- Joined
- Jan 26, 2017
- Messages
- 17,754
- Reaction score
- 31,373
That was an implication of the 2014 finding, but still only suggests that the UV thing wasn't the full of it, but that does just amount to a case study and not the general scientific consensus, like in this 2017 publishing
Are you even reading the info you are posting???? Check the first one. You deserve 20 gifs laughing at your ass.
"The findings, which were detailed today (Jan. 26) in the journal Nature, also hint that light skin evolved not to adjust to the lower-light conditions in Europe compared with Africa, but instead to the new diet that emerged after the agricultural revolution,"
Functionally naked skin has been the physical interface between the physical environment and the human body for most of the history of the genus Homo, and hence skin coloration has been under intense natural selection. From an original condition of protective, dark, eumelanin-enriched coloration in early tropical-dwelling Homo and Homo sapiens, loss of melanin pigmentation occurred under natural selection as Homo sapiens dispersed into non-tropical latitudes of Africa and Eurasia.
...
Skin colour (as measured by skin reflectance) and levels of UVR are highly correlated.
...
The primary role of constitutive dark skin colour in hominin and modern human evolution is that of a natural sunscreen to conserve folate. Protection of epidermal DNA against strand breaks was the important secondary role played by dark skin colour.
...
The genus Homo and the species Homo sapiens emerged in equatorial Africa under conditions of intense and relatively invariant sunlight and UVR. Dispersal of hominins into non-equatorial Africa, Eurasia and the Americas involved movements into habitats with more seasonally variable patterns and differing wavelength mixtures of UVR. In this review, we shall confine our discussion to the consequences for skin colour of dispersal of Homo sapiens into Eurasia and the Americas, a process which began around 55,000 years ago.
...
Because eumelanin in skin is a highly effective sunscreen, the potential for cutaneous vitamin D production is reduced by dark skin. Darkly pigmented hominins dispersing out of equatorial Africa thus faced conditions that significantly affected their vitamin D physiology. Penetration of UVR into the skin is related to the amount and distribution of melanin; larger and more superficial melanosomes and ‘melanin dust’ present in the stratum corneum are highly effective at reducing UVB transmission
...
For people with dark skin living outside of the tropics, and especially north or south of 43°, there is insufficient UVB available in the sunlight outside of the time immediately around the summer solstice to satisfy the body's vitamin D requirement. Long-term occupation of non-tropical latitudes, thus, would not have been possible without loss of some constitutive eumelanin pigmentation in order to prevent the serious sequelae of vitamin D deficiency.
And here's the part you're looking for
At extreme high latitudes, year-round occupation is not possible without a diet that is centred on consumption and storage of vitamin-D rich foods such as oily fish, marine mammals, or caribou and reindeer, which concentrate vitamin D in their muscle meat and fat.
But notice that it is a specific and partial explanation because ultimately
Depigmented skin evolved not once, but multiple times in human history, and was accomplished by different combinations of genetic mutations. For modern European populations, different signatures of selection on the MC1R and SLC24A5 genes imply that both natural selection and genetic drift contributed to the evolution of depigmented skin.
...
The fact that depigmented skin evolved independently in the ancestors of modern Europeans and East Asians suggests that at least two (and probably more) distinct genetic mutation events occurred and that multiple loci underwent positive selection in these two regions receiving relatively low levels of UVB. The most likely reason for this was that it was associated with a loss of skin pigment that favoured vitamin D production under conditions of low UVB. Depigmented skin also evolved independently in Homo neanderthalensis probably for the same reason.
...
There has been a cause and effect relationship between UVR and skin pigmentation in human evolution, and skin colour phenotypes have been modified under the action of natural selection to maintain an optimum balance between photoprotection and photosynthesis over spatially varying conditions of UVR. Skin colour thus evolved as the product of two opposing clines, one emphasizing dark pigmentation and photoprotection against high loads of UVA and UVB near the equator, the other favouring depigmented skin to promote seasonal, UVB-induced photosynthesis of vitamin D3 nearer the poles.
...
The most important points to reinforce here are that the geographical gradient of human skin colour evolved under the influence of natural selection, and that very similar skin colour phenotypes (dark, light and intermediate) have evolved independently numerous times under similar UVR conditions. Diverse combinations of skin colour genes occurred during the course of prehistory as the combined result of natural selection, gene flow due to migration, and founder effect or genetic drift due to population bottlenecks occurring in the course of dispersal events
...
Skin coloration has been strongly influenced by natural selection, globally and throughout human prehistory, because of the importance of melanin as a natural sunscreen on naked skin.
