# Human Genetic Diversity: Lewontin's Fallacy

(Redirected from Lewontin's Fallacy)
 Infobox Multi-Locus Allele Clusters   In a haploid population, when a single locus is considered (blue), with two alleles, + and - we can see a differential geographical distribution between Population I (70% +) and Population II (30% +). When we want to assign an individual to one of these populations using this single locus we will assign any + to population I because the probability (p) of this allele belonging to Population I is p = 0.7, the probability (q) of incorrectly assigning this allele to Population I is q = 1 − p, or 0.3. This amounts to a Bernoulli trial because the answer to the question "is this the correct population?" is a simple yes or no. This makes the test Binomially distributed but with a single trial. But when three loci per individual are taken into account, each with p = 0.7 for a + allele in Population I the average number of + alleles per individual becomes kp = 2.1 (number of trials (k = 3) × probability for each allele (p = 0.7)) and 0.9 (3 × 0.3) + alleles per individual in Population II. This is sometimes referred to as the population trait value. Because alleles are discrete entities we can only assign an individual to a population based on the number of whole + alleles it contains. Therefore we will assign any individual with three or two + alleles to Population I, and any individual with one or fewer + alleles to population II. The binomial distribution with three trials and a probability of 0.7 shows that the probability of an individual from this population having a single + allele is 0.189 and for zero + alleles it is 0.027, which gives a misclassification rate of 0.189 + 0.027 = 0.216, which is a smaller chance of misclassification than for a single allele. Misclassification becomes much smaller as we use more alleles. When more loci are taken into account, each new locus adds an extra independent test to the binomial distribution, decreasing the chance of misclassification. Using modern computer software and the abundance of genetic data now available, it is possible not only to distinguish such correlations for hundreds or even thousands of alleles, which form clusters, it is also possible to assign individuals to given populations with very little chance of error. It should be noted, however, that genes tend to vary clinally, and there are likely to be intermediate populations that reside in the geographical areas between our sample populations (Population III, for example, may lie equidistantly from Population I and Population II). In this case it may well be that Population III may display characteristics of both population I and Population II and have intermediate frequencies for many of the alleles used for classification, causing this population to be more prone to misclassification.

"Human Genetic Diversity: Lewontin's Fallacy" is a 2003 paper by A. W. F. Edwards. He criticises an argument first made by Richard Lewontin in his 1972 article "The Apportionment of Human Diversity",[1] which argued that division of humanity into races is taxonomically invalid.[2] Edwards' critique is discussed in a number of academic and popular science books, not all of which endorse his conclusion.[3][4]

## Lewontin's argument

In the 1972 study "The Apportionment of Human Diversity", Richard Lewontin performed a fixation index (FST) statistical analysis using 17 markers including blood group proteins. His results were that the majority of genetic differences between humans, 85.4%, were found within a population, 8.3% of genetic differences were found between populations within a race, and only 6.3% was found to differentiate the various races which in the study were Caucasian, African, Mongoloid, South Asian Aborigines, Amerinds, Oceanians, and Australian Aborigines. (Later studies have generally agreed although sometimes with somewhat different values such as 75% for variation within a population.)[5] Lewontin argued "Since such racial classification is now seen to be of virtually no genetic or taxonomic significance either, no justification can be offered for its continuance."

This argument has been cited as evidence that racial categories are biologically meaningless, and that behavioral differences between groups cannot have any genetic underpinnings.[6] One example being the "Statement on 'Race'" published by the American Anthropological Association in 1998 which rejected the existence of races as unambiguous, clearly demarcated, biologically distinct groups.[7]

## Edwards' critique

Edwards argued that while Lewontin's statements on variability are correct when examining the frequency of different alleles (variants of a particular gene) at an individual locus (the location of a particular gene) between individuals, it is nonetheless possible to classify individuals into different racial groups with an accuracy that approaches 100 percent when one takes into account the frequency of the alleles at several loci at the same time. This happens because differences in the frequency of alleles at different loci are correlated across populations — the alleles that are more frequent in a population at two or more loci are correlated when we consider the two populations simultaneously. Or in other words, the frequency of the alleles tends to cluster differently for different populations.[8]

In Edwards's words, "most of the information that distinguishes populations is hidden in the correlation structure of the data." These relationships can be extracted using commonly-used ordination and cluster analysis techniques. Edwards argued that, even if the probability of misclassifying an individual based on the frequency of alleles at a single locus is as high as 30 percent (as Lewontin reported in 1972), the misclassification probability becomes close to zero if enough loci are studied.[9]

Edwards's paper stated that the underlying logic was discussed in the early years of the 20th century. Edwards wrote that he and Luigi Luca Cavalli-Sforza had presented a contrasting analysis to Lewontin's, using very similar data, already at the 1963 International Congress of Genetics. Lewontin participated in the conference but did not refer to this in his later paper. Edwards argued that Lewontin used his analysis to attack human classification in science for social reasons.[9]

Evolutionary biologist Richard Dawkins agreed with Edwards' view and summarized it as "However small the racial partition of the total variation may be, if such racial characteristics as there are highly correlate with other racial characteristics, they are by definition informative, and therefore of taxonomic significance."[3] Neven Sesardic has argued that, unbeknownst to Edwards, Jeffry B. Mitton already made the same argument about Lewontin's claim in two articles published in The American Naturalist in the late 1970s.[10]

Biological anthropologists such as Jonathan Marks and philosophers Jonathan Kaplan and Rasmus Winther have argued that while Edwards's argument is correct it does not invalidate Lewontin's original argument, because racial groups being genetically distinct on average does not mean that racial groups are the most basic biological divisions of the world's population. Nor does it mean that races are not social constructs as is the prevailing view among anthropologists and social scientists, because the particular genetic differences that correspond to races only become salient when racial categories take on social importance. According to this view Edwards and Lewontin are therefore both correct.[11][12][13]

Similarly, Marks agrees with Edwards that correlations between geographical areas and genetics obviously exist in human populations, but goes on to note that "What is unclear is what this has to do with 'race' as that term has been used through much in the twentieth century - the mere fact that we can find groups to be different and can reliably allot people to them is trivial. Again, the point of the theory of race was to discover large clusters of people that are principally homogeneous within and heterogeneous between, contrasting groups. Lewontin's analysis shows that such groups do not exist in the human species, and Edwards' critique does not contradict that interpretation."[14]

The view that while geographic clustering of biological traits does exist this does not lend biological validity to racial groups was proposed by several evolutionary anthropologists and geneticists prior to the publication of Edwards critique of Lewontin.[15][16][17][18][19]

In the 2007 paper "Genetic Similarities Within and Between Human Populations",[20] Witherspoon et al. attempt to answer the question, "How often is a pair of individuals from one population genetically more dissimilar than two individuals chosen from two different populations?". The answer depends on the number of polymorphisms used to define that dissimilarity, and the populations being compared. When they analysed three geographically distinct populations (European, African and East Asian) and measured genetic similarity over many thousands of loci, the answer to their question was "never". However, measuring similarity using smaller numbers of loci yielded substantial overlap between these populations. Rates of between-population similarity also increased when geographically intermediate and admixed populations were included in the analysis.[20]

Witherspoon et al. conclude that, "Since an individual's geographic ancestry can often be inferred from his or her genetic makeup, knowledge of one's population of origin should allow some inferences about individual genotypes. To the extent that phenotypically important genetic variation resembles the variation studied here, we may extrapolate from genotypic to phenotypic patterns. [...] The fact that, given enough genetic data, individuals can be correctly assigned to their populations of origin is compatible with the observation that most human genetic variation is found within populations, not between them. It is also compatible with our finding that, even when the most distinct populations are considered and hundreds of loci are used, individuals are frequently more similar to members of other populations than to members of their own population. Thus, caution should be used when using geographic or genetic ancestry to make inferences about individual phenotypes."[20]

## References

1. ^ Made in "The Apportionment of Human Diversity" (1972)
2. ^ Edwards AW (August 2003). "Human genetic diversity: Lewontin's fallacy". BioEssays 25 (8): 798–801. doi:10.1002/bies.10315. PMID 12879450.
3. ^ a b Dawkins, Richard; Wong, Yan (2005). The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution. Houghton Mifflin Harcourt. pp. 406–407. Retrieved July 13, 2011.
4. ^ Sohini Ramachandran, Hua Tang, Ryan N. Gutenkunst, and Carlos D. Bustamante, "Genetics and Genomics of Human Population Structure", chapter 20 in M.R. Speicher et al. (eds.), Vogel and Motulsky’s Human Genetics: Problems and Approaches, 4th ed., Springer, 2010, ISBN 3-540-37653-4, p. 596
5. ^ Risch, Neil; Burchard, Esteban; Ziv, Elad; Tang, Hua (2002). "Categorization of humans in biomedical research: genes, race and disease.". Genome Biology 3 (7): comment2007.1. doi:10.1186/gb-2002-3-7-comment2007. PMC 139378. PMID 12184798.
6. ^ Muehlenbein, Michael P. (2010). Human Evolutionary Biology. Cambridge University Press. p. 270. Retrieved July 13, 2011.
7. ^ American Anthropological Association (May 17, 1998). Statement on 'race'.
8. ^ Solomos, John; Collins, Patricia Hill (2009). The SAGE Handbook of Race and Ethnic Studies. SAGE Publications. pp. 114–115. Retrieved July 13, 2011.
9. ^ a b McCabe, Linda L.; McCabe, Edward R. B. (2008). DNA: promise and peril. University of California Press. pp. 76–77. Retrieved July 13, 2011.
10. ^ Sesardic, Neven (2010). "Race: A Social Destruction of a Biological Concept". Biology & Philosophy 25 (2): 143. doi:10.1007/s10539-009-9193-7. Mitton's articles are the following:
• Mitton, Jeffry B. (April 1977). "Genetic Differentiation of Races of Man as Judged by Single-Locus and Multilocus Analyses". The American Naturalist 111 (978): 203–212. doi:10.1086/283155.
• Mitton, Jeffry B. (1978). "Measurement of Differentiation: Reply to Lewontin, Powell, and Taylor". The American Naturalist 112 (988): 1142–1144. doi:10.1086/283359.
11. ^ Kaplan, Jonathan Michael (January 2011) ‘Race’: What Biology Can Tell Us about a Social Construct. In: Encyclopedia of Life Sciences (ELS). John Wiley & Sons, Ltd: Chichester
12. ^ Winther, Rasmus Grønfeldt (2011) ¿La cosificación genética de la 'raza'? Un análisis crítico in C López-Beltrán (ed.) Genes (&) Mestizos. Genómica y raza en la biomedicina mexicana. Ficticia editorial
13. ^ Kaplan, Jonathan Michael, Winther, Rasmus Grønfeldt (2012). Prisoners of Abstraction? The Theory and Measure of Genetic Variation, and the Very Concept of 'Race' Biological Theory 7 http://philpapers.org/archive/KAPPOA.14.pdf
14. ^ Marks, J. (2010) Ten facts about human variation. In: Human Evolutionary Biology, edited by M. Muehlenbein. New York: Cambridge University Press, pp . 265-276.[1]
15. ^ Weiss KM and Fullerton SM (2005) Racing around, getting nowhere. Evolutionary Anthropology 14: 165–169
16. ^ Graves, Joseph. 2001. The Emperor's New Clothes. Rutgers University Press<
17. ^ Loring Brace, C. 2005. Race is a four letter word. Oxford University Press.
18. ^ http://www.aaanet.org/resources/A-Public-Education-Program.cfm
19. ^ http://www.aaanet.org/stmts/racepp.htm
20. ^ a b c Witherspoon DJ, Wooding S, Rogers AR, et al. (May 2007). "Genetic Similarities Within and Between Human Populations". Genetics 176 (1): 358. doi:10.1534/genetics.106.067355. PMC 1893020. PMID 17339205.