Race and genetics

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This article deals with racial concepts defined by genetic distance and not craniofacially (based on skull measurements) or by typology (physical type). Races categorized using alternative methods yield different groups, making them non-concordant.^[1]

Views on race and genetics vary considerably between and within academic disciplines. Many views are complex, and are distinguished by subtle differences. Often the significance of differences between views is related to the use of race in biomedicine. This article compares the major contemporary views on race.

[edit] Summary of contemporary views

[edit] Race as a biological construct

• The term 'race' is usually used as a synonym for subspecies by biologists, though there is a degree of confusion over the term and both terms have a variety of meanings. There is no consensus definition for either subspecies or "race" in biology.^[2][3][4] Some biologists do not accept the concept of classification below the species level whatsoever, arguing that subspecific classifications are not biological units and that they are subjective and arbitrary.^[5]
• Taxonomic: "An aggregate of phenotypically similar populations of a species, inhabiting a geographic subdivision of the range of a species, and differing taxonomically from other populations of the species."^[6]
• Population: "Races are genetically distinct Mendelian populations. They are neither individuals nor particular genotypes, they consist of individuals who differ genetically among themselves."^[7]
• Lineage: "A [race] is a distinct evolutionary lineage within a species. This definition requires that a [race] be genetically differentiated due to barriers to genetic exchange that have persisted for long periods of time; that is, the [race] must have historical continuity in addition to current genetic differentiation."^[8]
• The phylogeographic criteria for 'subspecies' were established in the early 1990s.^[9][10]

  members of a subspecies would share a unique, geographic locale, a set of phylogenetically concordant phenotypic characters, and a unique natural history relative to other subdivisions of the species. Although subspecies are not reproductively isolated, they will normally be allopatric and exhibit recognizable phylogenetic partitioning. ... evidence for phylogenetic distinction must normally come from the concordant distributions of multiple, independent genetically based traits.^[11]

[edit] Genetic variation and human populations

Infobox Multi Locus Allele Clusters In a haploid population, when a single locus is considered (blue), with two alleles, wild-type (+) and mutant (-) we can see a differential geographical distribution between Population I and Population II, but there is a 30% chance of wrongly assigning any individual to either population based on a single allele. × + - Population I 70% 30% Population II 30% 70% For three loci blue, red and green, it becomes apparent that there is a correlation between certain allele frequencies. In this example Population I displays a correlation between wild-type blue (+) 70%, mutant red (-) 70% and wild type green (+) 70%. Population II has a correlation between the -, + and - alleles, each having a 70% frequency in this population. The genetic variation remains the same in these populations, irresepctive of the allele examined, but using a three locus approach, there is a much reduced chance of wrongly assigning any individual to a given population. × + - + - + - Population I 70% 30% 30% 70% 70% 30% Population II 30% 70% 70% 30% 30% 70% For an organism of genotype +/-/+, for each locus the chance of missclassification is 0.3 (30%), but when all three loci are take into account, the organism can be assigned to Population I with a 0.3x0.3x0.3 chance of error, that is a 0.027 (2.7%) chance of error. The two populations still share exactly the same alleles, but the frequency of these alleles varies between the populations. Using modern computer software and the abundance of genetic data now available, it is possible not only to distinguish such correlations for hundreds or even thousands of alleles, which form clusters, it is also possible to assign individuals to given populations with very little chance of error. It should be noted, however, that genes tend to vary clinally, and there are likely to be intermediate populations that reside in the geographical areas between our sample populations (Population III, for example, may lie equidistantly from Population I and Population II). In this case it may well be that Population III may display characteristics of both population I and Population II. For example Population III may be defined thus: × + - + - + - Population III 50% 50% 50% 50% 50% 50% In which case any individual from Population III is likely to be misclassified equally into either Population I or Population II.(Edwards (2003)Kittles and Weiss (2003))

[edit] Genetic variation is structured by geographic origin

Human genetic variation can be used to deduce the geographical origins of an individual's recent ancestors, this is possible because alleles that vary geographically often correlate with alleles for other loci that vary geographically (and form clusters), it is possible to measure this correlation, which enables humans to be successfully grouped into populations, the greater the number of loci studied, the more accurately individuals can be correctly assigned to a group.^[12] This is possible because individuals from geographically proximate regions share much more recent common ancestry with each other than they do with individuals from geographically disparate regions, with the result that they are likely to be genetically more similar, therefore close geographical proximity strongly correlates with genetic similarity.^[13][14]

[edit] Multilocus Allele Clusters

Human population structure can be inferred from multilocus DNA sequence data. In Rosenberg et al. (2002, 2005), individuals from 52 populations were examined at 993 DNA markers. These data was used to partitioned individuals into K = 2, 3, 4, 5 or 6 clusters. In this figure, the average fractional membership of individuals from each population is represented by horizontal bars partitioned into K colored segments. 2 cluster analysis separated Africa and Eurasia from East Asia, Oceania, and America, 3 clusters separated Africa and Eurasia, 4 clusters separated America, 5 clusters separated Oceania (green), and 6 clusters subdivided native Americans.

Since the 1980s it has been known that human genetic variation is low relative to other species, this is usually attributed to the recent origins of our species, and tends to support the recent single-origin hypothesis (or Out of Africa).^[15] It has also been claimed that most of this small variation is distributed at the individual and local level (about 90-94%), with the remaining 6-10% distributed at the continental (or racial) level.^{[16][17][18][19]} This observation has been used to argue that racial classifications are not valid when within group variation exceeds between group variation.^[20]

However, A. W. F. Edwards claimed in 2003 that this conclusion is unwarranted because it assumes that all loci are independent, Edwards argues that this is not the case

The genes at a single locus are hardly informative about the population to which their bearer belongs...Each additional locus contributes equally to the within-population and between-population sums of squares, whose proportions therefore remain unchanged but, at the same time, it contributes information about classification which is cumulative over loci because their gene frequencies are correlated...it will be possible to identify the two clusters with a risk of misclassification which tends to zero as the number of loci increases.^[21]

Edwards states that genes should not be taken into account on an individual basis, just as a single characteristic (such as skin colour or eye colour) cannot be used to determine the geographic origin of a person's recent ancestors, so the same for the allelic frequency of an individual locus. Conversely, just as physical features tend to correlate (for example blue eye colour correlates with pale skin colour, that is skin colour and eye colour), and are not independent, so different alleles for several loci tend to correlate and are not independent. This is the basis of multi-locus allele clustering.

It has been argued that the calculation of within group and between group diversity has violated certain assumptions regarding human genetic variation. Calculation of this variation is known as F_ST and Long and Kittles (2003) have questioned the validity of this reproducible statistic. The first problem is that effective population size is assumed to be equal in the calculation of F_ST, if population sizes vary, then allele relatedness among alleles will also vary. The second problem is that F_ST calculation has assumed that each population is evolutionarily independent. Calculation of F_ST can therefore only be made for the set of populations being observed, and generalisations from specific data sets cannot be applied to the species as a whole.^[20]

Long and Kittles tested four models for determining F_ST and concluded that the model used most often for estimating this statistic is the simplest and worst fitting. Their best fit model was still a poor fit for the observed genetic variation, and calculation of F_ST for this model can only be made on a population by population basis. They conclude that African populations have the highest level of genetic diversity, with diversity much reduced in populations outside of Africa. They postulate that if an extra-terrestrial alien life form killed the entire human species, but kept a single population which it preserved, the choice of population to keep would greatly effect the level of diversity represented. If an African population were selected then no diversity would be lost, whereas nearly a third of genetic diversity would be lost if a Papuan New Guinea population were chosen. Indeed within population genetic diversity in African populations has been shown to be greater than between population genetic diversity for Asians and Europeans. They conclude that their findings are consistent with the American Association of Physical Anthropologists 1996 statement on race

that all human populations derive from a common ancestral group, that there is great genetic diversity within all human populations, and that the geographic pattern of variation is complex and presents no major discontinuity.

They also state that none of the race concepts they discuss are compatible with their results.^[20]

[edit] Distribution of variation

Two random humans are expected to differ at approximately 1 in 1000 nucleotides, whereas two random chimpanzees differ at 1 in 500 nucleotide pairs. Therefore with a genome of approximate 3 billion nucleotides, on average two humans differ at approximately 3 million nucleotides. Most of these single nucleotide polymorphisms (SNPs) are neutral, but some are functional and influence the phenotypic differences between humans. It is estimated that about 10 million SNPs exist in human populations, where the rarer SNP allele has a frequency of at least 1% (see International HapMap Project).

In the field of population genetics, it is believed that the distribution of neutral polymorphisms among contemporary humans reflects human demographic history. It is believed that humans passed through a population bottleneck before a rapid expansion coinciding with migrations out of Africa leading to an African-Eurasian divergence around 100,000 years ago (ca. 5,000 generations), followed by a European-Asian divergence about 40,000 years ago (ca. 2,000 generations). Richard G. Klein, Nicholas Wade and Spencer Wells, have postulated that modern humans did not leave Africa and successfully colonize the rest of the world until as recently as 50,000 years B.P., pushing back the dates for subsequent population splits as well.

The rapid expansion of a previously small population has two important effects on the distribution of genetic variation. First, the so-called founder effect occurs when founder populations bring only a subset of the genetic variation from their ancestral population. Second, as founders become more geographically separated, the probability that two individuals from different founder populations will mate becomes smaller. The effect of this assortative mating is to reduce gene flow between geographical groups, and to increase the genetic distance between groups. The expansion of humans from Africa affected the distribution of genetic variation in two other ways. First, smaller (founder) populations experience greater genetic drift because of increased fluctuations in neutral polymorphisms. Second, new polymorphisms that arose in one group were less likely to be transmitted to other groups as gene flow was restricted.

Many other geographic, climatic, and historical factors have contributed to the patterns of human genetic variation seen in the world today. For example, population processes associated with colonization, periods of geographic isolation, socially reinforced endogamy, and natural selection all have affected allele frequencies in certain populations (Jorde et al. 2000b; Bamshad and Wooding 2003). In general, however, the recency of our common ancestry and continual gene flow among human groups have limited genetic differentiation in our species.

[edit] Substructure in the human population

Triangle plot shows average admixture of five North American ethnic groups. Individuals that self-identify with each group can be found at many locations on the map, but on average groups tend to cluster differently.^[22]

New data on human genetic variation has reignited the debate surrounding race. Most of the controversy surrounds the question of how to interpret these new data, and whether conclusions based on existing data are sound. Some researchers endorse the view that continental groups do not constitute different subspecies. However, some still debate whether evolutionary lineages should rightly be called "races". These questions are particularly pressing for biomedicine, where self-described race is often used as an indicator of ancestry (see race in biomedicine below).

Although the genetic differences among human groups are relatively small, these differences in certain genes such as duffy, ABCC11, SLC24A5, called ancestry-informative markers (AIMs) nevertheless can be used to reliably situate many individuals within broad, geographically based groupings or self-identified race. For example, computer analyses of hundreds of polymorphic loci sampled in globally distributed populations have revealed the existence of genetic clustering that roughly is associated with groups that historically have occupied large continental and subcontinental regions (Rosenberg et al. 2002; Bamshad et al. 2003).

Some commentators have argued that these patterns of variation provide a biological justification for the use of traditional racial categories. They argue that the continental clusterings correspond roughly with the division of human beings into sub-Saharan Africans; Europeans, North Africans, Western Asians, and South Asians; Eastern Asians; Polynesians and other inhabitants of Oceania; and Native Americans (Risch et al. 2002). Other observers disagree, saying that the same data undercut traditional notions of racial groups (King and Motulsky 2002; Calafell 2003; Tishkoff and Kidd 2004). They point out, for example, that major populations considered races or subgroups within races do not necessarily form their own clusters. Thus, samples taken from India and Pakistan affiliate with Europeans or eastern Asians rather than separating into a distinct cluster.

Furthermore, because human genetic variation is clinal, many individuals affiliate with two or more continental groups. Thus, the genetically based "biogeographical ancestry" assigned to any given person generally will be broadly distributed and will be accompanied by sizable uncertainties (Pfaff et al. 2004).

In many parts of the world, groups have mixed in such a way that many individuals have relatively recent ancestors from widely separated regions. Although genetic analyses of large numbers of loci can produce estimates of the percentage of a person's ancestors coming from various continental populations (Shriver et al. 2003; Bamshad et al. 2004), these estimates may assume a false distinctiveness of the parental populations, since human groups have exchanged mates from local to continental scales throughout history (Cavalli-Sforza et al. 1994; Hoerder 2002). Even with large numbers of markers, information for estimating admixture proportions of individuals or groups is limited, and estimates typically will have wide CIs (Pfaff et al. 2004).

[edit] Biogeographic Ancestry

[edit] Anthropology

Biogeographic ancestry is an anthropological concept of lineage that looks at kinship and descent based on biogeography, a combination of biology and geography.

The study of ancestry based mitochondrial DNA, ALU polymorphisms, and other genetic markers has significant implications in law enforcement, medicine, archaeology, and anthropology.

Some scientists believe genetic ancestry can help to focus the search for genes that affect individuals' risks of diseases, as well as prevalence and distribution of disease. Others advocate using it as a means of profiling persons for the purposes of law enforcement. In many of the cases, the term is used synonymously with race and can be used to partially determine the genetic admixture of an individual. However, each individual human may express the same gene differently than another, and each individual is partially a unique mix of genes unlike any other.

The field is sometimes controversial because of the ethical issues raised by DNA profiling and race theories that can be abused for political and social ends. Some critics argue that biogeographic ancestry is simply a means of reification for a social construct. The number of categories and the criteria used to group humans is also very arbitrary and often based on customs or traditions. The results are also only probable, with many individual exceptions.

Opponents of racial groupings argue that a distinct difference is only one of the two conditions for racial classification; the second condition is a lack of significant gene flow between populations. Humans are classified as monotypic, because phenotypes gradually fade into one another in many parts of the world. Although there has historically been little or no gene flow between some human populations such as the aboriginal Australians and black Africans, they argue, one cannot assume there has been little interracial gene flow, as the interbreeding of locally adjacent populations may produce common traits. Some researchers report enough such gene flow has occurred that the most recent common ancestor of all humans alive today may have lived as recently as 3,500 years ago, the work also estimated that everyone alive 7400 years ago was either an ancestor of all humans alive today, or of nobody currently living, before this time all humanity alive today share exactly the same ancestors.^[23] although critics say this is not necessarily significant gene flow.^{[citation needed]}

[edit] Genetics

An alternative to the use of racial or ethnic categories is to categorize individuals in terms of ancestry. Ancestry may be defined geographically (e.g., Asian, sub-Saharan African, or northern European), geopolitically (e.g., Vietnamese, Zambian, or Norwegian), or culturally (e.g., Brahmin, Lemba, or Apache). The definition of ancestry may recognize a single predominant source or multiple sources. Ancestry can be ascribed to an individual by an observer, as was the case with the U.S. census prior to 1960; it can be identified by an individual from a list of possibilities or with use of terms drawn from that person's experience; or it can be calculated from genetic data by use of loci with allele frequencies that differ geographically, as described above. At least among those individuals who participate in biomedical research, genetic estimates of biogeographical ancestry generally agree with self-assessed ancestry (Tang et al. 2005), but in an unknown percentage of cases, they do not (Brodwin 2002; Kaplan 2003).

Genetic data can be used to infer population structure and assign individuals to groups that often correspond with their self-identified geographical ancestry. The inference of population structure from multilocus genotyping depends on the selection of a large number of informative genetic markers. These studies usually find that groups of humans living on the same continent are more similar to one another than to groups living on different continents. Many such studies are criticized for assigning group identity a priori. However, even if group identity is stripped and group identity assigned a posteriori using only genetic data, population structure can still be inferred. For example, using 993 markers, Rosenberg et al. (2005) were able to assign 1,048 individuals from 52 populations around the globe to one of six genetic clusters, which correspond to major geographic regions.

However, in analyses that assign individuals to group it becomes less apparent that self-described racial groups are reliable indicators of ancestry. One cause of the reduced power of the assignment of individuals to groups is admixture. Some racial or ethnic groups, especially Hispanic groups, do not have homogenous ancestry. For example, self-described African Americans tend to have a mix of West African and European ancestry. Shriver et al. (2003) found that on average African Americans have ~80% African ancestry. Also, for example, ~30% of students who self identified as white in a Northeastern US college have less than 90% European ancestry.

Nevertheless, recent research indicates that self-described race is a near-perfect indicator of an individual's genetic profile, at least in the United States. Using 326 genetic markers, Tang et al. (2005) identified 4 genetic clusters among 3,636 individuals sampled from 15 locations in the United States, and were able to correctly assign individuals to groups that correspond with their self-described race (white, African American, East Asian, or Hispanic) for all but 5 individuals (an error rate of 0.14%). They conclude that ancient ancestry, which correlates tightly with self-described race and not current residence, is the major determinant of genetic structure in the U.S. population.

Geneticist Neil Risch from Stanford University and 3 other scientists commented on this in their study: "More recently, a survey of 3,899 SNPs in 313 genes based on US populations (Caucasians, African-Americans, Asians and Hispanics) once again provided distinct and non-overlapping clustering of the Caucasian, African-American and Asian samples...The results confirmed the integrity of the self-described ancestry of these individuals" Populations in their research "clustered into the five continental groups"^[24]

Genetic techniques that distinguish ancestry between continents can also be used to describe ancestry within continents. However, the study of intra-continental ancestry may require a greater number of informative markers. Populations from neighboring geographic regions typically share more recent common ancestors. As a result, allele frequencies will be correlated between these groups. This phenomenon is often seen as a cline of allele frequencies. The existence of allelic clines has been offered as evidence that individuals cannot be allocated into genetic clusters (Kittles & Weiss 2003). However, others argue that low levels of differentiation between groups merely make the assignment to groups more difficult, not impossible (Bamshad et al. 2004).

Also, clines and clusters, seemingly discordant perspectives on human genetic diversity may be reconciled. A recent comprehensive study has stated:

At the same time, we find that human genetic diversity consists not only of clines, but also of clusters, which STRUCTURE observes to be repeatable and robust.^[25]

Despite its seemingly objective nature, ancestry also has limitations as a way of categorizing people (Elliott and Brodwin 2002). When asked about the ancestry of their parents and grandparents, many people cannot provide accurate answers. In one series of focus groups in the state of Georgia, 40% of ∼100 respondents said they did not know one or more of their four grandparents well enough to be certain how that person(s) would identify racially (Condit et al. 2003). Misattributed paternity or adoption can separate biogeographical ancestry from socially defined ancestry. Furthermore, the exponentially increasing number of our ancestors makes ancestry a quantitative rather than qualitative trait—5 centuries (or 20 generations) ago, each person had a maximum of >1 million ancestors (Ohno 1996). To complicate matters further, recent analyses suggest that everyone living today has exactly the same set of genealogical ancestors who lived as recently as a few thousand years in the past, although we have received our genetic inheritance in different proportions from those ancestors (Rohde et al. 2004).

The delicacy of this definition has left the issue much in debate, especially among physical anthropologists, for if clines lead to large areas of near-homogeneity, such as Kenya, Sweden and Japan, then the people in these areas seem marked off by delimiters resembling nothing so much as the traditional physiological touchstones of "race". Currently, the question of whether human genetic variation is better described as clinal (i.e. no races) or cladistic (i.e. races are real) is largely fading.

The problem arises of distinguishing black Africans as a racial group; it doesn't work because it is a paraphyletic classification. In other words, under a phylogenetic classification, considering black Africans as a single racial group would require one to include every living person on Earth within that single African "race", because the genetic variation of the rest of the world represents essentially a single subtree within that of Africa. Also, it has long been known that groups such as the Khoisan were as different from other sub-Saharan groups as are Europeans and Asians (though even with the Khoisan the distinction is no longer so clearcut, as a large amount of intermarriage with both Europeans and Bantu-language speakers has occurred over the last three centuries).

Rachel Caspari (2003) argued that clades are by definition monophyletic groups (a taxon that includes all descendants of a given ancestor); since races are not monophyletic, they cannot be clades.

In the end, the terms "race," "ethnicity," and "ancestry" all describe just a small part of the complex web of biological and social connections that link individuals and groups to each other.

[edit] Do Biologically Distinct Races Exist?

Further information: Subspecies

Ongoing debate exists over the merit of the concept of 'race', especially from the perspective of genetics. Some scientists argue that common racial classifications are insufficient, inaccurate, or biologically meaningless.^[26] The claim has also been made that many "well-intentioned"^[27] statements regarding a lack of identifiable human variation are false, and do not "derive from an objective scientific perspective."^[28] They argue instead "that from both an objective and scientific (genetic and epidemiologic) perspective there is great validity in racial/ethnic self-categorizations, both from the research and public policy points of view."^[28]

[edit] Is the variation by geographic origin distinct enough to count as race?

it is not surprising that numerous human population genetic studies have come to the identical conclusion - that genetic differentiation is greatest when defined on a continental basis........the greatest genetic structure that exists in the human population occurs at the racial level.^[29]

However, Claudia Travassos and David R. Williams claim that Risch is actually using race to mean continent of origin.

Race is defined by these authors as the person's primary continent of origin based on the evolutionary tree.^[30]

Risch et al also state: "The greatest genetic variation occurs within Africans, with variation outside Africa representing either a subset of African diversity or newly arisen variants."^[29]

While geographical origin can be inferred from genetics, observed geographically distributed human genetic variation does not amount to the sort of discontinuous distribution that would be expected if the human population were descended from distinct lineages, neither is the variation great enough for human populations to be considered subspecies, the usual biological synonym for race.^[8]

In fact, Sierre and Paablo describe the pattern as one of gradients of allele frequencies that extend over the entire world, rather than discrete clusters.

Leroi points out the arbitrariness of racial lines drawn through the human species

While races of traditional anthropology is not a technical term and definition may vary according to context, according to National Human Genome Center at Howard University, Races of traditional anthropology include Mongoloid, Australoid, Caucasoid, Negroid.^[33]

And the National Human Genome Center at Howard University states,

Risch, in the source quoted above, has even said that the concept of race is intrinsically unscientific

From a biological taxonomic point of view humans all occupy the same subspecific taxon and are designated Homo sapiens sapiens, (Homo sapiens is the binominal species name, the subspecific name also being sapiens). Some scientists argue that common racial classifications are insufficient, inaccurate, or biologically meaningless.^[34] The biological meaninglessness of race does not preclude the importance of human genetic diversity as it applies to geographically distributed populations. Often "race" is used in a non-biological self defined sense to infer the geographical ancestry of a person: "from both an objective and scientific (genetic and epidemiologic) perspective there is great validity in racial/ethnic self-categorizations, both from the research and public policy points of view."^[29] It is well known that many alleles vary in frequency across human populations. However from a biological point of view "race" is usually considered a synonym for subspecies, and in turn the definition of a subspecies requires a far greater degree of diversity than is seen in the human global population.

Race is generally used as a synonym for subspecies, which traditionally is a geographically circumscribed, genetically differentiated population. Sometimes traits show independent patterns of geographical variation such that some combination will distinguish most populations from all others. To avoid making "race" the equivalent of a local population, minimal thresholds of differentiation are imposed. Human "races" are below the thresholds used in other species, so valid traditional subspecies do not exist in humans. A "subspecies" can also be defined as a distinct evolutionary lineage within a species. Genetic surveys and the analyses of DNA haplotype trees show that human "races" are not distinct lineages, and that this is not due to recent admixture; human races are not and never were "pure". Instead, human evolution has been and is characterised by many locally differentiated populations coexisting at any given time, but with sufficient genetic contact to make all humanity a single lineage sharing a common evolutionary fate.^[35]

Recent work in anthropological genetics suggests that the traditional, historic and socially-constructed ‘racial’ aggregates that have permeated the Western biomedical literature since the 18th century are largely genetic illusions. Important human biological variation exists, but classical races, as the term is used systematically and taxonomically in the natural sciences, appears inapplicable to modern humans.....Our species collective origins are too recent, the extent of gene flow between us is too great, and our current diversity is too evolutionarily superficial to warrant the racial or subspecies level of differentiation among contemporary humans. Human variability does not neatly package itself into separate and discrete categories, as the term race would indicate. In fact, from a scientific point of view, we humans are a single, highly variable, polytypic race—Homo sapiens sapiens. The second ‘sapiens’ is actually the subspecies or race category. What biodiversity exists among modern humans exists taxonomically below the subspecies level.^[36]

Even geneticists that support the concept of biological races maintain that subdividing the human population along the lines of continental races is simply the most convenient method.

Some researchers have used the work of Cavalli-Sforza as support for the idea that races are objectively verifiable, however Cavalli-Sforza, himself, has said, "the idea of race in the human species serves no purpose" and that his research is "expected to undermine the popular belief that there are clearly defined races, [and] to contribute to the elimination of racism". He has also said,

Additionally, according to an article published in The Economist, the work of Cavalli-Sforza "challenges the assumption that there are significant genetic differences between human races, and indeed, the idea that 'race' has any useful biological meaning at all." [3] (The Human Genome Survey, 1 July 2000, pg. 11)

Neil Risch, who has published many papers regarding human genetic variation argues that one of the problems with race is definition (though the usual definition is that "race" equates to subspecies) others agree with Risch:

'Race' is not being defined or used consistently; its referents are varied and shift depending on context. The term is often used colloquially to refer to a range of human groupings. Religious, cultural, social, national, ethnic, linguistic, genetic, geographical and anatomical groups have been and sometimes still are called 'races'. In anthropology, the meaning of race became formalized for humans and restricted to units based on biological variation in keeping with general zoological practice8. Classifications were based on somatic traits......'Race' is applied in formal taxonomy to variation below the species level. In traditional approaches, substantively morphologically distinct populations or collections of populations occupying a section of a species range are called subspecies and given a three-part Latin name. In current systematic practice, the designation 'subspecies' is used to indicate an objective degree of microevolutionary divergence.....We argue that the correct use of the term 'race' is the most current taxonomic one, because it has been formalized. 'Race' gains its force from its natural science root. The term denotes 'natural' distinctions and connotes differences not susceptible to change. One is led to ask, therefore, whether everything that is called a 'racial' difference is actually natural. 'Racial' differences carry a different weight than cultural differences. In terms of taxonomic precision and best practice, is it scientifically correct to identify European Americans, Asians and Pacific Islanders, Han Chinese, Hispanics and African Americans of Middle Passage descent as different races? Although individuals may refer to themselves as belonging to a particular 'race', it is doubtful that this has been done with knowledge of, or concern for, zoological taxonomy, because the common use of the term has come from sociopolitical discourse. Individuals learned the 'race' to which they were assigned.^[37]

In response to the statement “Genome variation research does not support the existence of human races.” Risch says:

What is your definition of races? If you define it a certain way, maybe that's a valid statement. There is obviously still disagreement.....Scientists always disagree! A lot of the problem is terminology. I'm not even sure what race means, people use it in many different ways.

So Risch seems not to be using the standard biological definition of "race", but rather a socially constructed definition of "race" (see above), and to be applying this to the small level of genetic variation that is geographically distributed. Risch uses the term "race/ethnicity" for his social construct. He goes on to conclude that few biological definitions are precise:

In our own studies, to avoid coming up with our own definition of race, we tend to use the definition others have employed, for example, the US census definition of race. There is also the concept of the major geographical structuring that exists in human populations—continental divisions—which has led to genetic differentiation. But if you expect absolute precision in any of these definitions, you can undermine any definitional system. Any category you come up with is going to be imperfect, but that doesn't preclude you from using it or the fact that it has utility. We talk about the prejudicial aspect of this. If you demand that kind of accuracy, then one could make the same arguments about sex and age! You'll like this. In a recent study, when we looked at the correlation between genetic structure [based on microsatellite markers] versus self-description, we found 99.9% concordance between the two. We actually had a higher discordance rate between self-reported sex and markers on the X chromosome! So you could argue that sex is also a problematic category. And there are differences between sex and gender; self-identification may not be correlated with biology perfectly. And there is sexism. And you can talk about age the same way. A person's chronological age does not correspond perfectly with his biological age for a variety of reasons, both inherited and non-inherited. Perhaps just using someone's actual birth year is not a very good way of measuring age. Does that mean we should throw it out? No. Also, there is ageism—prejudice related to age in our society. A lot of these arguments, which have a political or social aspect to them, can be made about all categories, not just the race/ethnicity one.^[38]

Risch is one of the scientists that deem that the genetic variation seen within the human population is of biomedical importance, but not all scientists agree with this position.

Underpinning the medical acceptance of biological race has been the assumption that substantial human genetic variability is at the core of racial group-level human differences. In the United States, the groups of choice, for comparative health status studies are usually identified by such terms as ‘Black’, ‘White’, ‘Latino’ or ‘Hispanic’, and ‘Asian’. Significant within-group variation is often ignored and this inherent variability is now returning to haunt researchers searching for broad racial generalizations. The key questions in using these macroethnic ‘racial’ groups have been (and continue to be): (1) Do these groups represent statistically valid biological categories? And (2) can they be used as reliable shortcuts to making predictions (probability statements) about group disease susceptibilities and health status? The answers to both of these questions are a resounding No.^[36]

The genetic distance plot of Sforza, which has been interpreted in terms of 19th century typological groups, has been used by Arthur Jensen a race and IQ psychologist to promote the idea that the traditional races of craniofacial anthropology have been confirmed by genetics:

On pgs 430-431 of the g factor Jensen writes:

Cavalli-Sforza et al. transformed the distance matrix to a correlation matrix consisting of 861 correlation coefficients among the forty-two populations, so they could apply principal components (PC) analysis on their genetic data...PC analysis is a wholly objective mathematical procedure. It requires no decisions or judgments on anyone's part and yields identical results for everyone who does the calculations correctly...The important point is that if various populations were fairly homogenous in genetic composition, differing no more genetically than could be attributable only to random variation, a PC analysis would not be able to cluster the populations into a number of groups according to their genetic propinquity. In fact, a PC analysis shows that most of the forty-two populations fall very distinctly into the quadrents formed by using the first and second principal component as axes...They form quite widely separated clusters of the various populations that resemble the "classic" major racial groups-Caucasoids in the upper right, Negroids in the lower right, North East Asians in the upper left, and South East Asians (including South Chinese) and Pacific Islanders in the lower left...I have tried other objective methods of clustering on the same data (varimax rotation of the principal components, common factor analysis, and hierarchical cluster analysis). All of these types of analysis yield essentially the same picture and identify the same major racial groupings.

Genetic Distance Maps
genetic chart made by Cavalli-Sforza circa 1980	This genetic distance map was made in 2007 using statistical Euclidean distance.[39]
Note: "Genetic distance analyses strongly and uniformly indicate that human 'races' cannot be represented as branches on an evolutionary tree." Further, "an apparent genetic time of divergence does not necessarily imply a time of population splitting—or any population split at all."[40]

Elsewhere in Jensen's writings, he equates North East Asians with mongoloids, which along with Caucasoids and Negroids, form what Jensen describes as the three broadest population groups. To test the reliability of these broadgroupings, Jensen performed his own independent varimax rotated principal component analysis described on paged 518 of the g factor:

I have used a somewhat different collection of only 26 populations from around the world that were studied by the population genetecists Nei & Roychoudhury (1993), whose article provides the genetic distance matrix among the 26 population samples, based on 29 polymorphic genes with 121 alleles...The population clusters are defined by their largest loadings (shown in boldface type) on one of the components. A population's proximity to the central tendency of a cluster is related to the size of its loading in that cluster. Note that some groups have major and minor loadings on different components, which represent not discrete categories, but central tendencies...The genetic groupings are clearly similar to those obtained by Cavali-Sforza et al. using other methods applied to other samples.

It should be noted however that Cavali-Sforza himself denies that race is a useful concept on the genetic level, and that unlike Jensen, most anthropologists have traditionally recognized only the three main races (lumping South East Asians, Amerindians, and Eskimos in with Mongoloids and some have considered aboriginal Australians and Papuan New Guineans to be Caucasoid).

[edit] Genetics and the 5 race model

Noah A. Rosenberg and Jonathan K. Pritchard, geneticists from the laboratory of Marcus W. Feldman of Stanford University, assayed 377 polymorphisms in more than 1,000 people from 52 ethnic groups in Africa, Asia, Europe and the Americas. They looked at the varying frequencies of these polymorphisms and concluded

without using prior information about the origins of individuals, we identified six main genetic clusters, five of which correspond to major geographic regions, and subclusters that often correspond to individual populations.^[41]

we found that individuals could be partitioned into six main genetic clusters, five of which corresponded to Africa, Europe and the part of Asia south and west of the Himalayas, East Asia, Oceania, and the Americas^[42]

Dr. Neil Risch of Stanford University has shown that self identified ethnic identity correlates with genetic structure, this is different to the previous study in that groups were pre-sorted by self-identification.

Subjects identified themselves as belonging to one of four major racial/ethnic groups (white, African American, East Asian, and Hispanic) and were recruited from 15 different geographic locales within the United States and Taiwan. Genetic cluster analysis of the microsatellite markers produced four major clusters, which showed near-perfect correspondence with the four self-reported race/ethnicity categories.^[43]

[edit] See also

• Human mitochondrial DNA haplogroups
• Genetic history of Europe

[edit] Footnotes

[edit] References

• Avise, J.C., Ball, R.M. 1990. Principles of genealogical concordance in species concepts and biological taxonomy. Oxford Surveys in Evolutionary Biology 7:45-67.
• Bamshad M., Wooding, S., Salisbury, B. A. and Stephens, J. C. (2004). Deconstructing the relationship between genetics and race. Nature Reviews Genetics, Vol 5 pp. 598-605. Retrieved 28 December 2006.
• Bamshad M. (2005). "Genetic Influences on Health: Does Race Matter?". Journal of the American Medical Association 294: 937-946. 
• Collins, F. S. (2004). "What we do and don't know about 'race', 'ethnicity', genetics and health at the dawn of the genome era". Nature Genetics. DOI:10.1038/ng1436. 

• Dobzhansky, T. (1970). Genetics of the Evolutionary Process. New York, NY: Columbia University Press.
• Edwards, A., W., F. (2003) Human genetic diversity: Lewontin’s fallacy. BioEssays 25:798–801, ß. Full PDF version
• Fernández JR, Shriver MD, Beasley TM, Rafla-Demetrious N, Parra E, Albu J, Nicklas B, Ryan AS, McKeigue PM, Hoggart CL, Weinsier RL, Allison DB (2003). "Association of African Genetic Admixture with Resting Metabolic Rate and Obesity Among Women". Obesity Research 11: 904-911. 
• Helms, J. E., Jernigan, M. and Mascher, J. (Jan 2005). "The Meaning of Race in Psychology and How to Change It: A Methodological Perspective". American Psychologist 60 (1): 27-36. DOI:10.1037/0003-066x.60.1.27. 
• Jackson, F. L. C. (2004). Book chapter: Human genetic variation and health: new assessment approaches based on ethnogenetic layering British Medical Bulletin 2004; 69: 215–235 DOI: 10.1093/bmb/ldh012. Retrieved 29 December 2006.
• Keita, S. O. Y. (1993) The subspecies concept in zoology and anthropology, a brief historical review and test of a classification scheme. Journal of Black Studies 23:416-445.
• Keita, S. O. Y., Kittles, R. A., Royal, C. D. M., Bonney, G. E., Furbert-Harris, P., Dunston, D. M., and Rotimi, C. M. (2004). Conceptualizing human variation: Nature Genetics 36, S17 - S20 (2004) DOI:10.1038/ng1455
• Kittles and Weiss RACE, ANCESTRY, AND GENES: Implications for Defining Disease Risk Annu. Rev. Genomics Hum. Genet. 2003. 4:33–67 DOI:10.1146/annurev.genom.4.070802.110356
• Lewonin, R. C. (2005). Confusions About Human Races from Race and Genomics, Social Sciences Research Council. Retrieved 28 December 2006.
• Leroy, A. M. (2005). A Family Tree in Every Gene. Published: March 14, 2005, The New York Times, p. A23. [8]. Retrieved 08 January 2006.
• Long and Kittles (2003). Human genetic variation and the nonexistence of human races: Human Biology, V. 75, no. 4, pp. 449-471. [PDF. Retrieved 10 January 2007.
• Mayr, E. (1969). Principles of Systematic Zoology. New York, NY: McGraw-Hill.
• Miththapala, S., Seidensticker, J., O’Brien, S.J. 1996. Phylogeographic Subspecies Recognition in Leopards (Panthera pardus): Molecular Genetic Variation. Conservation Biology 10:1115-1132.
• O’Brien, S.J., Mayr, E. 1991. Bureaucratic Mischief: Recognizing Endangered Species and Subspecies. Science. 2 51:1187-1188.
• Parra, Kittles and Shriver. (2004) Implicatins of correlations between skin color and genetic ancestry for biomedical research'Nature Genetics Supplement 36: 11 S54-S60 DOI:10.1038/ng1440
• * Pigliucci, Kaplan On the Concept of Biological Race and Its Applicability to Humans [9]
• Risch, N., Burchard, E., Ziv, E. and Tang, H. (2002). "Categorization of humans in biomedical research: genes, race and disease". Genome Biology 3 (7): comment2007.2001 - comment2007.2012. 
• Race, Ethnicity, and Genetics Working Group, National Human Genome Research Institute. (2005) The Use of Racial, Ethnic, and Ancestral Categories in Human Genetics Research Am. J. Hum. Genet. 77:000–000
• Rohde, Olson and Chang (2004) Modelling the recent common ancestry of all living humans Nature 431: 562-566 DOI:10.1038/nature02842. Retrieved 05 March 2007.
• Rosenberg NA, Pritchard JK, Weber JL, Cann HM, Kidd KK, et al. (2002) Genetic structure of human populations. Science 298: 2381–2385.Abstract
• Rosenberg1, N. A., Mahajan, s., Ramachandran, S., Zhao, C., Pritchard, J. K., Feldman, M. W. (2005) Clines, Clusters, and the Effect of Study Design on the Inference of Human Population Structure. PLoS Genet 1(6): e70: DOI:10.1371/journal.pgen.0010070
• Serre, D and Pääbö, S. (2004) Evidence for Gradients of Human Genetic Diversity Within and Among Continents Genome Research 14:1679-1685, 2004 DOI:10.1101/gr.2529604. Retrieved 08 January 2006.
• Smedley, A. and Smedley, B. D. (Jan 2005). "Race as Biology Is Fiction, Racism as a Social Problem Is Real: Anthropological and Historical Perspectives on the Social Construction of Race". American Psychologist 60 (1): 16-26. DOI:10.1037/0003-066x.60.1.16. 
• Tang, Hua., Tom Quertermous, Beatriz Rodriguez, Sharon L. R. Kardia, Xiaofeng Zhu, Andrew Brown,7 James S. Pankow,8 Michael A. Province,9 Steven C. Hunt, Eric Boerwinkle, Nicholas J. Schork, and Neil J. Risch (2005) Genetic Structure, Self-Identified Race/Ethnicity, and Confounding in Case-Control Association Studies Am. J. Hum. Genet. 76:268–275.
• Templeton, A.R. (1998). Human races: A genetic and evolutionary perspective. Am. Anthropol. 100, 632–650.Partial access to article. Retrieved 01 January 2007.
• Travassos, C. and Williams, D. R. (2004). The concept and measurement of race and their relationship to public health: a review focused on Brazil and the United States: Cadernos de Saúde Pública v.20 n.3. DOI:10.1590/S0102-311X2004000300003
• Nature Genetics (2004). "Implications of biogeography of human populations for 'race' and medicine" 36: S21 - S27. 

[edit] External links

• Minorities, Race, and Genomics via Human Genome Project information.