Understanding through Discussion


Welcome! You are not logged in. [ Login ]
EvC Forum active members: 69 (9033 total)
78 online now:
anglagard, dwise1, kjsimons, PaulK, Percy (Admin), Phat (AdminPhat), ringo, Tangle (8 members, 70 visitors)
Newest Member: Johnny
Upcoming Birthdays: Percy
Post Volume: Total: 885,078 Year: 2,724/14,102 Month: 389/703 Week: 42/168 Day: 11/31 Hour: 0/1


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   Skin colors and latitude
contracycle
Inactive Member


Message 16 of 65 (158655)
11-12-2004 8:58 AM


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


Replies to this message:
 Message 17 by macaroniandcheese, posted 11-12-2004 12:25 PM contracycle has responded

  
macaroniandcheese 
Suspended Member (Idle past 2791 days)
Posts: 4258
Joined: 05-24-2004


Message 17 of 65 (158736)
11-12-2004 12:25 PM
Reply to: Message 16 by contracycle
11-12-2004 8:58 AM


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


This message is a reply to:
 Message 16 by contracycle, posted 11-12-2004 8:58 AM contracycle has responded

Replies to this message:
 Message 18 by contracycle, posted 11-16-2004 9:44 AM macaroniandcheese has not yet responded
 Message 22 by Coragyps, posted 11-16-2004 12:33 PM macaroniandcheese has responded

  
contracycle
Inactive Member


Message 18 of 65 (160060)
11-16-2004 9:44 AM
Reply to: Message 17 by macaroniandcheese
11-12-2004 12:25 PM


quote:
plus. you want ambient uv? go to the north pole. jebus. it reflects off everything. are people dark there? no.

And is there much exposed skin in the north pole?


This message is a reply to:
 Message 17 by macaroniandcheese, posted 11-12-2004 12:25 PM macaroniandcheese has not yet responded

Replies to this message:
 Message 19 by mark24, posted 11-16-2004 10:05 AM contracycle has not yet responded

  
mark24
Member (Idle past 4059 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

  
macaroniandcheese 
Suspended Member (Idle past 2791 days)
Posts: 4258
Joined: 05-24-2004


Message 20 of 65 (160075)
11-16-2004 11:07 AM
Reply to: Message 19 by mark24
11-16-2004 10:05 AM


and what about the light-skinned people in papua new guinea? they've been there for ages.

This message is a reply to:
 Message 19 by mark24, posted 11-16-2004 10:05 AM mark24 has responded

Replies to this message:
 Message 21 by mark24, posted 11-16-2004 11:47 AM macaroniandcheese has responded

  
mark24
Member (Idle past 4059 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

  
Coragyps
Member
Posts: 5551
From: Snyder, Texas, USA
Joined: 11-12-2002


Message 22 of 65 (160094)
11-16-2004 12:33 PM
Reply to: Message 17 by macaroniandcheese
11-12-2004 12:25 PM


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.


This message is a reply to:
 Message 17 by macaroniandcheese, posted 11-12-2004 12:25 PM macaroniandcheese has responded

Replies to this message:
 Message 24 by macaroniandcheese, posted 11-16-2004 1:07 PM Coragyps has not yet responded

  
macaroniandcheese 
Suspended Member (Idle past 2791 days)
Posts: 4258
Joined: 05-24-2004


Message 23 of 65 (160097)
11-16-2004 1:06 PM
Reply to: Message 21 by mark24
11-16-2004 11:47 AM


unless jared diamond is wrong...

This message is a reply to:
 Message 21 by mark24, posted 11-16-2004 11:47 AM mark24 has not yet responded

  
macaroniandcheese 
Suspended Member (Idle past 2791 days)
Posts: 4258
Joined: 05-24-2004


Message 24 of 65 (160098)
11-16-2004 1:07 PM
Reply to: Message 22 by Coragyps
11-16-2004 12:33 PM


yes but if you want ambience... the uv that does exist is going to be reflected off everything.

This message is a reply to:
 Message 22 by Coragyps, posted 11-16-2004 12:33 PM Coragyps has not yet responded

Replies to this message:
 Message 25 by mark24, posted 11-16-2004 4:11 PM macaroniandcheese has responded

  
mark24
Member (Idle past 4059 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

  
macaroniandcheese 
Suspended Member (Idle past 2791 days)
Posts: 4258
Joined: 05-24-2004


Message 26 of 65 (160285)
11-16-2004 10:54 PM
Reply to: Message 25 by mark24
11-16-2004 4:11 PM


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.

This message is a reply to:
 Message 25 by mark24, posted 11-16-2004 4:11 PM mark24 has not yet responded

Replies to this message:
 Message 27 by Parsimonious_Razor, posted 11-17-2004 12:57 AM macaroniandcheese has responded

  
Parsimonious_Razor
Inactive Member


Message 27 of 65 (160308)
11-17-2004 12:57 AM
Reply to: Message 26 by macaroniandcheese
11-16-2004 10:54 PM


An Interesting Find
I ran into this the recently I thought it was an interesting find:

quote:
"A biological issue that has not been satisfactorily resolved is the role of melanin in skin and other animal tissues. A hypothesis is outlined here to account for the evolution of black skin and the ubiquity of melanin in vertebrate tissues. Evidence is presented that melanization of skin and other tissues forms an important component of the innate immune defense system. A major function of melanocytes, melanosomes and melanin in skin is to inhibit the proliferation of bacterial, fungal and other parasitic infections of the dermis and epidermis. This function can potentially explain (a) the latitudinal gradient in melanization of human skin; (b) the fact that melanocyte and melanization patterns among different parts of the vertebrate body do not reflect exposure to radiation; (c) provide a theoretical framework for recent empirical findings concerning the antimicrobial activity of melanocytes and melanosomes and their regulation by known mediators of inflammatory responses."

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.


This message is a reply to:
 Message 26 by macaroniandcheese, posted 11-16-2004 10:54 PM macaroniandcheese has responded

Replies to this message:
 Message 28 by macaroniandcheese, posted 11-17-2004 1:18 AM Parsimonious_Razor has not yet responded

  
macaroniandcheese 
Suspended Member (Idle past 2791 days)
Posts: 4258
Joined: 05-24-2004


Message 28 of 65 (160318)
11-17-2004 1:18 AM
Reply to: Message 27 by Parsimonious_Razor
11-17-2004 12:57 AM


Re: An Interesting Find
that sounds so much cooler than the other latitude arguments.

This message is a reply to:
 Message 27 by Parsimonious_Razor, posted 11-17-2004 12:57 AM Parsimonious_Razor has not yet responded

Replies to this message:
 Message 29 by mark24, posted 11-17-2004 3:18 AM macaroniandcheese has responded

  
mark24
Member (Idle past 4059 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

  
macaroniandcheese 
Suspended Member (Idle past 2791 days)
Posts: 4258
Joined: 05-24-2004


Message 30 of 65 (160457)
11-17-2004 10:28 AM
Reply to: Message 29 by mark24
11-17-2004 3:18 AM


Re: An Interesting Find
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?

This message is a reply to:
 Message 29 by mark24, posted 11-17-2004 3:18 AM mark24 has responded

Replies to this message:
 Message 31 by mark24, posted 11-17-2004 11:04 AM macaroniandcheese has responded

  
Newer Topic | Older Topic
Jump to:


Copyright 2001-2018 by EvC Forum, All Rights Reserved

™ Version 4.0 Beta
Innovative software from Qwixotic © 2021