TOWhen we say someone is black or white, we may think that they belong to a biological category defined by their color. Many people believe that skin pigmentation reflects belonging to a race, “each of the groups into which some biological species are subdivided and whose differential characters are perpetuated by inheritance,” according to the RAE. That 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). The color of the skin depends on the amount and proportion of both. This depends on different genes: some affect the amount of pigment in the melanocytes and others on the proportion between the two types of melanin. Therefore, very similar colors can be the result of different combinations and obey different genetic configurations.
Africans, in general, are dark skinned. The Dinka, from East Africa, have it very dark; the San, from the south of the continent, clearer. 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 them of different colors, although not as dark as Africans.
If we look at the color of the skin hidden under the thick fur of chimpanzees, it is most likely that our hominin ancestors had it light. About two million years ago, members of our lineage saw the thickness and consistency of their fur reduced, turning it into a thin layer of hair. This transformation exposed the skin to ultraviolet solar radiation, which can cause cancer and also eliminate a substance of great physiological importance, folic acid. Surely for this reason, genetic variants that darkened the skin were selected, because melanin protects it from such damage.
Human beings 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 too is a deficiency. 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 possibilities such as sexual selection in favor of lighter skin, human skin has been lightening in some geographic areas due to natural selection.
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Furthermore, 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 current human beings is the result of a complex sequence of biological and demographic events. It is not possible to biologically delimit some groups and others according to that trait.
Genetic diversity exists
The above 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 with very few.
The Inuit tolerate the cold better than other human beings and have desaturases that allow them to eat an exclusively carnivorous diet without causing the problems that it would cause to other human beings.
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 “sea nomads”) to remain submerged in apnea for up to thirteen minutes.
Most Europeans and European descendants, as well as members of other human groups in Africa, the Arabian Peninsula, and the Indian subcontinent, retain the ability to digest lactose in milk into adulthood.
Tibetans have a lower blood concentration of hemoglobin and a higher density of capillaries. Both traits appear to have a genetic basis.
In West African people who speak 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 due to the effect of various selective pressures.
A useful concept?
There are those who maintain that the category “race” is useful in our species for socio-health purposes. It has been observed, for example, that Americans of African origin (commonly called “African Americans”) have a greater propensity to suffer from certain diseases. That is why they defend the use of the term “race” to differentiate blacks from whites. An example is the greater genetic-based propensity of African Americans to suffer from prostate cancer. Most of them descend from enslaved people from West African towns in which the responsible genetic variant is very common. When the gene in question has, in those same people, European ancestry, the frequency of that 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 difficulties. We classify animals into phyla, classes, orders, families, genera, species and, in some cases, subspecies. Intermediate categories can also be defined. But we don’t have races. Below the species or subspecies, there are populations.
In domestic animals we do usually talk about breeds, but that is a very special case, since 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 occurred, as in other animals, due to random mutations and the effect of natural selection on the frequency of genetic variants in each population, gene flow caused by migrations and crossings 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 to invoke its existence. Nor is there any to justify, on non-existent bases, other differences.
Author: Juan Ignacio Pérez Iglesias – Professor of Physiology, University of the Basque Country / Euskal Herriko Unibertsitatea
Article published in and transferred for publication in .