Evolution.

Society for Experimental Biology (Great Britain)

Date:: 1953

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

Credit: Evolution. Source: Wellcome Collection.

442/484 (page 410)

$412 SOCIAL BEHAVIOUR AND PRIMATE EVOLUTION however, can be revealed if a table is constructed for the proportion of time during which two males are likely to be in the presence of, and therefore, in competition for, an oestrous female, in a society in which there are approxi¬ mately the same number of each sex at maturity, but in which the female's oestrous period is of different lengths. Table I. Relation between proportion of reproductive cycle spent in oestrus by the females to proportion of total time under mating provocation for the males in a society of equal sex ratio No. of females in the group (iV) Calculated from : loo x x X (percentage of time R females are together in oestrus, where the cycles occur independent of each other), when i? = number of females in oestrus, ^) = fraction of total time spent in oestrus by any one female, 5 = (i —p). Table I shows calculation for the smallest unit of society capable of setting up a trigonal relation between the sexes, and for twice that number, we see that, in those primate societies in which the female is in oestrus for more than one-quarter to one-third of the cycle, the males will be under mating provocation (type i) longer than out of it, but that the reverse is true for other societies in which the oestrous interval in the female is less. In those species, therefore, where more than one-quarter of the cycle is spent in oestrus, the element of conflict is the rule rather than the excep¬ tion, and when it reaches one-half, conflict is likely to be an ever-present element. Since a preponderance of females in the hetero-sexual groups of subhuman primates is the rule, the disparity between proportion of total time under provocation between primates and other mammals will be more pronounced than the table suggests. In these conditions the probability of continual sexual provocation and competition between males is thus very high.$

Evolution.

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