Imakandi Post time: 2017-9-5 00:36
Vitamin D is added to milk, bro.
Yeah and milk and eggs come from store. No, really they come from cows and hens.
Vitamin D is added to milk in areas where human body cannot produce it enough naturally, and in other areas where it is deemed more vital than what the bodies can produce naturally.
UV radiation from sun is necessary to produce it naturally, so D supplements in milk are generally used in northern and southern latitudes where UV is more limited than closer to equator.
In the ancient times when the early human populations were migrating, vitamin D was not added to milk, and in fact the existence of vitamin D or any vitamin for that matter was not known to humans. They were hunter-gatherers who didn't go to high school.
Humans wandered north and surprisingly the freaks of nature with whiter skin and lactose tolerance survived better than the black skinned mainstream folks - because their bodies could better produce more vitamin D under limited UV, and they could continue to drink milk as adults to get vitamin D from milk - which contains some of it naturally.
Lactose intolerance of which some people in north suffer, is actually the normal and original operating mode of human body. Lactose tolerance is a lucky genetic abnormality.
NoisyCricket Post time: 2017-12-16 15:03
Why do some race have lighter skin?
Because in their biological history those races have benefited from the lighter skin. They have ventured to regions where there is less sunlight than in tropic, and their bodies have adapted to absorb more sunlight in shorter time.
Considering only biology, black skinned people will have less healthy babies the more north or south from the tropic they go, while white skinned will have less healthy babies the closer to tropic they go.
Of course in modern world, medicine and artifical conditions make this less important, but the current variation in skin colors was created long ago when those things did not exist.