- 1 The word "race" and the phrase "human races" as used in biology- defining the terms
- 2 Genetic markers of populations
- 3 Mitochondrial DNA
- 4 Y chromosome
- 5 History of Biology: Race and Biology
- 6 Current thinking:Race and Biology
- 7 Current thinking in biology: species and subspecies
- 8 References
- 9 Further reading
- 10 External links
See race for a more general treatment of the concept of human races, and see subspecies for the concept of "race" as applied to all species; the following article concerns how biologists have approached human races.
Races of humans have been delineated by many cultures over human history, using the word "race" in one of two general senses: as a variety, or as a group of related descendants. At one time, however, "race" was applied to human beings as a biological term for human subspecies. Some of the earlier modern biologists even argued that these races represented different modern human species, rather than subspecies, but the notion that the biology of all the different ethnic groups of people was that of only one kind, that there were no subspecies of man, received little or no credence. In that era, the word "race" (often capitalized) was used in the scientific literature of biology and anthropology as a technical term in both of those disciplines to refer to these subspecies, sometimes broken down into many groups, often into four of five.
This idea that Homo sapiens consists of different subspecies called races, has been debunked as biology entered the era of molecular genetics and with the sequencing of the human genome. In general culture, the notion of distinct races characterized by a combination of geographic ancestry and particular physical features including hair texture, skin color, and facial features, remains widespread. It is often assumed by non-scientists that these races are still recognized as biologically distinct, as they were for a time in the past. In order to understand why this longstanding notion is no longer held to be valid by scientsts, certain background knowledge is required. That knowledge includes a basic understanding of vertebrate taxonomy, the history of the idea of "the races of man" in modern biology, and an introduction to the variability of the human genome. This article attempts to present that background, along with a contemporary view of how subspecies are defined in biology.
Why were the races ever thought to be distinct subspecies? The idea that there was a natural and inherent difference in people of different nations and appearance predates modern biology. It was an assumption made by many of the European scientists involved in natural philosophy and early biology. As biology became a formal science, and taxonomies of living things were developed by Linneas and others, human beings were included. With the exploration of the world by Europeans, who piloted systematics in biology, various peoples with appearances that were distinctive were added into these classifications, just as novel vertebrate animals, plants, insects and other living things were classified in studies of natural history. Scientists such as Linneas, Cuvier and Darwin assumed that these different visages of human beings hailing from various areas of the world, were biologically distinct. With advances in human genetics and molecular biology in more recent times, investigation of human types that differ in appearance along these racial categories have failed to find diagnostic criteria for Race. There are biological variations in physical features among human beings, of that, this is no question. These variations exist is height, weight, muscle mass distribution, size of the ears, the hands, the feet, ratio of bone to cartilage in the nose, and, on an entirely different level, in chemical variations of proteins, blood types, and sequences of DNA. However, these variations are continuous across individuals, and though many are inherited and can therefore be used to help determine ancestry, none of them include the discontinuous qualties that separate, say, men from women. Whereas gender (sex) has been shown to have a set of biological features (despite some gray areas for specific individuals), such that almost every human being can be said- after a laboratory examination of chromosomes and sequencing of genotype, to be a man (boy) or woman (girl), there are no distinct set of biological criteria that can be used to determine the race of an individual in an unambiguous sense. Instead, race is based on a combination of appearance and ancestry.
The word "race" and the phrase "human races" as used in biology- defining the terms
The term, "race" in current biology has several legitimate meanings- some are used only infrequently or only in certain contexts. In the 19th century, and before, the word "race" was often used in biology as a synonym for a kind or kindred of creature or plant, and the term race was generally applied to all manner of living things as a synonym for species, and, alternatively, to describe the set of relatives or descendants of a designated individual. For example, the full title of one of Charles Darwin's books, published in 1859, is On the Origin of Species By Means of Natural Selection, or, the Preservation of Favoured Races in the Struggle for Life. Today some biologists still use the word race to refer to kinds or strains of animals, and, more often, of plants.
The word, "race" has been applied to people in common rather than technical usage; as a kind, or sort, of person- such as "the race of women" or the "race of gamblers", sometimes in a poetic or humorous way. In fact, the word race is popularly used to refer to all mankind, or Homo sapiens, as the human race, to distinguish us from other kinds (races) of living things. Most notably, race, in both biology and popular usage, is used to designate categories of human ethnic groups. The history of the word "race" used as a designation for ethnic groups in biology has few poetic or humorous associations. Instead, that history is strongly figured in the support of a number of social, health science, and military undertakings that have ranged from Negro slavery to Eugenics to The Holocaust, and Apartheid, and been generally accepted to be among the most shameful accomplishments of the human race. Particularly since the aftermath of the Holocaust , when the result of the biological thinking that allowed the Nazi regime to rationalize genocide became clearly understood, there has been a great reluctance within anthropology, medicine, and other fields of human biology to approach basic research according to racial ideation. Today, it is difficult to find chapters in current textbooks in any of these fields entitled "Race", for example. When such articles or chapters are encountered, they more often discuss race as a specific kindred, rather than the "races of man", or they discuss cultural characteristics, like "Use of surgical services by blacks in Chicago". That was not true in texts of these disciplines before World War II.
This is a remarkable testament to the impact of social history on biology, because, during this same post-WW II era, the power of molecular biology and, most particularly, molecular genetics, has been a driving force in biological research and lends itself to the analysis of inherited features and the biology of kindreds. In one meaning of the word "race", that is not used technically as a biological term, race refers to all of the descendents of an individual (The race of Abraham, the race of King Henry), and in that sense only much of modern human genetics has focused on the study of race. Even though these studies have not been generally aimed at comparing the classic races of mankind that were and are popularly acknowledged: Caucasian, Negroid, Mongoloid, there has been so much analysis of kindreds that fall into these groups that it is possible to discuss the findings in terms of that meaning of race. What has been found out so far, is that there are no qualitative biological differences that correspond to these groups and currently, in human biology , including health science and anthropology, the term race is not held to have any absolute biological meaning outside of explicitly defined kinship groups. Of course, there are biological studies of "whites" and "blacks", for example, in health sciences; but these are descriptive studies of response to medication, or prevalence of disease, in socially defined groups - often self-defined, and they have the same kind of significance as studies of urban populations, or residents of certain geographic areas; in other words the groups are defined by non-biological, criteria and then studied for biological characteristics.
Historically, there have been biological definitions of races. By the nineteenth century, western biologists separated human beings into various racial classifications under the assumption that there were distinct biological differences between them, similar to the differences between species, or subspecies. In fact, some biologists of that era argued that certain races of human beings were not the same species as other races. More recently, molecular genetic analysis has shown that there do not appear to be measureable genetic differences according to these classic racial groups. However, when populations of people are related, then they do tend to share certain forms of genes and other kinds of genetic markers. Some of these markers are particular sequences of nucleotides in DNA that are different in different people, and inherited by their offspring. These sequences, which include microsatellite DNA, are often so highly variable that they are therefore especially useful for looking for inherited relationships, even though these distinctively variable sequences do not code for proteins, as genes do. Genetic polymorphisms have been used to construct theoretical family trees of man, and to plot historical migrations according to where populations with shared polymorphisms appear. However useful these genetic markers are, they have not revealed the kinds of qualitative differences that were once assumed to be inherent features of human races, tribes, and ethnic groups by eugeneticists, sociologists and sociobiological theorists of the past.
Genetic markers of populations
Since the development of PCR and other rapid, powerful DNA chemistry laboratory techniques, there have been multiple investigations of how the frequency of certain sequences vary in different populations. These different forms of DNA are called polymorphisms and, since they vary on an inherited basis, polymorphisms can be useful for tracing the ancestries of populations. For example, in 1966 the Gm ab3st gene was shown to be common in Mongoloid people, including Asians and Native Americans. Since then, four different varieties of the gene, Gm haplotypes, have been described: Gm ag, axg, ab3st, and afb1b3. When individuals have these GM haplotypes, they fall into one of two patterns- " the first is a southern group characterized by a remarkably high frequency of Gm afb1b3 and a low frequency of Gm ag, and the second, a northern group characterized by a high frequency of both Gm ag and Gm ab3st but an extremely low frequency of Gm afb1b3." . By studying the frequencies of these genes in populations throughout the world, researchers have concluded that the Japanese race belongs to northern Mongoloids and that the origin of the Japanese race was in Siberia, and most likely in the Baikal area of the Soviet Union. This kind of genetic marker research is fairly typical of racial studies in current biology. In other words, it is possible to make correlations in the historical migration of peoples and gene markers, and the word "race" is used as descendents of an individual or closely related people, rather than as one of the "Races of Man" as proposed in earlier centuries.
Mitochondrial DNA is different that the DNA in the nucleus of cells. Unlike nuclear DNA, mitochondrial DNA does not undergo recombination between sperm and egg, but is inherited intact from the mother. Mitichondria contain the cytochrome system for oxidative phosphorylation in metabolism, and mitochondrial DNA can be assayed by probing with sequences that are known to be contained in the genes that code for cytochromes, such as cytochrome b.
History of Biology: Race and Biology
Current thinking:Race and Biology
The current thinking about race and biology is not simply a reaction to political change, but also reflects a different concept of the importance of breeds and subspecies in taxonomy. In so far as the traditional notions of race correlated with ideas of species and subspecies in biology, changes in the views towards human races parallel some of the changes in views towards the subclassification of animals.
Breeds and subspecies of other species, like dogs or horses, for example, exist because of restricted choice of mates. Natural breeds are those that have come about because of physical isolation - for example, populations on islands. When purebred breeds of horses and dogs are established through artificial selection, then the "isolation" is imposed by the owner, who restricts the mate of the animal to another member of the breed. Even then, however, especially with breeds that recently established (like most dog breeds), there must be active selection of which "pedigreed" individuals are allowed to mate if the characteristics of the breed are to be maintained. In other words, if every pedigreed Labrador retriever was allowed to breed, after several generations the puppies would not necessarily look or act like Labrador retrievers. That's because the breed standard, which is the desired phenotype, is applied to each potential parent before breeding. This kind of ongoing selection is why so-called field labs might be reliable retrievers in the hunt, but not look like picture-book labs, and "show Labrador retrievers" who are bred after earning championships in conformational dog shows generally look very much like the breed standard, but might not be reliable hunting dogs.
As refined techniques in genetics have been used to examine specimens of different breeds, the variations that are found to be distinctive generally have to do with one of two findings. Either the gene is one that is known to produce a certain phenotypic trait, and is present in animals of the breed who exhibit the trait, or the gene haplotype or a genetic polymorphism is found in the breed and indicates the ancestry of the breed. For example, Chunky broiler chickens can be distinguished from White Leghorn, Fayoumi, and Black Minorca chickens by two polymorphisms in the cytochrome b region. Those markers likely came from a maternal ancestor that was not related to the chickens who make up those other breeds.
Current thinking in biology: species and subspecies
- Matsumoto H (1988) Characteristics of Mongoloid and neighboring populations based on the genetic markers of human immunoglobulins. Human genetics 80:207-18