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From: "R. & G. Stevens" <>
Subject: Re: [DNA] White skin color gene
Date: Sat, 11 Nov 2006 09:03:58 -0500
References: <000201c7054d$fa6433c0$354c2b3f@DW>


----- Original Message -----
From: "David Wilson" <>
To: <>
Sent: Friday, November 10, 2006 11:58 PM
Subject: Re: [DNA] White skin color gene


> One theory is that skin color is connected with hairlessness. Our close
> human relatives, the chimpanzees, are asserted to be lighter-skinned under
> their hair. The proposal is that the earliest modern humans in Africa were
> also light skinned under theirs. When the ancestors of modern humans lost
> their hair, skin darkened over the entire body to protect it. When humans
> left Africa and spread east and north, the ones heading north entered an
> environment in which there was less pressure to maintain dark skin, and
> lighter skin re-emerged. Sexual selection pressures may then have played a
> stronger rule in expansion of lighter skin than did natural selection.
> (For
> that matter, sexual selection may have played a role in darkening the skin
> of hairless hominids in the first place.)
>
> I'm not sure I think there is merit in this argument. I'm just offering it
> as one that I have encountered.
>
> David Wilson
______________________________________________________________________________________________________________________

I read somewhere long ago that light-colored skin is an advantage in the
grayer, cloudier zones of the world in that it allows greater absorption of
sunlight and manufacture of vitamin D. Dark skin, on the other hand,
protects one from harmful UV rays but also inhibits vitamin D production in
less sunny regions. I cannot remember where I read this, but I seem to
recall that north of 42 degrees north latitude (and south of 42 degrees
south latitude) very dark-skinned people are subject to rickets (from
vitamin D deficiency) if they do not supplement their diets with vitamin D.
Light-skinned people are prone to melanoma in very sunny regions unless they
cover their skin or use some other form of skin protection.

Rich

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