This is truly the age of dogma when it comes to differences between groups. Some will blindly deny that intergroup differences in performances are anything other than "stereotypes," "perceptions," or discrimination.
At the other end of the spectrum, the dogma is that mental differences especially, whether among individuals or groups, are innate in the genes. Reaction against this view is so strong in some places that it can literally be a federal case to give IQ tests to black children.
Both these opposing views go back for centuries. Back in the 18th century, Adam Smith said that the difference between porters and philosophers were due to education and suggested that there are fewer innate differences among human beings than among dogs.
On the other side, an Islamic scholar of the 10th century noted that Europeans grow more pale the farther north you go and also that the "farther they are to the north the more stupid, gross, and brutish they are."
This correlation between skin color and mental ability would of course be anathema to the politically correct today -- and the question as to whether it was true or false would never get off the ground. But what were the facts, as of the 10th century?
Since antiquity, Mediterranean Europe -- especially at the eastern end -- had been far more advanced than northern Europe in technology, organization, literacy and all the things that make for a more advanced society. The fact that this has all changed in the centuries since then does not mean that this 10th century scholar was not correct in what he said when he said it.
At the very least, he was there and we were not.
Unfortunately, facts have played a very subordinate role in much discussion of differences among groups, races, nations, and civilizations -- whether among those arguing for innate equality or for innate inequality.
In the early 20th century, many believers in innate inequality presented what may have seemed like a logically airtight argument that our national IQ was in danger of declining over time, because people with low IQs usually had more children than people with high IQs. The eugenics movement and the birth control movement sought to counter this trend by reducing the number of children born to low IQ people.
The logical airtightness of this argument turned out to be its greatest vulnerability when confronted with hard facts. Extensive research by Professor James R. Flynn, an American expatriate in New Zealand, has shown that in fact whole nations have had their performances on mental tests rise by substantial amounts over the years.