined by the fact that everyone speaks the same language. The most likely explanation for this layer is that it represents a trading network that allows communities to buffer themselves against the risk of environmental turbulence because it covers an area large enough to access a range of habitats. The sample of tropical hunter-gatherers compiled by Layton and O’Hara had an average 150-community territory size of 5,000 km2, so the 9–10 communities that would be included in the tribe would have a combined territory of around 50,000 km2 (an area roughly 225 km by 225 km) to draw on in times of ecological collapse within their own territory (or, for that matter, raiding by other groups). That would provide an area large enough to ensure plenty of refuges in times of disaster, since catastrophes are rarely so widespread.
As such, it seems plausible to suggest that tribal level groupings probably arose by extending the subsidiary trading arrangements from 150-level communities to ever wider circles as environmental conditions became progressively more stressful during the last Ice Age beginning around 100,000 years or so ago, and coinciding with the last increase in brain size. It is likely that this layer was crucial in allowing modern humans to colonize high-latitude habitats in Eurasia as successfully as they did after 40,000 years ago. Maintaining such extended social networks probably depends on shared culture and moral views (to ensure honesty and reliable reciprocity), and so may have been unique to AMH [anatomically modern humans]. Here, then, may lie the origins of Deacon’s symbolic community, with their ability to negotiate contracts. Being able to draw on such an extended network for support may also have been critical whenever modern humans and Neanderthals fell into conflict: Neanderthals may have been simply unable to cope with the overwhelming odds that AMH groups could call up when they needed to.
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The Source of today’s exhibit has been:
Robin Dunbar, Human Evolution, Penguin 2014
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