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Letters to and from the Editor

We feel it is necessary to correct a misleading impression given by Professor Jensen in his article, "The Phylogeny and Ontogeny of Intelligence" [I]. Jensen writes, "It is now generally accepted by geneticists, psychologists, and sociologists who have reviewed the evidence that social class differences in mental abilities have a substantial genetic component." This statement should be considered in rela' tion to the following facts which at least many geneticists would accept: (i) The proportion of the IQ variance that arises from genetic variety in a population is less than 100 percent, (ii) IQ is a continuous variable, and it is not yet possible to determine gene frequencies, (iii) It follows "that we cannot at present answer the question whether there is any genetic component of social class or race differences in mean IQ" [2]. It is also impossible to say whether there is any environmental component, for this is, in fact, the same question. Thus, as it is impossible to quantify either the genetic or the environmental component of social class differences in mean IQ, we feel it is unwise to say that there is "a substantial genetic component" in these differences. We find it disturbing that Jensen chooses to ignore these facts.