Human races do not exist
When we say that someone is black or white, we may think that he or she belongs to a biological category defined by his or her color. Many people believe that skin pigmentation reflects belonging to a race, “one of the main groups that humans can be divided into according to their physical differences, for example the colour of their skin; the fact of belonging to one of these groups”, according to the Oxford Learner’s Dictionary (similarly in Spanish: “each of the groups into which some biological species are subdivided and whose differential characters are perpetuated by inheritance”, according to the Spanish Royal Academy).
This notion, in the case of our species, is meaningless. From a biological point of view, human races do not exist.
In the skin there are melanocytes, cells that produce and contain pigments. There are two types of pigments, called melanin: one is brownish brown (eumelanin) and the other is yellowish red (pheomelanin). Skin color depends on the amount and proportion of both. This depends on different genes: some affect the amount of pigment in the melanocytes and others the proportion between the two types of melanin. Therefore, very similar colors may be the result of different combinations and obey different genetic configurations.
Africans, in general, are dark-skinned. The Dinka, from East Africa, are very dark; the San, from the south of the continent, are lighter. The natives of southern India, New Guinea and Australia are also dark-skinned. In Central Asia and the Far East, as well as in Europe, the skins are generally light. Native Americans have a different color, although not as dark as Africans.
If we go by the color of the skin hidden under the thick fur of chimpanzees, it is most likely that our hominin ancestors had light skin. About two million years ago, members of our lineage saw the thickness and consistency of their fur reduce and become a thin layer of hair. This transformation exposed the skin to solar ultraviolet radiation, which can cause cancer and also eliminate a substance of great physiological importance, folic acid. It is probably for this reason that genetic variants that darken the skin were selected, because melanin protects it from such damage.
Humans have reached almost all latitudes. Our skin has been exposed to different radiation conditions. Just as an excess of ultraviolet rays can be very harmful, so is a lack of it. Without this radiation, vitamin D cannot be synthesized, the deficiency of which causes rickets and other health problems. For this reason, without ruling out other possible reasons such as sexual selection in favor of lighter skins, human skin has become lighter in some geographical areas by natural selection.
In addition, population movements have led to the mixing of lineages, each with its genetic traits and pigmentary characteristics, to give rise to multiple configurations. The color of present-day humans is the result of a complex sequence of biological and demographic events. It is not possible to biologically demarcate one group from another on the basis of this trait.
Genetic diversity exists
The foregoing is not intended to deny genetic diversity in the human species. There is diversity, of course.
There are populations with numerous copies of the α-amylase gene, and others in which there are very few.
The Inuit tolerate the cold better than other humans and have desaturases that allow them to eat an exclusively carnivorous diet without causing them the problems that would cause other humans.
African pygmies have genetic variants related to the immune system. A mutation in the PDE10A gene – which encodes a phosphodiesterase – allows the Bajau Laut (the so-called “nomads of the sea”) to remain submerged in apnea for up to thirteen minutes.
Most Europeans and descendants of Europeans, as well as members of other human groups in Africa, the Arabian Peninsula and the Indian subcontinent retain the ability to digest milk lactose in adulthood.
Tibetans have a lower blood hemoglobin concentration and a higher density of capillaries. Both traits appear to be genetically based.
In West African peoples speaking Kwa languages, sickle cell anemia is much more prevalent than in other Africans.
These traits that characterize human populations have no correspondence with skin color. Nor do differences in skin color correspond to many other traits that also vary according to other patterns and by the effect of various selective pressures.
A useful concept?
Some argue that the category “race” is useful in our species for socio-health purposes. It has been observed, for example, that North Americans of African origin (commonly called “African Americans”) are more prone to certain diseases. This is why they defend the use of the term “race” to differentiate blacks from whites. One example is the greater propensity –genetically based– of African Americans to suffer from prostate cancer. Most of them are descended from enslaved people from West African villages in which the genetic variant responsible is very common. When the gene in question is of European ancestry in these same people, the frequency of this variant is much lower. And they all have dark skin.
Biological categories are problematic. In the animal world, different lineages and groups of lineages are differentiated, not without difficulty. We classify animals into phyla, classes, orders, families, genera, species and, in some cases, subspecies. Intermediate categories can also be defined. But we do not have races. Below the species or subspecies, there are populations.
In domestic animals we usually speak of breeds, but that is a very special case, because they have been obtained by artificial selection of certain attributes. It is, therefore, a category that cannot be transferred to the rest.
Of course, there is genetic diversity in the human species. It has been produced, as in other animals, by random mutations and by the effect of natural selection on the frequency of genetic variants in each population, gene flow caused by migrations and crosses between individuals from different populations, and genetic drift. But there are no homogeneous sets of variants that allow us to define large human groups that we can call races.
There is, therefore, no basis for invoking their existence. Nor is there any basis for justifying, on non-existent grounds, other differences.
Note: This article is the English version of one published in Spanish in The Conversation and was first published in Book reviews & random thoughts. The first version of this article was originally published in Cuaderno de Cultura Científica, a publication of the Chair of Scientific Culture of the University of the Basque Country (UPV/EHU).