Geography and Skin Color

I thought some people might find this abstract interesting in light of a previous discussion on here in which someone was pushing the claim that differences in skin coloration had something to do with a general preference amongst men worldwide for light-skinned women.

Skin coloration in indigenous peoples is strongly related to levels of ultraviolet radiation (UVR). In this study, the relationships of skin reflectance to seasonal UVR levels and other environmental variables were investigated, with the aim of determining which variables contributed most significantly to skin reflectance. The UVR data recorded by satellite were combined with environmental variables and data on human skin reflectance in a geographic information system (GIS). These were then analyzed visually and statistically through exploratory data analysis, correlation analysis, principal components analysis, least-squares regression analysis, and nonlinear techniques. The main finding of this study was that the evolution of skin reflectance could be almost fully modeled as a linear effect of UVR in the autumn alone. This linear model needs only minor modification, by the introduction of terms for the maximum amount of UVR, and for summer precipitation and winter precipitation, to account for almost all the variation in skin reflectance.

In plain English, we don't need to posit any hypothetical ingrained yearning for Scandinavian women amongst all the men of the world to obtain the results we see out there across the globe, and we don't even need to buy the claim that men anywhere have any consistent preference one way or another; all we need to do is take a look at latitude, and the assumption of a linear relationship between UVR exposure and fertility does the whole job for us. Sexual selection is a superfluous hypothesis in explaining human color variation.

Comments

[dearieme]

The nuances of skin colour didn't really occur to me until middle age when I saw a young Indian woman wearing gold rings and necklace. The gold looked better on her particular hue of skin than I'd ever seen before. For gold, or at least gold of the particular composition that she was wearing, her skin was the perfect complement. Or vice versa. My point is not racial, of course, but aesthetic.

[Jim]

"we don't even need to buy the claim that men anywhere have any consistent preference one way or another..."

It obviously flips all over the map, sometimes within the lifespan of a single generation. Compare the fashion in body shape in the US now to what it was in the twenties or so.

Ever since someone pointed out that both ceratopsians and cervids evolved hug racks of antlers or rills as a form of sexual competition rather than purely for defense, I have wondered how many human traits serve the same function. What other advantage can there be to blond hair, blue eyes, dark skin (*darker than needed for protection) and a lot of other variations from the default settings for humans? They look like attention-grabbers. Certainly blue eyes can be arresting to the point of creepiness if you aren't used to that.

*What I mean is that since Senegal can hardly be any sunnier than Cambodia, there has to be some explanantion for why Wolof are darker than Khmer.

[Abiola Lapite]

"What I mean is that since Senegal can hardly be any sunnier than Cambodia, there has to be some explanantion for why Wolof are darker than Khmer"

Sexual selection has absolutely nothing to do with it. The ancestors of the residents of Senegalese have been in high UV exposure zones longer than those of the Khmer, who migrated downwards not so long ago. It's precisely the same reason why Africans are darker than natives of the Americas residing at the same latitude.

[Jim]

I understand the difference in time depth. I'll try a different example; let's say people we compare them with people in Kenya. Same conditions.

No, wait on the difference in exposure to UV for the Khmer - the straightest path out of Africa to SE Asia leads through equally sunny areas. It amounts to the same length of time.

We need Razib to tell us how long it would take to achieve that degree of mutation. It certainly took less time to lose pigmentation in Eurpe and Siberia.

[Abiola Lapite]

"No, wait on the difference in exposure to UV for the Khmer - the straightest path out of Africa to SE Asia leads through equally sunny areas. It amounts to the same length of time."

Rubbish. The ancestors of the Khmer came primarily from the North; why do you think they look Sinified?

"We need Razib to tell us how long it would take to achieve that degree of mutation."

WTF? As if Razib had some expertise in population genetics that I lack! I don't "need" him or anyone else to tell me anything; what you have to say on this issue is simply a load of bunk.

"It certainly took less time to lose pigmentation in Eurpe and Siberia."

Believe whatever you want. You don't know what the hell you're talking about.

[Julian Elson]

I wonder if the selection of lighter skins is compounded not only by the latitude effect of sun exposure per se, but by the coldness of the weather which forces more clothing in colder areas and less clothing in warmer ones?

As far as I can tell, the basic tradeoff for skin colors is sunburn resistance vs. vitamin D production. If both tropicals and extreme-climate dwellers wore equal amounts of clothing, then you would already see some effects in skin color variation, but the extreme-dwellers' need for vitamin D is compounded by the fact that they cover most of their skin for a lot of the year, while the tropicals' need for sunburn protection is compounded by the fact that they cover less of their skin. (this assumes that clothing styles are a function of environment, though that doesn't explain some of the really weird clothing styles, like high-heel shoes, those Karen neck stretchy rings, or ties)

I wonder if vitamin D deficiency is a big problem among burka-wearing Afghan women.

[Julian Elson]

(if this is the case, one would model two factors, I suppose: weather and sunlight. These two are usually related, but one might find exceptions: for example, the gulf stream's warming of Europe might lead one to expect Europeans to have darker skin than folk of an area with equal latitude, but without warming weather patterns, who had wear more clothing than typical Europeans. Maybe the Chaplin paper has already taken all of this into account.)

[Mitch]

Not that facts really mean much in discussions like these, but anyway, the following Scientific American article explains things simply/was entertaining enough for me:

google Skin Deep Scientific American jablonski

(oops, the coauthor of the sciam article wrote the article you're referring to, so not exactly independent corroboration).

[Jim]

“Rubbish. The ancestors of the Khmer came primarily from the North; why do you think they look Sinified?”

In comparison to other groups in the area, such as the Vietnamese on one side and the Thai on the other, they are the least Sinified of all. The Austroasiatic languages, Mon-Khmer and Munda, all orient east-west and even if there were at once time more of these languages to the north than survive now, it is unlikely that China was ever the proto-homeland, and suggestions to that effect appear to be made more in the interest of thoroughness than because there is any real substance to them. Language is obviously not conclusive, but in the main it correlates with genetic groupings and is one piece of admissible evidence.

As for genetic grouping:

There is no unified Sinitic genetic grouping - Cavalli-Sforza's discussion of the bifurcation of northern and southern Chinese populations going back to the Paleolithic:
http://www.pnas.org/cgi/content/full/95/20/11501

But even if there were, the ultimate origin of such a group is probably south of China - SE Asian origin East Asian populations:
http://72.14.207.104/search?q=cache:ls7j5qZaBWkJ:hpgl.stanford.edu/publications/HG_2000_v107_p582.pdf+sinitic+haplotype&hl=en

Though of course there may have been several remigrations southward giving rise to admixtures in pre-existing SE Asian populations, populations which had never left.

Discussion of Austric populations, geographical distribution, long-range linguistic affliations and physical anthropology:
http://www.angelfire.com/rant/tgpedersen/austric.txt

Blood type comparison between Thai, of obvious northern origin, and Khmer:
http://content.karger.com/ProdukteDB/produkte.asp?Aktion=ShowPDF&ProduktNr=224250&Ausgabe=227582&ArtikelNr=48600&filename=48600.pdf

Mon-Khmer and Nicobarese mitochondrial DNA comparison.
http://muse.jhu.edu/cgi-bin/access.cgi?uri=/journals/human_biology/v073/73.5prasad.pdf&session=57343762

“WTF? As if Razib had some expertise in population genetics that I lack!”
Not more expertise necessarily, but more interest to go into detail. That’s all I meant.

"It certainly took less time to lose pigmentation in Europe and Siberia." believe whatever you want. You don't know what the hell you're talking about.
The recentness of settlement in Europe and Siberia is not a matter of belief, it is uncontroversial. It is known when the ice sheets melted and settlement became possible. Any adaptations to those environments would postdate that settlement.

[Abiola Lapite]

"Mon-Khmer and Nicobarese mitochondrial DNA comparison."

Do you realize how ridiculous it is to use what is effectively a *single* locus to say something about relatedness? Clearly not; as I said, you don't know what you're talking about.

"The recentness of settlement in Europe and Siberia is not a matter of belief, it is uncontroversial."

Oh really? What are your "uncontroversial" sources, and what do they tell you?

"It is known when the ice sheets melted and settlement became possible."

You have me in stitches here - this is so ridiculous that I can't stop myself from laughing. So when exactly are you saying Europe was settled again?

[Jim]

Glad to make you laugh. I am accomplishing something at least with this.

Now that I look around a bit, whever the ice was or whenever it receded, the refugia had been settled for 40,000 years or so and that amounts to settlement of a kind. That conditions the genetic situation, not actual amount of available land to settle. So I concede that point.

As for that digression about the Khmer and other tropical Asian populations, the case doesn't stand or fall on any one fact, and I didn't offer just one. One locus is ridiculous, but that wasn't the all of the evidence. The point is that there is no real evidence for a northern origin for the Khmer, unlike the Thai or the Viet. Admixture from the north is not the same thing as northern origin.

Anyway, back to your main point about the linear relationship between UV exposure and skin tone - here again, as the abstract points out, it is actual UV exposure that matters, and SE Asia gets clouded over a lot. That may be all ther is to it.

[Lycansupreme]

Have any of you guys actually seen Cambodians or went to Cambodia, and not just guesstimated about their appearance from that skin color distribution chart (whose accuracy is quite questionable)? Not only are their features a bit different from other southeast asians, but their skin color is alot darker as well. I wouldn't say it is pitch black like some African tribes but they are still *very dark*, like Indian subcontinental folks. Which, surprisingly, has been by noted by some Westerners who have traveled or even lived there. This is what I've gathered not only from numerous Internet postings, but also people who have traveled or lived there, from travel guide books, and even some Khmers themselves (albeit not always enthusiastically). I'll post some links later on.

[Chuckles]

I doubt that many African "tribes" are as pitch black as you suggest.

[Lycansupreme]

I said *SOME*, not all African tribes/ethnic groups.

[Lycansupreme]

http://www.khmerinstitute.org/reviews/rev2a.html
"Loung later follows up this description of her Chinese mother by making a generalized description that "[p]ure Khmer have curly black hair, flat noses, full lips, and dark chocolate skin."

http://www.vagabonding.com/travelogue/000061.html
"Khmers are unique and handsome in appearance. Distinct from their Southeast Asian neighbors, Khmers more closely resemble people from the Indian Subcontinent. This makes sense, as Cambodia was historically an important station on the Indian-Chinese trade route."

http://www.deanbarrettmystery.com/one_night_in_bangkok.htm
"My first impression was how dark the hundreds of Cambodians staring at us were. It reminded me of my travels in India. No, they were not that dark, but darker than the city Thais, certainly."

http://www.128ontour.com/rbericht13-17e.htm
"After two hard days of cycling we reached Phnom Penh. It is still amazing despite of all the things we know how different the Cambodian people look compared to the Vietnamese. Their skin has the colour of coffee, most of them have real dark, round eyes – not at all like what we imagine when we think of Asia. "

http://www.iamtonyang.com/index.php?date=050404
"i arrived in cambodia last night. as soon as we left the vietnam-cambodia border crossing after a long wait, i was in love with the country. it's the first time where i've been somewhere and it felt FOREIGN. there are more dusty dirt rounds here than actual paved streets, and everything here is written in khmer, even the street signs, so i have no idea where i am. the people here are beautiful, dark like indians but with asian features."

http://www.worldrambler.com/article29.htm
"Passing through the villages I can see the lack of infrastructure this was all reminding me much like India. Even the people them selves. More dark skin and less Asian looking The people here did not quite look like their neighbors of Vietnam or Thailand."

[Lycansupreme]

The below passage is from a white western male who is actually teaching in living in Cambodia:

http://drouillard.blogspot.com/
"3.22.2005
I experienced some blatant racism today: a candidate for a teaching job came into our school requesting an interview. I was chatting with the Director of Studies in his office at the time when this became known. The Cambodian director of studies (the one who deals primarily with the Cambodian clientele) told the foreign (American) director that she was waiting and said, almost literally, not to hire her ("we're not interested in hiring her") even though she is American, and our school is called the American Academic Center--it's connection to America supposedly being its American Teachers. The expressly understood reason was because she's black. Of course Cambodians aren't really that far from being considered "black" as it were, they have the same nose and with enough sunlight, some pretty dark skin. Self hatred is the most potent kind. "

"3.10.2005
It's tragicomedy to see what some of the women do to their faces---white powder pasted on and crusty like they woke up in the morning and and the first thing they did was douse their faces in flour. You can just imagine the other silly Khmer women complimenting her beautiful complexion: she's like a silly, serious and entirely unfunny clown-lady. But that's reality and how is that relevant? You can see the lines underneath their chin where the black skin starts again and it's obvious that they've been powdering their face like this for their entire lives. Tracing the face just under the chin resides a permanent powder-ending line. The notion that this could be mistaken for natural must be one of the great follies of the 21st century. This smothers patently obvious, rips apart blatant and stifles appalling--meaning is inundating by such unholy behavior. You're possessed and unable to react, to laugh, smile, gawk; all you can hope to do is make a mental photo for processing at later date. A different time, a different place where you can safely decipher its meaning.

Those are the "affluent" women--i.e. the ones who's husbands work for the military or government. The average Khmer woman can't afford white powder and must rely on her natural skin tone and staying out of the sun to maintain that coveted whiteness.

Along with a cultural disdain for blackness there's a similar disdain for small noses with rounded nostrils. My rather fleshy pointy European nose has been a point of fascination for many a Khmer woman. Some of them want to touch it and run their hands from bridge to point as if a genie would come out and grant them one wish--the wish, of course, would be to have white skin.

When I've asked my students to compare themselves to their siblings in writing exercises, most of them mention skin color. I.E. "my brother is taller than me and darker. But I am more clever. Etc." "

[PnP]

Do these anthropologists actually bother to visit all the countries when they do all this research and make these statements? Or do they just rely on second-hand knowledge and stereotypes (i.e. all southeast asians look alike)? Hell, I live around a large cambodian-american community and alot of them are quite dark-skinned.