It should be noted that there is considerable controversy surrounding sex
differences in cognition. Some researchers claim that the average differences
between males and females are usually small and often statistically insignifi-
cant (Hyde, 1981) whereas others claim that the differences are substantial
(Eagly, 1995). Some researchers claim that the differences may have been
declining in recent years (Feingold, 1988; Voyer, Voyer, & Bryden, 1995) but
others claim that the differences have remained stable (Halpern, 1992). And, of
course, the biggest controversy has to do with whether cognitive differences
between the sexes are due to the different genes that the sexes inherit or to the
different environments and cultures in which they grow up.
Genetic Basis of Sex Differences in Cognition What is the cause of the sex dif-
ferences in cognition? Obviously, boys and girls are treated differently and
encouraged in different ways (Halpern, 1992). Boys are more likely to be
encouraged to pursue careers in science, engineering, and mechanics, where
mathematical and spatial skills are important. Girls are more likely to be en-
couraged to pursue careers in teaching and in child rearing, where communi-
cation skills are important.
Still, many researchers have proposed genetically based biological explana-
tions for male–female differences in cognition (e.g., Kimura, 1992). Usually the
ultimate cause of sex differences is attributed to the supposedly different selec-
tive pressures on males and females as humans evolved. Supposedly, males did
the hunting, and so evolved better spatial skills for orienting to and trans-
forming spatial information; and females did the gathering and child rearing,
and so evolved better spatial memory and verbal skills.
What biological mechanism might be controlled by the genes that underlie
sex differences in cognition? One example of a biological mechanism that may
plausiblybecodedforinthegenesandthatmaygiverisetosexdifferencesin
cognition is the production of sex hormones. Sex hormones, such as testoster-
one, are known to influence the organization of the mammalian brain during
critical periods in prenatal development (Geschwind & Galabura, 1987; Hal-
pern & Cass, 1994). A variety of research supports a correlation between sex
hormones and performance on sex-differentiating cognitive tasks.
Women who were exposed to abnormally high levels of the male hormone
androgenin uteroscore higher than do controls on tests of spatial ability
(Resnick,Berenbaum,Gottesman,&Bouchard,1986).Oldermalesgiventes-
tosterone improve on visual-spatial tasks (Janowsky, Oviatt, & Orwoll, 1994).
Women do better on cognitive tasks that favor women over men, like verbal
skills, and worse on cognitive tasks that favor men, like spatial rotation, when
they are in the midluteal phase of the menstrual cycle than when they are in the
late menstrual phase. Levels of estrogen and progesterone are higher during
the midluteal phase (Hampson & Kimura, 1988; Hampson, 1990a, 1990b; see
Kimura & Hampson, 1994). Men do better on tasks that favor men over women
during the spring, when their testosterone levels are relatively low, than in the
autumn, when their testosterone levels are relatively high (Kimura & Toussaint,
1991; see Kimura & Hampson, 1994). And it isn’t just that men do better in the
spring, when a young man’s fancy supposedly turns to love–men’s perfor-
mance on tasks that do not favor men over women, such as reasoning, is the
804 R. Kim Guenther