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Author | Topic: Skin colors and latitude | |||||||||||||||||||||||
contracycle Inactive Member |
In africa itself, there is a large variety in skin tone, which makes me doubt a purely developmental change model. Central africans can be very dark, almost blue-black, while southern africans are often very light tan. Thus I prefer the ambient UV approach.
Any comments on the following? "Skin color is one of the most conspicuous ways in which humans vary and has been widely used to define human races. Here we present new evidence indicating that variations in skin color are adaptive, and are related to the regulation of ultraviolet (UV) radiation penetration.... Skin coloration in humans is adaptive and labile. Skin pigmentation levels have changed more than once in human evolution. Because of this, skin coloration is of no value in determining phylogenetic relationships among modern human groups." (N. Jablonski and G. Chaplin, J Hum Evol, 2000) http://www.angeltowns.com/members/racialreal/skincolor.html
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macaroniandcheese  Suspended Member (Idle past 3956 days) Posts: 4258 Joined: |
yes congrats. i was referring to the genetic difference from the ancestors of the bushmen who have been shown to be the oldest via y-chromosome and mitochondrial studies.
plus. you want ambient uv? go to the north pole. jebus. it reflects off everything. are people dark there? no. This message has been edited by brennakimi, 11-12-2004 12:26 PM
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contracycle Inactive Member |
quote: And is there much exposed skin in the north pole?
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mark24 Member (Idle past 5223 days) Posts: 3857 From: UK Joined: |
Contracycle, Bren,
There's nothing wrong with the ambient UV approach, it's just that it is blurred by the migratory habits of ancient humans. The Inuit may very well have relatively high levels of melanin as an adaptation to high UV in the past, but it's now an anachronism since they now live in polar regions. By & large, human populations that have been indigenous for long periods of time in the tropics have darker skin as an adaptation to UV. Mark There are 10 kinds of people in this world; those that understand binary, & those that don't
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macaroniandcheese  Suspended Member (Idle past 3956 days) Posts: 4258 Joined: |
and what about the light-skinned people in papua new guinea? they've been there for ages.
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mark24 Member (Idle past 5223 days) Posts: 3857 From: UK Joined: |
Bren,
As far as I was aware the people of the Solomons & Papua/NG were dark skinned, much more so than the "typical" polynesian.
Here are some more images. They don't look very light skinned to me compared to their more northerly polynesian neighbours. Mark There are 10 kinds of people in this world; those that understand binary, & those that don't
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Coragyps Member (Idle past 762 days) Posts: 5553 From: Snyder, Texas, USA Joined: |
plus. you want ambient uv? go to the north pole.
Actually, there's not that much UV in the arctic. The amount of UV that gets absorbed by the atmosphere goes up very quickly with decreasing altitude, and the Sun never gets higher than 46 degrees even at the Arctic Circle - only 23 degrees at the poles. I don't know if the details of this are online, but it was published in Sky and Telescope maybe ten years ago. The article might even be entombed in a box in my garage.
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macaroniandcheese  Suspended Member (Idle past 3956 days) Posts: 4258 Joined: |
unless jared diamond is wrong...
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macaroniandcheese  Suspended Member (Idle past 3956 days) Posts: 4258 Joined: |
yes but if you want ambience... the uv that does exist is going to be reflected off everything.
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mark24 Member (Idle past 5223 days) Posts: 3857 From: UK Joined: |
Bren,
the uv that does exist is going to be reflected off everything. So what? Sunlight, & therefore UV levels, are much more intense at the equator than the poles. Melanin is an adaptation to high UV levels. There's no point having it, otherwise. In fact there is a very good reason not to have melanin if it can be done without, vitamin D production occurs in the skin & melanin impedes said production. Black children in scandinavia have a higher than average chance of developing rickets, which is why the ancient caucasian stock dropped high melanin levels in the skin like an evolutionary hot potato. The broad pattern of black skin/white skin is associated with latitude in general, it's inescapable. Confused by patterns of human migration & dispersal (about which a lot is known), I agree, but the pattern exists. Melanin exists to block damaging UV radiation which is most intense in the tropics, I'm not sure what you are arguing for or against? Mark There are 10 kinds of people in this world; those that understand binary, & those that don't
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macaroniandcheese  Suspended Member (Idle past 3956 days) Posts: 4258 Joined: |
well see i was involved in this topic a long time ago and then it was very clear that sexual selection was responsible for skin tone (at least the furtherance of darker or lighter varieties in a given area). but now i might just be arguing.
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Parsimonious_Razor Inactive Member |
I ran into this the recently I thought it was an interesting find:
quote: Mackintosh, James (2001). The antimicrobial properties of melanocytes, melanosomes and melanin and the evolution of black skin. Journal of Theoritical Biology 211(2): 101-113. The idea is that melanization of the skin is actually a responce to paraisitization and that variance along latitude is due to parasite load decreasing as you move north and that variance longitudinal might be due to climate shifts that increase or decrease the parasite load.
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macaroniandcheese  Suspended Member (Idle past 3956 days) Posts: 4258 Joined: |
that sounds so much cooler than the other latitude arguments.
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mark24 Member (Idle past 5223 days) Posts: 3857 From: UK Joined: |
Bren,
Re: message 27. So why do caucasians go brown in the sun, because of the heightened risk of parasitisation? If sexual selection was seriously involved in the maintainence of skin melanisation, why did caucasians lose it, & why does it show a pattern of high skin melanisation at higher latitudes? I maintain the most important factor of the maintainence of the phenotype "high melanisation" is high UV. Mark There are 10 kinds of people in this world; those that understand binary, & those that don't
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macaroniandcheese  Suspended Member (Idle past 3956 days) Posts: 4258 Joined: |
because caucasians decided that they liked white skin better. that they found it more attractive. lighter people had lighter families and were attracted to other lighter people. it may have been driven by a purpose, but the aborigines haven't lost their melanin and they've been closer to the pole for longer than anyone has been anywhere outside of africa. why?
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