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Physiology & Medicine / Re: Hair Colour ?......Eye Colour ?...why ?
« on: 03/07/2006 13:11:47 »
Melanin protects us, to some degree from the damaging effects of the sun, and so people livingclose to the equator will have dark skin and eyes, to prevent too much uv damage. The downside of a lot of melanin is that it reduces the amount of vitamin d you can make. Near to the equator, where sun is not a problem, vitamin d is not a problem, but closer to the poles, where sun is limited, a dark skin could result in ricketts, so closer to the poles, there has been an advantage to reducing the level of melanin. Melanin is what causes hair and eye colour too. Skin and hair pigment is made up of different types of melanin. There are two broad groups of melanin, eumelanin, which is brown, and phaeomelanin, which is red. If you have high levels of melanin, the hair and eyes will basically look black, but as the total level of melanin falls, differences in hair and eye colour will show. It is not fully understood why there are some people with very dark hair but fair skin, but people are working on it!