Why are the people of Africa black

Biology: When people went black

Has evolution varied skin color for any good reason? That is controversial. But the dark skin of the first ancestors was a good protection against early death from cancer.

The most outward characteristic of people, the color of their skin, is also the most controversial, at least since racists of all stripes tried to draw brief conclusions about intellectual performance and moral integrity from the color, which began at the end of the 18th century. Perhaps that is why Darwin of all people did not want to see a product of adaptation to the environment in skin color, Jared Diamond followed him later (Discover, November 1994): The colors either came by chance, like the grooves in our fingertips, or they were there regional preferences or sexual selection based on them, as is the case with the size of the breasts and buttocks.

That would be surprising, however, a lot about our skin needs explanation, first of all the fact that our ancestors became naked monkeys (yes, Desmond Morris), who shed the skins, except for remains, especially on the head and the shame. There are many hypotheses about this, often strange ones - the depilation served to protect against fur parasites, even against fire - presumably it was about cooling: The dwindling hair roots were replaced by sweat glands when our ancestors came down from the trees and out of the woods When the sun hits the savannah, especially on the head, protective hair remains there, the UV in sunlight damages DNA and causes tumors.

And what did the skin look like when it appeared on the rest of the body? Nobody knows either, but one can assume that the skin was light, white. Chimpanzees have such a color under their fur, and even hairless parts of the body, such as the hands, are light in the young. Our white skin - which is why anthropology calls us “Caucasians” - we do not, of course, have these first ancestors who initially turned black in Africa, later they hiked Eurasia, there they became light again.

Why bright? Why dark

There are also hypotheses for this, especially that when lightening the skin and thus letting in sunlight it was about vitamin D or rickets. Vitamin D is synthesized in our skin under the influence of sunlight; it is needed, for example, for building bones, and in extreme cases there is a risk of rickets. However, it only raged in the lightless tenements of the 19th century, and vitamin D is also in many foods, especially fish. And: light skin has a price. Sunlight also destroys something that's important for development, folic acid. Against this, eumelanin protects - this is the pigment that colors the skin dark - or the gene responsible for it, MC1R. There is only one variant of this in black Africans, in Europeans - we also have this pigment, in addition to our light-colored pheomelanin - there are many, in chimpanzees too: So something in Africa must have selected one variant, namely about 1, The African version is 2 million years old. That goes very roughly together with the first ancestor who walked upright for a long time, Homo erectus 1.8 million years ago.

Why did he finally turn black? Everard Home postulated early on from being “scorched by the sun” (Phil. Trans. Roy. Soc. January 1, 1821). And what's the point of scorching? Cancer! But Home and those who took him on later received little applause: Evolution begins at the reproductive age, cancer often comes later.

But not always, deadly skin cancers come early.
And they strike, even today, with white black Africans, albinos. There are relatively many - it is every five thousandth, with us every twenty thousandth - and they don't get old, Mel Greaves (Institute of Cancer Research, London) has evaluated the statistics: Over 80 percent of albinos in equatorial countries Africa die before the thirtieth year of skin cancer (Proc. Roy. Soc. B, February 26). "While Darwin said skin tones had nothing to do with customization, today's clinical evidence strongly suggests that early history cancer was an important factor in the development of dark skin," Greaves concludes.

("Die Presse", print edition, 02.26.2014)