Wie die Hautfarbe in Afrika und außerhalb Afrikas evoluierte

Wie die Hautfarbe in Afrika und außerhalb Afrikas evoluierte

Eine neue Studie bringt folgende Erkenntnisse mit sich (1):

1. Das Gen, das in Europa helle Haut hervor bringt (SLC24A5), findet sich auch in Äthiopien. Dorthin mag es mit den ersten Bauern des Levanteraumes gekommen sein (oder später). Aber trotz des Besitzes dieses Gens haben viele Afrikaner dunklere Haut als man bei Besitz desselben annehmen sollte.

2. Gene, die helle Körpermerkmale bei Europäern hervorrufen (HERC2 und OCA2), finden sich auch bei den Buschleuten in Südafrika. Sie sind schon dort entstanden (sie gelangten nicht über Rückwanderung dorthin, sondern von dort nach Europa).

3. Ein weiteres Gen (MFSD12) braucht Sequenzen, die seine Ablesung verhindern, damit die dunkle Hautfarbe entsteht, für die heute Afrikaner bekannt sind, aber nicht nur bei ihnen, sondern auch bei Melanesiern und australischen Ureinwohnern.

Hier noch der Originaltext:
"The first surprise was that SLC24A5, which swept Europe, is also common in East Africa—found in as many as half the members of some Ethiopian groups. This variant arose 30,000 years ago and was probably brought to eastern Africa by people migrating from the Middle East, Tishkoff says. But though many East Africans have this gene, they don’t have white skin, probably because it is just one of several genes that shape their skin color. The team also found variants of two neighboring genes, HERC2 and OCA2, which are associated with light skin, eyes, and hair in Europeans but arose in Africa; these variants are ancient and common in the light-skinned San people. The team proposes that the variants arose in Africa as early as 1 million years ago and spread later to Europeans and Asians. “Many of the gene variants that cause light skin in Europe have origins in Africa,” Tishkoff says. The most dramatic discovery concerned a gene known as MFSD12. Two mutations that decrease expression of this gene were found in high frequencies in people with the darkest skin. These variants arose about a half-million years ago, suggesting that human ancestors before that time may have had moderately dark skin, rather than the deep black hue created today by these mutations. These same two variants are found in Melanesians, Australian Aborigines, and some Indians. These people may have inherited the variants from ancient migrants from Africa who followed a “southern route” out of East Africa, along the southern coast of India to Melanesia and Australia, Tishkoff says. (...) This great migration may have included people carrying variants for both light and dark skin, but the dark variants later were lost in Eurasians. To understand how the MFSD12 mutations help make darker skin, the researchers reduced expression of the gene in cultured cells, mimicking the action of the variants in dark-skinned people. The cells produced more eumelanin, the pigment responsible for black and brown skin, hair, and eyes. The mutations may also change skin color by blocking yellow pigments: When the researchers knocked out MFSD12 in zebrafish and mice, red and yellow pigments were lost, and the mice’s light brown coats turned gray. “This new mechanism for producing intensely dark pigmentation is really the big story,” says Nina Jablonski, an anthropologist at Pennsylvania State University in State College."

1. How Africans evolved a palette of skin tones. Ann Gibbons; Science 13 Oct 2017; Vol. 358, Issue 6360, pp. 157-158; DOI: 10.1126/science.358.6360.157
http://science.sciencemag.org/content/358/6360/157
http://science.sciencemag.org/content/358/6360/157