We may speak here of the experiments on brain weight which were published and much discussed about thirty years ago. Romanes, among others, insisted that the male brain was, on the average, several grams heavier than the female brain, and for a time it was supposed that the fact of innate female inferiority had been thus satisfactorily established. However, it was later demonstrated that relative to total body weight the female brain is as heavy as the male brain. It was also found that no positive correlation can be established between brain weight and intellect.
In 1906 Helen Bradford Thompson published her dissertation, from Chicago University, entitled "The Mental Traits of Sex." This volume gives a summary of the scattered bits of experimental work done previous to that time, and presents her numerous experiments on a group of men and a group of women at Chicago University. The result of her tests in various mental traits is that the differences between the sexes were in no case as great as the individual differences within either sex. Men differed from each other in these experiments (as did women also, among themselves), as much as men differed from women. In only two of the many traits tested was a reliable difference found between the central tendencies of the sexes. In speed of voluntary movement (tapping) men were quicker than women, and in memory women were superior to men. On the whole, however, the result indicated equality of mental ability between the sexes.[15] It will be enough for the present purposes to say that after about twenty years of collecting data by scientific experiment, the hypothesis that there is any innate sex difference in average intellectual ability has been abandoned by all psychologists who base their statements on scientific evidence. For example, Dr. E. L. Thorndike, in the most recent edition of "Educational Psychology" (1914), writes as follows, in summing up the experimental work on sex differences in average intellectual ability:
"The most important characteristic of these differences is their small amount. The individual differences within either sex so enormously outweigh any difference between the sexes that for all practical purposes any such difference may be disregarded.... As is well known the experiments of the past generation in educating women have shown their equal competence in school work of elementary, secondary and collegiate grade.... The psychologist's measurements lead to the conclusion that this equality of achievement comes from an equality of natural gifts, not from an overstraining of the lesser talents of women."