How Europeans evolved white skin

[PNGarrison]

"Even lactase persistence does not bestow a purely biological advantage per se so great as to explain its rapid predominance in Northern Europe and its considerable presence even in Southern Europe. After all, there are plenty of other foods to consume besides raw milk. Rather, social behavior must also have played a role, just as it does today: Once milk-drinking becomes common in a society (or at least among the privileged class), those who are lactose-intolerant are considered diseased or at least annoying, and therefore socially disadvantaged."

How do you know what part of the selection coefficient of lactase persistence or light skin is attributable to a direct biological effect or to social effect? I've never seen any way to measure that. You can measure an allele frequency at one time and at a later time and calculate a selection coefficient but it is extremely difficult to tell what mechanisms contribute to it.

You are making an assertion, but I can't see what objective support you have for it. "Political correctness" is a common insult in political "arguments," but it doesn't have much relevance in science.

[PNGarrison]

"Why do I get the impression that this article is about shoring up the recent paper on a massive invasion from the Steppe in to western Europe 4,500ybp?"

The article on natural selection used the same data set as the recent paper about the steppe "invasion."

[PNGarrison]

Direct Estimates of Natural Selection in Iberia Indicate Calcium Absorption Was Not the Only Driver of Lactase Persistence in Europe

http://mbe.oxfordjournals.org/content/early/2014/02/17/molbev.msu049.full

Interesting in regard to this area. They rightly refer to the proposals on mechanisms as "speculation."

[lgmayka]

"Political correctness" is a common insult in political "arguments," but it doesn't have much relevance in science.

You are correct that political correctness has no place in real science, but we nevertheless see it often--very often in pop-sci articles written by sensationalistic journalists, but sometimes even in scholarly papers, due either to the authors' own bias or simply as a way to get through peer review.

In late 2012, some authors--one of whom is personally known to me--published a paper with important new data. The paper's conclusion, however, gave a politically correct and totally unjustified interpretation. The author known to me later confided that the conclusion had to be written thus, otherwise powerful people in academia would never have permitted its publication, at least not in a timely fashion.

The general rule in academia is: If the data is reliable, great! Use it! But form your own conclusions. In particular, a graduate student trying to get his PhD in a reasonable timeframe is not going to waste three years of his life debating his thesis' conclusion with powerful people--he will simply rewrite it the way they want it. He knows that the data is the valuable, enduring part of the thesis anyway.

[PNGarrison]

You didn't explain how you know what part of the selection coefficient it due to what mechanisms. The paper I referenced actually provided a way to get at one aspect of it. They looked at ancient DNA in southern Europe where lack of sunlight would not be an issue and still found strong selection for lactase persistence. They can't say what causes the selection but the vitamin D mechanism seems to be ruled out for these samples.

[1798]

You didn't explain how you know what part of the selection coefficient it due to what mechanisms. The paper I referenced actually provided a way to get at one aspect of it. They looked at ancient DNA in southern Europe where lack of sunlight would not be an issue and still found strong selection for lactase persistence. They can't say what causes the selection but the vitamin D mechanism seems to be ruled out for these samples.

What has lactase persistence got to do with light skin?

[dna]

What has lactase persistence got to do with light skin?

Vitamin D is in milk.

Lactose is in milk.

Lactase persistence is needed to consume milk beyond early childhood years.

W. (Mr.)

[1798]

Vitamin D is in milk.

Lactose is in milk.

Lactase persistence is needed to consume milk beyond early childhood years.

W. (Mr.)

So what you are saying is that if an African drinks a lot of milk his skin will become white.

[Jomid59]

So what you are saying is that if an African drinks a lot of milk his skin will become white.

Maybe we will find out....

"one uncontested truth is the demand for milk is growing across the continent. A recent survey published by global packaging company Tetra Pak is projecting Africa to see an increase of more than 50 percent in liquid dairy consumption"

http://www.africa.com/blog/dairy-consumption-in-africa-part-1/