Evolution of Social Systems

  • Robin I. M. Dunbar
Part of the Studies in Behavioural Adaptation book series (SBA)


A species’ social system does not materialise out of nowhere fully formed. It evolves by modification from the social systems of its immediate ancestors. This being so, an important test of our understanding of primate social systems is whether we can use our theoretical principles to reconstruct phylogenies for the social evolution of particular taxonomic groups. Such phytogenies must be consistent with what is known both of the species’ phylogenetic history (i.e. the sequence of speciation events) and with the palaeo-environments through which they passed. Moreover, to be really useful, such reconstructions have to be able to specify not just why changes took place but also how they were brought about. In other words, we need to be able to point to the relationships that changed and show both why these changes might have been necessary and how their occurrence would have caused the appropriate changes in the ancestral taxon’s social system.


Dominant Male Party Size Olive Baboon Journey Length Chimpanzee Population 
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  1. 1.
    Wrangham (1986) offers two sets of data to substantiate this claim. One is that Wrangham and Smuts (1980) and Bygott (1974) found that females and males, respectively, spent significantly less time feeding when in groups than when alone (though this might, of course, be influenced by what other activities animals form groups in order to do — e.g. mate). The other is that he found a significant negative regression for time spent feeding plotted against group size, apparently based on pooling data given by Wrangham (1977) for three different seasons. If each season’s data are analysed separately, there is a significant negative correlation for one set of dry season data (rs= −0.587, n=12, p=0.022 1-tailed) but not for the following dry season (rs= −0.067, n=9, P=0.432 1-tailed), whereas the intervening wet season yields a near-significant positive correlation (rs= 0.323, n=17, p=0.897 1-tailed). Fisher’s procedure for combining significance levels from different tests of the same hypothesis (see Sokal and Rolf 1969, p. 621) indicates that there is no overall underlying trend (X2 = 9.529, df=6, p > 0.10). Although it seems likely that the Gombe chimpanzees may sometimes face significant disruption to their feeding time budgets by foraging in groups, this is by no means always the case (suggesting perhaps that it is only when there is competition for preferred foods that problems arise: see Wrangham 1977).Google Scholar

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© Robin Dunbar 1988

Authors and Affiliations

  • Robin I. M. Dunbar
    • 1
  1. 1.Department of ZoologyUniversity of LiverpoolUK

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