I distinguish three versions of the idea of a peculiarly female intelligence, each devised by men to explain and justify their superior social position. First, from Aristotle through to the nineteenth century, the difference was understood in terms of polarities, e.g., female intuition version male reason. Abilities such as abstract thought, considered alien to women, were seen as indispensable for grasping moral principles. Influenced by Darwin’s theory of evolution, Francis Galton replaced the polarities with a single continuous general intelligence (“natural ability”), which be believed was inherited by men and women. This second version granted women and men the same kind of intelligence, although women, on average, were believed to have less of it. In the early twentieth century, Louis Terman put an end to this view by eliminating particular items from the Stanford-Binet test so that the means of male and female intelligence were the same – otherwise, female means would, in fact, have been higher. A third version, promoted by the sexologist Havelock Ellis, again attempted to defend male hegemony by asserting that women have lower variability in physical and mental traits.

We conclude that there are no overall (average) differences between women and men in general intelligence, but there are some large and persistent differences on cognitive abilities that on average favor males (e.g. mathematics, mental rotation, mechanical) or favor females (verbal ability, most tests of memory). There are more males in the low end of the intelligence distribution, at least in part, for sex-related genetic reasons. There is no genetic evidence for more males in the high end of the intelligence distribution. Paradoxically, societies with greater gender equality do not show reduced differences on many cognitive measures. Our conclusions are about group differences. Thus, these mean differences have no clinical or social significance at the individual level.