Evolution.

Society for Experimental Biology

Date:: 1953

Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Evolution. Source: Wellcome Collection.

448/484 (page 416)

4i8 social behaviour and primate evolution but exclusive dominance like that described by Zuckerman for the baboon, is not found, unless Macaca nemestrinus be an exception. Extra group males in the large genus of macaques live both temporarily isolated, and also, more frequently, in uni-sexual male groupings. (Carpenter, 19420.) Carpenter summarizes Zuckerman's evidence on baboons in these terms ' in organised heterosexual groupings one may assume that the socionomic sex ratio is even more unequal than that of Howlers and Spiders; there are more intra-group females than males'. He also makes the following statements : Orang outans. While on the west coast of Sumatra, I was fortunate enough to be able to observe a group of orang outans. This group consisted of two adult females with young babies, judged to be about two years of age, and a large adult male. Chimpanzees and gorillas. Although complete information is still lacking on these important African anthropoids, it would seem from the reports of Bingham and Nissen that their grouping patterns are somewhat similar. Available informa¬ tion would suggest that the typical group consists of a dominant male with several other less dominant males, and a larger number of females, plus a series of young. This brief survey indicates several important characteristics of groupings in monkeys and apes : (1) There is a marked variability from genus to genus among the non-human primates, both in total size, and in patterning of groups. (2) Organised groups of primates usually contain more adult females than males. The Gibbon, which lives in families is a known exception, and there may be other species which have different grouping patterns. (3) Extra group males are found to live temporarily alone or in uni-sexual groupings, and, in some instances, females also are found to live temporarily alone. (Carpenter, 19426.) Since the information available to us suggests that the sex ratio at birth is equal, and that the viability of males and females does not differ to any marked extent, we must assume that the existence of a socionomic index in these monkeys is a consequence of the degree of dominance of the overlord males. Even if this were not so, the existence of male bands and solitary males is itself sufficient evidence of the exclusion of some males from the heterosexual groupings, and thus of the appropriation of the females by a few males. The existence of this socionomic index can be inferred despite the fact that these groups may exist singly or in association with one another, and with the surplus males. The heterosexual group appears to exist singly in the gorilla, chimpanzee and orang-outan. They are observed associated together as troups in the baboons and langurs. We have seen that there will be surplus males to be accounted for in any primate population. In many cases these males are associated diffusely with single heterosexual groups