Human Genetic Diversity: Lewontin's Fallacy

Last updated

"Human Genetic Diversity: Lewontin's Fallacy" is a 2003 paper by A. W. F. Edwards. [1] He criticises an argument first made in Richard Lewontin's 1972 article "The Apportionment of Human Diversity", that the practice of dividing humanity into races is taxonomically invalid because any given individual will often have more in common genetically with members of other population groups than with members of their own. [2] Edwards argued that this does not refute the biological reality of race since genetic analysis can usually make correct inferences about the perceived race of a person from whom a sample is taken, and that the rate of success increases when more genetic loci are examined. [1]

Contents

Edwards' paper was reprinted, commented upon by experts such as Noah Rosenberg, [3] and given further context in an interview with philosopher of science Rasmus Grønfeldt Winther in a 2018 anthology. [4] Edwards' critique is discussed in a number of academic and popular science books, with varying degrees of support. [5] [6] [7]

Some scholars, including Winther and Jonathan Marks, dispute the premise of "Lewontin's fallacy", arguing that Edwards' critique does not actually contradict Lewontin's argument. [7] [8] [9] A 2007 paper in Genetics by David J. Witherspoon et al. concluded that the two arguments are in fact compatible, and that Lewontin's observation about the distribution of genetic differences across ancestral population groups applies "even when the most distinct populations are considered and hundreds of loci are used". [10]

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, from individuals across classically defined "races" (Caucasian, African, Mongoloid, South Asian Aborigines, Amerinds, Oceanians, and Australian Aborigines). He found that the majority of the total genetic variation between humans (i.e., of the 0.1% of DNA that varies between individuals), 85.4%, is found within populations, 8.3% of the variation is found between populations within a "race", and only 6.3% was found to account for the racial classification. Numerous later studies have confirmed his findings. [6] Based on this analysis, Lewontin concluded, "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 are not caused by genetic differences. [7] One example is 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. [11]

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. [12]

In Edwards' 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% (as Lewontin reported in 1972), the misclassification probability becomes close to zero if enough loci are studied. [13]

Edwards' 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. [13]

Support and criticism

Evolutionary biologist Richard Dawkins discusses genetic variation across human races in his book The Ancestor's Tale . [5] In the chapter "The Grasshopper's Tale", he characterizes the genetic variation between races as a very small fraction of the total human genetic variation, but he disagrees with Lewontin's conclusions about taxonomy, writing: "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." [5] Neven Sesardić has argued that, unbeknownst to Edwards, Jeffry B. Mitton had already made the same argument about Lewontin's claim in two articles published in The American Naturalist in the late 1970s. [14] [15] [16]

Biological anthropologist Jonathan M. Marks agrees with Edwards that correlations between geographical areas and genetics obviously exist in human populations but goes on to write:

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. [7]

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. [11] [17] [18] [19] [20]

In the 2007 paper "Genetic Similarities Within and Between Human Populations", [10] 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. [10]

Witherspoon et al. write:

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. ... However, the typical frequencies of alleles responsible for common complex diseases remain unknown. 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. [10]

Witherspoon et al. add: "A final complication arises when racial classifications are used as proxies for geographic ancestry. Although many concepts of race are correlated with geographic ancestry, the two are not interchangeable, and relying on racial classifications will reduce predictive power still further." [10]

In a 2014 paper, Rasmus Grønfeldt Winther argues that "Lewontin's fallacy" is effectively a misnomer, as there really are two different sets of methods and questions at play in studying the genomic population structure of our species: "variance partitioning" and "clustering analysis". According to Winther, they are "two sides of the same mathematics coin" and neither "necessarily implies anything about the reality of human groups". [8]

See also

Related Research Articles

Race is a categorization of humans based on shared physical or social qualities into groups generally viewed as distinct within a given society. The term came into common usage during the 16th century, when it was used to refer to groups of various kinds, including those characterized by close kinship relations. By the 17th century, the term began to refer to physical (phenotypical) traits, and then later to national affiliations. Modern science regards race as a social construct, an identity which is assigned based on rules made by society. While partly based on physical similarities within groups, race does not have an inherent physical or biological meaning. The concept of race is foundational to racism, the belief that humans can be divided based on the superiority of one race over another.

<span class="mw-page-title-main">Luigi Luca Cavalli-Sforza</span> Italian population geneticist (1922–2018)

Luigi Luca Cavalli-Sforza was an Italian geneticist. He was a population geneticist who taught at the University of Parma, the University of Pavia and then at Stanford University.

<span class="mw-page-title-main">Population bottleneck</span> Effects of a sharp reduction in numbers on the diversity and robustness of a population

A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population due to environmental events such as famines, earthquakes, floods, fires, disease, and droughts; or human activities such as genocide, speciocide, widespread violence or intentional culling. Such events can reduce the variation in the gene pool of a population; thereafter, a smaller population, with a smaller genetic diversity, remains to pass on genes to future generations of offspring. Genetic diversity remains lower, increasing only when gene flow from another population occurs or very slowly increasing with time as random mutations occur. This results in a reduction in the robustness of the population and in its ability to adapt to and survive selecting environmental changes, such as climate change or a shift in available resources. Alternatively, if survivors of the bottleneck are the individuals with the greatest genetic fitness, the frequency of the fitter genes within the gene pool is increased, while the pool itself is reduced.

Population genetics is a subfield of genetics that deals with genetic differences within and among populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and population structure.

<span class="mw-page-title-main">Human leukocyte antigen</span> Genes on human chromosome 6

The human leukocyte antigen (HLA) system or complex of genes on chromosome 6 in humans which encode cell-surface proteins responsible for regulation of the immune system. The HLA system is also known as the human version of the major histocompatibility complex (MHC) found in many animals.

<span class="mw-page-title-main">Human variability</span> Range of possible values for any characteristic of human beings

Human variability, or human variation, is the range of possible values for any characteristic, physical or mental, of human beings.

<span class="mw-page-title-main">Richard Lewontin</span> American evolutionary biologist and mathematician (1929–2021)

Richard Charles Lewontin was an American evolutionary biologist, mathematician, geneticist, and social commentator. A leader in developing the mathematical basis of population genetics and evolutionary theory, he applied techniques from molecular biology, such as gel electrophoresis, to questions of genetic variation and evolution.

<span class="mw-page-title-main">Genetic variation</span> Difference in DNA among individuals or populations

Genetic variation is the difference in DNA among individuals or the differences between populations among the same species. The multiple sources of genetic variation include mutation and genetic recombination. Mutations are the ultimate sources of genetic variation, but other mechanisms, such as genetic drift, contribute to it, as well.

In population genetics, F-statistics describe the statistically expected level of heterozygosity in a population; more specifically the expected degree of (usually) a reduction in heterozygosity when compared to Hardy–Weinberg expectation.

Researchers have investigated the relationship between race and genetics as part of efforts to understand how biology may or may not contribute to human racial categorization. Today, the consensus among scientists is that race is a social construct, and that using it as a proxy for genetic differences among populations is misleading.

<span class="mw-page-title-main">A. W. F. Edwards</span> British statistician and geneticist (born 1935)

Anthony William Fairbank Edwards, FRS is a British statistician, geneticist and evolutionary biologist. Edwards is regarded as one of Britain's most distinguished geneticists, and as one of the most influential mathematical geneticists in the history. He is the son of the surgeon Harold C. Edwards, and brother of medical geneticist John H. Edwards. Edwards has sometimes been called "Fisher's Edwards" to distinguish him from his brother, because he was mentored by Ronald Fisher. He has always had a high regard for Fisher's scientific contributions and has written extensively on them. To mark the Fisher centenary in 1990, Edwards proposed a commemorative Sir Ronald Fisher window be installed in the Dining Hall of Gonville & Caius College. When the window was removed in 2020, he vigorously opposed the move.

Genetic association is when one or more genotypes within a population co-occur with a phenotypic trait more often than would be expected by chance occurrence.

<span class="mw-page-title-main">Human genetic variation</span> Genetic diversity in human populations

Human genetic variation is the genetic differences in and among populations. There may be multiple variants of any given gene in the human population (alleles), a situation called polymorphism.

Social interpretations of race regard the common categorizations of people into different races. Race is often culturally understood to be rigid categories in which people can be classified based on biological markers or physical traits such as skin colour or facial features. This rigid definition of race is no longer accepted by scientific communities. Instead, the concept of 'race' is viewed as a social construct. This means, in simple terms, that it is a human invention and not a biological fact. The concept of 'race' has developed over time in order to accommodate different societies' needs of organising themselves as separate from the 'other'. The 'other' was usually viewed as inferior and, as such, was assigned worse qualities. Our current idea of race was developed primarily during the Enlightenment, in which scientists attempted to define racial boundaries, but their cultural biases ultimately impacted their findings and reproduced the prejudices that still exist in our society today.

Background selection describes the loss of genetic diversity at a locus due to negative selection against deleterious alleles with which it is in linkage disequilibrium. The name emphasizes the fact that the genetic background, or genomic environment, of a mutation has a significant impact on whether it will be preserved versus lost from a population. Background selection contradicts the assumption of the neutral theory of molecular evolution that the fixation or loss of a neutral allele can be described by one-locus models of genetic drift, independently from other loci. As well as reducing neutral nucleotide diversity, background selection reduces the fixation probability of beneficial mutations, and increases the fixation probability of deleterious mutations.

Race and health refers to how being identified with a specific race influences health. Race is a complex concept that has changed across chronological eras and depends on both self-identification and social recognition. In the study of race and health, scientists organize people in racial categories depending on different factors such as: phenotype, ancestry, social identity, genetic makeup and lived experience. "Race" and ethnicity often remain undifferentiated in health research.

In paternity testing, Paternity Index (PI) is a calculated value generated for a single genetic marker or locus and is associated with the statistical strength or weight of that locus in favor of or against parentage given the phenotypes of the tested participants and the inheritance scenario. Phenotype typically refers to physical characteristics such as body plan, color, behavior, etc. in organisms. However, the term used in the area of DNA paternity testing refers to what is observed directly in the laboratory. Laboratories involved in parentage testing and other fields of human identity employ genetic testing panels that contain a battery of loci each of which is selected due to extensive allelic variations within and between populations. These genetic variations are not assumed to bestow physical and/or behavioral attributes to the person carrying the allelic arrangement(s) and therefore are not subject to selective pressure and follow Hardy Weinberg inheritance patterns.

The stepwise mutation model (SMM) is a mathematical theory, developed by Motoo Kimura and Tomoko Ohta, that allows for investigation of the equilibrium distribution of allelic frequencies in a finite population where neutral alleles are produced in step-wise fashion.

Human genetic clustering refers to patterns of relative genetic similarity among human individuals and populations, as well as the wide range of scientific and statistical methods used to study this aspect of human genetic variation.

"The Apportionment of Human Diversity" is a 1972 paper on racial categorisation by American evolutionary biologist Richard Lewontin. In it, Lewontin presented an analysis of genetic diversity amongst people from different conventionally-defined races. His main finding, that there is more genetic variation within these populations than between them, is considered a landmark in the study of human genetic variation and contributed to the abandonment of race as a scientific concept.

References

  1. 1 2 Edwards, A. W. F. (2003). "Human genetic diversity: Lewontin's fallacy". BioEssays. 25 (8): 798–801. doi:10.1002/bies.10315. PMID   12879450.
  2. ↑ Lewontin, R. C. (1972). "The Apportionment of Human Diversity". Evolutionary Biology. pp. 381–398. doi:10.1007/978-1-4684-9063-3_14. ISBN   978-1-4684-9065-7. S2CID   21095796.
  3. ↑ Rosenberg, N. (2018). "Variance-Partitioning and Classification in Human Population Genetics". In R.G. Winther (ed.). Phylogenetic Inference, Selection Theory, and History of Science: Selected Papers of AWF Edwards with Commentaries. Cambridge University Press. pp. 399–403. ISBN   9781107111721.
  4. ↑ Edwards, A.W.F. (2018). "Human Genetic Diversity: Lewontin's Fallacy". In R.G. Winther (ed.). Phylogenetic Inference, Selection Theory, and History of Science: Selected Papers of AWF Edwards with Commentaries. Cambridge University Press. pp. 249–253. ISBN   9781107111721.
  5. 1 2 3 Dawkins, R. (2005). The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution . with additional research by Y. Wong. New York: Houghton Mifflin Harcourt. pp.  406–407. ISBN   9780618619160.
  6. 1 2 Ramachandran, S.; Tang, H.; Gutenkunst, R. N.; Bustamante, C. D. (2010). "Chapter 20: Genetics and Genomics of Human Population Structure" (PDF). In Speicher, M. R.; et al. (eds.). Vogel and Motulsky's Human Genetics: Problems and Approaches. Heidelberg: Springer. p. 596. doi:10.1007/978-3-540-37654-5. ISBN   978-3-540-37653-8. Archived from the original (PDF) on 3 December 2013. Retrieved 29 October 2013.
  7. 1 2 3 4 Marks, Jonathan M. (2010). "Ten Facts about Human Variation". In Muehlenbein, M. P. (ed.). Human Evolutionary Biology. Cambridge University Press. p. 270. ISBN   9781139789004.
  8. 1 2 Winther, R.G. (2018). "The Genetic Reification of "Race"? A Story of Two Mathematical Methods". In R.G. Winther (ed.). Phylogenetic Inference, Selection Theory, and History of Science: Selected Papers of AWF Edwards with Commentaries. Cambridge University Press. pp. 489, 488–508. ISBN   9781107111721.
  9. ↑ Winther, R.G. (2018). "Race and Biology". In Paul C. Taylor; Linda Martín Alcoff; Luvell Anderson (eds.). The Routledge Companion to the Philosophy of Race. Cambridge University Press. pp. 305–320. ISBN   9781107111721.
  10. 1 2 3 4 5 Witherspoon, David. J.; Wooding, S.; Rogers, A. R.; Marchani, E. E.; Watkins, W. S.; Batzer, M. A.; Jorde, L. B. (2007). "Genetic Similarities Within and Between Human Populations". Genetics. 176 (1): 351–359. doi:10.1534/genetics.106.067355. PMC   1893020 . PMID   17339205.
  11. 1 2 American Anthropological Association (1998). "American Anthropological Association Statement on 'Race'".
  12. ↑ Bhatt, C. (2010). "The spirit lives on: race and the disciplines". In Hill Collins, P.; Solomos, J. (eds.). The SAGE handbook of race and ethnic studies. London: SAGE. p. 115. ISBN   9780761942207.
  13. 1 2 McCabe, Linda L.; McCabe, Edward R. B. (2008). DNA: promise and peril. University of California Press. pp. 76–77. ISBN   9780520933934 . Retrieved July 13, 2011.
  14. ↑ Sesardić, Neven (2010). "Race: a social destruction of a biological concept". Biology & Philosophy. 25 (2): 143–162. CiteSeerX   10.1.1.638.939 . doi:10.1007/s10539-009-9193-7. S2CID   3013094.
  15. ↑ Mitton, J. B. (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. S2CID   85018125.
  16. ↑ Mitton, J. B. (1978). "Measurement of Differentiation: Reply to Lewontin, Powell, and Taylor". The American Naturalist. 112 (988): 1142–1144. doi:10.1086/283359. S2CID   86524123.
  17. ↑ Weiss, K. M.; Fullerton, S. M. (2005). "Racing around, getting nowhere". Evolutionary Anthropology: Issues, News, and Reviews. 14 (5): 165. doi: 10.1002/evan.20079 . S2CID   84927946.
  18. ↑ Graves, Joseph L. (2003). The Emperor's New Clothes: Biological Theories of Race at the Millennium . Rutgers University Press. ISBN   978-0-8135-2847-2.
  19. ↑ Brace, C (2005). "Race" is a four-letter word : the genesis of the concept. New York: Oxford University Press. ISBN   9780195173512.
  20. ↑ "RACE: Are We So Different? - Learn and Teach". www.aaanet.org.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.