Science Forums 2

[Essay]

Originally Posted by questor

...observe the different skin colors in Homo Sapiens.to see these results. These of course are macro variations and we do not know the biochemical reactions in genes that ocurred to cause these differences. Some think...

Some research....

Why does nobody call Questor on this claim? I think we have a good understanding of the biochemical details of how skin color changes over the different latitudes, over the millennia.

[googled: folate melanin pigmentation]

Originally Posted by wiki

Human skin color - Wikipedia, the free encyclopedia
see the sections: "Health related effects"
& "Genetics of skin color variation"

"...Europeans may have been dark as recently as 13,000 years ago."

Well, I thought it was 20 kya, but... you get the idea.

...or....

Originally Posted by Smithsonian Institution

Differences between Races
Nutrient photolysis of folate, mentioned above, is thought to have played an important role in natural selection and the evolution of darker skin colors. Folic acid is required for normal DNA biosynthesis, and folate (a conjugated form of folic acid) is required for bone marrow maturation and red blood cell development. Research has also shown a causal relationship between neural tube defects and folate lysis. In addition, tests on lab mice and rats have shown that folate deficiency can cause male infertility (by arresting spermatogenesis). Putting all of these clues together, it's reasonable to hypothesize that Homo ergaster individuals that had greater protection against UV radiation were likely to produce more offspring than those with lower concentrations of melanin, eventually leading to darker skin colors associated with tropical environments.

As populations spread from Africa, it seems likely that dark skin color was less well suited to environments with lower UV radiation levels in the temperate zone. While dangerous in excess, UV radiation is essential for the synthesis of previtamin D3, which is needed for calcium absorption and normal skeletal development. In tropical areas, there is no problem receiving enough UV light for D3 synthesis. In higher latitudes, though, where exposure to UV light is significantly less, a high concentration of melanin may hinder the passage of enough radiation to synthesize the necessary amount of the vitamin precursor. Medical records show that people with darker skin living in the higher latitudes are at greater risk for vitamin D3 deficiency (which can trigger the onset of various bone density diseases that can result in immobilization, deformities, and death). For this reason, it is believed that as populations moved north, natural selection favored lighter shades of skin. The point is that by understanding the biological benefits of traits, it is possible to understand the evolution of them.

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