The Tragedy of Isolation

In the 20th century, Western intellectuals' two most dominant explanations of disparities in economic, educational and other achievements were innate racial differences in ability (in the early decades) and racial discrimination (in the later decades).
In neither era were the intelligentsia receptive to other explanations. In each era, they were convinced that they had the answer -- and dismissed and disparaged those who offered other answers.
Differences in mental test scores among different racial and ethnic groups were taken as proof of genetic differences in innate mental ability during the Progressive era in the early 20th century. Progressives regarded the fact that the average IQ test score among whites was higher than the average among blacks as conclusive proof of genetic determinism.

http://townhall.com/columnists/thomassowell/2013/07/30/the-tragedy-of-isolation-n1651724