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Sex Differences in Intelligence

16 February, 2016 - 09:24

As discussed in the introduction to Intelligence and Language , Lawrence Summers’s claim about the reasons why women might be underrepresented in the hard sciences was based in part on the assumption that environment, such as the presence of gender discrimination or social norms, was important but also in part on the possibility that women may be less genetically capable of performing some tasks than are men. These claims, and the responses they provoked, provide another example of how cultural interpretations of the meanings of IQ can create disagreements and even guide public policy. The fact that women earn many fewer degrees in the hard sciences than do men is not debatable (as shown in Figure 9.4), but the rea sons for these differences are.

Figure 9.4 Bachelor’s Degrees Earned by Women in Selected Fields (2006) 
Women tend to earn more degrees in the biological and social sciences, whereas men earn more in engineering, math, and the physical sciences. National Science Foundation (2010). Downloaded from: 

Differences in degree choice are probably not due to overall intelligence because men and women have almost identical intelligence as measured by standard IQ and aptitude tests (Hyde, 2005). 1 On the other hand, it is possible that the differences are due to variability in intelligence, because more men than women have very high (as well as very low) intelligence. Perhaps success in the mathematical and physical sciences requires very high IQ, and this favors men.

There are also observed sex differences on some particular types of tasks. Women tend to do better than men on some verbal tasks, including spelling, writing, and pronouncing words (Halpern et al., 2007), 2 and they have better emotional intelligence in the sense that they are better at detecting and recognizing the emotions of others (McClure, 2000). 3

On average, men do better than women on tasks requiring spatial ability, such as the mental rotation tasks shown in Figure 9.10 (Voyer, Voyer, & Bryden, 1995). 4 Boys tend to do better than girls on both geography and geometry tasks (Vogel, 1996). 5 On the math part of the Scholastic Assessment Test (SAT), boys with scores of 700 or above outnumber girls by more than 10 to 1 (Benbow & Stanley, 1983), 6 but there are also more boys in the lowest end of the distribution as well.

Figure 9.5
Men outperform women on measures of spatial rotation, such as this task requires, but women are better at recognizing the emotions of others.Source: Adapted from Halpern, D. F., Benbow, C. P., Geary, D. C., Gur, R. C., Hyde, J. S., & Gernsbache, M. A. (2007). The science of sex differences in science and mathematics. Psychological Science in the Public Interest, 8(1),1–51. 

Although these differences are real, and can be important, keep in mind that like virtually all sex group differences, the average difference between men and women is small compared to the average differences within each sex. There are many women who are better than the average man on spatial tasks, and many men who score higher than the average women in terms of emotional intelligence. Sex differences in intelligence allow us to make statements only about average differences and do not say much about any individual person.

Although society may not want to hear it, differences between men and women may be in part genetically determined, perhaps by differences in brain lateralization or by hormones (Kimura & Hampson, 1994; Voyer, Voyer, & Bryden, 1995). 7 But nurture is also likely important (Newcombe & Huttenlocker, 2006). 8 As infants, boys and girls show no or few differences in spatial or c ounting abilities, suggesting that the differences occur at least in part as a result of socialization (Spelke, 2005). 9 Furthermore, the number of women entering the hard sciences has been increasing steadily over the past years, again suggesting that some of the differences may have been due to gender discrimination and societal expectations about the appropriate roles and skills of women.