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.

447/484 (page 415)

SOCIAL BEHAVIOUR AND PRIMATE EVOLUTION 417 groups of primates inhabiting neighbouring territories, and may enable one group to extend its territory at the expense of another, but for our purposes the part it plays in regulating the sexual behaviour is of the greatest importance. Dominance can be recognized by the various ways in which one male temporarily, or for prolonged periods, interferes with, or wholly prevents, mating behaviour between a particular female or a group of females, and other males. For example, in the gibbon, the young male on reaching maturity is gradually compelled to leave the family group, either together with a sibling, or singly, in which event pairing may take place with a female which can be attracted away from another group. Sexual approach to the adult female of the family is prevented by the dominant male as soon as the young gibbon reaches maturity. In the societies of howler monkeys, one male may form a temporary consort relation with a female simultaneously preventing the approach of another. In macaques and baboons, dominance establishes a rigid male hierarchy, which in different ways allows the dominant male or overlord exclusive access to the greatest number of females at the peak of heat. In these ways domi¬ nance is recognized in the relation between individuals, but it can also be inferred from the numbers of each type of individual constituting a group. Carpenter has carried out an extensive survey of the types of associations found in different species of monkeys. Zuckerman's work on the Hymadrya baboon in captivity, and in the wild state, is an intensive study of the re¬ lations between individual primates in a typical primate society. F rom these studies it is clear that the primate social organization arises from a group within which it is possible to identify a dominant male, or overlord, a number of females attached to him termed the harem, the young animals and the surplus males or bachelors. The existence of surplus males arises from the appropriation of more than one female by the overlord. Carpenter (1942 è) has termed the ratio of males to females in the societies of different primates the socionomic index. This index is characteristic of each genus. For example, in the howler monkey {Alouatta palliata) there is a ratio of i male to 2-3 females. The excess males are solitary. In the spider monkey {Atelesgeojfoyi), on the other hand, there is a ratio of i male to 1-6 females. The group is less cohesive than in the howler monkey, and the excess males are found in groups. The socionomic index for macaques has not been recorded from the wild, but in the Santiago colony established by Carpenter the ratio of females to males was 6 : i. The number of females predominate over the number of males in every observed group of macaques, and for all species except Macaca nemestrinus, which is little known. Within organised groups, the males dominate all other individuals, EBS VII 27