Echoes of the past: hereditarianism and A Troublesome Inheritance.

Abstract

In 1969, Arthur Jensen ignited adecades-long debate when he wrote thatit is a ‘‘not unreasonable hypothesis thatgenetic factors are strongly implicated inthe average Negro–white intelligence dif-ference’’ [1]. From this he inferred thateducational interventions in communitieswhose members have lower measuredintelligence quotient (IQ) could not suc-ceed.The errors in Jensen’s choice of data [2]and statistical methods used to compute aheritability of about 80% for measured IQwere pointed out by numerous geneticistsand statisticians. 25 years after Jensen’sincendiary paper, Herrnstein and Mur-ray’s book, The Bell Curve [3], drewinferences similar to Jensen’s that differ-ences among races and social classes in IQwere genetically based. The Bell Curveelicited a flood of strong criticisms of thedata used, the statistical analyses, and thepolicy inferences [4]. Much of the criticismof Jensen and Herrnstein and Murraycenters on their interpretation of herita-bility of IQ. In 1975, Richard Lewontinand I [5] stressed the failure of theheritability statistic to do what theseauthors claim; namely, to show that IQis largely genetically determined andhence that traits related to IQ, such aseducational or economic success, would beimpervious to environmental intervention.As pointed out by Nicholas Wade inthe first half of A Troublesome Inheri-tance, we are now in a genomic age,where individual differences at the level ofDNA can be detected. The early chapterspresent a hodgepodge of historical ideasabout race, aggression, and genetics. Onpage 57, Wade gives an inkling of whatwill come in the last half of the book:‘‘important aspects of human social be-havior are shaped by the genes’’ and‘‘these behavior traits are likely to varyfrom one race to another, sometimessignificantly so’’ [6].Whereas inferences on the causes ofhuman behavioral variation referred toabove were based on correlations betweenrelatives, on pages 97–99 Wade developshis arguments for the genetic basis of socialbehaviors in the second half of A TroubledInheritance from results on worldwidevariation in DNA polymorphisms, namelymicrosatellite polymorphisms (The Rosen-berg-Feldman studies) [7,8] and singlenucleotide polymorphisms (another Stan-ford study) [9], from the Human GenomeDiversity Panel [10]. Here, as in hisprevious journalism about these studies,Wade exhibits a complete lack of under-standing of their implications. For exam-ple, he does not mention the finding,stressed in both studies, that only 5%–10%of the worldwide genomic variation isbetween continental groups, while the vastmajority is between individuals withinpopulations.Using data from 15 protein genes, R. C.Lewontin in 1972 [11] was the first topoint out that the overwhelming majorityof human genotypic variation is withinpopulations, and that continental ‘‘races’’differed little genetically. 25 years later,Barbujani et al. [12] came to the sameconclusion from their study of 109 DNAmarkers. Wade (page 120) criticizes Le-wontin’s conclusion that ‘‘racial classifica-tion is now seen to be of virtually nogenetic or taxonomic significance’’ asrepresenting Lewontin’s ‘‘political stakein the issue.’’From the data and analyses of world-wide molecular genomic variation, Rich-ard Lewontin and I amplified the conclu-sions of Lewontin and Barbujani et al. asfollows: ‘‘The repeated and consistentresults on the apportionment of geneticdiversity…show that the genes underlyingthe phenotypic differences used to assignrace categories are atypical of the genomein general and are not a reliable index tothe amount of genetic differentiationbetween groups. Thus, racial assignmentloses any general biological interest. Forthe human species, race assignment ofindividuals does not carry with it anygeneral implication about genetic differ-entiation’’ [13]. The increased resolutionon patterns of human variation that wenow have has enabled us to understand agreat deal about human migration, ad-mixture, population size, and naturalselection. However, it has not told us thatthe earlier studies underestimated thebiological reality of race.Even though the between-continentfraction of genetic variation is small, asthe reader discovers on leaving the firsthalf of A Troublesome Inheritance, Wade’serroneous interpretation of its significancefor racial differences becomes the basis for