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Author Topic:   Skin colors and latitude
mark24
Member (Idle past 4034 days)
Posts: 3857
From: UK
Joined: 12-01-2001


Message 19 of 65 (160063)
11-16-2004 10:05 AM
Reply to: Message 18 by contracycle
11-16-2004 9:44 AM


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

This message is a reply to:
 Message 18 by contracycle, posted 11-16-2004 9:44 AM contracycle has not yet responded

Replies to this message:
 Message 20 by macaroniandcheese, posted 11-16-2004 11:07 AM mark24 has responded

  
mark24
Member (Idle past 4034 days)
Posts: 3857
From: UK
Joined: 12-01-2001


Message 21 of 65 (160086)
11-16-2004 11:47 AM
Reply to: Message 20 by macaroniandcheese
11-16-2004 11:07 AM


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

This message is a reply to:
 Message 20 by macaroniandcheese, posted 11-16-2004 11:07 AM macaroniandcheese has responded

Replies to this message:
 Message 23 by macaroniandcheese, posted 11-16-2004 1:06 PM mark24 has not yet responded

  
mark24
Member (Idle past 4034 days)
Posts: 3857
From: UK
Joined: 12-01-2001


Message 25 of 65 (160168)
11-16-2004 4:11 PM
Reply to: Message 24 by macaroniandcheese
11-16-2004 1:07 PM


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

This message is a reply to:
 Message 24 by macaroniandcheese, posted 11-16-2004 1:07 PM macaroniandcheese has responded

Replies to this message:
 Message 26 by macaroniandcheese, posted 11-16-2004 10:54 PM mark24 has not yet responded

  
mark24
Member (Idle past 4034 days)
Posts: 3857
From: UK
Joined: 12-01-2001


Message 29 of 65 (160340)
11-17-2004 3:18 AM
Reply to: Message 28 by macaroniandcheese
11-17-2004 1:18 AM


Re: An Interesting Find
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

This message is a reply to:
 Message 28 by macaroniandcheese, posted 11-17-2004 1:18 AM macaroniandcheese has responded

Replies to this message:
 Message 30 by macaroniandcheese, posted 11-17-2004 10:28 AM mark24 has responded

  
mark24
Member (Idle past 4034 days)
Posts: 3857
From: UK
Joined: 12-01-2001


Message 31 of 65 (160486)
11-17-2004 11:04 AM
Reply to: Message 30 by macaroniandcheese
11-17-2004 10:28 AM


Re: An Interesting Find
Bren,

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...

Caucasians lost their melanism for a purpose, it interfered with vitamin D production in the skin, I've already talked about this, as evidenced by higher than average incidences of rickets in Scandinavian black children.

Now, we have the knowledge that high UV is harmful & blocked by melanin. We also know that UV & sunlight levels in general are higher as you approach the equator. We also know that humans manufacture vitamin D in their skins & this is associated with light. Ergo, low melanin levels are adaptations to maintain vitamin D production, where there is lessened selective pressure for high level melanism due to low UV levels. High melanin levels are an adaptation to high UV. The different environments provide selective pressures that go in opposite directions as regards melanism.

Now, what do you have to support the sexual selection theory of melanism?

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?

Because they ran around half naked in tropical desert sunshine, perhaps? And I wouldn't describe a country in the tropics that strays extremely close to the equator as being close to the pole! This is evidence for me, not you.

Mark


There are 10 kinds of people in this world; those that understand binary, & those that don't

This message is a reply to:
 Message 30 by macaroniandcheese, posted 11-17-2004 10:28 AM macaroniandcheese has responded

Replies to this message:
 Message 33 by macaroniandcheese, posted 11-17-2004 11:40 AM mark24 has responded

  
mark24
Member (Idle past 4034 days)
Posts: 3857
From: UK
Joined: 12-01-2001


Message 34 of 65 (160545)
11-17-2004 1:17 PM
Reply to: Message 33 by macaroniandcheese
11-17-2004 11:40 AM


Re: An Interesting Find
Bren,

go read jared diamond- the third chimpanzee and leave me alone.

No, I'm not arguing against Jared, I'm arguing against you. I have presented evidence that supports melanism level being related to sunlight levels & therefore latitude. You have asserted without evidence that sexual selection is involved. I don't deny that it may have a bearing, but I'm certainly not going to accept it on your say so sans evidence.

Mark


There are 10 kinds of people in this world; those that understand binary, & those that don't

This message is a reply to:
 Message 33 by macaroniandcheese, posted 11-17-2004 11:40 AM macaroniandcheese has responded

Replies to this message:
 Message 35 by macaroniandcheese, posted 11-17-2004 3:03 PM mark24 has responded

  
mark24
Member (Idle past 4034 days)
Posts: 3857
From: UK
Joined: 12-01-2001


Message 36 of 65 (160663)
11-17-2004 6:08 PM
Reply to: Message 35 by macaroniandcheese
11-17-2004 3:03 PM


Re: An Interesting Find
Bren,

ok how's this. lighter skinned black women are becoming more and more prevalent while darker skinned black women are becoming rarer. darker skinned black men are becoming more and more prevalent and lighter skinned black men rarer. why?

I'm not aware that this is true at all. As far as I'm aware skin colour is not sex-linked chromosomally, therefore what you suggest can't be true. Think about it, parents don't produce lighter females & darker males. The premise being, if you read your text carefully, that females are likely to be lighter, males darker. The offspring are likely to be inbetween. The next generation gets the same mixing.

I think you are confusing, if you excuse the potentially racist overtone (not intended, but descriptive), the "international chocolate" colour of many "blacks", of whom many would be lucky to trace 1/8th of their recent ancestry to Africa. This has nothing to do with sexual selection since males are just as likely to be "mixed race" as females.

Can you name an indigenous population where the females are lighter than males? The very notion belies an ignorance of how genotype affects phenotype, & particularly how such geno/phenotypes are linked to sex chromosomes based upon rather obvious observations of human population in general.

In my last post I asked you to support your sexual selection hypothesis, you haven't done so, in fact you have proposed something contradicted by genetics & not supported by it.

Mark


There are 10 kinds of people in this world; those that understand binary, & those that don't

This message is a reply to:
 Message 35 by macaroniandcheese, posted 11-17-2004 3:03 PM macaroniandcheese has responded

Replies to this message:
 Message 41 by macaroniandcheese, posted 11-18-2004 3:37 PM mark24 has responded

  
mark24
Member (Idle past 4034 days)
Posts: 3857
From: UK
Joined: 12-01-2001


Message 44 of 65 (161195)
11-18-2004 4:32 PM
Reply to: Message 41 by macaroniandcheese
11-18-2004 3:37 PM


Re: An Interesting Find
Bren,

there is no indigenous group of darker males and lighter females... these traits are being selected for by conscious personal choice with whom to mate.

Then why did you say black females are getting lighter & males darker?

Bren writes:

lighter skinned black women are becoming more and more prevalent while darker skinned black women are becoming rarer. darker skinned black men are becoming more and more prevalent and lighter skinned black men rarer

Mark


There are 10 kinds of people in this world; those that understand binary, & those that don't

This message is a reply to:
 Message 41 by macaroniandcheese, posted 11-18-2004 3:37 PM macaroniandcheese has responded

Replies to this message:
 Message 46 by macaroniandcheese, posted 11-19-2004 1:58 AM mark24 has responded

  
mark24
Member (Idle past 4034 days)
Posts: 3857
From: UK
Joined: 12-01-2001


Message 47 of 65 (161385)
11-19-2004 3:26 AM
Reply to: Message 46 by macaroniandcheese
11-19-2004 1:58 AM


Re: An Interesting Find
Bren,

there are no original indigenous groups like that... however, the people in non-indigenous areas are moving in those directions.

Where? And why are there no indigenous populations where this occurs?

As explained previously, & you agreed, skin colour is not sex-linked, therefore when a dark skinned man mates with a light skinned female the offspring is in general inbetween as regards skin colour. This is in evidence in countries like the Dominican Republic where most of the population is a light cross between european whites & black negro. If your hypothesis were true the men would be black & the females white. They aren't, they have become homogenised.

Mark

This message has been edited by mark24, 11-19-2004 03:28 AM


There are 10 kinds of people in this world; those that understand binary, & those that don't

This message is a reply to:
 Message 46 by macaroniandcheese, posted 11-19-2004 1:58 AM macaroniandcheese has responded

Replies to this message:
 Message 49 by Parsimonious_Razor, posted 11-19-2004 1:21 PM mark24 has responded
 Message 50 by macaroniandcheese, posted 11-19-2004 1:41 PM mark24 has responded

  
mark24
Member (Idle past 4034 days)
Posts: 3857
From: UK
Joined: 12-01-2001


Message 52 of 65 (161512)
11-19-2004 2:00 PM
Reply to: Message 50 by macaroniandcheese
11-19-2004 1:41 PM


Re: An Interesting Find
Brennaki,

you don't pay much attention to people do you?

What are you talking about? I have directly challenged you on this more than once, & you accuse me of not paying attention? Draw a line under it.

You have claimed that male preference for light skin & vice versa for females is somehow able to lead to entire populations of light or dark skins? I have been alluding to this problem since you broached the subject, how can this occur? If you have light females & dark males how will all males end up light as in europeans, or vice versa in africans? I have seen the evidence that others have presented on sexual dimorphism as regards skin colour, but still fail to see how this leads to an entire population being light or dark.

Contracycle put it better than I could:

I find it prima facie plausible that men on aggregate are darker than women in a given population, but cannot see how this can give rise to a specifically white local population alone. Because if lightness of tone is a female sexual signifier, and so is darkness in men (the tall, dark stranger of fiction one presumes), then the next generation should show much the same dimorphism, not be driven down only one path.

Do you understand this? It explains the appearance & maintenance of the sexual dimorphism, but in no way explains a directional shift that would drive the entire population lighter or darker.

Mark


There are 10 kinds of people in this world; those that understand binary, & those that don't

This message is a reply to:
 Message 50 by macaroniandcheese, posted 11-19-2004 1:41 PM macaroniandcheese has responded

Replies to this message:
 Message 54 by Parsimonious_Razor, posted 11-19-2004 2:05 PM mark24 has responded
 Message 59 by macaroniandcheese, posted 11-20-2004 12:39 AM mark24 has responded

  
mark24
Member (Idle past 4034 days)
Posts: 3857
From: UK
Joined: 12-01-2001


Message 55 of 65 (161515)
11-19-2004 2:07 PM
Reply to: Message 49 by Parsimonious_Razor
11-19-2004 1:21 PM


Re: An Interesting Find
Hi Parsimonious,

Thanks for your information.

I have the same conceptual problem as contracycle with the sexual selection of males for light females, & females for dark males being able to produce a directional pressure in one way or the other. Surely it would simply maintain sexual dimorphism as is in the next generation?

Mark


There are 10 kinds of people in this world; those that understand binary, & those that don't

This message is a reply to:
 Message 49 by Parsimonious_Razor, posted 11-19-2004 1:21 PM Parsimonious_Razor has not yet responded

  
mark24
Member (Idle past 4034 days)
Posts: 3857
From: UK
Joined: 12-01-2001


Message 56 of 65 (161520)
11-19-2004 2:22 PM
Reply to: Message 54 by Parsimonious_Razor
11-19-2004 2:05 PM


Re: An Interesting Find
PR,

I have not seen any evidence that there is sexual preference for DARKER men

Yes, that makes sense, but it also contradicts Brennakimi who maintains that there is sexual preference for darker men among females. Regardless, I'll take your word over hers unless she can produce evidence to support this.

but also have seen no convincing evidence that there is preference for lighter men.

But assuming random sorting during meiosis it wouldn't matter, if one sex had a preference, & the other didn't either way, then there would be a directional pressure in favour of that sex across the population as a whole.

Mark


This message is a reply to:
 Message 54 by Parsimonious_Razor, posted 11-19-2004 2:05 PM Parsimonious_Razor has responded

Replies to this message:
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mark24
Member (Idle past 4034 days)
Posts: 3857
From: UK
Joined: 12-01-2001


Message 61 of 65 (162334)
11-22-2004 11:32 AM
Reply to: Message 59 by macaroniandcheese
11-20-2004 12:39 AM


Re: An Interesting Find
Brennakimi,

If you read my responses to Parsimonious Razor, you will see that I 1/ understand what sexual selection is, & 2/ accept his rationale for itas regards melanisation in humans.

You have hopelessly confused the issue by asserting that males prefer lighter females, & females darker men. As has been pointed out to you by both contracycle & myself, & you have utterly failed to address the issues raised, namely that this leads to pressures both for & against melanisation. At best it maintains sexual dimorphism, but does not drive it in either direction.

Do you understand? It would have been helpful if you had attempted to understand the corollary of your assertion earlier, & you would have saved us both time. Do you see your error?

Mark


There are 10 kinds of people in this world; those that understand binary, & those that don't

This message is a reply to:
 Message 59 by macaroniandcheese, posted 11-20-2004 12:39 AM macaroniandcheese has not yet responded

  
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