Sex differences across different racial ability levels: Theories of origin and societal consequences

• Published in: Intelligence (Norwood) 2015-09, Vol.52, p.44-62
• Main Author: Nyborg, Helmuth
• Format: Article
• Language: English
• Subjects: Academic achievement; Age differences; Development; Evolution; Gender differences; Intelligence tests; National Longitudinal Survey of Youth 1997; Occupational achievement; Puberty; Race differences; Racial differences; Sex differences; Steroid hormones; Teenagers
• ISSN: 0160-2896; 1873-7935
• DOI: 10.1016/j.intell.2015.04.005

Jensen (1971) found that black girls score 3 IQ points higher than black boys, and white boys 1.5 IQ points higher than white girls. He, nevertheless, concluded that this did not support his Race×Sex×Ability interaction theory. Jensen (1998) further analyzed data, some from the National Longitudinal Survey of Youth (NLSY79), and suggested that there is no sex difference in general intelligence, g. Other studies have questioned Jensen's null sex difference theory. The present study tested both theories with data from the ensuring NLSY97 survey, which represents the 15+ million 12–17year old adolescents living in the US in 1997. Total sample analyses confirmed the existence of significant inverse white–black IQ sex differences, and disconfirmed the null sex difference theory. Separate race–age analyses demonstrated, however, that robust IQ sex differences materialize only after age 16, with no white–black interaction. At age 17, female IQ trails male by 3.6–7.03 points in three races, respectively. Classical IQ probability curves foretell that more males than females will enter the highest echelons of society, irrespective of race, and white Male/Female ratios at IQ 145 successfully predicted real-life sex differences in educational and occupational achievement. White males with IQ 55 can be expected to run a very high risk of encountering severe achievement problems, a risk shared to some extent with Hispanic male, but black females with this low IQ can be expected to perform worse than black males. The paper finally proposed models to account for the origin of sex and race differences in IQ and related educational and occupational differences, involving gene copy numbers, brain size, and steroid hormones. It was suggested that the evolutionary background and physiological nature of sex and race differences explain why social engineering fails to eradicate them. •Representative US NLSY97 data demonstrate significant IQ sex differences after age 15.•White female IQ reach an asymptote, and Hispanic and black female IQ decline at that age.•The larger male variability potentiates IQ sex ratios at the lower and higher ends of the IQ distribution.•Postpubertal Male/Female ratios at IQ 145 predict high educational and occupational achievement well.•Models are presented to explain the origin and persistence of race and sex differences.