Melanin Review Project

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by symetriag
Last updated 6 years ago


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Melanin Review Project


•In 2000, we advanced the theory that dark skin pigmentation in humans had evolved primarily to prevent reduction of fertility due to the photolysis of folate present in cutaneous blood vessels. Presented evidence that folate depletion by UVR would precipitate folate deficiencies that would, in turn, lead to potentially fatal birth defects such as neural tube defects (NTDs).•Due to the direct action of folate on the normalization of neural tube development due to its role in the division of rapidly dividing cells.•Folate regulates melanin production because it is required for the synthesis of GTP, which is a substrate for de novo production of tetrahydrobiopterin (BH4) and 6BH4 in melanocytes and keratinocytes. •High evolutionary valence because it directly affects reproductive success and survival early in life.•Evolution of Light Pigmentation of high latitudes has long been related to the significance of production of vitamin D in the skin under conditions of reduced sunlight. •Photosynthesis of the skin (Vitamin D) depends upon the solar zenith angle, which changes with season, latitude, and time of day, is further controlled by amount of pigment and thickness of skin.•Generally low a highly seasonally variable levels for UVB created a selective environment favoring the capture of UVB photons required for vitamin D3 photosynthesis through loss of melanin pigmentation. •Genetic verification of three independent occurrences of evolution of depigmented skin hominin populations has been documented in the lineages leading to modern Northern Europeans and modern East Asians and in Homa Neanderthalensis. Geographic Variation in UV Radiation•The dispersals of hominins out of Africa that occurred about 1,916 and 80ka, respectively involved the movement of people out of highly, UVR-rich environments into habitats that were much more mixed seasonal pattern, intensity, and wavelength mixture of UVR.•Africa receives high and uniform amounts, whereas Northern Eurasia receives negligible amounts.

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•The product of two clines produced by natural selection to adjust levels of contributive pigmentation to levels, of UV radiation (UVR).•One cline generated by high UVR near the equator and led to the evolution of dark, photo protective, eumelanin-rich pigmentation.•The other produced by the requirement for UVB photons to sustain cutaneous photosynthesis of vitamin D3 in low-UVB environment, resulted in the evolution of depigmented skin.•Hominins dispersed outside of the tropics, experienced different intensities and seasonal mixtures of UVA and UVB.•Since mid-18th century, skin color has been the single most important physical trait used to define human groups (races, subspecies, and species).

By: Sy'metria Guidry & Justin Strother

•Mid-18th century naturalist such as John Mitchell and, later, Samuel Stanhope Smith recognized a pronounced latitudinal g pigmentation among the world’s peoples-from dark near the equator to light towards the poles-mainly to differences in sunshine heat experienced by people at different latitudes. “This general uniformly in the effect,” Smith wrote, “indicates an influence in climate that, under the same circumstances, will always operate in the same manner.• Thermoregulation- the loss of body hair in humans was accompanied by enhanced barrier functions of the stratum corneum, including the evolution of other epidermal keratins, reduced the skin’s permeability and improved it’s abilities to resist abrasion and microbial attack. •Sexual Selection was not the primary, or even, a major, determinant of skin pigmentation, although the preference by males in some cultures for females of lighter color probably has heightened sexual dimorphism in skin pigmentation in some populations. •It was Natural Selection that produced the conspicuous gradient of skin tones groups observed in our species. •Skin cancers are mostly consequences of modern human migration and resulting mismatches between skin pigmentation and geography/lifestyles.


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