The Time of Ovulation in Chimpanzees *

Objectivity in sex research during the past fifteen years has been attained chiefly in animal laboratories. The difficulty of applying rigidly controlled scientific technics to the problems of human sex physiology has been a serious handicap and pardy accounts for the fact that less is known about the sexual cycle in man than in some of the lower primates. Prominent among the controversial problems in this field is the question of the time of ovulation. Although the hypothesis of periodic fertility and sterility in the primates is now widely accepted, especially among biologists, evidence of skepticism may be seen in the frequent communications to medical, scientific, and lay journals which attempt to contradict such views. Many of these reports are of case histories based upon testimony, and, as such, are scarcely acceptable as scientific evidence. Using strictly experimental technics, observations are now being made by Burr and his associates (Burr, Lane, and Nims,8 Burr and Musselman9) which may indeed change the entire status of the problem within the near future. It is significant that, in a recent examination and summary of the data on ovulation time in women, Hartman24 presents, as an important part of the evidence for periodic fertility, the results of his observations on monkeys. Of all the evidence available to Hartman at the time, only a small portion was comparable in accuracy and completeness to the observations on monkeys. Because the sexual cycle of the monkey is identical or very similar to that of women in all essential characteristics, Hartman's data constitute some of the best evidence we have for the primates in general (Willson34). Most of the advantages in using monkeys for sex research purposes are to be found also in the use of chimpanzees. In addition, there are a few characteristics which make these apes particularly desirable as subjects for studies of ovulation time: (1) doser morphological and physiological affinities with man, (2) especially prominent variations in size and appearance of the ano-genital region