populations, reproductively isolated for millennia, will evolve genetic liabilities equal to the last decimal place. What do we know about mean genetic differences? Studies of red cell polymorphisms, proteins, and isozymes have consistently shown considerably more variability within a race than between races (Hartl, 1980; Nei, 1985; Nei and Roychoudhury, 1974, 1982). To put this in different terms, the "average" U.S. Oriental, "average" U.S. black, and "average'' U.S. white are genetically more similar to one another than three randomly selected individuals within, say, the U.S. white population. Hence, if these results can be extrapolated to a polygenic system contributing to liability for violence, then the genetic effects on race differences in violence are probably small and secondary to the genetic differences within races.

Faced with a literature equivocal on whether there is a significant genetic effect on violence in Scandinavian samples, the absence of data on within-group heritability for minorities, abrupt historical trends largely unexplainable by genetic drift or natural selection, and molecular genetic evidence suggesting a low between-to-within ratio of genetic group differences, one might conclude that models attributing racial differences mostly to environmental factors have more plausibility than those that explain them mostly in terms of genetics. At the very least, there is no positive evidence to suggest that heritability plays an important role in group differences in violence within the United States.

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