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[QUOTE]Originally posted by DD'eDeN: [QB] [Note: The Black Sea Deluge occurred about 7,700 years ago (7.7ka), pushing semi-isolated populations outward in all directions. DD] - - - How Europeans evolved white skin Ann Gibbons 2.4.15 Science Most of us think of Europe as the ancestral home of white people. A new study shows that pale skin, tallness & the ability to digest milk as adults arrived in most of Europe rel.recently. The work (AAPA) offers dramatic evidence of recent evolution in Europe, it shows that most modern Europeans don't look much like those of 8 ka. In the past year, researchers have sequenced the genomes of ancient populations, rather than only a few individuals. By comparing key parts of the DNA across the genomes of 83 ancient individuals from archaeological sites throughout Europe, they reported earlier this year that Europeans today are a mix of the blending of at least 3 ancient populations of hunter-gatherers & farmers who moved into Europe in separate migrations over the past 8 ka. The study revealed that a massive migration of Yamnaya herders from the steppes north of the Black Sea may have brought Indo-European languages to Europe c 4.5 ka. <http://news.sciencemag.org/archaeology/2015/02/mysterious-indo-european-ho meland-may-have-been-steppes-ukraine-and-russia> Now, a new study from the same team drills down further to search for genes that were under strong natural selection, including traits that spread rapidly throughout Europe in the past 8 ka. By comparing the ancient European genomes with those of recent ones from the 1000 Genomes Project, Iain Mathieson found 5 genes associated with changes in diet & skin pigmentation that underwent strong natural selection. The scientists confirmed an earlier report that the H/Gs hunter-gatherers in Europe could not digest the sugars in milk 8 ka. They also noted an interesting twist: the first farmers also couldn't digest milk. The farmers who came from the Near East c 7.8 ka & the Yamnaya pastoralists who came from the steppes 4.8 ka lacked the version of the LCT gene that allows adults to digest sugars in milk. It wasn't until c 4.3 ka that lactose tolerance swept through Europe. When it comes to skin color, the team found a patchwork of evolution in different places, and 3 separate genes that produce light skin, telling a complex story for how Europeans' skin evolved to be much lighter during the past 8 ka. Hs who came out of Africa to originally settle Europe c 40 ka are presumed to have had dark skin, which is advantageous in sunny latitudes. The new data confirm that c 8.5 ka, early H/Gs in Spain, Luxembourg & Hungary also had darker skin: They lacked versions of 2 genes (SLC24A5 & SLC45A2- that lead to depigmentation in Europeans today. But in the far north (where low light levels would favor pale skin) the team found a different picture in H/Gs: 7 people from S-Sweden (Motala 7.7 ka) had both light skin gene variants, SLC24A5 & SLC45A2. They also had a 3d gene (HERC2/OCA2) which causes blue eyes, and may also contribute to light skin & blond hair. Thus ancient H/Gs of the far north were already pale & blue-eyed, but those of C- & S-Europe 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 H/Gs, one of their light-skin genes swept through Europe, so that C- & S-Europeans also began to have lighter skin. The other gene variant (SLC45A2) was at low levels until c 5.8 ka, when it swept up to high frequency. The team also tracked complex traits, such as height, which are the result of the interaction of many genes. They found that selection strongly favored several gene variants for tallness in N- & C-Europeans, starting 8 ka, with a boost coming from the Yamnaya migration, starting 4.8 ka. The Yamnaya have the greatest genetic potential for being tall of any of the populations, which is consistent with measurements of their ancient skeletons. In contrast, selection favored shorter people in Italy & Spain starting 8ka. [Note: short people are the original phenotype, tall people evolved due to selection for open areas, longer strides (less mechanical energy per pace) in coordination with longer lower limb pendulum effect. (cf Okapi vs giraffes, forest elephant vs savanna elephant, forest antelope vs plains antelope, etc.) DD] <http://biorxiv.org/content/early/2015/03/13/016477> Spaniards, in particular, shrank in stature 6 ka, perhaps as a result of adapting to colder Tps & a poor diet. The team found no immune genes under intense selection, which is counter to hypotheses that diseases would have increased after the development of agriculture. The paper doesn't specify why these genes might have been under such strong selection. But the likely explanation for the pigmentation genes is to maximize vitamin D synthesis. <http://www.sciencemag.org/content/346/6212/934.summary?sid=91e8ebfd-8581-4 bd7-bac5-26dc16bf5a87>, Nina Jablonski looked at the poster's results at the meeting. People living in northern latitudes often don't get enough UV to synthesize vitamin D in their skin, so natural selection has favored 2 genetic solutions to that problem: - evolving pale skin that absorbs UV more efficiently, - or favoring lactose tolerance to be able to digest the sugars & vitamin D naturally found in milk: "What we thought was a fairly simple picture of the emergence of depigmented skin in Europe is an exciting patchwork of selection as populations disperse into northern latitudes. This data shows how much recent evolution has taken place." - - - [M Verhaegen @ AAT] "I just sent this comment: Very interesting article, thanks a lot. I have 2 comments. 1) There are a lot of possible 'explanations' for skin color in humans: it is thought that melanin (& pheo-melanin?) hinders production of folic acid & of vit.D (although we get most vit.D from eating fish etc.), melanin hinders proliferation of bacteria (cf. more pigment in genital skin, darker nipples during pregnancy & lactation), and is thought to protect against skin cancer (although patients treated for psoriasis with PUVA get more skin cancer on their genitals than elsewhere), but the simplest explanation (+ anti-bacterial?) is that, like fur color in most mammals, human skin color makes more invisible against the background (camouflage theory of Raymond Cowles), cf white polar bears, grey grizzleys, brown bears in temperate climate, black bear in (sub)tropical forests. KhoiSan (Kalahari), Berbers (Sahel) & Austr.aboriginals are brown, much lighter than tropical Africans. In Europe, Scandinavians are pale but tan in summer (even get counter-shadow), Brits in sunlit forest are reddish & have freckles (pheo-melanin), Medit.people are darker etc. Gorillas on the forest floor are black, but orangs higher in the trees are reddish etc. 2) On linguistic grounds (Dutch 'tooi' (ornament) is etymologically derived from 'touw' (cord)) I proposed (1997 in Dutch) that the corded beaker people might have spoken an Indo-European language, possibly Germanic (which fits the geographical distribution). The Yamnaya seem to have adopted an IE language, possibly Germanic: this might explain the creolisation we see in proto-Germanic. If the Yamnaya were light-colored & very tall (see Ann Gibbons' article), this fits my idea they adopted proto-Germanic. The distribution of Yamnaya genes outside the Germanic-speaking regions of Europe can be explained by the mass migrations 3d-5th centuries." - - - Comment by somitc @ AAT: "Doesn't explain why Asians and American Indians that received the same sunlight as Europeans are not as light skinned as Europeans. One speculation that I read claimed the cause was the Gulf Stream starting in the U.S. Mississippi River. The Gulf Stream keeps Europe warm enough to grow folic acid depleting foods like wheat so early Europeans needed more sunlight to get through their skin to compensate. Having the same sunlight as American Indians and Asians meant that lighter skin was needed. I'm no expert in any area but suspect that many people being far from the ocean also meant that more vitamin D had to come from the sun instead of from ocean food or lighter skin was needed to convert some vitamin A to vitamin D." - - - comment by christianengelbrecht@AAT "Populations inhabiting the same lattitude don't necessarily receive the same degree of solar radiation across the generations. Another factor to consider besides same lattitude is degree of terrestrial vegetation, which can shield much of the sun. Ie. if a region is more dominated by woodland, e.g. the tundra to temperate forests of C Europe, Scandinavia, the Baltic and Russia, these populations (case in point, Russians, Finns, Baltic and Scandinavian peoples are traditionally the palest of ethnicities) would've gotten paler in those regions than, say, the more open Asian and American plains, plus the ice covered polar regions with almost no vegetation. Therefore e.g. E Asian Turkish, Inuit, Samoyedic, Amerindian peoples, etc. would be darker by comparison, even though they would've adapted at similar lattitudes." [/QB][/QUOTE]
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