CanyonWind wrote:
I haven't heard of a skin color latitudunal gradient among western hemosphere natives, who live from the arctic to tierra del fuego. They might have been here 40,000 years, which might translate to two thousand generations. Skin color ususlly has variation among human groups, so it seems that natural selection could have got started on producing the standard color gradient if it wanted to.
I'm not aware that people in equitorial africa are darker than native people in southern africa. I guess people have moved around a lot, and the same would apply to western hemisphere natives, but people in europe have moved around a lot too.
This makes less sense the more I think about it. I love stuff like that.
There have been actually several anthropological studies, and yes, generally, people are darker the closer you get to the equator. Now, plop yourself down in any one place and you will find a lot of variation in skin color, but on *average* , people are lighter skinned near the arctic and anartci. And the anthroplogists measure 'where the sun don't shine', like the armpit and groin, so they aren't just measuring amount of skin tan.
And there is a biological reason -- you need a certain amount of sunlight to synthesize vitamin D. Melatonin blocks sunlight. If you have too much melatonin, you don't get enough vitamin D. It you have too little, you can get sun poisoning.
For instance, in Finland, they have taken a lot of Somalians in as refugees. They have a lot of problems with vitamin D, especially in the winter, and they have to take supplements.