It may seem irrelevant to dwell upon anatomical data, when the purpose of this chapter is to deal with mental aptitudes. The pertinence of the data cited, however, lies in the fact that if any sex difference in physical variability could be established, this would suggest (though it would not prove) the existence of a sex difference in mental variability also. No experimental studies have ever been made for the express purpose of determining whether there exist sex differences in mental variability. Such scattered data as we possess have come incidentally from studies made with some other chief purpose in view. Such data were collected and summarized in the American Journal of Sociology for January, 1914. There was at that time very little evidence that could be cited on this subject, but such as there was gave no ground for maintaining the existence of any sex difference in variability. Since 1914 Trabue's experiments, with "completion tests," performed on about 1,300 school children, have been published; the Courtis arithmetic tests on several thousands of school children in New York have been made public; Terman has tested 1,000 unselected children by the Binet-Simon tests; and Pyle has undertaken his study in the measurement of school children. The evidence from these extensive experiments is in all cases that there is no sex difference in mental variability, as thus measured.
It is necessary also for the reader to bear in mind that there is as yet much controversy among those best equipped to understand the problems of variation, as to the proper methods of measuring comparative variability. The mathematical considerations involved need not be rehearsed here. But until it has been definitely determined just how comparative variability can be scientifically measured, it would seem premature to make any final statement as to sex differences in this respect.
We can therefore answer our second question thus: There is little or no agreement among those best qualified to speak, as to what constitutes the scientific method of measuring comparative variability. But according to the methods now deemed the most reliable, and according to those studies wherein presumably correct methods of measurement have been employed, there is no reason to suppose that there is any sex difference in variability, so far as the numerous traits tested are concerned. There has never been an experimental study made in which the sampling from both sexes was large, random, equal, and from groups of equal homogeneity socially and racially, that showed any reliable sex difference in variability. If we adhere to the literature of fact, we must conclude that, so far as we know, human females differ from each other as much as do human males in abilities and aptitudes.
We now come to the inquiry as to whether there are any special causes of intellectual inefficiency which affect one sex but not the other. Under this topic we may consider the periodic function, which characterizes girls and women, but which does not characterize boys and men. This periodic function has always been the object of superstition and taboo, and is such even among the civilized peoples of today. The literature of opinion is replete with references to it as a source of intellectual weakness and irresponsibility. We may let Frederick Harrison speak for a large group of writers on this point:
"Supposing all other forces equal, it is just the percentage of periodical unfitness which makes the whole difference between the working capacity of the sexes. It is owing to a very natural shrinking from hard facts, and a somewhat misplaced conventionality that this fundamental point has been kept out of sight."
The literature of opinion abounds in different notions, inconsistencies, and contradictory instances in the matter of the periodic function, and its alleged enormous influence on the intellectual and vocational life of women. Much of the opposition to the education of women was based on it, and it has even been exploited as a good reason why political freedom should be denied to women. It is positively stated that women are on this account unfitted to pursue professional and commercial life; yet it is not proposed that cooks, scrub women, mothers, nursemaids, housekeepers or dancers should be periodically relieved from their labors and responsibilities.
There is almost no literature of fact concerning the periodic function as related to the mental abilities of women. No effort had ever been made to subject this matter to study by instruments and methods of precision until very recently. Psychologists, while often stating the influence of periodicity on mental life to be fundamental and characteristic, entirely neglected to consider it when performing experiments on women subjects. In 1909 Voitsecovsky, at Petrograd, performed an experiment on six women by means of instruments of precision. He thought he found a positive result and that there was shown to be an actual influence of periodicity on certain mental functions. His conclusions are, however, largely invalidated by the fact that all his subjects knew the purpose of the experiment, and by the fact that he neglected to use, as a control, human beings not subject to the phenomenon in question. He also neglected to present his data in full, so that the reliability of his conclusions might be calculated.
Two studies of this phenomenon appeared in 1914. The first was a study by Dr. A. E. Arnold, as to the effect of school work on the periodic function, and this is reported in the January number of the American Physical Education Review. This investigator suspected, from his experience as a physician and teacher, "that much of the incapacity claimed was fictitious," and he determined, as an experiment, to institute a régime whereby no student under his supervision would be excused periodically from mental or physical duties, except in cases where some pathological condition existed. In summing up the data he says: "So far our results show all improvement [in the health of students]."
The second study, which appeared in 1914, was by the present writer. She made a prolonged and careful experimental study of twenty-three women (using as a control the records of men subjects), and failed to demonstrate any influence of periodicity on those mental abilities which she tested. These included speed and accuracy of perception, controlled association, steadiness, speed of voluntary movement, fatigability, and rate of learning.
A great amount of scientific work remains to be done before any final answer of any kind can be given to the question, Does functional periodicity exercise a fundamental and characteristic influence on the intellectual abilities of women? We must answer our third question in this way: There is very little experimental evidence on which to base a reply, but the few data which we do possess show no influence, either detrimental or beneficial.