Talk:Human skin color

What about the new theory that melanin is an anti-infection agent and that rather than people evolving lower melanin in order to let in more light, they did it because they weren't as healthy and so couldn't afford the metabolic cost of melanin production? According to this theory, melanin corresponds to humidity levels (which many viruses and bacteria depend on) instead of light levels. --Ark

Hum, -- never came up in my immunology, antomomy or human evolution classes and I can't find anything (http://www.google.com/search?q=melanin+humidity+infection+%22skin+color++%22&hl=en&lr=&as_qdr=all&start=20&sa=N) about it on Google either. It does sound interesting. Do you have a webpage or better yet a peer-reviewed journal article to point me to for more information? --maveric149, Tuesday, June 11, 2002

Heh. It came up either in Scientific American or New Scientist. Probably sometime in the last year. In the last two years definitely. :)

Basically it was speculation based on some preliminary finding. I don't remember what the finding was though. I just mentioned it because like you said, it's so interesting. -- Ark

Cool I try to find it. It's probably a bit too new and unvarified to include in this article though. --maveric149

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What does this mean?

In general, people with recent ancestors in sunny regions have darker skin than people with recent ancestors in regions that lack much sunlight.

Was the above sentence intended to support idea that acquired characteristics can be inherited? I thought Lysenkoism[?] had been thoroughly discredited. --Ed Poor 19:59 Sep 6, 2002 (UCT)

I think you can get that with usual natural selection arguments. White skin is more susceptible to skin cancer, so you could eliminate them from the gene pool because of that.AstroNomer (Who is not a biologist and is just waving hands)

• I also am not a biologist. However, my understanding is:
  • If you are born light-skinned in a region with intense sunlight levels, your chances of skin cancer are much greater. Ergo genes for fair skin are much less likely to be passed on. There are probably other factors like increased vulnerability to disease as a result that would intensify this.
  • If you are born dark-skinned in a region with low sunlight levels, your body doesn't synthesize as much of a certain nutrient (vitamin D?), which is best catalyzed by sunlight on skin. Ergo, your resistance to disease and such goes down, and again, your genes are far less likely to be passed down through the generations.
• Over many generations this dual selection effect may lead to the grouping of prevalent skin colors according to the amount of sunlight received by, oh, the past few hundred generations in a given locale. -- April

Right, I understand about the "genes being passed on" part. And it accords with ethnographical observations of Northern Europeans being light-skinned and equatorial Africans and Caribbeanns being dark-skinned.

My confusion was about the "recent ancestors" claim in the sentence I first quoted way above. I'd like to revise it so it doesn't give the impression that the process takes place over a couple of generations. Doesn't it take centuries before we start to see any significant differences? --Ed Poor

I see what you mean. Probably he was meaning e.g. african-americans: they have "recent ancestors" from Africa, that were dark skinned because they had had lots of ancestors living there. There is a step missing in the chain.AstroNomer

• Going out on a limb here, with my shaky bio knowledge, but I'd guess that the genes for most skin levels would be present, if not common or commonly expressed, in just about any population. So if two groups of humans colonize a high-sunlight planet and a low-sunlight planet, and then are cut off from intermarriage outside the group, we'd start seeing significant changes between the populations in... well, if you take a "generation" as about 20 years... at a very rough guess, maybe a few centuries?

• I suspect that by "recent" the person was thinking "hundreds or thousands of years in the same place" as opposed to, say, ten thousand to a hundred thousand years, which is (I think) the scale of many major population migrations. Add a lot of caveats that I could be talking complete nonsense here, 'cause I'm far from expert. :) -- April

I thought of "recent ancestors" as not more than 4 generations back, like my great-great-grandparents, who are Polish and Russian Jews (on my mother's side). Thanks for the scientific help. I think I have enough information to edit the article.