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Degrees of Mixture, Degrees of Freedom
Genomics, Multiculturalism, and Race in Latin America
By Peter Wade
Duke University PressCopyright © 2017 Duke University Press
All rights reserved.
Purity and Mixture in Human Population Genetics
In this chapter, I argue that the life sciences' understandings of human diversity — and biological diversity more widely — have been characterized by a version of the same tension between concepts of (relative) purity and mixture that I outlined in the introduction. This may sound counterintuitive for recent biology, in which the word purity is anachronistic, but I argue that, although the word itself may not be used, an underlying concept of relative purity can be found in debates about how to sample populations, in which "isolates" are counterposed to "grids," and about evolution, in which "trees of life" are counterposed to "nets." In a final section, I address the question of how to conceive of "relations" between "science" and "society" in ways that might avoid an implied dualism.
It may seem that, in the nineteenth century, the concept of purity was an accepted one, principally in relation to theories about race. Young contends that the concept of hybridity, as used in recent cultural theory, "has not slipped out of the mantle of the past," in which nineteenth-century theorists of race posited pure, fixed races, which were the antecedents that produced the hybrids (Young 1995: 25). In fact, even for these theorists, the "pure, fixed race" was an ideal type, not observable in reality, but instead inferred from the multiplicity of mixtures that scientists confronted in the present, which were shaped by "chance, variation, migration, intermixture and changing environments" (William Z. Ripley, cited by Stepan 1982: 62). For Nott and Gliddon, authors of Types of Mankind (1854), a racial type could "outlive its language, history, religion, customs and recollections"; it was an underlying and fixed structure, a kind of purity. But they also recognized that contemporary populations were shaped by "climate, mixture of races, invasion of foreigners, progress of civilization, or other known influences," which meant the underlying type was an abstraction that had to be inferred from the observable diversity produced by various processes of mixture (cited by Banton 1987: 41).
At this time and into the early twentieth century, soft theories of inheritance held sway. These proposed that the physical substance passed on through the mechanisms of heredity could be shaped by the environment within a single generation, implying that racial type was not fixed, but had to be maintained through constant regulation. For example, a European's racial status — understood as a biocultural constitution in which the moral and the physical were entangled — could be altered by the influence of a tropical climate and cultural environment (Stoler 1995: ch. 4; 2002: ch. 3, ch. 4). Purity was not a simple matter: it existed in a precarious relationship with mixture (Wade 2015: 76–78). The same was true for animal breeding: the notion of pedigree was based on purity, and breeders controlled the purity of their breeds and took care to avoid "mongrelization." Yet new pedigrees could also be founded by intentional and controlled cross-breeding, and pedigrees could be reinvigorated by the careful introduction of wild strains. Not surprisingly, disputes abounded about the purity or otherwise of the pedigree of particular animals. The concept of pure pedigree existed in constant tension with the concept of mixture. The former could not do without the latter; the latter made little sense without the former. The key was in the regulation of mixture, which entailed the hierarchical evaluation of different types. Unwanted mixture — with animals deemed of inferior type — was to be avoided (Ritvo 1997: ch. 3).
Populations and Isolates
After World War II and in the wake of Nazi theories of race and eugenics — which had been critiqued by some U.S. and European scientists, including German ones, from the 1930s (Barkan 1992; Lipphardt 2012) — there was a broad turn toward antiracism in science and society (see chapter 2). This involved an attack on the idea of racial hierarchy and a discrediting of the racial science that had legitimated hierarchy, but it involved an ambivalent and uneven challenge to the concept of biological race as a way of describing human diversity. The great critic of the "fallacy of race," Ashley Montagu, wrote that "in the biological sense there do, of course, exist races of mankind" — he identified the four distinctive "divisions" of Negroid, Australoid, Caucasoid, and Mongoloid — while also emphasizing the characteristically human history of migration and hybridization, and highlighting that these races were all "much mixed and of exceedingly complex descent" (Montagu 1942: 2–5). Ideas of pure races were put into question: the 1951 UNESCO statement, "The Nature of Race and Race Differences," drafted by life scientists, said, "There is no evidence for the existence of so-called 'pure' races" (UNESCO 1952: 14). But race remained as a way of describing human diversity, understood as a dynamic product of evolutionary processes and migrations, which could be appreciated in terms of statistical variations (Reardon 2005). Thus the earlier 1950 UNESCO statement, "The Race Question," said that "the term 'race' designates a group or population characterized by some concentrations, relative as to frequency and distribution, of hereditary particles (genes) or physical characters" (UNESCO 1950), and the influential geneticist Theodosius Dobzhansky said that "race differences are objectively ascertainable biological phenomena" (Livingstone and Dobzhansky 1962). However, there was also a tendency to drop the tainted terminology of race and talk instead of "populations": "Humans were no longer divided into races with typical traits, but instead into populations that differed in allelic frequencies" (Lipphardt 2013: 57). Populations could be large — and coterminous with the classic races. Or they could be small and more local — not dissimilar from the many subraces and racial variants identified by previous racial scientists, such as John Beddoe in his book The Races of Britain (1862) or William Z. Ripley in The Races of Europe (1899).
Alongside this shift toward a dynamic view of human diversity, driven by the convergence of evolutionary theory and the empirical study of genetic variation, including the study of blood type systems (see chapter 2), there was a continuing concern with studying the genetics of "isolated" populations and endogamous groups — which often turned out to be minority indigenous or ethnic groups, located at the bottom of colonial and/or national political hierarchies and in the geographical peripheries of the nation. The construct of the isolate — or the endogamous community, the breeding unit, or the reproductive community — derives directly from evolutionary theory, which posits that local populations biologically evolve within their local environment (through natural and sexual selection, genetic drift, founder effects, and endogamic mating), thus creating a dynamic relationship between geography and genetics (Nash 2015: 21–25). Scientists thought this process could be observed best in a population that seemed relatively isolated in a reproductive sense. Among humans, such reproductive "isolation" can be caused by environmental barriers (rivers, mountains, seas, etc.), but also by cultural factors, such as language, religion, class, marriage rules, and so on. This meant that human isolates did not have to be geographically isolated; they could also be, for example, religious or cultural groups that had strong endogamic tendencies. The population isolate figured in genetic science as a kind of natural laboratory. Postwar genetics institutes, such as the Cancer Research Centre in Bombay, the Institute for the Study of Human Variation at Columbia University, and the Laboratory of Human Genetics in Paraná, Brazil, shared a "preoccupation on the empirical and conceptual level ... [with] 'endogamous groups,' 'isolates,' 'inbreeding' and 'consanguinity'" (Lipphardt 2013: 58–63). Not surprisingly, many of these isolates — for example, Basques and Australian Aborigines — had been the focus of scientific attention in the past, but now they were being studied using genetic techniques. In the United States, Native Americans were likewise considered to be scientifically interesting isolates that could shed light on human evolution, history, and "race" (Iverson 2007). The study of "isolates" was thought by geneticists at the 1950 Cold Spring Harbor Symposium in Quantitative Biology to contribute to a "genetical definition of race"; isolates seen as geographically insulated from the mixings and movements caused by modernization were of particular interest — for example, Amazonian indigenous groups (Reardon 2005: 65, 67; see also Santos 2002; Santos, Lindee, and Souza 2014).
Defining an isolate was not easy, in large part because geneticists were also aware that movement and mixing were the norm among humans. But isolates could still be defined for genetic purposes, and in relative terms: human populations were rarely completely isolated for long periods, but they could be considered isolated enough for long enough to make them genetically interesting (Lipphardt 2012). To determine whether a given population could be considered an isolate, geneticists had to depend on historians, ethnographers, demographers, and the self-perceptions and oral histories of population members themselves (Lipphardt 2013: 66). Given the perceived importance of cultural factors in creating reproductive isolation, geneticists necessarily used cultural criteria to define the populations they sampled.
The Human Genome Diversity Project
From its inception in 1991, the Human Genome Diversity Project displayed a similar concern with isolated populations, apparently less affected by mixing and migration. As with 1950s life sciences, the underlying agenda was humanist and antiracist: the exploration of human genetic diversity was seen as a contribution to this mission, and key figures in the HGDP, such as Luigi Cavalli-Sforza, had impeccable antiracist credentials. Yet the plan to sample indigenous peoples, who often had histories of colonial and postcolonial subordination, ran into accusations of imperialism and racism, alleging that indigenous people's blood and genes would be used — perhaps commercialized — for the benefit of others, especially in the West (Reardon 2005). A project conceived as fomenting (racial) democracy ran up against the frictions caused by the insistent tension between democracy and hierarchy. To those who foregrounded the role of hierarchy — its victims, or those who claimed to speak on their behalf — an apparently democratic mission appeared to be racist because it was targeting "isolated" populations, and this evoked "archaic racialist language and thought, clearly loaded with astonishing archaic assumptions of primordial division and purity of certain large segments of the human species" (Marks 2001: 370). Later projects that have also aimed to map global genetic diversity — such as the Genographic Project and the Hap-Map Project — have not run into the same level of opposition, but they have been accused of reifying, and often tacitly racializing, the populations they sample (Bliss 2009; Nash 2015; Reardon 2007; Tall Bear 2007).
Issues of hierarchy also insistently arose because of the way the HGDP scientists dealt ethically with sampling subjects. In response to criticisms of the project as a form of biocolonialism, they introduced what they considered to be ethically progressive, group-based informed consent protocols. But these initiatives seemed to cede to the scientists the right to define a group and to make the assumption that it was fairly homogeneous, such that a group-based consent would speak unproblematically for everyone in the group, in the same way that a sample from the population would speak genetically for the whole population (Reardon 2005, 2008). Later initiatives, such as the Hap-Map Project, while claiming to avoid these ethical problems by including the subjects/objects in a collaborative and democratic way, still failed to address the underlying problem that it was the scientists and their priorities that defined what constituted a population in the first place (Reardon 2007). Concepts of isolation, purity, and homogeneity became entangled and, by evoking hierarchies of race and power, haunted projects focusing on diversity, which aimed to foment democracy and antiracism.
One issue that exercised HGDP scientists early on was the question of how to sample humans; this was a general expression of the question of how to define an isolated population. The most common technique adopted to define a population — and the one that prevailed in the HGDP and still does in most genetic studies of human diversity today — is to choose a population defined by cultural and historical criteria: an ethnic group, a nation, a regional group, and so on. The alternative is to use a random grid, paying no initial attention to social divisions (Reardon 2005: 77–78). Geneticists know that genetic variation is clinal, characterized by gradual changes in the frequency of certain genetic variants over geographical space; there are no clear boundaries because humans are a recent species that has moved across the globe in a continuous fashion — and quite quickly in evolutionary terms — and people have constantly moved and mixed with their neighbors. A grid method of sampling is best suited to capturing this clinal variation. A population-based method of sampling also reveals such clines, insofar as it is possible to see shared genetic traits that have different frequencies in different places, but it also carries an inherent logic of dividing people into populations, which then inevitably take on an appearance of homogeneity: the population in question is defined by criteria of language, culture, history, and so on, which by definition are implied to characterize the whole population and demarcate it from other populations, evoking some kind of separating boundary. If the population is then characterized genetically, on the basis of a sample, its members then also logically and by definition appear to share a genetic profile, which differentiates them from other populations.
Of course, geneticists know that all populations share the vast majority of DNA and that differences are mainly in the frequency with which certain variants appear. Yet sampling "populations" tends to mask that basic reality and create what Pálsson calls an "island model" of insular populations (Nash 2015: 80–81; Pálsson 2007: 179–81). Population becomes reified: "Merely to offer a genetic description of a population in terms of frequencies of various alleles, perhaps to make predictions about future evolutionary changes or hypothesize about past evolutionary history, assumes the existence of an entity with discernible boundaries and determinate parts" (Gannett 2003: 998). The island model glosses over the fact that the concept of population is "not epistemologically tidy," as Zack puts it: "There are no generally accepted answers to the following questions: How many generations of isolation are necessary to form a population? How large must a population be? What proportion of population members must reproduce in a given generation for it to qualify as a breeding unit? How much gene flow into or out of a population can take place before the population is a different population?" (Zack 2002: 69). In talk of populations, there is little or no explicit reference to purity — the word is at odds with everything we now know about human population genetics. But we can see the tension at work between polar concepts of purity and mixture: insular populations inevitably represent a relative degree of purity; a population-based sampling strategy inevitably tends to "purify" populations, compared to a grid-based strategy.
DNA Ancestry Testing and Parental Populations
The island model tendency is especially evident in recent techniques of DNA ancestry testing, which assign proportions of a population's or a person's genetic ancestry to notional parental populations located in the past (see chapters 3–9). Typically, these parental populations are biogeographic continental populations that indicate African, European, Asian, and Amerindian genetic ancestry, although more geographically specific assignations are also made. Such measurements of "racial mixing" go back to the 1940s (see chapter 2), but at that time it was done for populations. Advances in DNA analysis have allowed measurements of "admixture" to be made for individuals, although the margin of error is greater, and tracing a person's ancestry to specific geographical locations or ancestral populations is fraught with uncertainty. Today, the terminology of race is rarely used, having been replaced by terms such as "biogeographical ancestry" (BGA) or sometimes "ethnic origin" (Gannett 2014).
Excerpted from Degrees of Mixture, Degrees of Freedom by Peter Wade. Copyright © 2017 Duke University Press. Excerpted by permission of Duke University Press.
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Table of ContentsPreface vii
Introduction. Mixture as a Biological Process 1
I. Purity and Mixture
1. Purity and Mixture in Human Population Genetics 27
2. From Eugenics to Blood Types 53
II. Genetics and Multiculturalism
3. Changing Practices 85
4. Colombia, Country of Regions 99
5. Brazil, Race, and Affirmative Action 122
6. Mexico, Public Health, and State Genomics 146
7. Genomics & Multiculturalism: Comparisons and Continuities 166
III. Narrating Mixture
8. Gender, Genealogy, and Mestizaje 191
9. The Geneticization of Race and Diversity in Everyday Life 223
What People are Saying About This
"Degrees of Mixture, Degrees of Freedom is an incisive and sophisticated work by an accomplished scholar of race and genetics in the Americas. Peter Wade examines the stakes in construing or imagining mestizaje to be an antidote to racial divisions, while also surveying the ranges of its actual rates of occurrence among the distinct continental populations that were thrown together through European colonization of the Americas. This impressively written book will be well received and well read."
"This bold comparative study of the complex intersectionality of mestizo nationalisms offers a persuasive and sophisticated analysis of racialization and de-racialization as forms of identity, power, and aspiration. Meticulously charting the ambivalent meanings of race, Peter Wade also tracks their continuous connection to hierarchies of status and ancestry in a comparative study that opens up important new approaches to genomics as both professional science and everyday life."