Complex sentence: Richard E. Nisbett has said that the question of whether IQ differences between Blacks and Whites have a genetic basis goes back at least a thousand years, when invading Moors speculated that Europeans might be congenitally incapable of abstract thought.
Split into simpler sentences: Richard E. Nisbett has said that the question of whether IQ differences between Blacks and Whites have a genetic basis goes back at least a thousand years, to the time when the Moors invaded Europe. The Moors speculated that Europeans might be congenitally incapable of abstract thought.