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.

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434 SOCIAL BEHAVIOUR AND PRIMATE EVOLUTION govern their activity, and thus lose the abihty to accurately forecast the social repercussion of their own actions (Ward, 1948 è). Ward also states that the behaviour changes produced by unilateral operation lasted at least a month, and there was no difference between the effects of lesions placed on the left- or right-hand sides. Bilateral operation, however, produced a slightly more marked change which, he states, was permanent. This example clearly illustrates that in Macaca mulatta the neuro-anatomical basis for the pattern of primate behaviour, the evolu¬ tionary implication of which has already been discussed, has neocortical components. Equilibration demands of the animal an intensification of the control over its emotional responses, both facilitatory and inhibitory. It seems reasonable, therefore, to suggest that one of the major differences between a lower mammal, such as a rat, and a primate may be that in the former the control of approach and the evocation of emotion are two aspects of a single response to a negative sign, and that the capacity to differentiate these responses is limited by a physiological and possibly anatomical feature. In the primate, these two elements appear to be less rigidly associated. VII. CONSPECTUS We have identified two aspects to the uniqueness of primate behaviour. The first arises out of the fact that in those primates in which the female is receptive for longer than one-third of the cycle, mating becomes a form of behaviour possible at most times, and thus becomes of equal rank to other behavioural activities of the group. The second is the element of conñict which arises out of this situation and affects all the other activities of the group. In the evolution of the primates, these two elements combine to produce the unique type of selection. However, in studies of the behaviour of contemporary primates these two components are separable. Consider the form of the argument. We have drawn attention to two prominent characteristic features of the primates. One is an aspect of their behaviour, and the other comprises the enlargement of a certain structure in the brain. This parallel in itself is not especially significant, since similar parallel developments could be identified in the primates. What is significant is, first, that the anatomical changes in the brain are of a generalized type in a region concerned with the integration of all other brain functions; the new form of behaviour which we have described is also generalized. This means that it is possible to relate one to the other. The second point is, that these two features are also comparable in an evolu¬ tionary context, since we have adduced arguments to show that the behaviour will be selected, and we know that the anatomical enlargement