http://www.sciencedaily.com/releases/2012/04/120415150123.htm they established a clear causative relationship between genetics and performance on standardized IQ tests. To say that all races have perfectly equal IQ bell curves is a pretty big claim. There are so many genetic differences that influence a persons intelligence that the only way different races would have the same exact bell curves would be if these genetic variables are either equally distributed or balanced (ie: Alice has one gene that leads to higher verbal intelligence, Bob has a gene that leads to higher visual intelligence, and in the end their GIQ is equal yet for different reasons) throughout the various races. The probability of this being the case is essentially zero, and actually studies have shown that this disparity between the IQ bell curves of various races exists and is strongly linked to genetics.