Of course, we need not take their arguments at face value. As many, especially Professor Stephen Jay Gould of Harvard and even the authors of the Bell Curve themselves point out, just because there is a inheritable component to intelligence does not mean that the observed differences between groups are. Early this century some were worried that the immigration of Southern Europeans, with the significantly inheritable trait of small stature, would have a dysgenic effect on national height. Of course as soon as these immigrants adopted the diets of other Americans, differences in stature narrowed and the mean height of the population has actually increased. The weakest foundation upon which the authors construct their case is that group differences are immutable.
Evidence cited by the authors themselves is particularly instructive.
A study of children of American servicemen and German women showed no difference in the measurable intelligence of children of black and white fathers. Given the American ethos of opportunities open to all and difficulty that some groups especially blacks in overcoming negative stereotypes, Herrnstein and Murray must meet a heavy burden of proof. Weak and marginal evidence of the inheritability and immutability of intelligence differences between groups, especially in the light of persuasive arguments that explain observed differences in IQ by invoking other environmental factors is radically insufficient. There has been criticism that Herrnstein and Murray are making the case that there are inherent ethnic and racial group differences as an argument against affirmative action. In fact, the authors criticize affirmative action, but offer as a substitute watered-down version of it.