Thus our first question, Are there innate sex differences in average intelligence, which would call for differentiation of vocations on the ground of sex? may be thus answered: So far as the literature of fact tells us, we know of no considerable sex differences in average mental ability. The evidence of experimental science (and on this point there is now a large amount of evidence available) shows that by the test of averages the sexes have equal ability to perform mental tasks.
Our second question, Is there a sex difference in variability in mental traits which would call for a differentiation of vocation on the ground of sex? has not been so long, nor so thoroughly investigated by experimentalists as has the first question. What we are trying to discover here is whether, when tested in any given mental trait, a group of boys will differ more from one another than will a group of girls (similarly selected and equal in number) differ from one another. In other words, are the members of one sex very much alike in tastes, interests and abilities, while the members of the other sex differ over a wide range of tastes, interests and abilities? Obviously this might be the case, though the two groups yielded an average exactly the same in such traits. The answer to this second question will be of decided significance for vocational guidance. For example, if it were shown by experimental data that human females are, by original nature, rather closely alike, whereas human males differ from one another by wide extremes, we should have scientific grounds for concluding that social justice and social economy are well served by the present policy of guiding all females into a single occupation, while males are encouraged to enter the greatest possible variety of callings.
The first discussion of the comparative variability of the sexes was broached about a century ago by an anatomist, Meckel. It is very interesting (as well as amusing), in view of subsequent ideas about variability, to note what Meckel said. He thought the human female to be more variable than the human male, and he opined that, "since woman is the inferior animal and variability is a sign of inferiority," the conclusion was justified! Fifty years later, when Darwin put a different face upon variability, showing it to be an advantage and a characteristic affording the greatest hope for progress, the greater variability of the male began to be affirmed everywhere in the literature of opinion. Karl Pearson alone took issue with this view, which was current in the nineteenth century and is still widely credited, and pointed out that there existed as yet no literature of fact regarding comparative variability (though men of science had not on this account restrained themselves from uttering the most positive statements concerning it). Pearson thereupon actually gathered and computed hundreds of measurements of human beings, and presented his results in 1897, in a comprehensive article entitled "Variation in Man and Woman." He clearly demonstrated that there is, in fact, no indication of greater male variability, when actual anatomical measurements of adult human beings are treated with mathematical insight. Immediately Havelock Ellis, whose opinions were chiefly affected by Pearson's article, replied that when adults are made the subject of investigation, no information is gained regarding the matter of inherent or original differences in variability. Since birth, life and death, on account of social customs, etc., affect the sexes unequally, no one can say, in the case of adults, how much may be due to environment and how much to original nature. If Ellis had thought of this criticism before he wrote his own book, "Man and Woman," his chapter on "The Variational Tendency of Men" would certainly not have been published. However, his criticism of Pearson's material is no less just because he failed to apply it in his own case. It is true that measurements of adults do not tell us what might be the case with infants, who have not yet been subjected to the formative and selective influences of environment and training. Yet Pearson's article remained practically the only literature of fact regarding the comparative anatomical variability of the sexes until the year 1914. In 1914 Montague and Hollingworth published in the _American Journal of Sociology_ an article setting forth in full the measurements of two thousand new-born infants, one thousand of each sex. The statistical result shows no difference whatever in variability between the sexes.