He feels that these differences are genetically based, arguing that blacks consistently score lower on IQ tests (the mainstream basis for intelligence testing) than whites. Many surveys of experts who administer IQ tests, as well as behavioral geneticists, agree with Rushton that the IQ-Intelligence barrier is genetically based. .
To further reinforce his genetic basis theory, Rushton has proven that on average, blacks have smaller skulls than their white counterparts. Since brain size can, and has been, correlated with intelligence, Rushton feels that this proves blacks are genetically predetermined to have lower intelligence levels. This positive correlation between mental ability and brain size has been established in studies over the years using even the most high-tech instrumentation, such as magnetic resonance imaging. Along with longitudinal studies following kids of different races, time and time again scientists and psychologists, such as Rushton, have been able to reinforce the idea of a brain size-IQ link.
As I stated before, it has been recorded over time that Caucasians seem to consistently rank above their African-American counterparts in IQ test scores. Many contenders of Rushton's ideas argue that these scores are merely the product of culturally biased testing materials. Rushton himself highly contends this, stating that the tests seem to show similar patterns of internal item consistency and predictive validity for all groups, and the same differences are found on relatively culture-free tests. .
On the other hand of this debate, there are many supporters who firmly disagree with Professor Rushton. One such man, Zack Z. Cernovsky, a teacher and psychologist, argues that Rushton's data is based not on contemporary scientific research, but on racial prejudice. He asserts that the genetic basis model for intelligence ignores the plasticity of human beings which in itself is highly supported by empirical data.