4 mars 2016

La peau blanche a 8000 ans


Les humains blancs sont assez récents dans l'histoire de notre espèce. Extrait de l'article:

(...) Based on 83 human samples from Holocene Europe as analyzed under the 1000 Genomes Project , it is now found that for the majority of the time that humans have lived in Europe, the people had dark skin, and the genes signifying light skin only appear within the past 8,000 years. This recent and relatively quick process of natural selection suggests to researchers that the traits which spread rapidly were advantageous within that environment, according to the American Association for the Advancement of Science (AAAS) .

(...) AAAS reports that the “modern humans who came out of Africa to originally settle Europe about 40,000 years are presumed to have had dark skin, which is advantageous in sunny latitudes. And the new data confirm that about 8500 years ago, early hunter-gatherers in Spain, Luxembourg, and Hungary also had darker skin: 

(...) Then, the first farmers from the Near East arrived in Europe; they carried both genes for light skin. As they interbred with the indigenous hunter-gatherers, one of their light-skin genes swept through Europe, so that central and southern Europeans also began to have lighter skin. The other gene variant, SLC45A2, was at low levels until about 5800 years ago when it swept up to high frequency.”

This differed from the situation farther north. Ancient remains from southern Sweden 7,700 years ago were found to have the gene variants indicating light skin and blonde hair, and another gene, HERC2/OCA2, which causes blue eyes. This indicated to researchers that ancient hunter-gatherers of northern Europe were already pale and blue-eyed. This light skin trait would have been advantageous in the regions of less sunlight.

Mathieson and colleagues do not specify in the study why the genes were favored and spread as quickly as they did, but it is suggested that Vitamin D absorption likely played a role.

(...) Paleoanthropologist Nina Jablonski of Pennsylvania State University notes that people in less sunny climates required different skin pigmentations in order to absorb and synthesize Vitamin D.

(...) DNA taken from the wisdom tooth of a 7,000-year-old human found in Spain in 2006 overturned the popular image of light-skinned European hunter-gatherers. The study revealed that the individual had dark hair and the dark-skinned genes of an African. However, the man had blue eyes, an unexpected find by researchers. The hunter-gatherer is the oldest known individual in Europe found to have blue eyes.



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