Many researchers have expressed concerns about misrepresentations of human population genetics in a recent popular book by journalist Nicholas Wade: A Troublesome Inheritance (Penguin Press, NY, 2014). A letter signed by 143 scientists, including seven from Stanford, criticized the book in the New York Times Book Review on August 8, 2014. In this post, Prof. Marcus Feldman situates A Troublesome Inheritance in a problematic intellectual tradition, highlighting a number of the book’s major problems.
In 1969, Arthur Jensen1 ignited a decades-long debate when he wrote that it is a “not unreasonable hypothesis that genetic factors are strongly implicated in the average Negro-white intelligence difference.” From this he inferred that educational interventions in communities whose members have lower measured IQ could not succeed.
The errors in Jensen’s choice of data (from Burt2) and statistical methods used to compute a heritability of about 80% for measured IQ were pointed out by numerous geneticists and statisticians. Twenty-five years after Jensen’s incendiary paper, Herrnstein and Murray’s book The Bell Curve3 drew inferences similar to Jensen’s that differences among races and social classes in IQ were genetically based. The Bell Curve elicited a flood of strong criticisms of the data used, the statistical analyses, and the policy inferences.4 Much of the criticism of Jensen and Herrnstein and Murray centers on their interpretation of heritability of IQ. In 1975, Richard Lewontin and I5 stressed the failure of the heritability statistic to do what these authors claim, namely, to show that IQ is largely genetically determined and hence that traits related to IQ, such as educational or economic success, would be impervious to environmental intervention.
As pointed out by Nicholas Wade in the first half of A Troublesome Inheritance6, we are now in a genomic age, where individual differences at the level of DNA can be detected. These chapters present a hodgepodge of historical ideas about race, aggression, and genetics. We are given an inkling of what will come in the last half of the book on page 57: “important aspects of human social behavior are shaped by the genes” and “these behavior traits are likely to vary from one race to another, sometimes significantly so.”
Whereas inferences on the causes of human behavioral variation referred to above were based on correlations between relatives, Wade develops his arguments for the genetic basis of social behaviors in the second half of A Troublesome Inheritance from results on worldwide variation in DNA polymorphisms, namely microsatellite polymorphisms (“The Rosenberg-Feldman studies”7,8) and single nucleotide polymorphisms (another Stanford study; Li et al. 20089), from the Human Genome Diversity Panel.10 Here, as in his previous journalism about these studies, Wade exhibits a complete lack of understanding of their implications. For example, he does not mention the finding, stressed in both studies, that only 5–10% of the worldwide genomic variation is between continental groups, while the vast majority is between individuals within populations.
Using data from 15 protein genes, R. C. Lewontin in 197211 was the first to point out that the overwhelming majority of human genotypic variation is within populations, and that continental “races” differed little genetically. Twenty-five years later Barbujani et al.12 came to the same conclusion from their study of 109 DNA markers. Wade criticizes Lewontin’s conclusion that “racial classification is now seen to be of virtually no genetic or taxonomic significance” as representing Lewontin’s “political stake in the issue.”13
From the data and analyses of worldwide molecular genomic variation7,8,9, Richard Lewontin and I amplified the conclusions of Lewontin and Barbujani et al. as follows14: “The repeated and consistent results on the apportionment of genetic diversity … show that the genes underlying the phenotypic differences used to assign race categories are atypical of the genome in general and are not a reliable index to the amount of genetic differentiation between groups. Thus racial assignment loses any general biological interest. For the human species, race assignment of individuals does not carry with it any general implication about genetic differentiation.”
Even though the between-continent fraction of genetic variation is small, as the reader discovers on leaving the first half of A Troublesome Inheritance, Wade’s erroneous interpretation of its significance for racial differences becomes the basis for his entry into the “speculative arena at the interface of history, economics, and human evolution.”15 In the second half of the book, he claims that differences among continents in economic development, social institutions, and social behaviors are based in genetics. This classic correlation-causation error cannot be excused on the grounds that Wade is just speculating: continents can be distinguished genetically; they also have different economic and social histories. One cannot conclude, as Wade does, that the former causes the latter.
The first paragraph of Chapter 7 summarizes Wade’s process of inference: “Each of the major civilizations has developed institutions appropriate for its circumstances and survival. But these institutions, though heavily imbued with cultural traditions, rest on a bedrock of genetically shaped human behavior. And when a civilization produces a distinctive set of institutions that endures for many generations, that is the sign of a supporting suite of variations in the genes that influence human social behavior.”16 I will focus on two of the studies invoked by Wade to justify his totally unfounded claims that differences in the societies of different continents (which he terms “races” even though in a biological sense they are not understood as such) are due to their genetic differences.
The first is by Gregory Clark, an economic historian who studies changes in interpersonal violence, literacy, the propensity to save, and the propensity to work in the English population from 1200 CE to 1800 CE.17 As Wade puts it18, during this period “the nature of the people had changed.” Between 1200 and 1800 “these behavioral changes in the English population … gradually transformed a violent and undisciplined peasant population into an efficient and productive workforce.” How did this happen? “Clark has uncovered the simple genetic mechanism … the rich had more surviving children than the poor.”19 Wade explains further: “Most children of the rich had to sink in the social scale,”20 and as a result, “Their social descent had the far reaching genetic consequence that they carried with them the same behaviors that had made their parents rich.”21
Against the argument that changing culture may have been involved in the 600-year process, Wade states that these “behaviors emerged gradually over several centuries, a time course more typical of an evolutionary change than a cultural change.”22 To justify his claim that 600 years is enough time to have produced “significant changes in social behavior”23 of the English, Wade leans on experiments by Belyaev, who artificially selected silver foxes for tameness. The strength of this selection was extreme: “typically not more than 4 or 5 percent of male offspring and about 20 percent of female offspring have been allowed to breed.”24 The strongest natural selection on humans is orders of magnitude weaker than this “sufficiently intense”25 artificial selection imposed on the foxes. Few evolutionists would agree that 600 years, that is, about twenty-five generations, is long enough for such significant behavioral changes to be due to human genetic evolution; Here and elsewhere in the book, Wade uses “evolutionary” where it is obvious that he means “genetic”. “Ingrained” is another euphemism he occasionally uses. For example, “Tribal behavior is more deeply ingrained than are mere cultural prescriptions. Its longevity and stability point strongly to a genetic basis.”26 Galton and Pearson would have approved of Wade’s espousal of a genetic basis for class differences; there is more than a whiff of eugenics here.
Wade devotes almost four pages of Chapter 7, the longest chapter in the book, to IQ. After claiming27 that “Intelligence is almost certainly under genetic influence,” he goes on to discuss the relationship between wealth and IQ and invokes the work of Richard Lynn and Tatu Vanhanen, in particular their book IQ and Global Inequality.28 Lynn is notorious for his work as an associate editor of The Mankind Quarterly, described by the famous psychologist Leon Kamin29 as a “vulgarly racist” journal. Lynn’s 1991 paper on IQ of Africans is described by Kamin as “truly venomous racism, combined with scandalous disregard for scientific objectivity.” In 2002, Lynn wrote the nonsensical statement: “The conclusion that there is a true association between skin color and IQ is consistent with the hypothesis that genetic factors are partly responsible for the black-white difference in intelligence … the evidence that a statistically significant correlation is present confirms the genetic hypothesis.”30 In placing so much emphasis on the work of one of the most consistently racist psychologists (whose work was strongly supported by the notorious Pioneer Fund, which also supported William Shockley and was chaired by an even more notorious scholar, J. Philippe Rushton), Wade has chosen to ignore important studies on IQ and environment such as those by Brooks-Gunn et al.31 and Turkeheimer et al.32 Brooks-Gunn found that “adjustments for economic and social differences in the lives of black and white children all but eliminate differences in the IQ scores between the two groups,” suggesting that socio-economic status (SES) might be an important contributor to high heritability estimates. In the same vein, Turkheimer et al. found that heritability of IQ depended strongly on SES: there was a high heritability in higher SES environments but not in low SES environments. In choosing not to mention such studies that find very strong environmental contributions to IQ, while relying on Richard Lynn, Wade cements his hereditarian credentials.
Wade gives the appearance of care in interpreting Lynn and Vanhanen: “It is hard to know which way the arrow of causality may be pointing, whether higher IQ makes a nation wealthier or whether a wealthy nation enables its citizens to do better on IQ tests.”33 However, from his statements about “the strong heritability of intelligence”34 and his belief21, referring back to Clark, that in England “the children of the rich carried with them inheritance for the same behaviors that made their parents rich,” we can only assume that Wade believes there is a genetic basis for both IQ and wealth. His “arrow of causality” has two points, with genetics responsible for both IQ and wealth.
This section of the book is redolent of the claims of Jensen, as well as Herrnstein and Murray, mentioned at the beginning of this review. It also harks back to claims by Taubman35 in the 1970s, based on correlations between relatives, that variation between individuals in wealth has a strong genetic basis. It is most informative to compare Goldberger’s 197736 criticism of Taubman’s analysis with related negative evaluations of studies on heritability of IQ. By invoking Richard Lynn on racial variation in IQ and wealth, Wade departs from his “speculative arena,” leaving us to infer not only that he is a devout hereditarian, but also that he is comfortable with Lynn’s racist worldview.
Wade goes even further than proposing a genetic basis for continental variation in wealth; he would have us believe that differences in economic and political institutions among populations have a genetic basis. He criticizes the book Why Nations Fail by Acemoglu and Robinson37 because “they have ruled out the obvious possibility that variations in human behavior are the cause of good or bad institutions.”38 Variation in institutions is why “a part of the world has grown steadily and vastly richer over the past 300 years.”39 He concludes that a reasonable explanation for this variation “is available in terms of human evolution.”40
Wade is using “evolution” here to mean the production and maintenance of genetic differences, and “variations in human behavior” is his euphemism for racial, and hence (in his understanding) genetic differences. He appears to backtrack slightly in the final chapter, where he poses the paradox “that people as individuals are so similar yet human societies differ so copiously.”41 His resolution of the paradox is that these societal differences “stem from the quite minor variations in human social behavior … that have evolved within each race during its geographical and historical experience.”42 Again, “evolved” must be understood in genetic terms: it is “because of their institutions—which are largely cultural edifices resting on a base of genetically shaped social behaviors—that the societies of the West and East Asia are so different.”43
We can juxtapose Wade’s conclusions on the genetic basis of racial differences in wealth, economies, and institutions with those of Ashraf and Galor44 on a similar topic. Their claim was that the high and low molecular genetic diversity characteristic of African and Native American populations, respectively, “have been detrimental for the development of these regions,” while “the intermediate levels of diversity associated with European and Asian populations have been conducive for development.” Wade’s use of worldwide patterns of human molecular genetic variation to define races and his inference that genetic variation between races explains their economic differences are qualitatively similar to Ashraf and Galor’s thesis. Speculation aside, readers of A Troublesome Inheritance are advised to heed the admonition by Guedes et al.45 concerning Ashraf and Galor: “bold claims on the basis of weak data and methods can have profoundly detrimental social and political effects.”
Wade’s premise is that molecular population genetics has shown sufficient variation between continents to define races. He then argues that these genetic differences are responsible for differences in individual social behaviors that “undergird”46 societal institutions, which themselves differ among races. Echoes of the hereditarian arguments about racial difference in IQ and the reductionist arguments of sociobiology and evolutionary psychology resound in A Troublesome Inheritance. I have no trouble with the existence of human genetic variation. It is Wade’s dangerous interpretation, however speculative, of the meaning of this variation that is indeed troublesome.
Marcus W. Feldman is the Burnet C. and Mildred Finley Wohlford Professor in the School of Humanities and Sciences at Stanford and a Founding Director of CEHG.
[Correction: a previous version of this article said that 600 years is about 20 generations; it is actually closer to 25].
- Jensen, A. R. (1969) How much can we boost IQ and scholastic achievement. Harvard Educational Review 39: 1–123.
- See Kamin, L. J. (1974) The Science and Politics of IQ. Potomac, MD: Lawrence Erlbaum.
- Herrnstein, R. J., and C. Murray (1994). The Bell Curve: Intelligence and Class Structure in American Life. New York: Free Press.
- Jacoby, R., and N. Glauberman (eds.) (1995) The Bell Curve Debate. New York: Times Books.
- Feldman, M. W., and R. C. Lewontin (1975). The heritability hangup. Science 190: 1163–1168.
- I abbreviate A Troublesome Inheritance in this list of references as “ATI.”
- ATI, pp. 97–99: Rosenberg, N. A., et al. (2002) The genetic structure of human populations. Science 298: 2381–2385.
- Rosenberg, N.A., et al. (2005) Clines, clusters, and the effect of study design on the inference of human population structure. PLoS Genet. 1: 660–671.
- ATI, p 99: Li, J. Z., et al. (2008) Genome-wide characterization of genetic diversity in human populations. Science 319: 1100–1104.
- Cann, H. M., et al. (2002) A human diversity cell-line panel. Science 296: 261–262.
- Lewontin, R. C. (1972) The apportionment of human diversity. Evolutionary Biology 6: 381–398.
- Barbujani, G., et al. (1997) An apportionment of human DNA diversity. Proceedings of the National Academy of Sciences 94: 4516–4519.
- ATI, p. 120.
- Feldman, M.W., and R.C. Lewontin (2008) Race, ancestry, and medicine. Pp. 89–101 in Koenig, B.A. et al. (eds.) Revisiting Race in a Genomic Age. Rutgers University Press.
- ATI, p. 15.
- ATI, p. 150.
- Clark, G. (2007) A Farewell to Alms: A Brief Economic History of the World. Princeton, NJ: Princeton University Press.
- ATI, p. 154.
- ATI, p. 159.
- ATI, p. 160.
- ATI, p. 160.
- ATI, p. 160.
- ATI, p. 161.
- These experiments are reviewed by Belyaev’s long-time collaborator Lyudmila N. Trut (1999) Early canid domestication: the farm-fox experiment. American Scientist 87: 160–169.
- ATI, p. 161.
- ATI, p. 177.
- ATI, p. 190.
- Lynn, R., and T. Vanhanen (2006) IQ and Global Inequality. Augusta, GA: Washington Summit.
- Kamin, L. (1995) Lies, damned lies, and statistics. Pp. 81–105 Jacoby, R., and N. Glauberman (eds.) The Bell Curve Debate. New York: Times Books. (page 86)
- Lynn, R. (2002) Skin color and intelligence in African-Americans. Population and Environment 23: 365–374. (page 372)
- Brooks-Gunn, J., et al. (1996) Ethnic differences in children’s intelligence test scores: role of economic deprivation, home environment, and maternal characteristics. Child Development 67: 396–408.π
- Turkheimer, E., et al. (2003) Socio-economic status modifies heritability of IQ in young children. Psychological Science 14: 623–628.
- ATI, p. 192.
- ATI, p. 203.
- Taubman, P. (1976) The determinants of earnings: genetics, family, and other environments: a study of white male twins. American Economic Review 66: 858–870.
- Goldberger, A. S. (1977) The genetic determination of income. University of Wisconsin Social Systems Research Institute. Paper 7707.
- Acemoglu, D., and J. A. Robinson (2012) Why Nations Fail: The Origins of Power Prosperity and Poverty. New York: Crown.
- ATI, p. 196.
- ATI, p. 196.
- ATI, p. 196.
- ATI, p. 240.
- ATI, p. 241.
- ATI, p. 241.
- Ashraf, Q., and O. Galor (2013) The out-of-Africa hypothesis, human genetic diversity, and comparative economic development. American Economic Review 103: 1–46.
- Guedes, J. d’A., et al. (2013) Is poverty in our genes? Current Anthropology 54: 71–79.
- ATI, p. 126.