NEOCORTEX SIZE AND GROUP-SIZE IN PRIMATES - A TEST OF THE HYPOTHESIS

In this paper, the analysis of the factors influencing the evolution o f neocortex size in primates given in Dunbar (1992) is extended in thr ee specific ways. (1) An independent test is undertaken of the hypothe sis that group size is a function of relative neocortex size in primat es by using estimates of neocortex size to predict group size for thos e 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 dif fer in the degree of extractive foraging also differ in relative neoco rtex size. This particular version of the hypothesis is rejected. (3) These results are used to identify the ''cognitive'' group size for th ose species of baboons that live in multi-layered social systems.