In the United States, social and legal conventions developed over time that forced individuals of mixed ancestry into simplified racial categories. An example is the "one-drop rule" implemented in some state laws that treated anyone with a single known African American ancestor as black. The decennial censuses conducted since 1790 in the United States also created an incentive to establish racial categories and fit people into those categories. In other countries in the Americas where mixing among groups was 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).
Efforts to sort the increasingly mixed population of the United States into discrete categories generated many difficulties.. 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. 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, 42% of Latino respondents in the 2000 census ignored the specified racial categories and checked "some other race.
Historians, anthropologists and social scientists often describe human races as a social construct, preferring instead the term population, which can be given a clear operational definition. Even those who reject the formal concept of race, however, still use the word race in day-to-day speech. This may either be a matter of semantics, or an effect of an underlying cultural significance of race in racist societies. Regardless of the name, a working concept of sub-species grouping can be useful, because in the absence of cheap and widespread genetic tests, various race-linked gene mutations (see Cystic fibrosis, Lactose intolerance, Tay-Sachs Disease and Sickle cell anemia) are difficult to address without recourse to a category between "individual" and "species". As genetic tests for such conditions become cheaper, and as detailed haplotype maps and SNP databases become available, the need to resort to race should diminish. This is fortunate, as increasing interracial marriage is reducing the predictive power of race. For example, most babies born with Tay-Sachs in North America at present are not from Jewish families, despite stereotypes to contrary.
In everyday speech, race often describes populations better defined as ethnic groups, often leading to discrepancies between scientific views on race and popular usage of the term. For instance in many parts of the United States, categories such as Hispanic or Latino are viewed to constitute a race, though others see Hispanic as a linguistic and cultural grouping coming from a variety of backgrounds. In Europe, such a distinction, suggesting that South Europeans are not European or white, would seem odd at least or possibly even insulting. In the United States, in what is referred to as the one-drop rule, the term Black subsumes people with a broad range of ancestries under one label, even though many who are termed Black could be more accurately described as white through simple anthropologic or taxonomic method. In much of Europe groups such as Roma and Turks are commonly defined as racially distinct from White Europeans, though these groups could be considered "Caucasian" by old physical anthropological methods which employed finite nose measurements as the standard form of racial classifaction.
Some argue it is preferable when considering biological relations to think in terms of populations, and when considering cultural relations to think in terms of ethnicity, rather than of race. Instead of classing people into one "group", say "Caucasians" or Europeans you have Britons, Frenchmen, Germans, Nords, western Slavs and Celts rather than having a term implying a (possible) ancestry group in the Caucasus which is definitely too distant for any real consideration, and moreover reaching to groups including eastern Slavs, Roma, as well as Georgians, and others who differ notably, both in culture, and to a noteworthy extent in physical appearance, from the aforementioned ethnic groups. There can be as much difference between two ethnicities grouped into a single "race" as there can be between ethnicities grouped (often arbitrarily) into an another "race".
These developments had important consequences. For example, some scientists developed the notion of "population" to take the place of race. This substitution is not simply a matter of exchanging one word for another. Populations are, in a sense, simply statistical clusters that emerge from the choice of variables of interest; there is no preferred set of variables.
The "populationist" view does not deny that there are physical differences among peoples; it simply claims that the historical conceptions of "race" are not particularly useful in accounting for these differences scientifically. In particular, populationists claim that:
Since the 1960s, some anthropologists and teachers of anthropology have re-conceived "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 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.
Through this system of racial identification, parents and children and even brothers and sisters were frequently accepted as representatives of opposite racial types. In a fishing village in the state of Bahia, an investigator showed 100 people pictures of three sisters and they were asked to identify the races of each. In only six responses were the sisters identified by the same racial term. Fourteen responses used a different term for each sister. In another experiment nine portraits were shown to a hundred people. Forty different racial types were elicited. It was found, in addition, that a given Brazilian might be called by as many as thirteen different terms by other members of the community. These terms are spread out across practically the entire spectrum of theoretical racial types. A further consequence of the absence of a descent rule was that Brazilians apparently not only disagreed about the racial identity of specific individuals, but they also seemed to be in disagreement about the abstract meaning of the racial terms as defined by words and phrases. For example, 40% of a sample ranked moreno claro as a lighter type than mulato claro, while 60% reversed this order. A further note of confusion is that one person might employ different racial terms to describe the same person over a short time span. The choice of which racial description to use may vary according to both the personal relationships and moods of the individuals involved. The Brazilian census lists one's race according to the preference of the person being interviewed. As a consequence, hundreds of races appeared in the census results, ranging from blue (which is blacker than the usual black) to pink (which is whiter than the usual white).
However, Brazilians are not so naive to ignore one's racial origins just because of his (or her) better social status. An interesting example of this phenomenon has occurred recently, when the famous football (soccer) player Ronaldo declared publicly that he considered himself as white, thus linking racism to a form or another of class conflict. This caused a series of ironic notes on newspapers, which pointed out that he should have been proud of his African origin (which is obviously noticeable), a fact that must have made life for him (and for his ancestors) more difficult, so, being a successful personality was, in spite of that, a victory for him. What occurs in Brazil that differentiates it largely from the US or South Africa, for example, is that black or mixed-race people are, in fact, more accepted in social circles if they have more education, or have a successful life (a euphemism for "having a better salary"). As a consequence, inter-racial marriages are more common, and more accepted, among highly-educated Afro-Brazilians than lower-educated ones.
So, although the identification of a person by race is far more fluid and flexible in Brazil than in the U.S., there still are racial stereotypes and prejudices. African features have been considered less desirable; Blacks have been considered socially inferior, and Whites superior. These white supremacist values were a legacy of European colonization and the slave-based plantation system. The complexity of racial classifications in Brazil is reflective of the extent of miscegenation in Brazilian society, which remains highly, but not strictly, stratified along color lines. Henceforth, Brazil's desired image as a perfect "post-racist" country, composed of the "cosmic race" celebrated in 1925 by José Vasconcelos, must be met with caution, as sociologist Gilberto Freyre demonstrated in 1933 in Casa Grande e Senzala.
Michel Foucault showed the popular historical and political use of a non-essentialist notion of "race" used in the "race struggle" discourse during the 1688 Glorious Revolution and under Louis XIV's end of reign. In Foucault's view, this discourse developed in two different directions: Marxism, which seized the notion and transformed it into "class struggle" discourse, and racists, biologists and eugenicists who paved the way for 20th century "state racism".
During the Enlightenment, racial classifications were used to justify enslavement of those deemed to be of "inferior", non-White races, and thus supposedly best fitted for lives of toil under White supervision. These classifications made the distance between races seem nearly as broad as that between species, easing unsettling questions about the appropriateness of such treatment of humans. The practice was at the time generally accepted by both scientific and lay communities.
Arthur Gobineau's An Essay on the Inequality of the Human Races (1853-1855) was one of the milestones in the new racist discourse, along with Vacher de Lapouge's "anthroposociology" and Herder, who applied race to nationalist theory to develop militant ethnic nationalism. They posited the historical existence of national races such as German and French, branching from basal races supposed to have existed for millennia, such as the Aryan race, and believed political boundaries should mirror these supposed racial ones.
Later, one of Hitler's favorite sayings was, "Politics is applied biology". Hitler's ideas of racial purity led to unprecedented atrocities in Europe. Since then, ethnic cleansing has occurred in Cambodia, the Balkans, Sudan, and Rwanda. In one sense, ethnic cleansing is another name for the tribal warfare and mass murder that has afflicted human society for ages, but these crimes seem to gain intensity when believed to be scientifically sanctioned.
Racial inequality has been a concern of United States politicians and legislators since the country's founding. In the 19th century most White Americans (including abolitionists) explained racial inequality as an inevitable consequence of biological differences. Since the mid-20th century, political and civic leaders as well as scientists have debated to what extent racial inequality is cultural in origin. Some argue that current inequalities between Blacks and Whites are primarily cultural and historical, the result of past and present racism, slavery and segregation, and could be redressed through such programs as affirmative action and Head Start. Others work to reduce tax funding of remedial programs for minorities. They have based their advocacy on aptitude test data that, according to them, shows that racial ability differences are biological in origin and cannot be leveled even by intensive educational efforts. In electoral politics, many more ethnic minorities have won important offices in Western nations than in earlier times, although the highest offices tend to remain in the hands of Whites.
Dr. King's hope, expressed in his I Have a Dream speech, was that the civil rights struggle would one day produce a society where people were not "judged by the color of their skin, but by the content of their character."
Because of the identification of the concept of race with political oppression, many natural and social scientists today are wary of using the word "race" to refer to human variation, but instead use less emotive words such as "population" and "ethnicity." Some, however, argue that the concept of race, whatever the term used, is nevertheless of continuing utility and validity in scientific research. Science and politics frequently take opposite sides in debates that relate to human intelligence and biomedicine.
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. 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).
In many countries, 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 "light skin complexion", etc. There is controversy over the actual relationship between crimes, their assigned punishments, and the division of people into the so called "races." 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.
More recent work in racial taxonomy based on DNA cluster analysis (See Lewontin's Fallacy) has led law enforcement to pursue suspects based on their racial classification as derived from their DNA evidence left at the crime scene While controversial, DNA analysis has been successful in helping police determine the race of both victims and perpetrators. In an attempt to be less subjective, this classification is called "biogeographical ancestry" rather than "race" , but the terms for the BGA categories are the same. The difference is that ancestry-informative DNA markers identify continent-of-ancestry admixture, not ethnic self-identity. Hence, they cannot match the U.S. "races". For example, the DNA of an Arab-American, an African-American, and a Hispanic of precisely the same Afro-European genetic admixture would be "racially" indistinguishable. And a "White" woman with, say, 12 percent African ancestry (like Carol Channing) would show exactly the same BGA as a "Black" man of the same admixture (like Gregory Howard Williams).