Genetic varaition throughout the genome is responsible for variation in many traits. It is reasonable to assume that there is some genetic basis for intellegence, height, strength, impuslivity, etc. There are also genetic variations between peoples of different ethnic backgrounds which arise through either natural selection, genetic drift, or other random processes. Isn't it then at least feasible that there will be genetic differences between races with respect to average intellegence. Of course there may be huge overlap in the quanititative trait between different groups but on average one group can have a higher mean intellegence than the other. Of course environment would also play a large role.
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