The inheritance of inequality is strikingly large in America today: if the father's lifetime was 100% above the American average for his day, the son's lifetime income will on average be 65% above the American average for his day. That's a lot of inherited inequality. Is this unequal distribution of wealth, income, and status in the United States today the result of the fact that a genetic elite has risen to the top in a "fair" IQ-driven meritocracy?
No.
This high degree of inherited inequality isn't because high IQ genetic eliteness genes are being passed down from fathers to sons. As Samuel Bowles and Herbert Gintis (2002), "The Inheritance of Inequality," report:
The direct effect of IQ on earnings... presented in Bowles, Gintis, and Osborne (2002a)... is 0.15, indicating that a [one] standard deviation change in the cognitive score, holding constant... remaining variables... changes... earnings by about one-seventh of a standard deviation.... An estimate of the causal impact of childhood IQ on years of schooling... is 0.53 (Winship and Korenman 1999). A rough estimate of the direct and indirect effect of IQ on earnings... is then... 0.15+(0.53)(0.22) = 0.266....
h is the heritability of IQ.... The value cannot be higher than 1, and most recent estimates are substantially lower, possibly more like a half or less.... [C]ouples tend to be more similar in IQ than would occur by random mate choice.... [The] genetic correlation of parent and offspring [is] (1 + m)/2....
Using the values estimated above, we see that the contribution of genetic inheritance of IQ to the intergenerational transmission of income is (h2(1+m)/2)(0.266)2 = .035(1 + m)h2. If the heritability of IQ were 0.5 and the degree of assortation, m, were 0.2 (both reasonable, if only ball park estimates) and the genetic inheritance of IQ were the only mechanism accounting for intergenerational income transmission, then the intergenerational correlation [of lifetime income] would be 0.01, or roughly two percent the observed intergenerational correlation [of lifetime income between parents and children].
Two percent is simply not a large number. Factors that currently account for two percent of lifetime earnings inequality are simply not yet a big deal, and cannot be responsible for the fall in social mobility.
If there is ever to be a genetic elite, its members will surely exhibit two behavioral traits: a facility with math, and a near-intinctive tendency to do back-of-the-envelope quantitative checks of assertions.
Let me turn the microphone over to impeccably right-wing Jim Heckman, who comments on The Bell Curve:
The Book fails for five main reasons. 1. The central premise of this book is the empirically incorrect claim that a single factor - g or IQ - that explains linear correlations among test scores is primarily responsible for differences in individual performance in society at large.... There is much evidence that more than one factor -- as conventionally measured -- is required to explain conventional correlation matrices among test scores.... They do not emphasize how little of the variation in social outcomes is explained by AFQT or g. There is considerable room for factors other than their measure of ability to explain wages and other social outcomes. 2. In their empirical work, the authors assume that AFQT is a measure of immutable native intelligence. In fact, AFQT is an achievement test that can be manipulated by educational interventions. 3. The authors[']... implicit assumption of an immutable g that is all-powerful in determining social outcomes leads them to disregard a lot of evidence that a variety of relevant labor market and social skills can be improved. 4. The authors present no new evidence on the heritability of IQ or other socially productive characteristics.... [T]hey... [compare] IQ... [to] a crude measure of parental environmental influences. This comparison is misleading. It fails to recognize the crudity of their environmental measures and the environmental component that is built into their measure of IQ, which biases the evidence in favor of their position. Moreover, the comparison as they present it is intrinsically meaningless. 5. Finally, the authors' forecast of social trends is pure speculation... the social policy recommendations have an ad hoc flavor to them.... The appeal to Murray's version of communitarianism as a solution to the emerging problem of inequality among persons is a deus ex machina flight of fancy that is not credibly justified.
And take a look at http://www.j-bradford-delong.net/movable_type/2003_archives/001975.html as well.
Heckman's recanted.
http://www.gnxp.com/MT2/archives/002677.html
Posted by: Johnny Thunders | January 19, 2007 at 01:45 PM