[PDF download](https://www1.udel.edu/educ/gottfredson/30years/Rushton-Jensen30years.pdf#page=31) Page 31: >IQ test scores African: 85 European: 102 East Asian: 106 >Cranial capacity (cm3) African: 1,267 European: 1,347 East Asian: 1,364 >Cortical neurons (millions) African: 13,185 European: 13,665 East Asian: 13,767 >Gestation time African: Shorter European: Longer East Asian: Longer >From Race, Evolution, and Behavior: A Life History Perspective (p. 5), by J. P. Rushton, 2000, Port Huron, MI: Charles Darwin Research Institute. Copyright 2000 by J. P. Rushton. [page 36](https://www1.udel.edu/educ/gottfredson/30years/Rushton-Jensen30years.pdf#page=36) >Yet national data (reviewed in Section 3) show that the size of the mean Black–White group difference remains approximately constant at 1 standard deviation and shows no significant change throughout the developmental period after about 3 years of age. The follow-up results of the Minnesota Transracial Adoption Study (Table 2), and the fact that the heritability for IQ generally increases from about 0.40 in early childhood to about 0.80 in later maturity (Figure 3), both contradict the Dickens–Flynn thesis. >So too does the fact that both g estimates calculated from East Indians in South Africa and genetic estimates calculated from the Japanese in Japan are able to predict the magnitude of Black–White differences in South Africa and in the United States (see Sections 4 and 5). Such robust generalization implies that the mean Black–White group difference in IQ is sufficiently persistent across cultures as to be unaffected by major changes in gene– environment correlations. Dickens and Flynn (2001) provided no empirical evidence that gene– environment correlation constitutes either a large component of the phenotypic variance or that it increases with age (both of which are required by their model). [page 40](https://www1.udel.edu/educ/gottfredson/30years/Rushton-Jensen30years.pdf#page=40) >The hereditarian model made the novel prediction that the mean Black–White group difference in IQ is not the result of idiosyncratic cultural peculiarities in this or that test but would be more pronounced on highly g-loaded tests. Because the prediction was confirmed, it counts as evidence for the hereditarian position while also contradicting the prediction from the culture-only model that the differences are due to culturally loaded tests. In South Africa, g loadings calculated on East Indians predicted mean Black–White group differences, showing substantial cross-cultural generalizability. A test’s g loading is the best predictor, not just of its correlation with scholastic and workplace performance, but also of its correlation with reaction time measures, heritability coefficients determined from twin studies, inbreeding depression scores calculated in children of cousin-marriages, and neurological variables such as brain size, brain evoked potentials, brain pH levels, brain glucose metabolism, and nerve conduction velocity. Thus, we conclude the evidence reviewed in Section 4 strongly supports the hereditarian model (++) and argues against the culture-only model (-). >Race–IQ Differences Are Most Pronounced on the More Heritable Components of Tests With Little or No Evidence of Race-Specific Developmental Processes https://en.wikipedia.org/wiki/G_factor_(psychometrics) [page 41: Mean Race–IQ Differences Are Associated With Mean Brain Size Differences](https://www1.udel.edu/educ/gottfredson/30years/Rushton-Jensen30years.pdf#page=41) >Overall, MRI studies show that brain size is related to IQ differences within race. Moreover, the three-way pattern of group differences in average brain size is detectable at birth.