The Case Against Biological Realism About Race: from Darwin to the Post-Genomic Era

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The Case against Biological Realism about Race: From Darwin to the Post-Genomic Era

Kofª N. Maglo University of Cincinnati

This paper examines the claim that human variation reºects the existence of biologically real human races. It analyzes various concepts of race, including conceptions of race as a breeding population, continental cluster and ancestral line of descent, or clade. It argues that race functions, in contemporary human population genetics, more like a convenient instrumental concept than biological category for picking out subspeciªc evolutionary kinds. It shows that the rise of genomics most likely provided opponents of the biological reality of human races with at least as much ammunition as that of their counterparts the race realists. The paper also suggests that the roots of the current epistemic landscape of the debate can be traced back to Darwin’s essay on The Descent of Man.

[T]he races of man are not sufªciently distinct to inhabit the same country without fusion; and the absence of fusion affords the usual and best test of speciªc distinctiveness. (Charles Darwin [1871] 2004, p. 202)

The subspecies is merely a strictly utilitarian classiªcatory device for the pigeonholing of population samples. (Ernst Mayr 1954, p. 87)

Introduction Did human evolutionary history lead to a natural division of our species into subspecies, the so-called biological human races? The issue seemed to This paper and the previous one (Maglo 2010) grew out of an earlier version I presented at a roundtable on genetics and race at Harvard University in 2004, at the Annual Meeting of the American College of Epidemiology in Boston in 2004, and also at MIT in 2004 in the Program in Science, Technology, and Society (STS). I thank Philip Kitcher, Lisa Lloyd,

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have been beaten to death during the second half of the 20th century. But the situation in the biological sciences changed signiªcantly with the rise of genomic science at the close of the century. The issue of race in science, which most people had deemed passé and obsolete, has now resurfaced in heated disputes among scientists and philosophers. One group of researchers argues that race has an objective biological reality and is a valid predictive tool of genetic and phenotypic variation within our species, while another group counters that race is biologically meaningless and a weak predictive factor of human genetic and phenotypic variation. In what follows, I show that, despite the relative momentum gained by biological race realism in recent years, realists still fail to satisfactorily answer the enduring objections raised, some originally by Darwin himself, against the biological reality of race. In fact, with the genomic revolution, the “no biological human race” school has grown equally strong, highly empiricist, and very sophisticated. I thus maintain that, based on currently available evidence and methods, classiªcations of humans into races in biology very likely represent mere instrumental groupings rather than subspe- ciªc evolutionary branches, hereafter called subspeciªc evolutionary kinds.1 That is, unless future scientiªc ªndings suggest otherwise, race may be con-

Richard Burian and Quayshawn Spencer for their comments on the earlier version of this paper. In 2003, I started collaboration with scientists at the National Human Genome Center at Howard University. In Summer 2005, Esteban Burchard invited me to his Lab at the University of California, San Francisco (UCSF) where he leads a team of researchers working on asthma in Hispanics. During my stay in Burchard Lab, I was able to meet and interview Troy Duster and Neil Risch at their respective universities. These experiences, among others, motivated me to organize in 2007 a colloquium at the University of Cincinnati on “Race in the Age of Genomic Medicine: The Science and its Applications.” I am grateful to all the participants for their wonderful presentations and discussions. The issue of race in science and medicine, as I gradually came to grasp it, can roughly be sum- marized in the following words of the 19th century bio-medical scientist Claude Bernard ([1865] 1957, p. 39): “When two [biologists] or doctors quarrel, each maintaining his own ideas or theories, in the midst of their contradictory arguments, only one thing is abso- lutely certain: that both theories are insufªcient, and neither of them corresponds to the truth.” Although this statement may not be generally true, it seems to me particularly ap- plicable to the dispute between biological realists and eliminativists over race. Thus I ar- ticulated here an instrumentalist view of race as an alternative to both the realist and the eliminativist interpretations. However, it is in my previous paper, actually a follow-up of this one in the order of conception, that I initiated the discussion of the theoretical and ethical conditions for a possible instrumental use of race in the biomedical sciences. I have therefore chosen to focus in the present paper primarily on the issue about the alleged evolutionary divergence of human races. 1. Although I emphasize here human evolutionary history, the reader will soon realize that I do not completely neglect the issue about developmental kinds (See also Maglo 2010).

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sidered merely a convenient problem-solving tool—to be deployed in well- controlled situations with appropriate ethical safety nets—rather than a primary or fundamental category in human population genetics. The paper is an interdisciplinary paper that gathers evidence from history, genomics, and philosophy in order to answer the question of whether or not human races are evolutionary kinds. It starts with the clash between realists, instrumentalists, and eliminativists about race during the period prior to the DNA revolution. It then examines the genomic evidence for and against the existence of biological human races, focusing primarily on the issues of genetic diversity and cladistic ancestral lineage determination within the human species. Finally, the paper explores the philosophical implications of both the historical and the genomic debates over the biological reality of race. In all, it suggests that from Darwin to contemporary post-genomic scientists, the case against the existence of biological human races has grown sharper and more robust than recently thought. However, the paper not only places the genomic debate over race in historical and philosophical perspectives, but it also presents, beyond the issue of race, a new view about the objectivity of kinds in biology.

I. Historical Roots of the Key Epistemic Trends in the Scientiªc Debate over Race The current scientiªc debate over race appears to oppose two different schools of thought. On one side is the realist school, which posits that race is a valid biological concept and an objective fact of nature. On the other side is the “no biological human race” school, often conºated with a version of eliminativism which not only denies that the human species reached the level of intra-speciªc differentiations that may qualify as biological races, but also calls for the elimination of the concept of race from science, medicine, and public health policy (See Maglo 2010). His- torically, however, the epistemic landscape of the debate also encompasses alternative frameworks. For instance, Johan Friedrich Blumenbach—a key ªgure in the pre-Darwinian scientiªc investigation of human races—and Charles Darwin himself seemed to subscribe neither to realism nor eliminativism about race. Darwin, for one, entered the debate over race at a time when researchers were still divided about whether humans formed one single species. Even though scholars such as Kant and Blumenbach previously had defended monogenesis, or the notion that all humans de- scended from a common origin, polygenesis—the idea that different human races have different origins—was still rampant. For Darwin, however, “when the principle of evolution is generally accepted, as it surely will be before long, the dispute between the monogenists and the polygenists will die a silent and unobserved death” (Darwin 2004, p. 210). With the tri-

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umph of Darwin’s theory, the debate indeed shifted from the disunity of the species to whether human races constituted independent evolutionary branching at the subspecies level.2 Still, all along, the then-emerging race concept unsuccessfully confronted objections similar to Darwin’s arguments about the lack of sufªcient biological distinctiveness among so- called human races. According to Darwin, the strongest argument in favor of the unity of the species is that human races gradate into each other, indicating thus that there is no evolutionary branching within the species. This lack of sharp natural delineations, he noted, led to the proliferation of human races in science to the extent that there were as many human races as a re- searcher wanted to recognize. The situation, as Darwin put it, “shows that they graduate into each other, and that it is hardly possible to discover clear distinctive characters between them” (2004, p. 203). In current biology (and since J. S. Huxley), the phenomenon of insensible gradation of traits is referred to as clines, i.e., gradual variations in phenotypes across geographic areas. However, Darwin already made it clear that the gradual distribution of traits among humans cannot be explained simply by population admixture. In fact, Darwin’s point was that human beings are too similar to be cat- egorized into distinct evolutionary branches. He wrote:

Every naturalist who has had the misfortune to undertake the de- scription of a group of highly varying organisms, has encountered cases (I speak after experience) precisely like that of man; and if of a cautious disposition, he will end by uniting all the forms which graduate into each other, under a single species; for he will say to himself that he has no right to give names to objects which he could not deªne. (Darwin 2004, p. 203–4)3 2. However, conºicts arose even among evolutionary biologists, for example between monoregionalists and multiregionalists. Multiregionalism holds, roughly speaking, that Homo sapiens evolved on different continents from primitive stocks of Homo erectus that spread out of Africa. It has been eclipsed, at the dawn of the genomic revolution, by the monoregionalist hypothesis, which afªrms a recent common African origin of all extant humans (see below). 3. Darwin did not seem to view “discreteness” as an absolute criterion. He wrote: “In a series of forms graduating insensibly from some ape-like creature to man as he now exists, it would be impossible to ªx on any deªnite point when the term ‘man’ ought to be used. But this is a matter of very little importance. So again, it is almost a matter of indifference whether the so-called races of man are thus designated, or ranked as species or subspecies; but the latter term appears the more appropriate” (Darwin 2004, p. 210). Notice, however, that the Mendelian genetic breakthrough and the subsequent genomic revolution resolved the issue about the boundaries between Homo sapiens and chimpanzees (see below).

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Interestingly, in the post-Darwinian debate, describing human races in terms of distinct subspeciªc evolutionary kinds has indeed become the de- feating challenge to biological realism. However, none of this implies that, for research purposes or for the management of population health, we cannot meaningfully categorize humans, in the biological and biomedical sciences, into different groups based on various criteria. All that is being denied is the belief that the possibility of such categorizations implies the mapping of independent human evolutionary branches. That is, subspe- ciªc categorizations cannot be predicated on the biological reality of human races. Thus, Darwin did not appear to deny that the concept of race might have some value in science and medicine. Indeed, he forcefully probed the correlation between race and disease susceptibility even though he appeared to deny that race, as applied to humans, has any evolutionary meaning, given that group differences in epidemiological risk factors among humans need not to be driven only by evolutionary mechanisms (for more details, see Maglo 2010). Otherwise put, Darwin understood that, though not an evolutionary kind, race may be under certain conditions an epidemiologically signiªcant kind. So unlike eliminativists such as Herder (2000, p. 26), who declared that there is “no reason for this name,” i.e. race, Darwin seems simply to show a preference for the term subspecies. Nevertheless, he also cleverly acknowledged that researchers will continue to use the term race not due to any scientiªc necessity but because of habits. To be sure, Darwin was not the ªrst to use evidence from the clinal distribution of traits—or “the discreteness objection,” as I shall call it below—against the belief that human races resulted from naturally independent differentiations. The pre-Darwinian naturalist Blumenbach did as well. About a century before Darwin’s 1871 essay, Blumenbach ada- mantly maintained that there was no single characteristic common to one human group and absent from all other groups, and that “[i]nnumerable varieties of mankind run into one another by insensible degrees” (Blumen- bach 2000, p. 27). However, rather than calling for the elimination of the concept of race, Blumenbach instead delineated ªve racial groups corre- sponding more or less to our current continental genetic clusters (see below). Though he acknowledged the existence of an element of arbitrariness in taxonomic categorizations of humans, he maintained that some classiªcations, particularly those using a cluster of characteristics, are pref- erable to others. Accordingly, he invited the reader to compare and weigh the competing taxonomies, “and choose which of them he likes best” (Blumenbach 2000, p. 29). Robust racial classiªcations only give a rough or general picture of human variation, and the impossibility to identify sharp natural boundaries between human races demonstrates, Blumenbach

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concluded, that they all belong “to one and the same species” (Blumen- bach 2000, p. 37). Thus for Blumenbach, as was the case with Darwin later on, the sticking point was that there are no natural breaks within the human species’ continuum. That is, human races or subspecies are not naturally differentiated taxa or kinds. I suggest that instrumentalism rather than realism about race is the most plausible way to cash out the theoretical underpinnings of Blumen- bach’s and Darwin’s interpretations, since the classes or kinds being de- ªned do not reºect independent natural facts.4 Whatever it may be, the clinal distribution objection as construed by Blumenbach and Darwin clearly undermines two dominant versions of race realism of the time. These are race essentialism and race-based biological determinism. Race essentialists hold that biological membership is determined by the pos- session of an essential property—a necessary and sufªcient condition— according to which all members X of a class C are similar to each other but different from all outsiders. Though essentialism in biology is generally traced back to Aristotle and Plato, in the debate over race, Kant appears to be most representative of race essentialists. According to Kant, racial differentiation results from the interaction between the environment, biological “seeds,” and natural predispositions inborn in humans. This interaction produces unchangeable and race-speciªc characteristics, namely skin color, according to which all the members of a given race are similar to each other but different from all outsiders. Hence, once racial traits are developed, they become irreversible (Eze 1997; Bernasconi 2001; Zack 2002). Race-based biological determinism, on the other hand, results from a kind of combination of race essentialism and typological thinking—the view that not only are all the members of a given race deªned by necessary and sufªcient intrinsic and morphological characteristics, but that they also conform to race-speciªc behavioral and cognitive norms. In this deter- ministic view then, (1) fundamental biological factors determine racial differences in human behavioral norms to the extent that (2) social and

4. Instrumentalists typically reject the realist philosophy of science involved in the cor- respondence theory of truth, according to which “true” theories are determined by their relationship to independent natural referents. Instrumentalism simply holds that science is a search for problem-solving tools with regular predictive value rather than a search for ulti- mate causes, underlying natural structures, hidden variables, etc. On this account, race need not pick out independent biological facts in order to play a signiªcant role, for example, in science and medicine. That is, race need not be biologically real to be biologically or medically signiªcant (See Maglo 2010; Jackson 2004). Indeed, I construe “instrumental kind” here as a biologically (or medically) signiªcant kind that does not reºect an evolutionary branching phenomenon and sharp developmental boundaries.

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economic inequalities reºect differences in biological endowments and cannot be corrected by social policies. Thus, racial boundaries inform us not simply about the distribution of trivially adaptive traits but also about the distribution of cognitive capacities across the species, and ultimately determine immutable social statuses (Gould [1981] 1996).5 However, even in the pre-genomic era, a softer realism about race was already being advanced by sophisticated evolutionary biologists such as Theodosius Dobzhansky. For Dobzhansky, race was a local or breeding population distinguishable from other such breeding populations “in the varying incidence of deªnite genes” (Dobzhansky [1941] 2008a, p. 284). He accordingly urged that the notion of “pure races” be replaced with the population-thinking informed concept of geographic races, which are in fact geographically graded series or clines. Reframing race realism in light of population-thinking has the advantage of alleviating the burden of de- termining the necessary and sufªcient condition for racial membership. Indeed, as early as 1784, that is, a century after François Bernier apparently introduced the notion of race as a bio-geographic concept into the literature, the race eliminativist Herder assailed the concept, arguing that “[j]ust as in nature no two leaves of a tree are the same, even less so are two human faces” (2000, p. 23). There is no doubt that Dobzhansky’s soft realism is not vulnerable to similar objections. Nonetheless, the problem of equating race with breeding population is that it does not solve the fundamental issues of whether race is a biological category and a primary concept in human population genetics (Gannett 2004). No one denies that human populations differ in allele frequencies. The problem is that Dobzhansky seems to label any genetic differences racial differences while

5. Biological determinism about race was not just an 18th and 19th century phenomenon defended in various ways by philosophers such as David Hume and Hegel, by craniometrists such as Samuel Morton and Paul Broca or by theoretical polygenists such as Louis Agassiz. It survived Darwinian biology and the new trend towards population thinking, the view that human groups are made up of “unique” individuals rather than variants or “copies” of ideal types. Race-based biological determinism was a key but controversial assumption in American psychometric studies throughout the 20th century. It rests on the idea that group differences in IQ reºect differential racial genetic endowments. The issue is not that IQ research is useless. Even ªerce critics such as Stephen Jay Gould acknowledge that it can help improve the performance of people with learning disabilities, for example. In fact, Alfred Binet, the initiator of IQ studies, intended it as a tool for that purpose. But successive generations of researchers throughout the last century did not view IQ simply as a problem-solving tool. They saw in it a measure of something racially inherited and ªxed. In reality, “intelligence” is very likely inºuenced by a combination of both genetic and non-genetic factors. But, despite the fact that the question of which speciªc alleles and environmental causes are conducive to better cognitive performance remains largely unan- swered even in the age of genomics, race-based biological determinism is still rampant in the scientiªc literature (see criticism in Cooper 2005).

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at the same time claiming that not every racially distinct population is a race or should be recognized as such. He wrote, for example, in response to Frank Livingstone’s ([1962] 2008a) rejection of the application of the concept of geographic race to humans that: “Since human populations [. . .] often, differ in the frequencies of one or more, usually several to many, genetic variables, they are by this test racially distinct. But it does not follow that any racially distinct populations should be given racial (or subspe- ciªc) labels” (Dobzhansky 2008b, p. 298). The difªculties in Dobzhansky’s thought about the existence of biological human races were highlighted by Livingstone in his reply, in which he rejected as simply untenable “Dobzhansky’s dichotomy” between the issue of the putative biological reality of human races and the allegedly uncon- nected issue of the nomenclatorial recognition of such biological human races. Livingstone argued that: “the concepts of a science are also logically interconnected and form a coherent, consistent theory or system. The concepts of such a system are deªned in terms of one another and certain primitive terms, and then the formal, mathematical, or logical properties of the system derived” (2008b, p. 300). Livingstone’s point was that if the concept of race is being introduced in human population genetics because it allegedly has a scientiªc necessity and a unique explanatory value, then the nomenclatorial identiªcation of human races cannot be at the same time a matter of arbitrary choice. Indeed, there would have been very little to quarrel with had Dobzhansky simply argued that human races are convenient instrumental groupings that may be biologically signiªcant under certain conditions. To repeat, no one disputes the fact that human populations differ in the frequencies of one or more allelic variants. The question is whether these differential frequencies license biological race realism, i.e., Dobzhansky’s claim that human races are both evolutionary and adap- tively distinct groups.6 In fact, a careful examination indicates that the negative answer to this question lies in the same paper Dobzhansky devoted to promoting a positive response. He wrote: [T]he races may develop isolating mechanisms that would prevent them from interbreeding and hence from exchanging genes with each other. The establishment of isolation connotes the transforma- 6. We may distinguish purely evolutionary kinds from adaptive or developmental kinds and both from kinds resulting from a combination of both evolutionary and developmental processes of differentiation. With respect to mere developmental kinds, it is worth noting that since the 19th century, morphometric studies, blood-type analysis, epidemiological research, etc., have systematically failed to support the existence of natural boundaries between human races (Keita and Kittles 1997). Nevertheless, this does not mean that race cannot be a useful category, for example in public health settings and the like (Maglo 2010).

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tion of races into separate species and is therefore outside the scope of the present article. The point which should be made clear here is that a race becomes more and more a reality, and less and less an abstraction, as it approaches the species rank. Species attain the degree of existential concreteness which makes them independent actors in the drama of life...(Dobzhansky 2008a, p. 285; my emphasis)

To put the matter bluntly, Dobzhansky and his followers have yet to tell us which of the world’s breeding human populations are reaching “the rank of species” and are thus becoming less and less abstractions. If none such breeding human populations can be identiªed as being a species in statu nascendi, then we should consider the issue settled. That is, we should view race in human population genetics as an “abstraction” or, to put it in philosophical terms, as a nominalistic concept.7 In a word, the putative equivalence between breeding human population and biological race fails to overcome the very objections that have been raised against the biological reality of human races since Darwin, e.g., the scientiªc proliferation of human races and the nonexistence of natural boundaries between human races. For instance, we might count thousands of breeding populations in a single country such as India, which we shall now baptize, for no obvious scientiªc necessity, races. Furthermore, it is misleading to indiscrimi- nately label genetic differences between, say, the British and the Germans, the North Koreans and the South Koreans, the Sicilians and the Neapoli- tans, the Puerto Ricans and the Mexicans, or the Koisan and the Eskimos, as racial differences. Brieºy, the notion of biological human races as breeding populations creates more confusion than it helps dispel. For example, the idea that the Mormons of European descent in Utah, the Catholics of European descent in Pennsylvania, and the Protestants of European descent in South Carolina constitute three biologically real races because they are three distinct breeding populations is a bit more than unconvinc- ing. We will return to these theoretical issues in section III, where I shall reframe the debate in terms of natural kind or, better yet, evolutionary kind as opposed to mere instrumental kind.8 It sufªces to suggest here 7. My speciªc point here should not be misconstrued. It is about what, in Dobzhansky’s view, confers a biological reality to race. Whether it is in 1941 or later in 1962, for Dob- zhansky, differential genetic frequencies among groups are synonymous with human racial differences. 8. By “mere or convenient instrumental kind,” I mean a biologically signiªcant kind that does not map an evolutionary branching phenomenon but which is relevant to the resolution of concrete problems in the biological and biomedical sciences. I have already shown elsewhere that race may be a biologically signiªcant or medically relevant kind even if it is an invalid concept in light of human evolutionary biology (for more details about the notions of biological signiªcance and medical relevance, see Maglo 2010).

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that the very issues that divide 21st century genomic scientists, as we shall now see, hark back at least to the Darwinian period.

II. Constructing and Deconstructing the Concept of Race in Genomics The recent genomic revolution, instead of dramatically altering the epistemic landscape of this perennial debate, has simply given it a new momentum as well as some speciªc contours. Thus, there is currently a dominant concept of race in dispute among genomic scientists that, unlike Dobzhansky’s breeding population race concept, may be called the continental ancestry identiªcation race concept (Wilson et al. 2001; Risch et al. 2002; Burchard et al. 2003; Cooper et al. 2003). It is the most em- pirically and quantitatively documented concept of race in the genomic era and, again unlike Dobzhansky’s breeding population race concept, it limits the number of human races to around ªve.9 Various genomic approaches led to this concept. These include, for example, the possibility of partitioning our species into statistic clusters by use of multiallelic microsatellite markers, single nucleotide polymorphisms (SNP), etc.; the possibility of ªnding rare allelic variants that are conªned to some geographic regions; and the possibility of constructing ancestral-tree dia- grams or dendrograms reºecting the divergence in ancestral lineages at a continental level, the so-called continental clades. However, inferring the biological reality of race from continental membership identiªcation studies faces at least ªve different types of objections. These are: (1) the discreteness objection, (2) the sampling and computational artifact objection, (3) the proportionality or threshold objection, (4) the statistical bias objection, and (5) the ubiquitousness or para/polyphyletic objection. Interest- ingly, though these objections cast varying degrees of doubt on the reality of human races, understood as independent evolutionary branching within our species, and on the validity of race as a primary concept in human population genetics, they are all compatible with an instrumentalist view of race. What they deny is simply that continental genetic partitions constitute natural subdivisions or, more exactly, evolutionary kinds. That is, they only aim at undermining the claim that race is a fundamental or primitive category in human population genetics. Take, for example, a recent extensive examination of “race” in human population genetics by Rosenberg et al. (2002). Studying about 4,682 alleles from 377 autosomal microsatellite loci in 1,056 individuals from 52 worldwide populations, Rosenberg et al. were able to split these individuals into different sets of clusters. When the number K of clusters was set 9. Recall that Blumenbach’s concept of race already limited human races to ªve in the pre-Darwinian period (See above).

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to be 2, the partition seemed to show the migration event from Africa into the rest of the world. At K ϭ 5, the split was among (Tropical) Africans, Eurasians, East Asians, Oceanic populations, and Native Americans. The researchers did not interpret their ªndings as a conªrmation of the notion of race as applied to humans. In fact, even though they limited the number of clusters to 6 and argued that genetic clusters, roughly speaking, correspond to predeªned ancestry, they refrained from using the term race to characterize their ªndings. Yet race realists usually based their interpretations on similar studies. They take the possibility of identifying continental ancestral membership with relative accuracy to be proof of the reality and validity of the biological race concept (Risch et al. 2002; Burchard et al. 2003). The driving belief behind this race concept is that human evolutionary history accumulated enough differentiations between groups to enable continental clusters to map natural subdivisions within our species. Yet, other researchers counter that continental genetic clusters deemed to reºect natural subdivisions of our species are mere study design artifacts and that “there is no reason to assume that major genetic discontinuities exist between continents” (Serre and Pääbo 2004, p. 1679). That is, continental genetic groupings are mere sampling artifacts. According to this line of reasoning, to obtain the relatively sharp allele frequency breaks between the ªve continental genetic clusters, ancestral membership identi- ªcation studies adopt a sampling strategy called the island model rather than the regional continuity model. The island model considers our species to be a collection of well-deªned groups living far apart from one another. Samples based on this model reºect pre-selected and isolated or “extreme” populations, rather than reºecting the relatively contiguous spread of populations around the world. Furthermore, some other researchers even suggest that continental clusters may reºect more computational artifacts than biological realities and that while “it is uncertain what number of genetic clusters best ªt this data set, [. . .] there is no clear evidence that K ϭ 6 [or K ϭ 5] is the best estimate” (Bolnick 2008, p. 77). The philosophical idea behind the sampling artifact argument is that, from a methodological point of view, the preordaining of the world’s populations in order to collect data on targeted “extreme” populations has a tautological outlook if it is aimed at proving the existence of biological races understood as evolutionary kinds. That is to say, the algorithmic partition into continental genetic clusters is possible iff prior information about world populations allows ruling out a priori data considered to be potential falsiªers. But by “constraining” human evolutionary history through a particular sampling strategy designed to show a subdivision into racial groups, one gets what the sampling methodology has already

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more or less presupposed, i.e., isolated groups called races. If so, human races are by no means evolutionary kinds. Furthermore, even partitions based on the island model do not yield discrete groups. The discreteness argument, as we have seen above, claims indeed that for a taxonomic scheme to refer to naturally independent racial subdivisions within our species, it should allow sharp delineations of humans into continental groups with perhaps only zones of rarity. But continental populations form a continuum characterized by genetic clines, with some individuals having partial membership in more than one group. Thus, the clinal distribution of genetic allele frequencies indicates—just as was already obvious to Darwin based on the gradual distribution of morphological traits— that human evolutionary history has not yet reached the stage of biological subspecies differentiations. Not only do the sampling/computational artifact and discreteness objections cast serious doubt on the existence of evolutionary human races, but the line of analysis also seems to be strengthened by the proportionality or threshold objection. By the 1970s, studies in human population genetics began to show that about 85.4% of human genetic differences are within-group, i.e., at the individual level, while 15% (6.3% for continental groups and 8.3% for sub-continental groups) are to be found between groups (Lewontin 1972; Barbujani et al. 1997). At the turn of the 21st century, genomic studies revealed that human beings are about 99.99% similar. According to recent estimates, of our .01% genetic differences, approximately 95% are due to individual variation while about 5% can be explained by membership in a particular continental genetic group (Rosenberg et al. 2002; Bamshad et al. 2004). The proportionality argument requires that between-group variance be at the very least proportional to within-group variance, based on reasonable scientiªc standards, in order for a genomic classiªcatory scheme to pick out a real evolutionary branching phenomenon. Otherwise put, between-group variance should reach some threshold in order to give rise to a biological human subspecies concept. For instance, the Fst threshold for a geographically differentiated nonhuman sub-speciªc population ranges from 25% to 30%. In compari- son to the nonhuman Fst thresholds, the human Fst value appears to lack taxonomic signiªcance (Templeton 1999, p. 633). Notice however that the opposition to the view that the notion of subspecies or race captures evolutionary distinct groups is not limited to human population genetics. Genetic studies on apes, for example, are also increasingly challenging the validity of the notion of subspecies in this respect. When applied to some species, the concept appears at best to be a useful managerial tool rather than an indicator of evolutionary branching

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phenomena or of a discrete developmental taxonomy. Thus Fischer et al. recently argued that: The extent of genetic differentiation among groups of orangutans and chimpanzees lends no support to the notion that “subspecies” are genetically distinct entities. This may be of relevance for the management of wild and captive ape populations. (2006, p. 1135; my emphasis) I shall return to the instrumentalist view of race and subspecies in the last section of this paper. Sufªce it to show here that biological realism about human races lacks evidential support than typically thought. In fact, the implications of the recent statistical ªndings in human genomic science are a matter of controversy. For some, these ªndings indicate that any two individuals randomly chosen in any given population “are as different genetically as any two people selected from any two populations in the world” (Editorial of Nature Genetics, 2000). Race realists reject this interpretation, claiming that it is “both counter-intuitive and factually incor- rect.” They maintain that “two Caucasians are more similar to each other genetically than a Caucasian and an Asian” (Risch et al. 2002, p. 5). Yet, a study—tellingly entitled “Deconstructing the Relation between Genetics and Race” and published in Nature Review in 2004—shows that two randomly sampled individuals from the same continental group are more similar to each other approximately two-thirds of the time and more similar to individuals selected from different groups one-third of the time. But the caveat, as “deconstructionist” geneticists have pointed out, is that this “estimate is probably conservative as the proportion of compari- sons in which two individuals from different racial groups were more similar would have been higher if admixed populations such as African- Americans have also been sampled” (Bamshad et al. 2004, p. 604). “Sample bias” is an old issue in statistics that has emerged in the scien- tiªc debate over race, and questions have arisen not only about whether continental genetic clusters are mere sampling artifacts but also about whether they reºect statistical biases. Consider for the moment the caveat stated above. It indicates that some ªndings held to be strong proofs for the scientiªc validity and reality of race may not withstand close scrutiny because of the sampling strategy involved. For example, race realists claim that, “despite the admixture,” African-Americans belong “primarily” to the African “race” “from a genetic perspective” and should be treated as such in race debates (Risch et al. 2002, pp. 4–5). So the question is whether it is appropriate to require that potentially falsifying groups be sampled before race similarity is estimated.

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Furthermore, some researchers maintain that even the relative epistemic weight of continental genetic clusters may simply result from the violation of some important assumptions in the computation of the Fst, tool commonly used to assess population structure. According to the statistical bias objection, when robust mathematical models that control for the violation of key gene identity assumptions are used to account for human genetic variation, continental racial genetic clusters appear to have little, if any, explanatory value. For instance, in a study of dinucleotide repeat allele frequencies, the Fst computation failed to clearly delineate human sequences from those of chimpanzees (Long and Kittles 2003). It could almost be interpreted from this study that humans and chimpanzees share the same race, if we did not know that they belong to separate species. Yet, in reªning the Fst tool to control for the violation of the hidden assumptions that deªne Fst, the researchers found that the model that best ªts the data not only unambiguously splits chimpanzees from humans, but also shows that the genetic diversity in a Sokoto sample from Nigeria is greater than that exhibited by all the samples from all other continents combined. This means, for example, that if “a malevolent extraterrestrial wiped out the entire human species except for one local group” randomly chosen and “preserved in an extraterrestrial zoo [. . .] no genetic diversity would be lost if the Sokoto were chosen while nearly one-third would be lost by choosing the subpopulation from Papua New Guinea.” As the au- thors point out, it is “the simplest and the worst ªtting” Fst model that is used in continental ancestry identiªcation studies (Long and Kittles 2003, pp. 466–7). Bluntly speaking, biological races are statistical artifacts that have failed a crucial experiment. Whatever might be the value of similar Fst studies, the point they at- tempt to drive home can be scarcely misunderstood: racially classifying humans is akin to taxonomically masking human genetic variation. A key scientiªc discovery in the era of the DNA revolution is that sub-Saharan African populations, simply called Africans in genetic studies, harbor the greatest genetic variation within our species. The variation in the rest of the world is just a subset of the African genetic variation with some newly arisen alleles. To claim that there are ªve races from an evolutionary perspective by simply splitting the rest of the world into four sets of populations veils important information about human evolutionary history. Though it may be justiªed from an instrumentalist perspective to consider continental races as problem-solving tools, we should at the same time be wary that they mask, rather than explain, human genetic variation. Nonetheless, in addition to the undoubtedly important information about human genetic diversity, we may also want to understand, for exam-

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ple, the ancestral lineages of the members of a given population, continental or local. In this case, cladistic studies of ancestral lines of descent are very informative. These studies, instead of merely assessing overall genetic similarity, focus rather on identifying the common ancestor shared by the members of a given population. For example, taxa consisting only of a common ancestor and its descendents or resulting from evolutionary branching (cladogenesis), are called monophyletic or clades. A non- monophyletic group is paraphyletic when it does not comprise all the descendents of an ancestor. It is polyphyletic when it does not contain the last common ancestor of the members of the group. Accordingly, paraphyletic and polyphyletic groups are not considered proper clades that reºect evolutionary phenomena. But here again when sophisticated models that control for various statistical biases are applied to the human genetic data, it seems impossible to split our species into monophyletic continental clades. Indeed, human genetic studies increasingly show that: A classiªcation that takes into account evolutionary relationships and the nested pattern of diversity would require that Sub-Saharan Africans are not a race because the most exclusive group that includes all Sub-Saharan African populations also includes every non- Sub-Saharan African population. (Long et al. 2009, p. 32; See also Templeton 1999; Karafet et al. 2008; Hunley et al. 2009) The apparently easy way out of the difªculties of the racial cladistic approach may consist of simply equating race with clade by claiming that any individual sub-continental clade represents race. So if scientiªc in- vestigations reveal, for example, hundreds of human genetic clades in Sub- Saharan Africa alone, we should conclude that there are hundreds of Sub-Saharan African human races. Yet not only does this fallback fail to provide a solution to the problem of the scientiªc proliferation of human races but it also simply begs the question of the scientiªc necessity of race (Long et al. 2009; Maglo 2010). There is however more. In reality, there is more than one mode of inheritance and we may want to deªne, for example, autosomal, X-linked, mtDNA (mitochondrial DNA), or Y-chromosomal clades. It is possible, at least in principle, to determine the geographic origin of a clade. Recall that one of the key mo- ments of the DNA revolution was the discovery in the late 1980s and early 1990s that the extant females in our species trace their maternal ancestry ultimately to an African female ancestor bearing the genetic muta- tion that gave rise to the group of haplotypes phylogenetically classiªed as L1. Y-chromosomal studies also reached similar conclusions for human males. These ªndings were corroborated by the study of protein genetic markers and contributed to the rise of the “out-of-Africa hypothe-

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sis” (Cavalli-Sforza 1994). However, imposing racial interpretations on cladistic studies invites the same criticisms, including the lack of discreteness and sampling artifact objections. Moreover, as mentioned above, groupings which are not monophyletic are not considered evolutionary or natural kinds and racial groupings are anything but monophyletic. The ªrst issue to keep in mind is that the Fst computations for the distribution of autosomal, X-linked, mtDNA, or Y-chromosomal markers across geographic regions do not match (Tishkoff and Kidd 2004). Often- times, each of these markers tells us a different but complementary story about human evolutionary history and migration patterns. Take, for example, the Eurasian continental population which, in studies using autosome genetic markers, i.e., all the genes except the sex genes, are usually deªned by the following four sub-populations: Middle Easterners, (Asian) Indians, Europeans, and North Africans. While Eurasian women are predominantly on the mtDNA clade N, comprising the nested lineages H, U1– U7, J, K, I, T, W, X, and Nb1, which are by no means limited to Eurasia, 60% of Indian women are on the mtDNA haplogroup M, more exactly on the M1 clade, whose geographic origin is still disputed. They thus share a common ancestor with ϳ20% of Ethiopian, Somali, and Sudanese women (Passarino et al. 1998; Quintana-Murci et al. 1999; Kivisild et al. 2003; Stevanovitch et al. 2004; Underhill and Kivisild 2007). That is, (1) a continental population is made up of more than one clade; (2) many clades are ubiquitous, i.e., transcontinental; and (3) population history is not the same as gene history. Let me document these three claims further with Y-chromosome studies. Unlike the mtDNA nomenclature, there are many competing Y-chromosomal cladistic nomenclatures. In the 1990s, the nomenclature of male lineages derived from the P49a,f/TaqI haplotypes seemed to domi- nate in the literature. But at the turn of the 21st century, the study of the non-recombining Y-chromosome (NRY) showed a greater resolution and supplied the currently dominant cladistic system of male lines of descent (Underhill et al. 2001; Underhill and Kivisild 2007; Karafet et al. 2008). The tree under construction by the Y-Chromosome Consortium is a nested cladistic system of lineages partitioned into clades ranging from A to T (Y-chromosome Consortium 2002). The phylogeography of the NRY, just like the mtDNA, sheds a new light on Eurasian populations. Consider Europe for example, one of the sub-continental groups that has the small- est human genetic variation. It may be tempting to speculatively suggest that Europeans form a monophyletic group. However, on empirical grounds, European male lineages do not form a clade. The major European Y-chromosal clade, based on the currently available evidence, is the haplogroup R. But this clade is ubiquitous and is found not only across

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Eurasia but also across Africa. For example, the sub-clades R1a1* and R1b1* respectively reach as high a frequency as ϳ72% in some Indian castes and ϳ90% in some Northern Cameroonian ethnic groups (Sharma et al. 2009; Cruciani et al. 2002; Scozzari et al. 1999). That is, the majority of European males share paternal lineages with non-Europeans. While the second important European male clade, haplogroup I, seems so far to be conªned to Europe, a signiªcant proportion of males in southern and Eastern Europe and the Caucasus share the E clade lineages with African males. For instance, the E3b1-M78 sub-clade (nested in the African spe- ciªc E clade) was reported in some studies with moderate frequencies (sometimes as high as ϳ20 or ϳ27%) in Southern and Eastern Europe and the Balkans (Semino et al. 2004; Cruciani et al. 2004). In a word, Eu- rope forms a polyphyletic rather than a monophyletic taxon because Euro- pean males do not share a common ancestor. To be sure, the frequencies of E clade lineages in North Africa—often simplistically and misleadingly construed in genetic studies as Eurasia or Non-Africa—is very high contrary to received racial views. For example, ϳ76% of Moroccan, ϳ80% of Saharawi, ϳ65% of Algerian, and ϳ55% of Tunisian males, whether or not they self-identify as Arabs, do not share the Middle Eastern male lines of descent (12f2a), but instead share the E lineages with sub-Saharan Africans. The E clade unites ϳ70% of all Af- rican males from Algiers in North Africa to the Zulu land in South Africa, Northern Africans being predominantly on the nested E3b2-M81 and E3b1-M78 sub-lineages (Cruciani et al. 2004; Semino et al. 2004; Karafet et al. 2008). To wit, there seem to be higher frequencies of Eurasian paternal lines of descent in northern Cameroon (ϳ40%) than in Morocco and the Saharawish Republic, but the same as in Tunisia and Algeria (Scozzari et al. 1999; Cruciani et al. 2002). Thus, North African males can be said to be Africans based on the binary polymorphisms of the Y-chromosome. But they can also be said to be Eurasians based on the study of autosome genetic markers. That is, two different cladistic taxonomies derived from two different mode of inheritance radically cross-classify the same population. The obvious lessons are that: (1) a clade is a clade, not a race. The former is a relatively stable scientiªc concept, while the latter is an ambiguous, at times politically charged, concept even if it may nonetheless have a practical value under certain circumstances (See Maglo 2010); (2) cladistic nomenclature informs us primarily about gene history while the combination of clades in a given population constitutes one important indicator of the history of that population. The accumulating empirical evidence about human evolutionary history and migration patterns yielded by the study of the phylogeny of the mtDNA and the Y-chromosome allows us to perform the type of empirical

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scrutiny sketched above for all continental populations, including the Asian, the Australo-Melanesian, and the Native American. The conclusion appears to be that most clades are ubiquitous or transcontinental, and each of these continental populations is para/polyphyletic (Karafet et al. 2008). As the human population geneticist Alan Templeton put it about a decade ago: “human ‘races’ have no biological validity under the evolutionary lineage deªnition of species” (1999, p. 646). The question for us now is how to account philosophically for this long historical debate and the complex genomic evidence currently available.

III. Philosophical Implications The DNA revolution did not revive the controversy over race among scientists only. At the turn of the 21st century, philosophers of biology also started yielding to the optimistic resurgence of biological realism about race. But their hopes apparently dimmed in less than a decade. For instance, after attempting to revamp biological realism about race, Philip Kitcher ([1999] 2003; 2007) abruptly pulled the plug, so to speak, on the realists, claiming that his new defense of a pragmatic interpretation of natural kind “renders suspect a crucial part of the argument for grounding races in biology” (Kitcher 2007, p. 301). Kitcher was not the only philosopher to defend biological race realism prior to debunking it. Robin Andreasen (1998), for one, dropped biological realism about race in the same paper in which she tried to defend it. Her approach consisted of ap- propriating Cavalli-Sforza’s (1994) controversial treelike illustration of human evolution and migration, and of subjecting this tree to a method devised by the philosopher Elliot Sober to cut the branches of a dendro- gram.10 The method aims at indicating monophyletic branches of the tree of life. On these grounds, Andreasen emphatically claimed that Africans and Eurasians, as deªned in genetic studies, are monophyletic groups. Equating “race” with clade, she argued that most continental as well as sub-continental populations form clades and constitute human biological races. Yet, without any further empirical evidence, Andreasen also declared that these human “[r]aces once existed, but they are on their way out” (1998, p. 200). It is worth noting that Cavalli-Sforza himself interpreted the ªndings of his research as undermining the belief in the existence of biological human races (Cavalli-Sforza et al. 1994; Cavalli-Sforza 2001). That is, like Darwin and many other scientists before him, Cavalli-Sforza does not ap- 10. On the lack of ªt of illustrative dendrograms of human evolutionary history, see Templeton 1999.

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pear to see race as a fundamental biological category. In any event, I have already shown in section II above that the nitty-gritty empirical details of the available genomic evidence support the conclusion that neither Africans nor Eurasians are monophyletic groups. I also indicated why continental groups cannot be described as monophyletic groups. It sufªces here to emphasize that, in Andreasen’s account, biological race realism is, so to speak, a “once-upon-a-time-there-were-races” story. That is, according to this sym- pathetic view, insofar as our research objective in the 21st century is to ªnd the current biological relationship among extant humans, biological realism about race is inadequate. Though Andreasen later became unsure about the alleged ongoing extinction of biological human races, she still astutely and convincingly criticized Kitcher for being “more optimistic about the existence of human races today” than she was (Andreasen 2005, p. 96). In reality, it is hard nowadays to ªnd an unyielding defense of biological race realism in philosophy and, as a matter of fact, Kitcher (2007) has indeed started forcefully exposing the realistic mirage in the philosophy of biology of race. Yet, while the apparent demise of biological race realism may embolden the no-biological-human-race school, which simply denies the existence of biological human races, it does not necessarily vindicate eliminativism about race, the view that the concept of race should be dropped out from science, medicine, and public health policy. In fact, there are many circumstances where the use of the race concept in biological and medical ªelds may be justiªed even if the concept lacks biological reality. For instance, it may help probe environmental factors in disease etiology and surveillance, or help mitigate the effect of population structure in some public health studies. As some researchers recently put it:

Any study in the US that randomly samples subjects without re- gard to ancestry will obtain, on average, 75% Caucasians, 12% Af- rican Americans, 4% Asians, 12% Hispanics (broadly deªned) and few Paciªc Islanders, although these frequencies would vary region- ally. Thus, results from such studies would be largely derived from the Caucasian majority, with obtained parameter estimates that might not apply to the groups with minority representation. It might be possible in such studies to subsequently identify racial/ ethnic differences, either based on self-reported ancestry of the study subjects or by genetic cluster analysis. However, the low frequency of the non-Caucasian groups in the total sample would lead to reduced power to detect and investigate any racial/ethnic differences that might be present. The best way to avoid this power issue

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is to speciªcally over-sample the lower frequency racial/ethnic groups to obtain larger sample sizes. Obviously, the only way to ef- fectively and economically do so is based on self-identiªed ancestry, as genotype information from the population at large is not available and not likely to become so. (Risch et al. 2002, p. 11) The reason race may be a useful methodological tool under the circumstances described above is not that the concept is grounded in biology, but because racial politics and attitudes, whether government-sponsored or not, have preserved preexisting biological differences among groups that met in the US. These differences would have disappeared had mating been random.11 Limited gene-ºow over the last three hundred years or so ex- plains not the origin of the genetic differences—which are the result of geography and time (see section II)—but the lack of genetic homogeniza- tion in the US population. In similar cases, adapting Mayr-Dobzhansky’s methodological tool known as the biological species concept below the species level may help work out the rationale for kind making (Kitcher 2003; 2007). The idea behind the biological species concept is, roughly speaking, that when two populations living side by side do not interbreed at all or do so only at a low frequency, we may consider them as forming two different taxa or kinds. However, as suggested in section I, a success- ful application of this method to kind partition among humans does not license biological race realism. The biggest problem in this confusing debate is the failure to systematically, consistently develop an instrumentalist view of race. For example, Ernst Mayr (1954, p. 87), who earlier unambiguously maintained that the subspecies concept was “a purely subjective category” argued in 2002 that “[r]ecognizing races is only recognizing a biological fact” (Mayr 2002, p. 90). Now, for many, being “a biological fact” implies having a biological reality. But for Mayr, just as for Dobzhansky, human geographic races differ only in the statistical mean of some genetic alleles and sometimes in a single gene. Yet as Mayr put it: “[i]n a Darwinian population, there is a great variation around the mean. This variation has reality, while the mean value is simply an abstraction” (Mayr 2002, p. 91). That is, only individuals are real and the clearest challenge is in what philosophical terms to conceptualize what both Mayr and Dobzhansky refer to as “abstraction.” My suggestion is that, under the circumstances, race is best viewed as an instrumental rather than as a realistic concept. 11. Of course, random mating is an idealized condition perhaps comparable to friction- less motion in physics as Frank Livingston (2008b) already suggested about half a century ago.

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Let me further illustrate the point with the following thought experiment: suppose that a biologist, after researching the nonrandom mating patterns within the US or South African populations, argues that race is a biological reality. We might be willing to concede begrudgingly at least the soundness of the claim. Now imagine a biologist concluding, after ob- serving limited gene-ºow between two castes living side by side in India or Senegal, that caste is a biological category. We would at the very least be intrigued by this claim. Then suppose that a biologist, after noting reduced interbreeding between two populations living side by side in Northern Ireland or Iraq, argues that religious afªliation has a biological reality. At this point, we would have understood that under these circumstances the inference that from the biological species concept to reality is a misleading reality. All that the application of this methodological concept to a level below the human species shows is that race, caste systems, and religious afªliation may have an explanatory value with respect to population substructure in each of the three cases described above; this concept helps deªne breeding populations whether they are organized according to racial politics, caste system, or religious afªliation. That is, depending on the context, race, caste systems, and religious afªliation may be said to have biological signiªcance. They each represent a socially isolating mech- anism. Realizing this may help avoid attributing to race a trivial or an ob- scure and elusive biological reality. Now imagine further that scientists working in India or Senegal pro- pose that, for simplicity, we call a breeding population a caste, regardless of locality and mechanisms of formation. We might agree, although with the caveat that caste is just a handy concept to explain a relatively complex but scientiªcally well-understood phenomenon to people with a particular mindset in a particular culture. Or we might disagree on the ground that, as time passes and habits take over, the concept of caste may begin to appear to have a scientiªc necessity and a unique explanatory power that makes it a fundamental biological category, unlike any other notion— even religious afªliation or race. We might thus fear forgetting in the long run that caste is a mere placeholder for a population substructure engen- dered by nonrandom mating (due to varying causes) between members of two local populations living side by side. In a word, we might fear the potential reiªcation of caste in biology. But we might also resist the use of the term caste in biology because the social history of the concept is mor- ally tainted. Or alternatively, we might perhaps be inclined to accept it if it appears to have the potential to help rectify past wrongs, to contribute to creating more just societies, or to be an efªcient placeholder for un- known factors or a problem-solving tool in public health settings, etc.

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However, what is at stake is not merely about naming. After all, we conventionally give names to scientiªc entities and kinds provided that they do not cause ethical quandaries. My point was also that the adoption/ adaptation of the biological species concept in this debate has not proven that race, religious afªliation, or caste pick out evolutionary facts even though they may have some predictive value in cases like those described above. From the fact that a notion or variable has an explanatory value in an equation or experimental device, it does not follow that that notion necessarily maps an independent reality. Some may be surprised to learn, for example, that since the 18th century, physicists (not just philosophers) have been divided about whether the concept of force, which has such an extraordinary explanatory power in the paradigmatic equation f ϭ ma, has any scientiªc necessity and/or refers to anything at all in nature (Maglo 2007). As Frank Wilczek, winner of the Nobel Prize for physics, bluntly put it recently about the concept of force, “a big part of the explanation of its continued use is no doubt (intellectual) inertia” (2004, p. 12). Interest- ingly, however, the concept has practical value even in quantum mechan- ics, though it does not ªgure in its fundamental equations or in those of the theory of general relativity (Ravi 2005). Rather than suggesting that race, by any stretch of imagination, has a predictive value comparable to that of force in physics, the point I am try- ing to drive home is that validity, let alone utility, does not entail reality. Even if race has some explanatory and predictive function in some well- deªned circumstances—that is, even if race is considered a biologically signiªcant kind—that does not entail that race has a referent in nature. The geocentric concept has a reliable predictive value in navigational settings, although it is a ºawed concept in astronomy. “Reality” is a very con- tentious notion in the philosophy of science.12 Nonetheless, as the discus-

12. The philosophical debate over realism opposes antirealists to realists. Scientiªc antirealists uphold the view that theories are merely instruments that allow predictions, rather than explanations that purport to describe the way the world operates. At their best, scientiªc theories “save the phenomena” (van Fraassen 1980). Scientiªc realists, on the other hand, can be divided, roughly speaking, into realists about theories and realists about entities. Realists about theories claim that a) there are true theories, and that b) true theories postulate entities that exist independently in nature. Realists about entities resist claims about the truth value of theories but defend the independent existence of postulated scientiªc entities insofar as they can be manipulated in laboratory practice. For example, because genetic entities may be manipulated in gene therapy, one may accept the reality of genes but at the same time adopt an antirealist stance vis-à-vis any biological theory that postulates genes (Hacking 1983; Boyd 1983). These distinctions serve to highlight the un- warranted tendency in debates over race to move freely from the putative explanatory value of the concept to its alleged biological reality.

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sion in section II shows, a key concern among genomic scientists is knowing whether the partition of our species into genetic groups reºects independent evolutionary processes of differentiation or whether they are convenient groupings. Put in philosophical terms, scientists involved in this debate want to distinguish natural kinds from mere instrumental kinds. But just like the notion of reality, the notion of natural kind is controversial, particularly in the philosophy of biology. Natural kind terms are words in ordinary languages that are deªned by scientists, usually according to underlying micro-structures. For example, ordinary terms such as “water” and “gold” are deªned by H2O and the atomic number 79, respectively. But philosophers are divided about whether there are natural kinds in biology at all (Dupré 1995; Hacking 1999; Kitcher 2001). Argu- ments against natural kinds in the philosophy of biology range from the claim that, unlike natural kinds in physics and chemistry, kinds in biology, in this instance species, do not have essences, to the claim that they are individuals and are limited in space and time, to the claim that they are pragmatic kinds. Proponents of natural kinds in biology seem to concede the speciªcity of natural kinds in physics and chemistry but point out, for example, that a biological kind is a natural kind in the sense that it has a historical essence, or that its members share a number of characteristics that make them similar even though these characteristics may not be possessed by all and only all its members, the so-called homeostatic property cluster theory, etc. What is surprising is that both parties seem to agree on the a-historical and essentialist status of natural kinds in physics and chemistry, making the debate more reºective of the philosophy of science framework that the disputants have in common than of the actual semantics of the term. There is no compelling reason, for example, for a Carnapian or a Kuhnian to accept that H2O refers to anything outside the linguistic framework where it has been introduced or outside the paradigm that brought it into life in the history of science (Carnap 1991; Kuhn 1962). Kuhn (2000), for one, devoted time and energy to showing that the Twin-Earth thought experiment, as construed by Putnam, failed to demonstrate that H2Oisnot historical or that it does not have multiple referents in nature. However, my goal here is not to adjudicate the natural kind case between the Kuhnians or the Carnapians on the one hand and the Putnamians or the Kripkeans on the other hand. It sufªces to show that the a-historicist and essentialist requirements are just the requirements of a particular philosophy of science, and are at the very best limiting cases. In any event, as indicated above, what divides genomic scientists is whether human races are evolutionary subspeciªc branches or whether

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they are mere practical taxa. Scientists want to know whether there are obvious natural or evolutionary partitions within our species. The two key assumptions underwriting the discreteness, the sampling/computational artifact, the threshold, the statistical bias, and the para/polyphyletic arguments are indeed whether there are natural or evolutionary boundaries between continental groups called human races or whether they are merely instrumental delineations that may however be biomedically signiªcant or useful in some very speciªc contexts (Wilson et al. 2001; Serre and Pääbo 2004). Although kind making sometimes mirrors the commonsensical cu- linary distinction between onion and garlic (Dupré 1995; Kitcher 2001), I, for one, cannot help pointing out nonetheless that the distinction between chimpanzees and humans, for example, is fortunately not a matter of taste or even merely a matter of human interest. It is based on evolutionary differentiations. The rationale behind using data from chimpanzees to test the robustness of methods devised to sort out human races, as we have seen in section II, was indeed that both species are understood in science as two groups “naturally” divided by evolution rather than as merely convenient instrumental groupings mutatis mutandis accepted by scientists for practical purposes. Common sense also, cross-culturally, con- verges with science in classifying them as two naturally distinct groups. Be that as it may, the term natural kind, stripped from its alleged necessary essentialist and a-historical implications, and the term mere instrumental kind clearly capture the epistemic and ontological underpinnings of this enduring debate. It is my contention that, from Blumenbach and Darwin to contemporary post-genomic scientists, there is a line of researchers who consider human races as convenient instrumental kinds, while realists about race appear to view human races as natural kinds. Thus unlike Kitcher (2007), I do not believe that the way out of the realistic mirage over human races lies in the reinterpretation of natural kind in terms of pragmatic kind, but rather in the distinction between natural kinds—by which I simply mean biological kinds harboring what Dobzhansky called “existential concreteness” (2008a, p. 285)—and mere instrumental kinds, which both Dobzhansky and Mayr described as “abstractions.” As Dobzhansky put it long before the rise of genomics, racial differences between humans are “objectively ascertainable” and “facts of nature” (Dobzhansky 1962, pp. 266–7). But by also recognizing the practical dimension of the use of race, he maintained that theoretical and practical studies of race should not be at a crossroads but rather should be complementary. What I am suggesting is that it is the grounding of race in nature, for instance, àla Dobzhansky, that instrumentalists reject. However, unlike eliminativists, instrumentalists do not call for a straightforward elimination of the con-

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cept from areas like science, medicine, and public health policy. They simply argue that the use of the concept may be justiªed under certain circumstances where it may prove to be a harmless, efªcient problem-solving tool. That is, they hold that race may be biologically signiªcant under certain circumstances without necessarily being an evolutionary (or even a discrete developmental) kind. Put differently, instrumentalists about race believe that not any biologically signiªcant kind is a natural kind. For, biological signiªcance does not imply biological reality (Maglo 2010). Bio- logical kinds have differing ontological status and there is certainly more than one epistemic tool in the philosophical toolbox.

Conclusion I have argued that scientists remain deeply divided over the biological reality of race in the post-genomic era, just as they were in the time of Dar- win. The point of contention is whether genetic partitions of humans into continental groups map objective evolutionary differentiations within our species or whether they are mere instrumental classiªcations. In the philosophy of biology, some realists have simply retreated from their early defense of biological realism about race. However, it is worth noting that there is nothing peculiar to human biology that prevents evolutionary subspeciªc differentiations within our species. There is no metaphysical argument against the possibility of biological human races. Perhaps only two factors bedevil the realists’ project: the relatively young age of our species and the complexity of human migration patterns. For example, our remote ancestor split from chimpanzees, our nearest cousins, about 6 mil- lion years ago. But even today we share ϳ96% of our genetic material with chimpanzees. Homo sapiens, our species, appeared in history only ϳ200,000 years ago. The most recent common ancestors (male and female) of all extant humans were still roaming in Africa as late as 40,000 to 60,000 years ago. Humans then started crisscrossing the ªve continents, giving rise to the current world populations, sometimes by fusion. These factors probably explain why at this stage of our history human populations, however partitioned, appear to be anything but evolutionary kinds. Whatever it may be, after four hundred years or so of race research and despite the recent DNA revolution, it still remains a vexing issue whether, in our well-motivated endeavor to understand human variation, we approach race with a scientiªc mind or science with a racial mindset.

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