Well in this case, the conflation of race and culture is virtually a requirement. As far as we know, you can't do much really to bias an aptitude test in terms of biology because there is little correlation between race and biology¹. On the other hand, culture and race are relatively tightly correlated, so if you want to bias an aptitude test with respect to race, the surest way to do it is to bias it with respect to culture.
A great example is Jim Crow era voting rules. Black people obviously are not biologically disinclined to be able to read, but in 1900, it was a simple fact of southern American culture that a white person of voting age was less likely to be able to read than a black person of voting age. A black southerner of voting age was usually either a former slave, or the child of a former slave, and slaves did not have access to basic education. So a literacy test was, at that time, a racially biased test.
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¹ This is unsurprising when you realize, for example, that the combined population we put in the single box of "black" is more genetically diverse than the combined population of all the races we put outside of that box. Even though populations of different specific geographical origins do often have characteristic biological traits, the social concept of "race" is not strongly correlated with geographical origin.
> A black southerner of voting age was usually either a former slave, or the child of a former slave, and slaves did not have access to basic education. So a literacy test was, at that time, a racially biased test.
That wasn't the whole problem. The literacy tests were only administered to black voters in the first place because of a "grandfather clase"--anyone whose father and grandfather both had the right to vote had the right to vote automatically, and since the literacy tests were only implemented at the end of slavery, in practical terms they only applied to the black population. Naturally, since the test itself wouldn't disenfranchise whites (except for immigrants, but fuck them too) they were free to make it as difficult as possible.
A great example is Jim Crow era voting rules. Black people obviously are not biologically disinclined to be able to read, but in 1900, it was a simple fact of southern American culture that a white person of voting age was less likely to be able to read than a black person of voting age. A black southerner of voting age was usually either a former slave, or the child of a former slave, and slaves did not have access to basic education. So a literacy test was, at that time, a racially biased test.
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¹ This is unsurprising when you realize, for example, that the combined population we put in the single box of "black" is more genetically diverse than the combined population of all the races we put outside of that box. Even though populations of different specific geographical origins do often have characteristic biological traits, the social concept of "race" is not strongly correlated with geographical origin.