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.

465/484 (page 433)

SOCIAL BEHAVIOUR AND PRIMATE EVOLUTION 435 has, in fact, been selected. We have, therefore, suggested a causal link between the two. Whether or not the facts we have discussed have the significance we have placed on them, requires careful consideration in any theory of primate evolution. Conflict, as Neil Miller has shown, results from the equalization of the two opposing variables at the intersection of their gradients. Moreover, this intersection we have suggested can itself exist at various absolute intensities of the negative and positive elements. Conflict is thus a graded element, which, in primate behaviour and in the behaviour of a rat under the conditions of Miller's experiments, determines the position the animal takes up. At a given intensity of conflict, a greater facility for input from sources within the animal will increase the freedom of movement within the confines of the social environment. This is a single quantitative aspect of the enlargement of the neocortex and its dependent structures, which must be kept in sight, and may mean that in evolution the ability to with¬ stand conflict was a simple function of the increasing number of connexions between the cells throughout these structures as a whole. In these circum¬ stances we may usefully consider the hypothesis that man's elaborate behaviour is the consequence of enlargement of the cortex, which process lends to the particular regions of the cortex a functional potential far greater than that exhibited by the cortices of other mammals. The neuro-anatomical evidence, however, points to the localization of specific functions in distinct, but in the case of autonomic functions widely placed, areas of the cortex. An alternative hypothesis is thus available, namely, that the conditions of conflict create the circumstances, which require the continual re-integration of a variety of separate functions into a number of combinations for correct behaviour of any kind in the primate social setting. For example, we have observed that feeding behaviour is structured by the presence of equilibration in response to or even in the absence of threat from the dominant animals. However, in these circum¬ stances fear-provoking stimuli do not cause the animal to stop eating, but having secured food to equilibrate before eating it. We can see, therefore, that on our definition of conflict, the animal which, having equilibrated to a particular spot and settled down to eat, is nevertheless under a degree of sympathetic tone, and yet simultaneous specific parasympathetic activity is required to facilitate the digestive processes. Here, therefore, while general sympathetic tone may be raised, specific parasympathetic outflows may also be brought into operation by a mechanism revealed by Fulton's studies of cortical anatomy (1949). Carpenter's studies of primate society make it clear that not all males are occupied in sexual behaviour to the same extent as others. Indeed, 28-2