Lewontin's Fallacy



Human Genetic Diversity: Lewontin's Fallacy is a 2003 paper by A.W.F. Edwards that criticizes Richard Lewontin's 1972 conclusion that race is an invalid taxonomic construct because the probability of racial misclassification of an individual based on variation in a single genetic locus is approximately 30%.

Edwards argued that while Lewontin's statements on variability are correct when examining the frequency of specific loci between individuals, the probability of racial misclassification rapidly approaches 0% when one takes into account more loci. This happens because of correlations between the loci frequencies within each population. In Edwards' words, "most of the information that distinguishes populations is hidden in the correlation structure of the data." These correlations can be extracted using commonly-used ordination and cluster analysis techniques. As Edwards showed, even if the probability of misclassifying an individual's race based on a single locus is as high as 30% (as Lewontin reported in 1972), the misclassification probability based on 10 loci can drop to just a few percent.

Numerous studies have verified the ease with which genetic distinctions between races can be found. For instance, a 2001 paper by Wilson et al. reported that an analysis of 39 microsatellite loci divided their sample of 354 individuals into four natural clusters, which broadly correspond to four geographical areas (Western Eurasia, Sub-Saharan Africa, China, and New Guinea).

Whether or not Lewontin's Fallacy is a fallacy depends on how one defines the concept of "differences" between human groups. If "differences" are considered to exist when individuals can be accurately classified according to any single randomly chosen trait, then Lewontin's results imply that human races are not distinct in this sense. If, on the other hand, "real differences" are considered to exist when individuals can be accurately classified using a number of traits, then human races are distinct. The ability to accurately classify individuals using multiple loci is, of course, not simply a property of populations from different races -- any two populations can have their individuals accurately classified in this manner, if enough loci are used. Edwards' argument rests on the point that a relatively small set of loci can provide enough information to distinguish between races.

Similar conclusions have been drawn by several authors, such as Risch et al., who, in a 2002 letter to the journal Genome Biology, stated that "genetic differentiation is greatest when defined on a continental basis".