Race (human categorization)

==== Genetically differentiated populations ====
{{main|Race and genetics|Human genetic variation}}
Another way to look at differences between populations is to measure genetic differences rather than physical differences between groups. The mid-20th-century anthropologist [[William C. Boyd]] defined race as: "A population which differs significantly from other populations in regard to the frequency of one or more of the genes it possesses. It is an arbitrary matter which, and how many, gene loci we choose to consider as a significant 'constellation'".<ref name="boyd" /> Leonard Lieberman and Rodney Kirk have pointed out that "the paramount weakness of this statement is that if one gene can distinguish races then the number of races is as numerous as the number of human couples reproducing".<ref name="lieberman" /> Moreover, the anthropologist Stephen Molnar has suggested that the discordance of clines inevitably results in a multiplication of races that renders the concept itself useless.<ref name="molnar" /> The [[Human Genome Project]] states "People who have lived in the same geographic region for many generations may have some alleles in common, but no allele will be found in all members of one population and in no members of any other."<ref name="project" /> [[Massimo Pigliucci]] and Jonathan Kaplan argue that human races do exist, and that they correspond to the genetic classification of [[ecotype]]s, but that real human races do not correspond very much, if at all, to folk racial categories.<ref>{{cite journal |last1=Pigliucci |first1=Massimo |last2=Kaplan |first2=Jonathan |title=On the Concept of Biological Race and Its Applicability to Humans |journal=Philosophy of Science |date=December 2003 |volume=70 |issue=5 |pages=1161–1172 |doi=10.1086/377397 |s2cid=44750046 |url=http://philsci-archive.pitt.edu/1078/1/Kaplan-RaceFinalVersionPSA.doc}}</ref> In contrast, Walsh & Yun reviewed the literature in 2011 and reported: "Genetic studies using very few chromosomal loci find that genetic polymorphisms divide human populations into clusters with almost 100 percent accuracy and that they correspond to the traditional anthropological categories."<ref>{{cite journal |last1=Walsh |first1=Anthony |last2=Yun |first2=Ilhong |title=Race and Criminology in the Age of Genomic Science |journal=[[Social Science Quarterly]] |date=October 2011 |volume=92 |issue=5 |pages=1279–1296 |doi=10.1111/j.1540-6237.2011.00818.x}}</ref>

Some biologists argue that racial categories correlate with biological traits (e.g. [[phenotype]]), and that certain genetic markers have varying frequencies among human populations, some of which correspond more or less to traditional racial groupings.{{sfn|Bamshad|Wooding|Salisbury|Stephens|2004}}

===== Distribution of genetic variation =====
The distribution of genetic variants within and among human populations are impossible to describe succinctly because of the difficulty of defining a population, the clinal nature of variation, and heterogeneity across the genome (Long and Kittles 2003). In general, however, an average of 85% of statistical genetic variation exists within local populations, ≈7% is between local populations within the same continent, and ≈8% of variation occurs between large groups living on different continents.{{sfn|Lewontin|1972}}<ref>{{cite book |last1=Jorde |first1=Lynn B. |last2=Carey |first2=John C. |last3=Bamshad |first3=Michael J. |last4=White |first4=Raymond L. |date=2000 |title=Medical Genetics |edition=2nd |publisher=[[Mosby (imprint)|Mosby]] |isbn=978-0-8151-4608-7}}{{page needed|date=October 2021}}</ref> The [[recent African origin]] theory for humans would predict that in Africa there exists a great deal more diversity than elsewhere and that diversity should decrease the further from Africa a population is sampled. Hence, the 85% average figure is misleading: Long and Kittles find that rather than 85% of human genetic diversity existing in all human populations, about 100% of human diversity exists in a single African population, whereas only about 60% of human genetic diversity exists in the least diverse population they analyzed (the Surui, a population derived from New Guinea).{{sfn|Long|2009|p=802}} Statistical analysis that takes this difference into account confirms previous findings that "Western-based racial classifications have no taxonomic significance".<ref name=":12"/>

===== Cluster analysis =====
A 2002 study of random biallelic genetic loci found little to no evidence that humans were divided into distinct biological groups.<ref>{{cite journal |last1=Romualdi |first1=Chiara |last2=Balding |first2=David |author-link2=David Balding |last3=Nasidze |first3=Ivane S. |last4=Risch |first4=Gregory |last5=Robichaux |first5=Myles |last6=Sherry |first6=Stephen T. |last7=Stoneking |first7=Mark |author-link7=Mark Stoneking |last8=Batzer |first8=Mark A. |author-link8=Mark Batzer |last9=Barbujani |first9=Guido |author-link9=Guido Barbujani |date=April 2002 |title=Patterns of human diversity, within and among continents, inferred from biallelic DNA polymorphisms |journal=Genome Research |volume=12 |issue=4 |pages=602–612 |doi=10.1101/gr.214902 |issn=1088-9051 |pmid=11932244 |pmc=187513}}</ref>

In his 2003 paper, "[[Human Genetic Diversity: Lewontin's Fallacy]]", [[A. W. F. Edwards]] argued that rather than using a locus-by-locus analysis of variation to derive taxonomy, it is possible to construct a human classification system based on characteristic genetic patterns, or ''clusters'' [[Race and genetics#Structure|inferred from multilocus genetic data]].<ref name="edwards" /><ref name="Dawkins & Wong"/> Geographically based human studies since have shown that such genetic clusters can be derived from analyzing of a large number of loci which can assort individuals sampled into groups analogous to traditional continental racial groups.<ref name="Harpending; et al." />{{sfn|Tang|Quertermous|Rodriguez|Kardia|2005}} Joanna Mountain and [[Neil Risch]] cautioned that while genetic clusters may one day be shown to correspond to phenotypic variations between groups, such assumptions were premature as the relationship between genes and [[complex traits]] remains poorly understood.<ref name="mountain" /> However, Risch denied such limitations render the analysis useless: "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?&nbsp;... 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."<ref name="gitschier" />

Early human genetic cluster analysis studies were conducted with samples taken from ancestral population groups living at extreme geographic distances from each other. It was thought that such large geographic distances would maximize the genetic variation between the groups sampled in the analysis, and thus maximize the probability of finding cluster patterns unique to each group. In light of the historically recent acceleration of human migration (and correspondingly, human gene flow) on a global scale, further studies were conducted to judge the degree to which genetic cluster analysis can pattern ancestrally identified groups as well as geographically separated groups. One such study looked at a large multiethnic population in the United States, and "detected only modest genetic differentiation between different current geographic locales within each race/ethnicity group. Thus, ancient geographic ancestry, which is highly correlated with self-identified race/ethnicity&nbsp;– as opposed to current residence&nbsp;– is the major determinant of genetic structure in the U.S. population."{{sfn|Tang|Quertermous|Rodriguez|Kardia|2005}}

{{harvtxt|Witherspoon|Wooding|Rogers|Marchani|2007}} have argued that even when individuals can be reliably assigned to specific population groups, it may still be possible for two randomly chosen individuals from different populations/clusters to be more similar to each other than to a randomly chosen member of their own cluster. They found that many thousands of genetic markers had to be used in order for the answer to the question "How often is a pair of individuals from one population genetically more dissimilar than two individuals chosen from two different populations?" to be "never". This assumed three population groups separated by large geographic ranges (European, African and East Asian). The entire world population is much more complex and studying an increasing number of groups would require an increasing number of markers for the same answer. The authors conclude that "caution should be used when using geographic or genetic ancestry to make inferences about individual phenotypes".<ref name="Witherspoon, et al. 2007" /> Witherspoon, et al. concluded: "The fact that, given enough genetic data, individuals can be correctly assigned to their populations of origin is compatible with the observation that most human genetic variation is found within populations, not between them. It is also compatible with our finding that, even when the most distinct populations are considered and hundreds of loci are used, individuals are frequently more similar to members of other populations than to members of their own population."<ref name="Witherspoon, et al. 2007" />

Anthropologists such as [[C. Loring Brace]],<ref name="Brace 2005" /> the philosophers Jonathan Kaplan and Rasmus Winther,<ref name="encyclopedia" /><ref>{{cite journal |last1=Kaplan |first1=Jonathan Michael |last2=Winther |first2=Rasmus Grønfeldt |date=2014 |title=Realism, Antirealism, and Conventionalism About Race |url=https://philpapers.org/rec/KAPRAA |journal=[[Philosophy of Science (journal)|Philosophy of Science]] |volume=81 |issue=5 |pages=1039–1052 |doi=10.1086/678314 |s2cid=55148854}}</ref><ref>{{cite journal |last=Winther |first=Rasmus Grønfeldt |date=2015 |title=The Genetic Reification of 'Race'?: A Story of Two Mathematical Methods |url=http://philpapers.org/archive/WINTGR.pdf |journal=[[Critical Philosophy of Race]] |volume=2 |issue=2 |pages=204–223}}</ref>{{sfnp|Kaplan|Winther|2013}} and the geneticist [[Joseph L. Graves|Joseph Graves]],<ref>{{Cite web |last=Graves |first=Joseph |date=7 June 2006 |title=What We Know and What We Don't Know: Human Genetic Variation and the Social Construction of Race |url=http://raceandgenomics.ssrc.org/Graves/ |website=Race and Genomics}}</ref> have argued that the cluster structure of genetic data is dependent on the initial hypotheses of the researcher and the influence of these hypotheses on the choice of populations to sample. When one samples continental groups, the clusters become continental, but if one had chosen other sampling patterns, the clustering would be different. Weiss and Fullerton have noted that if one sampled only Icelanders, Mayans and Maoris, three distinct clusters would form and all other populations could be described as being clinally composed of admixtures of Maori, Icelandic and Mayan genetic materials.<ref name="evolutionary" /> Kaplan and Winther therefore argue that, seen in this way, both Lewontin and Edwards are right in their arguments. They conclude that while racial groups are characterized by different allele frequencies, this does not mean that racial classification is a natural taxonomy of the human species, because multiple other genetic patterns can be found in human populations that crosscut racial distinctions. Moreover, the genomic data underdetermines whether one [[Lumpers and splitters|wishes to see subdivisions (i.e., splitters) or a continuum (i.e., lumpers)]]. Under Kaplan and Winther's view, racial groupings are objective social constructions (see Mills 1998<ref>{{cite book |last=Mills |first=Charles W. |author-link=Charles Wade Mills |date=1988 |chapter=But What Are You Really? The Metaphysics of Race |title=Blackness visible: essays on philosophy and race |pages=41–66 |publisher=[[Cornell University Press]] |location=Ithaca, New York}}</ref>) that have conventional biological reality only insofar as the categories are chosen and constructed for pragmatic scientific reasons. In earlier work, Winther had identified "diversity partitioning" and "clustering analysis" as two separate methodologies, with distinct questions, assumptions, and protocols. Each is also associated with opposing ontological consequences vis-a-vis the metaphysics of race.<ref>{{cite web|url=http://philpapers.org/archive/WINTGR.pdf |title=The Genetic Reification of "Race"? A story of two mathematical methods |access-date=15 January 2020}}</ref> Philosopher Lisa Gannett has argued that biogeographical ancestry, a concept devised by [[Mark D. Shriver|Mark Shriver]] and [[Tony Frudakis]], is not an objective measure of the biological aspects of race as Shriver and Frudakis claim it is. She argues that it is actually just a "local category shaped by the U.S. context of its production, especially the forensic aim of being able to predict the race or ethnicity of an unknown suspect based on DNA found at the crime scene".<ref>{{cite journal |last=Gannett |first=Lisa |title=Biogeographical ancestry and race |journal=Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences |date=September 2014 |volume=47 |pages=173–184 |doi=10.1016/j.shpsc.2014.05.017 |pmid=24989973}}</ref>

===== Clines and clusters in genetic variation =====
Recent studies of human genetic clustering have included a debate over how genetic variation is organized, with clusters and clines as the main possible orderings. {{harvtxt|Serre|Pääbo|2004}} argued for smooth, clinal genetic variation in ancestral populations even in regions previously considered racially homogeneous, with the apparent gaps turning out to be artifacts of sampling techniques. {{harvtxt|Rosenberg|Mahajan|Ramachandran|Zhao|2005}} disputed this and offered an analysis of the Human Genetic Diversity Panel showing that there were small discontinuities in the smooth genetic variation for ancestral populations at the location of geographic barriers such as the [[Sahara]], the Oceans, and the [[Himalayas]]. Nonetheless, {{harvtxt|Rosenberg|Mahajan|Ramachandran|Zhao|2005}} stated that their findings "should not be taken as evidence of our support of any particular concept of biological race&nbsp;... Genetic differences among human populations derive mainly from gradations in allele frequencies rather than from distinctive 'diagnostic' genotypes." Using a sample of 40 populations distributed roughly evenly across the Earth's land surface, {{harvtxt|Xing|et al.|2010|p=208}} found that "genetic diversity is distributed in a more clinal pattern when more geographically intermediate populations are sampled".

[[Guido Barbujani]] has written that human genetic variation is generally distributed continuously in gradients across much of Earth, and that there is no evidence that genetic boundaries between human populations exist as would be necessary for human races to exist.{{sfn|Barbujani|2005}}

Over time, human genetic variation has formed a nested structure that is inconsistent with the concept of races that have evolved independently of one another.<ref>{{cite journal |last1=Hunley |first1=Keith L. |last2=Healy |first2=Meghan E. |last3=Long |first3=Jeffrey C. |author-link3=Jeffrey C. Long |date=18 February 2009 |title=The global pattern of gene identity variation reveals a history of long-range migrations, bottlenecks, and local mate exchange: Implications for biological race |journal=[[American Journal of Physical Anthropology]] |volume=139 |issue=1 |pages=35–46 |doi=10.1002/ajpa.20932 |pmid=19226641 |hdl=2027.42/62159 |hdl-access=free |url=https://deepblue.lib.umich.edu/bitstream/2027.42/62159/1/20932_ftp.pdf}}</ref>