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The term race or racial group usually refers to the concept of categorizing humans into populations or groups on the basis of various sets of characteristics. The most widely used human racial categories are based on visible traits (especially skin color, cranial or facial features and hair texture), and self-identification.

Conceptions of race, as well as specific ways of grouping races, vary by culture and over time, and are often controversial for scientific as well as social and political reasons. The controversy ultimately revolves around whether or not races are natural types or socially constructed, and the degree to which perceived differences in ability and achievement, categorized on the basis of race, are a product of inherited (i.e. genetic) traits or environmental, social and cultural factors.

Some argue that although race is a valid taxonomic concept in other species, it cannot be applied to humans. Many scientists have argued that race definitions are imprecise, arbitrary, derived from custom, have many exceptions, have many gradations, and that the numbers of races delineated vary according to the culture making the racial distinctions; thus they reject the notion that any definition of race pertaining to humans can have taxonomic rigour and validity. Today most scientists study human genotypic and phenotypic variation using concepts such as "population" and "clinal gradation". Many contend that while racial categorizations may be marked by phenotypic or genotypic traits, the idea of race itself, and actual divisions of persons into races or racial groups, are social constructs.

In ancient civilizations
Given visually complex social relationships, humans presumably have always observed and speculated about the physical differences among individuals and groups. But different societies have attributed markedly different meanings to these distinctions. For example, the Ancient Egyptian sacred text called Book of Gates identifies four categories that are now conventionally labeled "Egyptians", "Asiatics", "Libyans", and "Nubians", but such distinctions tended to conflate differences as defined by physical features such as skin tone, with tribal and national identity. Classical civilizations from Rome to China tended to invest much more importance in familial or tribal affiliation than with one's physical appearance (Dikötter 1992; Goldenberg 2003). Ancient Greek and Roman authors also attempted to explain and categorize visible biological differences among peoples known to them. Such categories often also included fantastical human-like beings that were supposed to exist in far-away lands. Some Roman writers adhered to an environmental determinism in which climate could affect the appearance and character of groups (Isaac 2004). In many ancient civilizations, individuals with widely varying physical appearances became full members of a society by growing up within that society or by adopting that society's cultural norms (Snowden 1983; Lewis 1990).

Julian the Apostate was an early observer of the differences in humans, based upon ethnic, cultural, and geographic traits, but as the ideology of "race" had not yet been constructed, he believed that they were the result of "Providence":

Come, tell me why it is that the Celts and the Germans are fierce, while the Hellenes and Romans are, generally speaking, inclined to political life and humane, though at the same time unyielding and warlike? Why the Egyptians are more intelligent and more given to crafts, and the Syrians unwarlike and effeminate, but at the same time intelligent, hot-tempered, vain and quick to learn? For if there is anyone who does not discern a reason for these differences among the nations, but rather declaims that all this so befell spontaneously, how, I ask, can he still believe that the universe is administered by a providence? — Julian, the Apostate.

Medieval models of "race" mixed Classical ideas with the notion that humanity as a whole was descended from Shem, Ham and Japheth, the three sons of Noah, producing distinct Semitic (Asian), Hamitic (African), and Japhetic (European) peoples.

In the 9th century, Al-Jahiz, an Afro-Arab biologist and Islamic philosopher of East African descent, was an early adherent of environmental determinism and explained how the environment can determine the physical characteristics of the inhabitants of a certain community. He used his theories on the struggle for existence and environmental determinism to explain the origins of different human skin colors, particularly black skin, which he believed to be the result of the environment. He cited a stony region of black basalt in the northern Najd as evidence for his theory:

""[It] is so unusual that its gazelles and ostriches, its insects and flies, its foxes, sheep and asses, its horses and its birds are all black. Blackness and whiteness are in fact caused by the properties of the region, as well as by the God-given nature of water and soil and by the proximity or remoteness of the sun and the intensity or mildness of its heat.""

Age of Discovery
The word "race", along with many of the ideas now associated with the term, were products of European imperialism and colonization during the age of exploration. (Smedley 1999) As Europeans encountered people from different parts of the world, they speculated about the physical, social, and cultural differences among various human groups. The rise of the Atlantic slave trade, which gradually displaced an earlier trade in slaves from throughout the world, created a further incentive to categorize human groups in order to justify the subordination of African slaves. (Meltzer 1993) Drawing on Classical sources and upon their own internal interactions &mdash; for example, the hostility between the English and Irish was a powerful influence on early thinking about the differences between people (Takaki 1993) &mdash; Europeans began to sort themselves and others into groups associated with physical appearance and with deeply ingrained behaviors and capacities. A set of folk beliefs took hold that linked inherited physical differences between groups to inherited intellectual, behavioral, and moral qualities. (Banton 1977) Although similar ideas can be found in other cultures (Lewis 1990; Dikötter 1992), they appear not to have had as much influence upon their social structures as was found in Europe and the parts of the world colonized by Europeans. However, often brutal conflicts between ethnic groups have existed throughout history and across the world.

Scientific concepts
The first scientific attempts to classify humans by categories of race date from the 17th century, along with the development of European imperialism and colonization around the world. The first post-Classical published classification of humans into distinct races seems to be François Bernier's Nouvelle division de la terre par les différents espèces ou races qui l'habitent ("New division of Earth by the different species or races which inhabit it"), published in 1684.

17th and 18th century
According to philosopher Michel Foucault, theories of both racial and class conflict can be traced to 17th century political debates about innate differences among ethnicities. In England radicals such as John Lilburne emphasised conflicts between Saxon and Norman peoples. In France Henri de Boulainvilliers argued that the Germanic Franks possessed a natural right to leadership, in contrast to descendants of the Gauls. In the 18th century, the differences among human groups became a focus of scientific investigation (Todorov 1993). Initially, scholars focused on cataloguing and describing "The Natural Varieties of Mankind," as Johann Friedrich Blumenbach entitled his 1775 text (which established the five major divisions of humans still reflected in some racial classifications, i.e., the Caucasoid race, Mongoloid race, Ethiopian race (later termed the Negroid race), American Indian race, and Malayan race). From the 17th through the 19th centuries, the merging of folk beliefs about group differences with scientific explanations of those differences produced what one scholar has called an "ideology of race" (Smedley 1999). According to this ideology, races are primordial, natural, enduring and distinct. It was further argued that some groups may be the result of mixture between formerly distinct populations, but that careful study could distinguish the ancestral races that had combined to produce admixed groups.

19th century
The 19th century saw attempts to change race from a taxonomic to a biological concept. In the 19th century a number of natural scientists wrote on race: Georges Cuvier, Charles Darwin, Alfred Wallace, Francis Galton, James Cowles Pritchard, Louis Agassiz, Charles Pickering, and Johann Friedrich Blumenbach. As the science of anthropology took shape in the 19th century, European and American scientists increasingly sought explanations for the behavioral and cultural differences they attributed to groups (Stanton 1960). For example, using anthropometrics, invented by Francis Galton and Alphonse Bertillon, they measured the shapes and sizes of skulls and related the results to group differences in intelligence or other attributes (Lieberman 2001).

These scientists made three claims about race: first, that races are objective, naturally occurring divisions of humanity; second, that there is a strong relationship between biological races and other human phenomena (such as forms of activity and interpersonal relations and culture, and by extension the relative material success of cultures), thus biologizing the notion of "race", as Foucault demonstrated in his historical analysis; third, that race is therefore a valid scientific category that can be used to explain and predict individual and group behavior. Races were distinguished by skin color, facial type, cranial profile and size, texture and color of hair. Moreover, races were almost universally considered to reflect group differences in moral character and intelligence.

The eugenics movement of the late 19th and early 20th centuries, inspired by Arthur Gobineau's An Essay on the Inequality of the Human Races (1853–1855) and Vacher de Lapouge's "anthroposociology", asserted as self-evident the biological inferiority of particular groups (Kevles 1985). In many parts of the world, the idea of race became a way of rigidly dividing groups by culture as well as by physical appearances (Hannaford 1996). Campaigns of oppression and genocide were often motivated by supposed racial differences (Horowitz 2001).

In Charles Darwin's most controversial book, The Descent of Man, he made strong suggestions of racial differences and European superiority. In Darwin's view, stronger tribes of humans always replaced weaker tribes. As savage tribes came in conflict with civilized nations, such as England, the less advanced people were destroyed. Nevertheless, he also noted the great difficulty naturalists had in trying to decide how many "races" there actually were (Darwin was himself a monogenist on the question of race, believing that all humans were of the same species and finding "race" to be a somewhat arbitrary distinction among some groups): Man has been studied more carefully than any other animal, and yet there is the greatest possible diversity amongst capable judges whether he should be classed as a single species or race, or as two (Virey), as three (Jacquinot), as four (Kant), five (Blumenbach), six (Buffon), seven (Hunter), eight (Agassiz), eleven (Pickering), fifteen (Bory St. Vincent), sixteen (Desmoulins), twenty-two (Morton), sixty (Crawfurd), or as sixty-three, according to Burke. This diversity of judgment does not prove that the races ought not to be ranked as species, but it shews that they graduate into each other, and that it is hardly possible to discover clear distinctive characters between them.

Models of human evolution
In a recent article, Leonard Lieberman and Fatimah Jackson have suggested that any new support for a biological concept of race will likely come from another source, namely, the study of human evolution. They therefore ask what, if any, implications current models of human evolution may have for any biological conception of race.

Today, all humans are classified as belonging to the species Homo sapiens and sub-species Homo sapiens sapiens. However, this is not the first species of hominids: the first species of genus Homo, Homo habilis, evolved in East Africa at least 2 million years ago, and members of this species populated different parts of Africa in a relatively short time. Homo erectus evolved more than 1.8 million years ago, and by 1.5 million years ago had spread throughout the Old World. Virtually all physical anthropologists agree that Homo sapiens evolved out of Homo erectus. Anthropologists have been divided as to whether Homo sapiens evolved as one interconnected species from H. erectus (called the Multiregional Model, or the Regional Continuity Model), or evolved only in East Africa, and then migrated out of Africa and replaced H. erectus populations throughout the Old World (called the Out of Africa Model or the Complete Replacement Model). Anthropologists continue to debate both possibilities, and the evidence is technically ambiguous as to which model is correct, although most anthropologists currently favor the Out of Africa model.

Lieberman and Jackson have argued that while advocates of both the Multiregional Model and the Out of Africa Model use the word race and make racial assumptions, none define the term. They conclude that "Each model has implications that both magnify and minimize the differences between races. Yet each model seems to take race and races as a conceptual reality. The net result is that those anthropologists who prefer to view races as a reality are encouraged to do so" and conclude that students of human evolution would be better off avoiding the word race, and instead describe genetic differences in terms of populations and clinal gradations.

Race as subspecies
With the advent of the modern synthesis in the early 20th century, many biologists sought to use evolutionary models and populations genetics in an attempt to formalise taxonomy. The Biological Species Concept (BSC) is the most widely used system for describing species, this concept defines a species as a group of organisms that interbreed in their natural environment and produce viable offspring. In practice species are not classified according to the BSC but according to typology by the use of a holotype, due to the difficulty of determining whether all members of a group of organisms do or can in practice potentially interbreed. BSC species are routinely classified on a subspecific level, though this classification is conducted differently for different taxons, for mammals the normal taxonomic unit below the species level is usually the subspecies. More recently the Phylogenetic Species Concept (PSC) has gained a substantial following. The PSC is based on the idea of a least-inclusive taxonomic unit (LITU), in phylogenetic classification no subspecies can exist because they would automatically constitute a LITU (any monophyletic group). Technically species cease to exist as do all hierarchical taxa, a LITU is effectively defined as any monophyletic taxon, phylogenetics is strongly influenced by cladistics which classifies organisms based on evolution rather than similarities between groups of organisms. In biology the term "race" is very rarely used because it is ambiguous, "'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'". Generally when it is used it is synonymous with subspecies. One of the main obstacles to identifying subspecies is that, while it is a recognised taxonomic term, it has no precise definition.

Species of organisms that are monotypic (i.e. form a single subspecies) display at least one of these properties:
 * All members of the species are very similar and cannot be sensibly divided into biologically significant subcategories.
 * The individuals vary considerably but the variation is essentially random and largely meaningless so far as genetic transmission of these variations is concerned (many plant species fit into this category, which is why horticulturists interested in preserving, say, a particular flower color avoid propagation from seed, and instead use vegetative methods like propagation from cuttings).
 * The variation among individuals is noticeable and follows a pattern, but there are no clear dividing lines among separate groups: they fade imperceptibly into one another. Such clinal variation displays a lack of allopatric partition between groups (i.e. a clearly defined boundary demarcating the subspecies), which is usually required before they are recognised as subspecies.

A polytypic species has two or more subspecies. These are separate populations that are more genetically different from one another and that are more reproductively isolated, gene flow between these populations is much reduced leading to genetic differentiation.

Morphological subspecies
Traditionally subspecies are seen as geographically isolated and genetically differentiated populations. Or to put it another way "the designation 'subspecies' is used to indicate an objective degree of microevolutionary divergence" One objection to this idea is that it does not identify any degree of differentiation, therefore any population that is somewhat biologically different could be considered a subspecies, even to the level of a local population. As a result it is necessary to impose a threshold on the level of difference that is required for a population to be designated a subspecies. This effectively means that populations of organisms must have reached a certain measurable level of difference in order to be recognised as subspecies. Dean Amadon proposed in 1949 that subspecies would be defined according to the seventy-five percent rule which means that 75% of a population must lie outside 99% of the range of other populations for a given defining morphological character or a set of characters. The 75 percent rule still has defenders but other scholars argue that it should be replaced with 90 or 95 percent rule.

In 1978, Sewall Wright suggested that human populations that have long inhabited separated parts of the world should, in general, be considered to be of different subspecies by the usual criterion that most individuals of such populations can be allocated correctly by inspection. It does not require a trained anthropologist to classify an array of Englishmen, West Africans, and Chinese with 100% accuracy by features, skin color, and type of hair in spite of so much variability within each of these groups that every individual can easily be distinguished from every other. However, it is customary to use the term race rather than subspecies for the major subdivisions of the human species as well as for minor ones.

On the other hand in practice subspecies are often defined by easily observable physical appearance, but there is not necessarily any evolutionary significance to these observed differences, so this form of classification has become less acceptable to evolutionary biologists. Likewise this typological approach to "race" is generally regarded as discredited by biologists and anthropologists.

Because of the difficulty in classifying subspecies morphologically, many biologists reject the concept altogether, citing problems such as:


 * Visible physical differences do not correlate with one another, leading to the possibility of different classifications for the same individual organisms.
 * Parallel evolution can lead to the existence of the appearance of similarities between groups of organisms that are not part of the same species.
 * The existence of isolated populations within previously designated subspecies.
 * That the criteria for classification are arbitrary.

Subspecies genetically differentiated populations
Another way to look at differences between populations is to measure genetic differences rather than physical differences, these should be less biased. Genetic differences between populations of organisms can be measured using the fixation index of Sewall Wright, which is often abbreviated to FST. This statistic is used to compare differences between any two given populations and can be used to measure genetic differences between populations for individual genes, or for many genes simultaneously. For example it is often stated that the fixation index for humans is about 0.15. This means that about 85% of the variation measured in the human population is within any population, and about 15% of the variation occurs between populations, or that any two individuals from different populations are almost as likely to be more similar to each other than either is to a member of their own group. It is often stated that human genetic variation is low compared to other mammalian species, and it has been claimed that this should be taken as evidence that there is no natural subdivision of the human population. Write himself believed that a value of 0.25 represented great genetic variation and that an FST of 0.15-0.25 represented moderate variation. It should however be noted that about 5% of human variation occurs between populations within continents, and therefor the FST between continental groups of humans (or races) is as low as 0.1 (or possibly lower).

In their 2003 paper "Human Genetic Diversity and the Nonexistence of Biological Races" Jeffrey Long and Rick Kittles give a long critique of the application of FST to human populations. They find that the figure of 85% is misleading because it implies that all human populations contain on average 85% of all genetic diversity. This does not correctly reflect human population history, they claim, because it treats all human groups as independent. A more realistic portrayal of the way human groups are related is to understand that some human groups are parental to other groups and that these groups represent paraphyletic groups to their descent groups. For example under the recent African origin theory the human population in Africa is paraphyletic to all other human groups because it represents the ancestral group from which all non-African populations derive, but more than that, non-African groups only derive from a small non-representative sample of this African population. This means that all non-African groups are more closely related to each other and to some African groups (probably east Africans) than they are to others, and further that the migration out of Africa represented a genetic bottleneck, with a great deal of the diversity that existed in Africa not being carried out of Africa by the emigrating groups. This view produces a version of human population movements that do not result in all human populations being independent, but rather produces a series of dilutions of diversity the further from Africa any population lives, each founding event representing a genetic subset of it's parental population. 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 70% of human genetic diversity exists in a population derived from New Guinea. Long and Kittles make the observation that this still produces a global human population that is genetically homogeneous compared to other mammalian populations.

Wright's F statistics are not used to determine whether a group can be described as a subspecies or not, though the statistic is used to measure the degree of differentiation between populations, the degree of genetic differentiation is not a marker of subspecies status. Generally taxonomists prefer to use phylogenetic analysis to determine whether a population can be considered a subspecies. Phylogenetic analysis relies on the concept of derived characteristics that are not shared between groups, this means that these populations are usually allopatric and therefore discretely bounded, this makes subspecies, evolutionarily speaking, monophyletic groups. The clinality of human genetic variation in general rules out any idea that human population groups can be considered monophyletic as there appears to always have been a great deal of gene flow between human populations.

Population genetics: population and cline
At the beginning of the 20th century, anthropologists questioned, and eventually abandoned, the claim that biologically distinct races are isomorphic with distinct linguistic, cultural, and social groups. Shortly thereafter, the rise of population genetics provided scientists with a new understanding of the sources of phenotypic variation. This new science has led many mainstream evolutionary scientists in anthropology and biology to question the very validity of race as a scientific concept describing an objectively real phenomenon. Those who came to reject the validity of the concept of race did so for four reasons: empirical, definitional, the availability of alternative concepts, and ethical (Lieberman and Byrne 1993).

The first to challenge the concept of race on empirical grounds were anthropologists Franz Boas, who demonstrated phenotypic plasticity due to environmental factors (Boas 1912), and Ashley Montagu (1941, 1942), who relied on evidence from genetics. Zoologists Edward O. Wilson and W. Brown then challenged the concept from the perspective of general animal systematics, and further rejected the claim that "races" were equivalent to "subspecies" (Wilson and Brown 1953).

Clines
One of the crucial innovations in reconceptualizing genotypic and phenotypic variation was anthropologist C. Loring Brace's observation that such variations, insofar as it is affected by natural selection, migration, or genetic drift, are distributed along geographic gradations or clines (Brace 1964). This point called attention to a problem common to phenotype-based descriptions of races (for example, those based on hair texture and skin color): they ignore a host of other similarities and differences (for example, blood type) that do not correlate highly with the markers for race. Thus, anthropologist Frank Livingstone's conclusion that, since clines cross racial boundaries, "there are no races, only clines" (Livingstone 1962: 279).

In a response to Livingston, Theodore Dobzhansky argued that when talking about "race" one must be attentive to how the term is being used: "I agree with Dr. Livingston that if races have to be 'discrete units,' then there are no races, and if 'race' is used as an 'explanation' of the human variability, rather than vice versa, then the explanation is invalid." He further argued that one could use the term race if one distinguished between "race differences" and "the race concept." The former refers to any distinction in gene frequencies between populations; the latter is "a matter of judgment." He further observed that even when there is clinal variation, "Race differences are objectively ascertainable biological phenomena .... but it does not follow that racially distinct populations must be given racial (or subspecific) labels." In short, Livingston and Dobzhansky agree that there are genetic differences among human beings; they also agree that the use of the race concept to classify people, and how the race concept is used, is a matter of social convention. They differ on whether the race concept remains a meaningful and useful social convention.

In 1964, biologists Paul Ehrlich and Holm pointed out cases where two or more clines are distributed discordantly&mdash;for example, melanin is distributed in a decreasing pattern from the equator north and south; frequencies for the haplotype for beta-S hemoglobin, on the other hand, radiate out of specific geographical points in Africa (Ehrlich and Holm 1964). As anthropologists Leonard Lieberman and Fatimah Linda Jackson observe, "Discordant patterns of heterogeneity falsify any description of a population as if it were genotypically or even phenotypically homogeneous" (Lieverman and Jackson 1995).

Patterns such as those seen in human physical and genetic variation as described above, have led to the consequence that the number and geographic location of any described races is highly dependent on the importance attributed to, and quantity of, the traits considered. For example if only skin colour and a "two race" system of classification were used, then one might classify Indigenous Australians in the same "race" as Black people, and Caucasians in the same "race" as East Asian people, but biologists and anthropologists would dispute that these classifications have any scientific validity. On the other hand the greater the number of traits (or alleles) considered, the more subdivisions of humanity are detected, due to the fact that traits and gene frequencies do not always correspond to the same geographical location, or as Ossario and Duster (2005) put it:

Populations
Population geneticists have debated as to whether the concept of population can provide a basis for a new conception of race. In order to do this a working definition of population must be found. Surprisingly there is no generally accepted concept of population that biologists use. It has been pointed out that the concept of population is central to ecology, evolutionary biology and conservation biology, but also that most definitions of population rely on qualitative descriptions such as "a group of organisms of the same species occupying a particular space at a particular time" Waples and Gaggiotti identify two broad types of definitions for populations, those that fall into an ecological paradigm and those that fall into an evolutionary paradigm. Examples such definitions are:
 * Ecological paradigm: A group of individuals of the same species that co-occur in space and time and have an opportunity to interact with each other.
 * Evolutionary paradigm: A group of individuals of the same species living in close enough proximity that any member of the group can potentially mate with any other member.

Richard Lewontin, claiming that 85 percent of human variation occurs within populations, and not among populations, argued that neither "race" nor "subspecies" were appropriate or useful ways to describe populations (Lewontin 1973). Nevertheless, barriers—which may be cultural or physical— between populations can limit gene flow and increase genetic differences. Recent work by population geneticists conducting research in Europe suggests that ethnic identity can be a barrier to gene flow. Others, such as Ernst Mayr, have argued for a notion of "geographic race". Some researchers report the variation between racial groups (measured by Sewall Wright's population structure statistic FST) accounts for as little as 5% of human genetic variation². Sewall Wright himself commented that if differences this large were seen in another species, they would be called subspecies. In 2003 A. W. F. Edwards argued that cluster analysis supersedes Lewontin's arguments (see below).

These empirical challenges to the concept of race forced evolutionary sciences to reconsider their definition of race. Mid-century, anthropologist William 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" (Boyd 1950).

Lieberman and Jackson (1994) have pointed out that "the 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." Moreover, anthropologist Stephen Molnar has suggested that the discordance of clines inevitably results in a multiplication of races that renders the concept itself useless (Molnar 1992).

The distribution of many physical traits resembles the distribution of genetic variation within and between human populations (American Association of Physical Anthropologists 1996; Keita and Kittles 1997). For example, ~90% of the variation in human head shapes occurs within every human group, and ~10% separates groups, with a greater variability of head shape among individuals with recent African ancestors (Relethford 2002).

Molecular genetics: lineages and clusters
With the recent availability of large amounts of human genetic data from many geographically distant human groups scientists have again started to investigate the relationships between people from various parts of the world. One method is to investigate DNA molecules that are passed down from mother to child (mtDNA) or from father to son (Y chromosomes), these form molecular lineages and can be informative regarding prehistoric population migrations. Alternatively autosomal alleles are investigated in an attempt to understand how much genetic material groups of people share. This work has led to a debate amongst geneticists, molecular anthropologists and medical doctors as to the validity of conceps such as "race". Some researchers insist that classifying people into groups based on ancestry may be important from medical and social policy points of view, and claim to be able to do so accurately. Others claim that individuals from different groups share far too much of their genetic material for group membership to have any medical implications. This has reignited the scientific debate over the validity of human classification and concepts of "race".

Molecular lineages, Y chromosomes and mitochondrial DNA
Mitochondria are intracellular organelles that contain DNA, this mitochondrial DNA (mtDNA) is passed in a direct female line of descent from mother to child. Human Y chromosomes are male specific sex chromosomes, any human that possesses a Y chromosome will be morphologically male. Y chromosomes are therefore passed from father to son. When a mutation arises in mtDNA or Y chromosome it is passed down a specific maternal or paternal line and because mutations accumulate on these molecules they can be used to identify specific molecular lineages. These mutations are derived from copying mistakes, when the DNA is copied it is possible that a single mistake occurs in the DNA sequence, these single mistakes are called single nucleotide polymorphisms (SNPs).



Mitochondrial DNA and Y chromosome research has produced three reproducible observations relevant to race and human evolution.

Firstly all mtDNA and Y chromosome lineages derive from a common ancestral molecule. For mtDNA this ancestor is estimated to have lived about 140,000-290,000 years ago (Mitochondrial Eve), while for Y chromosomes the ancestor is estimated to have lived about 70,000 years ago (Y chromosome Adam). These observations are robust, and the individuals that originally carried these ancestral molecules are the direct female and male line most recent common ancestors of all extant anatomically modern humans. The observation that these are the direct female line and male line ancestors of all living humans should not be interpreted as meaning that either was the first anatomically modern human. Nor should we assume that there were no other modern humans living concurrently with mitochondrial Eve or Y chromosome Adam. A more reasonable explanation is that other humans who lived at the same time did indeed reproduce and pass their genes down to extant humans, but that their mitochondrial and Y chromosomal lineages have been lost over time, probably due to random events (e.g. producing only male or female children). It is impossible to know to what extent these non-extant lineages have been lost, or how much they differed from the mtDNA or Y chromosome of our maternal and paternal lineage MRCA. The difference in dates between Y chromosome Adam and mitochondrial Eve is usually attributed to a higher extinction rate for Y chromosomes. This is probably because a few very successful men produce a great many children, while a larger number of less successful men will produce far fewer children.

Secondly mtDNA and Y chromosome work supports a recent African origin for anatomically modern humans, with the ancestors of all extant modern humans leaving Africa somewhere between 100,000 - 50,000 years ago.

Thirdly studies show that specific types (haplogroups) of mtDNA or Y chromosomes do not always cluster by geography, ethnicity or race, implying multiple lineages are involved in founding modern human populations, with many closely related lineages spread over large geographic areas, and many populations containing distantly related lineages. Keita et al. (2004) say, with reference to Y chromosome and mtDNA studies and their relevance to concepts of "race":

How much are genes shared? Clustering analyses and what they tell us
Human genetic variation is not distributed uniformly throughout the global population, the global range of human habitation means that there are great distance between some human populations (e.g. between South America and Southern Africa) and this will reduce gene flow between these populations. On the other hand environmental selection is also likely to play a role in differences between human populations. Conversely it is now believed that the majority of genetic differences between populations is selectively neutral. The existence of differences between peoples from different regions of the world is relevant to discussions about the concept of "race", some biologists believe that the language of "race" is relevant in describing human genetic variation. It is now possible to reasonably estimate the continents of origin of an individual's ancestors based on genetic data

Richard Lewontin has claimed that "race" is a meaningless classification because the majority of human variation is found within groups (~85%), and therefore two individuals from different "races" are almost as likely to be as similar to each other as either is to someone from their own "race". In 2003 A. W. F. Edwards rebuked this argument, claiming that Lewontin's conclusion ignores the fact that most of the information that distinguishes populations is hidden in the correlation structure of the data and not simply in the variation of the individual factors (see Infobox: Multi Locus Allele Clusters). Edwards concludes that "It is not true that 'racial classification is ... of virtually no genetic or taxonomic significance' or that 'you can't predict someone’s race by their genes'." Researchers such as Neil Risch and Noah Rosenberg have argued that a person's biological and cultural background may have important implications for medical treatment decisions, both for genetic and non-genetic reasons.

The results obtained by clustering analyses are dependent on several criteria:
 * The clusters produced are relative clusters and not absolute clusters, each cluster is the product of comparisons between sets of data derived for the study, results are therefore highly influenced by sampling strategies. (Edwards, 2003)
 * The geographic distribution of the populations sampled, because human genetic diversity is marked by isolation by distance, populations from geographically distant regions will form much more discrete clusters than those from geographically close regions. (Kittles and Weiss, 2003)
 * The number of genes used. The more genes used in a study the greater the resolution produced and therefore the greater number of clusters that will be identified. (Tang, 2005)

Rosenberg et al.'s (2002) paper "Genetic Structure of Human Populations." especially was taken up by Nicholas Wade in the New York Times as evidence that genetics studies supported the "popular conception" of race. On the other hand Rosenberg's work used samples from the Human Genome Diversity Project (HGDP), a project that has collected samples from individuals from 52 ethnic groups from various locations around the world. The HGDP has itself been criticised for collecting samples on an "ethnic group" basis, on the grounds that ethnic groups represent constructed categories rather than categories which are solely natural or biological. Scientists such as the molecular anthropologist Jonathan Marks, the geneticists David Serre, Svante Pääbo, Mary-Claire King and medical doctor Arno G. Motulsky argue that this is a biased sampling strategy, and that human samples should have been collected geographically, i.e. that samples should be collected from points on a grid overlaying a map of the world, and maintain that human genetic variation is not partitioned into discrete racial groups (clustered), but is spread in a clinal manner (isolation by distance) that is masked by this biased sampling strategy. The existence of allelic clines and the observation that the bulk of human variation is continuously distributed, has led scientists such as Kittles and Weiss (2003) to conclude that any categorization schema attempting to partition that variation meaningfully will necessarily create artificial truncations. It is for this reason, Reanne Frank argues, that attempts to allocate individuals into ancestry groupings based on genetic information have yielded varying results that are highly dependent on methodological design.

In a follow up paper "Clines, Clusters, and the Effect of Study Design on the Inference of Human Population Structure" in 2005, Rosenberg et al. maintain that their clustering analysis is robust. But they also agree that there is evidence for clinality (isolation by distance). Thirdly they distance themselves from the language of race, and do not use the term "race" in any of their publications: "The arguments about the existence or nonexistence of 'biological races' in the absence of a specific context are largely orthogonal to the question of scientific utility, and they should not obscure the fact that, ultimately, the primary goals for studies of genetic variation in humans are to make inferences about human evolutionary history, human biology, and the genetic causes of disease."

One of the underlying questions regarding the distribution of human genetic diversity is related to the degree to which genes are shared between the observed clusters, and therefore the extent that membership of a cluster can accurately predict an individuals genetic makeup or susceptibility to disease. This is at the core of Lewontin's argument. Lewontin used Sewall Wright's Fixation index (FST), to estimate that on average 85% of human genetic diversity is contained within groups. Are members of the same cluster always more genetically similar to each other than they are to members of a different cluster? Lewontin's argument is that within group differences are almost as high as between group differences, and therefore two individuals from different groups are almost as likely to be more similar to each other than they are to members of their own group. Can clusters correct for this finding? In 2004 Bamshad et al. used the data from Rosenberg et al. (2002) to investigate the extent of genetic differences between individuals within continental groups relative to genetic differences between individuals between continental groups. They found that though these individuals could be classified very accurately to continental clusters, there was a significant degree of genetic overlap on the individual level.

This question was addressed in more detail in a 2007 paper by Witherspoon et al. entitled "Genetic Similarities Within and Between Human Populations". Where they make the following observations:


 * Genetic differences between human continental populations account for only a small fraction of the differences between people.
 * Multilocus clusters provide accurate and reproducible results for dividing people into the correct populations.
 * Two individuals from different populations are often more genetically alike to each other than they are to individuals from their own population.

The paper states that "All three of the claims listed above appear in disputes over the significance of human population variation and 'race'" and asks "If multilocus statistics are so powerful, then how are we to understand this [last] finding?"

Witherspoon et al. (2007) attempt to reconcile these apparently contradictory findings, and show that the observed clustering of human populations into relatively discrete groups is a product of using what they call "population trait values". This means that each individual is compared to the "typical" trait for several populations, and assigned to a population based on the individual's overall similarity to one of the populations as a whole. They therefore claim that clustering analyses cannot necessarily be used to make inferences regarding the similarity or dissimilarity of individuals between or within clusters, but only for similarities or dissimilarities of individuals to the "trait values" of any given cluster. The paper measures the rate of misclassification using these "trait values" and calls this the "population trait value misclassiﬁcation rate" (CT). The paper investigates the similarities between individuals by use of what they term the "dissimilarity fraction" (ω): "the probability that a pair of individuals randomly chosen from different populations is genetically more similar than an independent pair chosen from any single population." Witherspoon et al. show that two individuals can be more genetically similar to each other than to the typical genetic type of their own respective populations, and yet be correctly assigned to their respective populations. An important observation is that the likelihood that two individuals from different populations will be more similar to each other genetically than two individuals from the same population depends on several criteria, most importantly the number of genes studied and the distinctiveness of the populations under investigation. For example when 10 loci are used to compare three geographically disparate populations (sub-Saharan African, East Asian and European) then individuals are more similar to members of a different group about 30% of the time. If the number of loci is increased to 100 individuals are more genetically similar to members of a different population ~20% of the time, and even using 1000 loci, ω ~ 10%. They do stated that for these very geographically separated populations it is possible to reduce this statistic to 0% when tens of thousands of loci are used. That means that individuals will always be more similar to members of their own population. But the paper notes that humans are not distributed inot geographically separated populations, omitting intermediate regions may produce a false distinctiveness for human diversity. The paper supports the observation that "highly accurate classification of individuals from continuously sampled (and therefore closely related) populations may be impossible". Furthermore the results indicate that clustering analyses and self reported ethnicity may not be good estimates for genetic susceptibility to disease risk. Witherspoon et al. conclude that:

Current views across disciplines
One result of debates over the meaning and validity of the concept "race" is that the current literature across different disciplines regarding human variation lacks consensus, though within some fields, such as biology, there is strong consensus. Some studies use the word race in its early essentialist taxonomic sense. Many others still use the term race, but use it to mean a population, clade, or haplogroup. Others eschew the concept of race altogether, and use the concept of population as a less problematical unit of analysis.

Since 1932, some college textbooks introducing physical anthropology have increasingly come to reject race as a valid concept: from 1932 to 1976, only seven out of thirty-two rejected race; from 1975 to 1984, thirteen out of thirty-three rejected race; from 1985 to 1993, thirteen out of nineteen rejected race. According to one academic journal entry, where 78 percent of the articles in the 1931 Journal of Physical Anthropology employed these or nearly synonymous terms reflecting a bio-race paradigm, only 36 percent did so in 1965, and just 28 percent did in 1996. The American Anthropological Association, drawing on biological research, currently holds that "The concept of race is a social and cultural construction... . Race simply cannot be tested or proven scientifically," and that, "It is clear that human populations are not unambiguous, clearly demarcated, biologically distinct groups. The concept of 'race' has no validity ... in the human species".

In an ongoing debate, some geneticists argue that race is neither a meaningful concept nor a useful heuristic device, and even that genetic differences among groups are biologically meaningless, on the grounds that more genetic variation exists within such races than among them, and that racial traits overlap without discrete boundaries. Other geneticists, in contrast, argue that categories of self-identified race/ethnicity or biogeographic ancestry are both valid and useful, that these categories correspond with clusters inferred from multilocus genetic data, and that this correspondence implies that genetic factors might contribute to unexplained phenotypic variation between groups.

In February, 2001, the editors of the medical journal Archives of Pediatrics and Adolescent Medicine asked authors to no longer use "race" as an explanatory variable and not to use obsolescent terms. Some other peer-reviewed journals, such as the New England Journal of Medicine and the American Journal of Public Health, have made similar endeavours. Furthermore, the National Institutes of Health recently issued a program announcement for grant applications through February 1, 2006, specifically seeking researchers who can investigate and publicize among primary care physicians the detrimental effects on the nation's health of the practice of medical racial profiling using such terms. The program announcement quoted the editors of one journal as saying that, "analysis by race and ethnicity has become an analytical knee-jerk reflex."

A survey, taken in 1985 (Lieberman et al. 1992), asked 1,200 American anthropologists how many disagree with the following proposition: "There are biological races in the species Homo sapiens." The responses were: The figure for physical anthropologists at PhD granting departments was slightly higher, rising from 41% to 42%, with 50% agreeing. This survey, however, did not specify any particular definition of race (although it did clearly specify biological race within the species Homo Sapiens); it is difficult to say whether those who supported the statement thought of race in taxonomic or population terms.
 * physical anthropologists 41%
 * cultural anthropologists 53%

The same survey, taken in 1999, showed the following changing results for anthropologists:
 * physical anthropologists 69%
 * cultural anthropologists 80%

In Poland the race concept was rejected by only 25 percent of anthropologists in 2001, although: "Unlike the U.S. anthropologists, Polish anthropologists tend to regard race as a term without taxonomic value, often as a substitute for population."

In the face of these issues, some evolutionary scientists have simply abandoned the concept of race in favor of "population." What distinguishes population from previous groupings of humans by race is that it refers to a breeding population (essential to genetic calculations) and not to a biological taxon. Other evolutionary scientists have abandoned the concept of race in favor of cline (meaning, how the frequency of a trait changes along a geographic gradient). (The concepts of population and cline are not, however, mutually exclusive and both are used by many evolutionary scientists.)

According to Jonathan Marks,
 * By the 1970s, it had become clear that (1)most human differences were cultural; (2) what was not cultural was principally polymorphic - that is to say, found in diverse groups of people at different frequencies; (3) what was not cultural or polymorphic was principally clinal - that is to say, gradually variable over geography; and (4) what was left - the component of human diversity that was not cultural, polymorphic, or clinal - was very small.


 * A consensus consequently developed among anthropologists and geneticists that race as the previous generation had known it - as largely discrete, geographically distinct, gene pools - did not exist.

In the face of this rejection of race by evolutionary scientists, many social scientists have replaced the word race with the word "ethnicity" to refer to self-identifying groups based on beliefs concerning shared culture, ancestry and history. Alongside empirical and conceptual problems with "race," following the Second World War, evolutionary and social scientists were acutely aware of how beliefs about race had been used to justify discrimination, apartheid, slavery, and genocide. This questioning gained momentum in the 1960s during the U.S. civil rights movement and the emergence of numerous anti-colonial movements worldwide. They thus came to understood that these justifications, even when expressed in language that sought to appear objective, were social constructs.

Races as social constructions
Even as the idea of "race" was becoming a powerful organizing principle in many societies, the shortcomings of the concept were apparent. In the Old World, the gradual transition in appearances from one group to adjacent groups emphasized that "one variety of mankind does so sensibly pass into the other, that you cannot mark out the limits between them," as Blumenbach observed in his writings on human variation (Marks 1995, p. 54). As anthropologists and other evolutionary scientists have shifted away from the language of race to the term population to talk about genetic differences, Historians, anthropologists and social scientists have re-conceptualized the term "race" as a cultural category or social construct, in other words, as a particular way that some people have of talking about themselves and others. As Stephan Palmie has recently summarized, race "is not a thing but a social relation"; or, in the words of Katya Gibel Mevorach, "a metonym," "a human invention whose criteria for differentiation are neither universal nor fixed but have always been used to manage difference." As such it cannot be a useful analytical concept; rather, the use of the term "race" itself must be analyzed. Moreover, they argue that biology will not explain why or how people use the idea of race: history and social relationships will. For example, the fact that in many parts of the United States, categories such as Hispanic or Latino are viewed to constitute a race (instead of an ethnic group) reflect this new idea of "race as a social construct". However, it may be in the interest of dominant groups to cluster Spanish speakers into a single, isolated population, rather than classifying them according to Race (as are the rest of U.S. racial groups). Especially in the context of the debate over immigration. "According to the 2000 census, two-thirds [of Hispanics] are of Mexican heritage . . . So, for practical purposes, when we speak of Hispanics and Latinos in the U.S., we’re really talking about Native Americans . . . [therefore] if being Hispanic carries any societal consequences that justify inclusion in the pantheon of great American racial minorities, they’re the result of having Native American blood. [But imagine the] the impact this would have on the illegal-immigration debate. It’s one thing to blame the fall of western civilization on illegal Mexican immigration, but quite thornier to blame it on illegal Amerindian immigration from Mexico."

In the United States

 * see also Admixture in the United States

The immigrants to the New World came largely from widely separated regions of the Old World—western and northern Europe, West Africa, and, later, eastern Asia and southern Europe. In the Americas, the immigrant populations began to mix among themselves and with the indigenous inhabitants of the continent. In the United States, for example, most people who self-identify as African American have some European ancestors — in one analysis of genetic markers that have differing frequencies between continents, European ancestry ranged from an estimated 7% for a sample of Jamaicans to ∼23% for a sample of African Americans from New Orleans (Parra et al. 1998). Similarly, many people who identify as European American have some African or Native American ancestors, either through openly interracial marriages or through the gradual inclusion of people with mixed ancestry into the majority population. In a survey of college students who self-identified as white in a northeastern U.S. university, ∼30% were estimated to have less than 90% European ancestry.

In the United States since its early history, Native Americans, African-Americans and European-Americans were classified as belonging to different races. For nearly three centuries, the criteria for membership in these groups were similar, comprising a person’s appearance, his fraction of known non-White ancestry, and his social circle.2 But the criteria for membership in these races diverged in the late 19th century. During Reconstruction, increasing numbers of Americans began to consider anyone with "one drop" of known "Black blood" to be Black regardless of appearance.3 By the early 20th century, this notion of invisible blackness was made statutory in many states and widely adopted nationwide.4 In contrast, Amerindians continue to be defined by a certain percentage of "Indian blood" (called blood quantum) due in large part to American slavery ethics. Finally, for the past century or so, to be White one had to have perceived "pure" White ancestry.

Efforts to sort the increasingly mixed population of the United States into discrete categories generated many difficulties (Spickard 1992). By the standards used in past censuses, many millions of children born in the United States have belonged to a different race than have one of their biological parents. Efforts to track mixing between groups led to a proliferation of categories (such as "mulatto" and "octoroon") and "blood quantum" distinctions that became increasingly untethered from self-reported ancestry. A person's racial identity can change over time, and self-ascribed race can differ from assigned race (Kressin et al. 2003). Until the 2000 census, Latinos were required to identify with a single race despite the long history of mixing in Latin America; partly as a result of the confusion generated by the distinction, 32.9% (U.S. census records) of Latino respondents in the 2000 census ignored the specified racial categories and checked "some other race". (Mays et al. 2003 claim a figure of 42%)

The difference between how Native American and Black identities are defined today (blood quantum versus one-drop) has demanded explanation. According to anthropologists such as Gerald Sider, the goal of such racial designations was to concentrate power, wealth, privilege and land in the hands of Whites in a society of White hegemony and privilege (Sider 1996; see also Fields 1990). The differences have little to do with biology and far more to do with the history of racism and specific forms of White supremacy (the social, geopolitical and economic agendas of dominant Whites vis-à-vis subordinate Blacks and Native Americans) especially the different roles Blacks and Amerindians occupied in White-dominated 19th century America. The theory suggests that the blood quantum definition of Native American identity enabled Whites to acquire Amerindian lands, while the one-drop rule of Black identity enabled Whites to preserve their agricultural labor force. The contrast presumably emerged because as peoples transported far from their land and kinship ties on another continent, Black labor was relatively easy to control, thus reducing Blacks to valuable commodities as agricultural laborers. In contrast, Amerindian labor was more difficult to control; moreover, Amerindians occupied large territories that became valuable as agricultural lands, especially with the invention of new technologies such as railroads; thus, the blood quantum definition enhanced White acquisition of Amerindian lands in a doctrine of Manifest Destiny that subjected them to marginalization and multiple episodic localized campaigns of extermination.

The political economy of race had different consequences for the descendants of aboriginal Americans and African slaves. The 19th century blood quantum rule meant that it was relatively easier for a person of mixed Euro-Amerindian ancestry to be accepted as White. The offspring of only a few generations of intermarriage between Amerindians and Whites likely would not have been considered Amerindian at all (at least not in a legal sense). Amerindians could have treaty rights to land, but because an individual with one Amerindian great-grandparent no longer was classified as Amerindian, they lost any legal claim to Amerindian land. According to the theory, this enabled Whites to acquire Amerindian lands. The irony is that the same individuals who could be denied legal standing because they were "too White" to claim property rights, might still be Amerindian enough to be considered as "breeds", stigmatized for their Native American ancestry.

The 20th century one-drop rule, on the other hand, made it relatively difficult for anyone of known Black ancestry to be accepted as White. The child of a Black sharecropper and a White person was considered Black. And, significant in terms of the economics of sharecropping, such a person also would likely be a sharecropper as well, thus adding to the employer's labor force.

In short, this theory suggests that in a 20th century economy that benefited from sharecropping, it was useful to have as many Blacks as possible. Conversely, in a 19th century nation bent on westward expansion, it was advantageous to diminish the numbers of those who could claim title to Amerindian lands by simply defining them out of existence.

It must be mentioned, however, that although some scholars of the Jim Crow period agree that the 20th century notion of invisible Blackness shifted the color line in the direction of paleness, thereby swelling the labor force in response to Southern Blacks' great migration northwards, others (Joel Williamson, C. Vann Woodward, George M. Fredrickson, Stetson Kennedy) see the one-drop rule as a simple consequence of the need to define Whiteness as being pure, thus justifying White-on-Black oppression. In any event, over the centuries when Whites wielded power over both Blacks and Amerindians and widely believed in their inherent superiority over people of color, it is no coincidence that the hardest racial group in which to prove membership was the White one.

In the United States, social and legal conventions developed over time that forced individuals of mixed ancestry into simplified racial categories (Gossett 1997). An example is the "one-drop rule" implemented in some state laws that treated anyone with a single known African American ancestor as black (Davis 2001). The decennial censuses conducted since 1790 in the United States also created an incentive to establish racial categories and fit people into those categories (Nobles 2000). In other countries in the Americas where mixing among groups was overtly more extensive, social categories have tended to be more numerous and fluid, with people moving into or out of categories on the basis of a combination of socioeconomic status, social class, ancestry, and appearance (Mörner 1967).

The term "Hispanic" as an ethnonym emerged in the 20th century with the rise of migration of laborers from American Spanish-speaking countries to the United States. It includes people who had been considered racially distinct (Black, White, Amerindian, Asian, and mixed groups) in their home countries. Today, the word "Latino" is often used as a synonym for "Hispanic". In contrast to "Latino"´or "Hispanic" "Anglo" is now used to refer to non-Hispanic White Americans or non-Hispanic European Americans, most of whom speak the English language but are not necessarily of English descent.

In Brazil
Compared to 19th century United States, 20th century Brazil was characterized by a perceived relative absence of sharply defined racial groups. According to anthropologist Marvin Harris (1989), this pattern reflects a different history and different social relations. Basically, race in Brazil was "biologized," but in a way that recognized the difference between ancestry (which determines genotype) and phenotypic differences. There, racial identity was not governed by such a rigid descent rule as in the United States. A Brazilian child was never automatically identified with the racial type of one or both parents, nor were there only a very limited number of categories to choose from. Over a dozen racial categories would be recognized in conformity with all the possible combinations of hair color, hair texture, eye color, and skin color. These types grade into each other like the colors of the spectrum, and no one category stands significantly isolated from the rest. That is, race referred preferencially to appearance, not heredity. The complexity of racial classifications in Brazil is reflective of the extent of miscegenation in Brazilian society, a society that remains highly, but not strictly, stratified along color lines. Henceforth, the Brazilian narrative of a perfect "post-racist" country, must be met with caution, as sociologist Gilberto Freyre demonstrated in 1933 in Casa Grande e Senzala.

Marketing of race: genetic lineages as social lineages
New research in molecular genetics, and the marketing of genetic identities through the analysis of one's Y chromosome, mtDNA or autosomal DNA, 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. Although the vast majority of researchers endorse the view that continental groups do not constitute different subspecies, and molecular geneticists generally reject the identification of mtDNA and Y chromosomal lineages or allele clusters with "races", some anthropologists have suggested that the marketing of genetic analysis to the general public in the form of "Personalized Genetic Histories" (PGH) is leading to a new social construction of race. See above sections Molecular lineages, Y chromosomes and mitochondrial DNA and How much are genes shared? Clustering analyses and what they tell us.

Typically, a consumer of a commercial PGH service sends in a sample of DNA which is analyzed by molecular biologists and is sent a report, of which the following is a sample
 * "African DNA Ancestry Report"

Although no single sentence in such a report is technically wrong, through the combination of these sentences, anthropologists and others have argued, the report is telling a story that connects a haplotype with a language and a group of tribes. This story is generally rejected by research scientists for the simple reason that an individual receives his or her Y chromosome or mtDNA from only one ancestor in every generation; consequently, with every generation one goes back in time, the percentage of ones ancestors it represents halves; if one goes back hundreds (let alone thousands) of years, it represents only a tiny fragment of one's ancestry. As Mark Shriver and Rick Kittles recently remarked,

Nevertheless, they acknowledge, such stories are increasingly appealing to the general public. Thus, in his book Blood of the Isles (published in the US and Canada as Saxons, Vikings and Celts: The Genetic Roots of Britain and Ireland), however, Bryan Sykes discusses how people who have been mtDNA tested by his commercial laboratory and been found to belong to the same haplogroup have parties together because they see this as some sort of "bond", even though these people may not actually share very much ancestry.

Through these kinds of reports, new advances in molecular genetics are being used to create or confirm stories have about social identities. Although these identities are not racial in the biological sense, they are in the cultural sense in that they link biological and cultural identities. Nadia Abu el-Haj has argued that the significance of genetic lineages in popular conceptions of race owes to the perception that while genetic lineages, like older notions of race, suggests some idea of biological relatedness, unlike older notions of race they are not directly connected to claims about human behaviour or character. Abu el-Haj has thus argued that "postgenomics does seem to be giving race a new lease on life." Nevertheless, Abu el-Haj argues that in order to understand what it means to think of race in terms of genetic lineages or clusters, one must understand that

Abu el-Haj argues that genomics and the mapping of lineages and clusters liberates "the new racial science from the older one by disentangling ancestry from culture and capacity." As an example, she refers to recent work by Hammer et al., which aimed to test the claim that present-day Jews are more closely related to one another than to neighbouring non-Jewish populations. Hammer ''et. al'' found that the degree of genetic similarity among Jews shifted depending on the locus investigated, and suggested that this was the result of natural selection acting on particular loci. They therefore focused on the non-recombining Y chromosome to "circumvent some of the complications associated with selection". As another example she points to work by Thomas et al., who sought to distinguish between the Y chromosomes of Jewish priests (in Judaism, membership in the priesthood is passed on through the father's line) and the Y chromosomes of non-Jews. Abu el-Haj concluded that this new "race science" calls attention to the importance of "ancestry" (narrowly defined, as it does not include all ancestors) in some religions and in popular culture, and peoples' desire to use science to confirm their claims about ancestry; this "race science," she argues is fundamentally different from older notions of race that were used to explain differences in human behaviour or social status:

On the other hand, there are tests that do not rely on molecular lineages, but rather on correlations between allele frequencies, often when allele frequencies correlate these are called clusters. Clustering analyses are less powerful than lineages because they cannot tell an historical story, they can only estimate the proportion of a person's ancestry from any given large geographical region. These sorts of tests use informative alleles called Ancestry-informative marker (AIM), which although shared across all human populations vary a great deal in frequency between groups of people living in geographically distant parts of the world. These tests use contemporary people sampled from certain parts of the world as references to determine the likely proportion of ancestry for any given individual. In a recent Public Service Broadcasting (PBS) programme on the subject of genetic ancestry testing the academic Henry Louis Gates: "wasn’t thrilled with the results (it turns out that 50 percent of his ancestors are likely European)". Charles Rotimi, of Howard University's National Human Genome Center, is one of many who have highlighted the methodological flaws in such research - that "the nature or appearance of genetic clustering (grouping) of people is a function of how populations are sampled, of how criteria for boundaries between clusters are set, and of the level of resolution used" all bias the results - and concluded that people should be very cautious about relating genetic lineages or clusters to their own sense of identity. (see also above section How much are genes shared? Clustering analyses and what they tell us)

Thus, in analyses that assign individuals to groups 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. 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, in a survey of college students who self-identified as “white” in a northeastern U.S. university, ~30% of whites had less than 90% European ancestry.

Stephan Palmie has responded to Abu el-Haj's claim that genetic lineages make possible a new, politically, economically, and socially benign notion of race and racial difference by suggesting that efforts to link genetic history and personal identity will inevitably "ground present social arrangements in a time-hallowed past," that is, use biology to explain cultural differences and social inequalities.

Race and intelligence
Researchers have reported differences in the average IQ test scores of various ethnic groups. The interpretation, causes, accuracy and reliability of these differences are highly controversial. Some researchers, such as Arthur Jensen, Richard Herrnstein, and Richard Lynn have argued that such differences are at least partially genetic. Others, for example Thomas Sowell, argue that the differences largely owe to social and economic inequalities. Still others have such as Stephen Jay Gould and Richard Lewontin have argued that categories such as "race" and "intelligence" are cultural constructs that render any attempt to explain such differences (whether genetically or sociologically) meaningless.

The Flynn effect is the rise of average Intelligence Quotient (IQ) test scores, an effect seen in most parts of the world, although at varying rates. Scholars therefore believe that rapid increases in average IQ seen in many places are much too fast to be as a result of changes in brain physiology and more likely as a result of environmental changes. The fact that environment has a significant effect on IQ demolishes the case for the use of IQ data as a source of genetic information.

In biomedicine
There is an active debate among biomedical researchers about the meaning and importance of race in their research. The primary impetus for considering race in biomedical research is the possibility of improving the prevention and treatment of diseases by predicting hard-to-ascertain factors on the basis of more easily ascertained characteristics. Some have argued that in the absence of cheap and widespread genetic tests, racial identification is the best way to predict for certain diseases, such as Cystic fibrosis, Lactose intolerance, Tay-Sachs Disease and sickle cell anemia, which are genetically linked and more prevalent in some populations than others. The most well-known examples of genetically-determined disorders that vary in incidence among populations would be sickle cell disease, thalassaemia, and Tay-Sachs disease.

There has been criticism of associating disorders with race. For example, in the United States sickle cell is typically associated with black people, but this trait is also found in people of Mediterranean, Middle Eastern or Indian ancestry. The sickle cell trait offers some resistance to malaria. In regions where malaria is present sickle cell has been positively selected and consequently the proportion of people with it is greater. Therefore, it has been argued that sickle cell should not be associated with a particular race, but rather with having ancestors who lived in a malaria-prone region. Africans living in areas where there is no malaria, such as the East African highlands, have prevalence of sickle cell as low as parts of Northern Europe.

Another example of the use of race in medicine is the recent U.S. FDA approval of BiDil, a medication for congestive heart failure targeted at black people in the United States. Several researchers have questioned the scientific basis for arguing the merits of a medication based on race, however. As Stephan Palmie has recently pointed out, black Americans were disproportionately affected by Hurricane Katrina, but for social and not climatological reasons; similarly, certain diseases may disproportionately affect different races, but not for biological reasons. Several researchers have suggested that BiDil was re-designated as a medicine for a race-specific illness because its manufacturer, Nitromed, needed to propose a new use for an existing medication in order to justify an extension of its patent and thus monopoly on the medication, not for pharmacological reasons.

Gene flow and intermixture also have an effect on predicting a relationship between race and "race linked disorders". Multiple sclerosis is typically associated with people of European descent and is of low risk to people of African descent. However, due to gene flow between the populations, African Americans have elevated levels of MS relative to Africans. Notable African Americans affected by MS include Richard Pryor and Montel Williams. As populations continue to mix, the role of socially constructed races may diminish in identifying diseases.

In law enforcement
In an attempt to provide general descriptions that may facilitate the job of law enforcement officers seeking to apprehend suspects, the United States FBI employs the term "race" to summarize the general appearance (skin color, hair texture, eye shape, and other such easily noticed characteristics) of individuals whom they are attempting to apprehend. From the perspective of law enforcement officers, it is generally more important to arrive at a description that will readily suggest the general appearance of an individual than to make a scientifically valid categorization by DNA or other such means. Thus in addition to assigning a wanted individual to a racial category, such a description will include: height, weight, eye color, scars and other distinguishing characteristics, etc. Scotland Yard use a classification based in the ethnic background of British society: W1 (White-British), W2 (White-Irish), W9 (Any other white background); M1 (White and black Caribbean), M2 (White and black African), M3 (White and Asian), M9 (Any other mixed background); A1 (Asian-Indian), A2 (Asian-Pakistani), A3 (Asian-Bangladeshi), A9 (Any other Asian background); B1 (Black Caribbean), B2 (Black African), B3 (Any other black background); O1 (Chinese), O9 (Any other). Some of the characteristics that constitute these groupings are biological and some are learned (cultural, linguistic, etc.) traits that are easy to notice.

In many countries, such as France, the state is legally banned from maintaining data based on race, which often makes the police issue wanted notices to the public that include labels like "dark skin complexion", etc. One of the factors that encourages this kind of circuitous wordings is that there is controversy over the actual relationship between crimes, their assigned punishments, and the division of people into the so called "races," leading officials to try to deemphasize the alleged race of suspects. In the United States, the practice of racial profiling has been ruled to be both unconstitutional and also to constitute a violation of civil rights. There is active debate regarding the cause of a marked correlation between the recorded crimes, punishments meted out, and the country's "racially divided" people. Many consider de facto racial profiling an example of institutional racism in law enforcement. The history of misuse of racial categories to adversely impact one or more groups and/or to offer protection and advantage to another has a clear impact on debate of the legitimate use of known phenotypical or genotypical characteristics tied to the presumed race of both victims and perpetrators by the government.

More recent work in racial taxonomy based on DNA cluster analysis (see Lewontin's Fallacy) has led law enforcement to narrow their search for individuals based on a range of phenotypical characteristics found consistent with DNA evidence.

While controversial, DNA analysis has been successful in helping police identify both victims and perpetrators by giving an indication of what phenotypical characteristics to look for and what community the individual may have lived in. For example, in one case phenotypical characteristics suggested that the friends and family of an unidentified victim would be found among the Asian community, but the DNA evidence directed official attention to missing Native Americans, where her true identity was eventually confirmed. In an attempt to avoid potentially misleading associations suggested by the word "race," this classification is called "biogeographical ancestry" (BGA), but the terms for the BGA categories are similar to those used as for race. The difference is that ancestry-informative DNA markers identify continent-of-ancestry admixture, not ethnic self-identity, and provide a wide range of phenotypical characteristics such that some people in a biogeographical category will not match the stereotypical image of an individual belonging to the corresponding race. To facilitate the work of officials trying to find individuals based on the evidence of their DNA traces, firms providing the genetic analyses also provide photographs showing a full range of phenotypical characteristics of people in each biogeographical group. Of special interest to officials trying to find individuals on the basis of DNA samples that indicate a diverse genetic background is what range of phenotypical characteristics people with that general mixture of genotypical characteristics may display.

Similarly, forensic anthropologists draw on highly heritable morphological features of human remains (e.g. cranial measurements) in order to aid in the identification of the body, including in terms of race. In a recent article anthropologist Norman Sauer asked, "if races don't exist, why are forensic anthropologists so good at identifying them." Sauer observed that the use of 19th century racial categories is widespread among forensic anthropologists:


 * "In many cases there is little doubt that an individual belonged to the Negro, Caucasian, or Mongoloid racial stock."
 * "Thus the forensic anthropologist uses the term race in the very broad sense to differentiate what are commonly known as white, black and yellow racial stocks."
 * "In estimating race forensically, we prefer to determine if the skeleton is Negroid, or Non-Negroid. If findings favor Non-Negroid, then further study is necessary to rule out Mongoloid."

According to Sauer, "The assessment of these categories is based upon copious amounts of research on the relationship between biological characteristics of the living and their skeletons." Nevertheless, he agrees with other anthropologists that race is not a valid biological taxonomic category, and that races are socially constructed. He argued there is nevertheless a strong relationship between the phenotypic features forensic anthropologists base their identifications on, and popular racial categories. Thus, he argued, forensic anthropologists apply a racial label to human remains because their analysis of physical morphology enables them to predict that when the person was alive, that particular racial label would have been applied to them.

Official statements and standards

 * American Anthropological Association's Statement on Race and RACE: Are we so different?a public education program developed by the American Anthropological Association.
 * American Association of Physical Anthropologists' Statement on Biological Aspects of Race
 * OMB Statistical Directive 15, "Standards for Maintaining, Collecting, and Presenting Federal Data on Race and Ethnicity", Federal Register, 30 October 1997.
 * "The Race Question", UNESCO, 1950
 * US Census Bureau: Definition of Race

Popular press

 * Richard Dawkins: Race and creation (extract from The Ancestor's Tale: A Pilgrimage to the Dawn of Life) - On race, its usage and a theory of how it evolved. (Prospect Magazine October 2004)
 * The Myth of Race On the lack of scientific basis for the concept of human races (Medicine Magazine, 2007).
 * Race - The power of an illusion Online companion to California Newsreel's 3-part documentary about race in society, science, and history.
 * Is Race "Real"? - forum organized by the Social Science Research Council, includes a March 2005 op-ed article by A.M. Leroi from the New York Times advocating biological conceptions of race and responses from scholars in a variety of fields. - More from Leori with responses
 * Steven and Hilary Rose, The Guardian, "Why we should give up on race", 9 April 2005
 * Times Online, "Gene tests prove that we are all the same under the skin", 27 October 2004.
 * Michael J. Bamshad, Steve E. Olson "Does Race Exist?", Scientific American, December 2003
 * "Gene Study Identifies 5 Main Human Populations, Linking Them to Geography", Nicholas Wade, NYTimes, December 2002. Covering
 * Scientific American Magazine (December 2003 Issue) Does race exists ?.
 * DNA Study published by United Press International showing how 30% of White Americans have at least one Black ancestor
 * Yehudi O. Webster Twenty-one Arguments for Abolishing Racial Classification, The Abolitionist Examiner, June 2000
 * The Tex(t)-Mex Galleryblog, An updated, online supplement to the University of Texas Press book (2007), Tex(t)-Mex
 * Times of India - Article about Asian racism
 * South China Morning Post - Going beyond ‘sorry’

Others

 * James, Michael (2008) Race, in the Stanford Encyclopedia of Philosophy.
 * Ten Things Everyone Should Know About Race by California Newsreel.
 * American Anthropological Association's educational website on race, geared for general public with links for primary school educators and researchers
 * Boas's remarks on race to a general audience
 * Catchpenny mysteries of ancient Egypt, "What race were the ancient Egyptians?", Larry Orcutt.
 * Judy Skatssoon, "New twist on out-of-Africa theory", ABC Science Online, Wednesday, 14 July 2004.
 * Racial & Ethnic Distribution of ABO Blood Types - bloodbook.com
 * Are White Athletes an Endangered Species? And Why is it Taboo to Talk About It? Discussion of racial differences in athletics
 * "Does Race Exist? A proponent's perspective" - The author argues that the evidence from forensic anthropology supports the idea of race.
 * "Does Race Exist? An antagonist's perspective" - The author argues that clinal variation undermines the idea of race.
 * "American Ethnography -- The concept of race" Ashley Montagu's article in American Anthropology from 1962.
 * "American Ethnography -- The genetical theory of race, and anthropological method" Ashley Montagu's article in American Anthropology from 1942.