Why are we white?

[shkrobius]

The common answer is that up North there is no selective pressure to keep sun-blocking melanin in the skin whereas the pale skin enhances photogeneration of vitamin D. Whitening of European skin is very recent, just 6-12 kya; http://www.sciencemag.org/cgi/content ( Read more... )

Comments

[i_eron]

Thank you for the paper pointers. I came across something by Cavalli-Sforza in the past, but "niasilil", these are much more interesting.
Yes, I have heard about the light versus darkness wars in India. I think this example is irrelevant. In this scenario some non-agricultural tribes have conquered an agricultural society. Agricultural societies are just so much more populous than most nomads. It is no wonder the Neolithic Europe conquest by "farmers" was different. Why do you call it "ethnic cleansing" and "genocide"? Europe was sparsely populated. The population density ceiling is much lower for hunters-gatherers than for farmers. Many farmers came, the total population grew. The 60% figure does not necessarily mean genocide, it may mean some nice mixing with the more advanced newcomers, or, more likely, something in between. This 40/60 ratio may well have been the same as the natives to newcomers population ratio. The comparable figures for the European colonization of the Americas are anywhere between 99 and 30% in different places.
What should be the right sequence of events? The transition to agriculture was very gradual and took a couple of thousands of years around 10-8 kya, right? It has happened somewhere in the region of Israel, Syria, Turkey and Iraq. Gradually the population grew and began to spread into the sparsely populated Europe. The first white people have appeared in Europe before the spread of agriculture - this is the key point. I do not have access to the Science paper, but you quote 6-12 kya, this is still before, not at the same time as, right? Do you think these early Middle-Eastern farmers were white (I mean, of the Norwegian sort rather than the Italian one)? Did they become white along their slow journey into Europe? If the conquering-assimilating white people have spread from the South-East, why the current color gradient is clearly North-South (except all those Saami, Iberian Irish and such)?
I did not explain myself well the first time. My suggestion depends on white skin coming before agriculture, or at least before the rapid population growth that followed it. In this case, the first white people must have consisted of a few tribes living among darker-skinned tribes. The question is then split into two: 1. How did they appear? 2. Why did they succeed to spread so widely? My partial answer is 1. Chance mutation 2. Chance victory in local tribal warfare, early adoption of agriculture, population growth. I am not arguing against the other explanations, they may enforce my argument by adding some advantage mechanism to the second “chance”, but they are not essential. I do not think the early Middle-Eastern farmers were whiter than the current ones. The white tribes might have picked up agriculture perhaps somewhere in the Eastern Europe, then spread West and South-West. For a large body of people to change skin color there has to be a strong and persistent selection mechanism. For a small number of people it may be chance.
Is the pale skin really recessive? Is it not just a matter of relative numbers of white and dark-skin people in the mix? It is a combination of many genes, not a single on/off, right?

[shkrobius]

Sparse population only makes the decimation of this population more complete. I meant genocide and ethnic cleansing technically, as the gene pool of the natives has dispappeared; whether it involved atrocity, who knows. I am inclined to think it was >> 60%, on several counts. First, the newcomers brought with them disease they acquired from domesticated animals. Second, unless there is total subjugation or replacement, the conquerors acquire the language of the conquered (there are exceptions, with the Nordic conquest of England, but even that is in doubt, I've written about it before: Why do we speak English?). The fact is that Indo-Aryan languages completely replaced the native ones. Another reason is that the gene is recessive. The pigmentation is controlled by many genes, but what makes European unique in its pinky lightness seems to be one gene, see below. Furthermore, as you correctly pointed out, there are recent precedents of population replacement during Columbian exchange. It makes sense that something much like this genocide happened during the conquest of Europe.

It is hard to argue with your updated scenario on the factual basis, as it is all conjectural, but the one I have in my mind is different, and it is tied with my ideas as to the general effect of agriculture on human evolution, which I consider to be supremely negative. Whiteness is only small part of it; the worst is dramatic shortening of life expectancy, adaptations to toil and periodic famine, and co-existence with animals. Rapid aging, disease, etc. ensued. Domestication of people by plants had a terrible tall on humanity, but it had one unforeseen consequence, which was concentrating population increase that, in the time of the famine, caused mass migrations. Sparsely populated Europe was no match to the waves of such migrants. I think that whiteness did originate in the Fertile Crescent; that we do not see much of it there presently is the reflection of its turbulent history. I consider it an adaptation to chronic vitamine D deficiency, and it makes sense that the first agricultural people paid the highest price for switching to the insanity of agriculture. Dietary complements were especially poor there, which is another reason to think of it as a cradle of whiteness. The whiteness of the European type was certainly a mutation and I bet the nomadic neighbors were all in shock. I have little doubt that the story of Cain's mark is historical; this mark (e.g., whiteness) are genetic adaptations to subsistence farming. The last laugh was of the mutants, because farming turned them into organized warriors; nothing stopped them when they started to roll out of the Fertile Crescent. So 99% of the Europeans have this slc24a5 gene; the North-South tan distribution is not from different expression of this particular gene, there are complementary genes that also regulate the actual skin color. To me, "whiteness" is not as much as the visible skin color, but the genetic mark of subsistence farming and early experiments with civilization. You suggest that whiteness appeared first, spread, resulted in a large white population, and then its possessors began to farm. I do not think it makes much sense. The mutant gene could've been in the population that switched to farming, but it is unlikely that it was frequent. To become so, there should be selective pressure. This gene is only one of many we have as genetic adaptation to farming, people just started looking for those. Think of the effect of introducing wheat farming to a population with gluten introlerance or cowherding to a population with lactose intolerance. The Africans are 90% lactose intolerant, for example. Farming is not just a matter of "learning" the craft and acculturation. Surviving on it year in and year out requires multiple adaptations, some of them quite extreme. I do mean it when I am talking about "white men's burden."

[i_eron]

Now I can see that your view is much more coherent that mine, so the best way forward is to probe your points. This is the summary of what I have understood - please correct me.
The first white people appeared as a minority among the farmer population of the Middle East; then participated in the replacement of the Neolithic population of Europe. The special whiteness has spread mostly in the Northern Europe due to being evolutionary advantageous in the cold climate for the farmers’ way of life. It has later disappeared in the Middle East’s farming societies ultimately because it is recessive and in the warm climate it is not advantageous.
I am not sure I got you right - if whiteness is an adaptation to farming in general (Cain's mark is a powerful story) and not only in combination with the cold climate, it is incredible that the ancient Egyptians, Babylonians and others were not commonly white which they were not. It is also strange that there is a clear gradual decrease in whiteness along the North-South direction in Europe. If whiteness is advantageous only in the cold climate, there is a difficulty explaining the necessary large percentage of the recessive whiteness gene in the immigrant farmers.
I have looked up the story of the slc24a5 gene. The changed form is found in almost all Europeans (presumably including Italians and Greeks) but in a very few of the other three major races. It is not said but I assume it appears in all white people including the ones in the Middle East and North India, not just in the European “especially pale” white, because it is clearly associated with the major race. It is also said to be responsible for between 25 and 38% of the whiteness. The D-vitamin and UV light explanation is then not about this particular gene at all, but about the skin color and a combination of other genes that cause it.
So, if your original question is about Cain’s mark, the genetic price for farming, it consists in part of this slc24a5 mutation and is present in North Africa and half of Asia, not just in Europe. Perhaps it was the transition to farming that formed the white race.
But if your question is about the “unique pink lightness” of the Northern Europeans, it should be the D-vitamin and similar stories, not the slc24a5 story and not the transition to farming.

[shkrobius]

You understood it more-or-less correct, with one caveat. Whiteness (pinky skin) is not exactly a mutation. It is the ancestral condition of the (hairy) hominids. Whiteness can be viewed as the return to this condition. As for the Egyptians, first, the Egyptians were not exactly Africans. I do not want to get into this controvercy, but you should realize that the race of the egyptians is by no means clear. Many mummies, for example, have red and blond hair, and there multiple depictions of very light and even pink skin people. As far as I know, the ancient and modern Egyptians genetically are very close and the modern ones group with Europe/Middle East, i.e. these are the same fertile crescent farming folks that found a new place for themselves. People that depend on rivers (Egyptians, Babylonians) for farming can afford having a bit darker skin due to vitamin D intake from complementary diet (fish). Observe that in the case of the ancient Egyptians there is not much evidence for genetic mixing with sub-Saharan Africans. Here are some papers by Cavalli-Sforza and the others http://www.geocities.com/enbp/genetics.html
The mummies have mainly been tested for haplogroups, the real genetic studies are still ahead. I think that Diamond and his ilk who believe in the acculturation to farming are simply wrong. The Egyptians were part of the same Middle Asian group of "white" farming people as the rest of us. The actual skin color does not matter as it varied wildly among the Egyptians. For years the afrocentrists were using M1 haplotype to argue that the Egyptians were not Eurasians. Now we know better
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1945034
Again, it all depends on what do you mean by whiteness. To me it is not the actual color of one's skin, it is having the gene(s) capable to cause significant decoloration of the pigments when there is vitamin D deficiency (for whatever reason - insolation, diet). You are correct that I view all people who share fertile crescent ancestry, with its extreme adaptations to symbiosis with cereal grasses, including this one, as "white." Being white is about having Cain's mark, and white skin is just the most visible part of it. Socialization (the emergence of a human hive) is another manifestation of this adaptation, and there are more. The general idea is that the agriculture is a form of symbiosis and the latter means adaptations on both ends. The "whites" are at the forefront of evolution shaped by the needs of our symbiont, the grassy plants, trying to expand their area for the expence of the forests. Adaptations of East Asians to rice farming is a rival attempt to the same end.