How Many Friends Does One Person Need? Dunbar’s Number and Other Evolutionary Quirks

Abstract

How Many Friends Does One Person Need? Dunbar's Number and Other Evolutionary Quirks Robin Dunbar Harvard University Press, 2010 University of Oxford Professor Robin Dunbar has written a series of essays exploring the evolutionary origins of a multitude of seemingly unrelated modern behaviors. He manages, though to smoothly transition between essays, chapter to chapter, and at the end of the book comes full circle back to his opening theme. There are those who have suggested that what distinguishes humans from other animals is the ability to use language, formulate moral codes or tool making. However, Dunbar suggests that the crucial differentiation between the primates, including humans, and other animals is the primates' highly involved social relationships, the source of cooperative social groups which facilitate individual survival and reproductive fitness. Culture, defined behavioral norms, and products of intellectual effort, such as literature and sciences, is seen as an extension of human biology and not a separate entity as currently claimed by social scientists. Human social interactions, then, leads to the formation of the things that we assume to be "uniquely" human. The source human culture is the brain, the neocortex in particular. The neocortex is not only the center of higher motor and sensory function but also of memory and reasoning. Dunbar demonstrates a positive correlation between primate neocortical size and group size. Since the human brain does not have an infinite capacity for memory and reasoning, there is an upper limit to the number of people with whom humans are able to have meaningful, face-to-face interactions and the limit is 150, i.e., "Dunbar's Number." In addition to social interaction, increasing neocortical size over the course of human evolution allowed for the development of other cognitive adaptations such as "mind reading," or the perception of others' intentions ("I believe that you think that..."). Increasing degrees of "intentionality" moved a personal belief to a shared community belief ("I want you to know that we both believe that God wants us to..." ). That humans are capable of stepping away from the world as it is and ponder on what could be has implications for the origin of religion and its role in binding community members. Humans somehow know when critical mass is attained - how human groups know when to break off at 150 is not explained - but Dunbar's Number repeatedly appears as an upper limit to group size, in hunter-gatherer, preagricultural tribes, in medieval-era English villages and into contemporary social networks. Despite the dominance of mass urban culture, intimate groupings the size of Dunbar's Number appear in various ways. Dunbar and his colleagues found that every Christmas, individuals send Christmas cards to an average of 68 households. Adding up the individuals in each household works out to a total of around 150. Businesses with less than 150 employees tend to have informal management structures and employees exhibit mutual cooperation and trust, whereas larger companies suffer from a "disproportionate amount of absenteeism and sickness". Here Dunbar only briefly alludes to the psychological effects seen in large groups which lack close interpersonal relationships, the effects of which are so striking that they cannot be easily overlooked. Particularly in the West, one can readily note a general lack of altruism and trust but an abundance of aggressive competition (Miller, 2009; Alkon, 2010). Perhaps extreme social disconnection underlies the infrequent but lethal shooting sprees in the US, wherein individualism is, perhaps excessively, valued. Similarly lethal violence is beginning to appear in other western countries - perhaps a similar, severe sense of alienation also motives these perpetrators.1 Rather than "mutual obligation and reciprocity," modern social interactions are structured by contracts and laws backed by coercion. …