What if the hereditarian hypothesis is true?

Abstract

(2005) review 10 bodies of evidence to support their argument that the long-standing, worldwide Black-White average differences in cognitive ability are more plausibly explained by their hereditarian (50% genetic causation) theory than by culture-only (0% genetic causation) theory. This commentary evaluates the relevance of their evidence, the overall strength of their case, the implications they draw for public policy, and the suggestion by some scholars that the nation is best served by telling benevolent lies about race and intelligence. Rushton and Jensen (2005) review the last 30 years of evidence on an important but spurned question: Is the average Black-White difference in phenotypic intelligence partly genetic in origin? Much relevant scientific evidence has accumulated since Jensen first asked the question in 1969, but openly addressing it still seems as politically unacceptable today as it was then. Taking the question seriously raises the possibility that the answer might be yes, which for some people is unthinkable. It is therefore no surprise that such research and researchers are often evaluated first against moral criteria and only secondarily, if at all, against scientific ones. My commentary therefore examines the Rushton-Jensen article against both the scientific and moral criteria typically applied to such work.The Hereditarian Hypothesis: What Is It? Rushton and Jensen's (2005) hereditarian hypothesis is that Black-White differences in general intelligence (IQ, or the general mental ability factor, g) are "substantially" genetic in origin, which they quantify as 50% genetic and 50% environmental. They specify 50% genetic because they hypothesize that race differences are simply aggregated individual differences and because researchers commonly summarize within-group IQ heritability as 50%. Rushton and Jensen do not attempt to prove conclusively a genetic component but to show that their hypothesis is more plausible than the culture-only hypothesis long favored by social scientists, which entails 0% genetic and 100% environmental causation. Scientific Foundations of the Hereditarian Hypothesis: How Sound?The hereditarian hypothesis becomes scientifically plausible only after five evidentiary prerequisites have been met: IQ differences among same-race individuals represent (a) real, (b) functionally important, and (c) substantially genetic differences in general intelligence (the g factor), and mean IQ differences between the races likewise reflect (d) real and (e) functionally important differences on the same g factor. A century of research strongly supports all five. It has provided a

Black–White differences on IQ and grades: The mediating role of elementary cognitive tasks

“…The partial restriction of range might explain why the BlackWhite IQ difference here (d = .45) was smaller than the typical one-standard deviation effect (d = 1.0) reported in the literature. A larger race difference emerged, however, for GPA where Black students averaged .73 standard deviations lower than the White student mean (this value is similar to those reported by Gottfredson, 2005a,b,c see Table 18.3, p. 536). In sum, significant race differences appeared for both IQ scores and GPAs.…”

Testing the cross-racial generality of Spearman's hypothesis in two samples

“…Large-scale intervention programs such as the well-known "Head Start" project have not produced lasting changes, and the evidence for the predominantly biological and genetic nature of g is growing by the day (Jensen, 1998). The findings by Rushton and Jensen is supported by Gottfredson (2005) who found the discussion of the W-B IQ gap (as presented by Rushton & Jensen, 2005a) consistent with a hereditarian 50% genetic causation theory." However, this view advocated by Jensen and Rushton is not without it critics.…”

Lifecourse Social Conditions and Racial and Ethnic Patterns of Cognitive Aging

“…On the other hand, regardless of the early childhood cognitive measures available, it is hard to be confident that attained schooling is not influenced by other, unmeasured, cognitive skills that themselves influence cognitive aging. This concern is especially troubling for advocates of primarily genetic explanations for racial and social disparities in cognitive outcomes (Gottfredson 2005). Although the hereditarian approach has rarely been extended to discussions of racial disparities in cognitive aging, it is a small extension from the growing debates about IQ and physical health (Deary and Batty 2007) to incorporating cognitive outcomes among the elderly.…”