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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). [17] But nurture is also likely important
(Newcombe & Huttenlocker, 2006). [18] As infants, boys and girls show no or few differences in
spatial or counting abilities, suggesting that the differences occur at least in part as a result of
socialization (Spelke, 2005). [19] 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.
Racial Differences in Intelligence
Although their bell curves overlap considerably, there are also differences in which members of
different racial and ethnic groups cluster along the IQ line. The bell curves for some groups
(Jews and East Asians) are centered somewhat higher than for Whites in general (Lynn, 1996;
Neisser et al., 1996). [20] Other groups, including Blacks and Hispanics, have averages somewhat
lower than those of Whites. The center of the IQ distribution for African Americans is about 85,
and that for Hispanics is about 93 (Hunt & Carlson, 2007). [21]
The observed average differences in intelligence between groups has at times led to malicious
and misguided attempts to try to correct for them through discriminatory treatment of people
from different races, ethnicities, and nationalities (Lewontin, Rose, & Kamin, 1984). [22] One of
the most egregious was the spread of eugenics, the proposal that one could improve the human
species by encouraging or permitting reproduction of only those people with genetic
characteristics judged desirable.
Eugenics became immensely popular in the United States in the early 20th century and was
supported by many prominent psychologists, including Sir Francis Galton. Dozens of
universities, including those in the Ivy League, offered courses in eugenics, and the topic was
presented in most high school and college biology texts (Selden, 1999). [23] Belief in the policies