When we say that someone is black or white, we may think that they belong to a biological category defined by their colour. Many people believe that skin pigmentation reflects belonging to a race, as defined by the Royal Spanish Academy in its second meaning: “each of the groups into which some biological species are subdivided and whose differential characteristics are perpetuated by inheritance”. And yet, in the case of our species, this notion is meaningless. Because 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 pigment, generically called melanin; one is brownish-brown (eumelanin) and the other is yellowish-red (phaeomelanin). Skin colour depends on the amount and proportion of both. And it so happens that this trait depends on different genes; some affect the amount of pigment in the melanocytes and others the proportion between the two types of melanin. Moreover, very similar colours may be the result of different combinations of these basic traits and be due to different genetic configurations.
Africans, in general, are dark-skinned. The Dinka, from East Africa, are very dark, while 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 colour, although not as dark as Africans.
If we go by the colour of the skin hidden under the thick fur of chimpanzees, it is most likely that our hominin* ancestors were light-skinned. Sometime around two million years ago, members of our lineage saw the thickness and consistency of their fur reduce to a thin layer of hair over much of the body’s surface. But this transformation brought with it exposure of the skin to ultraviolet radiation from the sun, which could cause cancer and also eliminate a substance of great physiological importance, folic acid. It is probably for this reason that genetic variants were selected that darkened the skin, because melanin protects it from the above-mentioned damage.
Humans have expanded and thus reached almost all latitudes. These movements have exposed the skin of their protagonists to very different radiation conditions. And just as an excess of ultraviolet radiation can be very harmful, so too is a lack of it, because without it, vitamin D cannot be synthesised, a deficiency of which causes rickets and other health problems. For this reason, without ruling out other possible reasons, human skin has become lighter in different geographical areas under the action of natural selection. In addition, population movements have led to the mixing of different lineages, each with its own genetic traits and pigmentary characteristics, to give rise to multiple configurations.
The colour of present-day humans is therefore the result of a complex sequence of biological and demographic events, and it is not possible to biologically demarcate one group from another. Differences in skin colour have no correspondence in countless other traits that also vary and do so according to other patterns and as a result of other selective pressures. There is, therefore, no basis for invoking the existence of races. Nor is there any basis for justifying, on non-existent grounds, other differences.
