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In this paper, the analysis of the factors influencing the evolution of neocortex size in primates given in Dunbar (1992) is extended in three specific ways. (1) An independent test is undertaken of the hypothesis that group size is a function of relative neocortex size in primates by using estimates of neocortex size to predict group size for those species that were not involved in the original analysis. The results confirm the results of the earlier analysis. (2) A more satisfactory test is attempted of the alternative hypothesis that species which differ in the degree of extractive foraging also differ in relative neocortex size. This particular version of the hypothesis is rejected. (3) These results are used to identify the "cognitive" group size for those species of baboons that live in multi-layered social systems. © 1995 Academic Press. All rights reserved.

Original publication




Journal article


Journal of Human Evolution

Publication Date





287 - 296