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wmfinck wrote:Wow, three months and no conversation, LOL.
Fenwick wrote:I was actually going to post a thread on this topic, but I'll have to do it tomorrow, I don't want to rush into things.
April 16, 2008
Science last year (thanks commenter!) had a news story about the evolution of European skin color:
“Researchers have disagreed for decades about an issue that is only skin-deep: How quickly did the first modern humans who swept into Europe acquire pale skin? Now a new report on the evolution of a gene for skin color suggests that Europeans lightened up quite recently, perhaps only 6000 to 12,000 years ago.
This contradicts a long-standing hypothesis that modern humans in Europe grew paler about 40,000 years ago, as soon as they migrated into northern latitudes. Under darker skies, pale skin absorbs more sunlight than dark skin, allowing ultraviolet rays to produce more vitamin D for bone growth and calcium absorption. "The [evolution of] light skin occurred long after the arrival of modern humans in Europe," molecular anthropologist Heather Norton of the University of Arizona, Tucson, said in her talk.”
This seems to be in agreement with accelerating recent selection in the human genome. The Science story is referring to the AAPA 2007 meeting. More from the Science story regarding the SLC24A5 gene:
“The genetic origin of the spectrum of human skin colors has been one of the big puzzles of biology. Researchers made a major breakthrough in 2005 by discovering a gene, SLC24A5, that apparently causes pale skin in many Europeans, but not in Asians. A team led by geneticist Keith Cheng of Pennsylvania State University (PSU) College of Medicine in Hershey found two variants of the gene that differed by just one amino acid. Nearly all Africans and East Asians had one allele, whereas 98% of the 120 Europeans they studied had the other (Science, 28 October 2005, p. 601).”
This is a wonderful confirmation of Cavalli-Sforza's prediction about recent selection for skin color:
“Either way, the implication is that our European ancestors were brown-skinned for tens of thousands of years--a suggestion made 30 years ago by Stanford University geneticist L. Luca Cavalli-Sforza. He argued that the early immigrants to Europe, who were hunter-gatherers, herders, and fishers, survived on ready-made sources of vitamin D in their diet. But when farming spread in the past 6000 years, he argued, Europeans had fewer sources of vitamin D in their food and needed to absorb more sunlight to produce the vitamin in their skin. Cultural factors such as heavier clothing might also have favored increased absorption of sunlight on the few exposed areas of skin, such as hands and faces, says paleo-anthropologist Nina Jablonski of PSU in State College.”
Perhaps it was the larger population sizes made possible by farming that made it possible for the adaptive mutation to arise in one individual, or the mutation pre-existed in early agriculturalists.
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