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« A Week with Gregory Cochran: Day One | Main | A Week with Gregory Cochran: Day Three »

January 27, 2009

A Week With Gregory Cochran: Day Two

Michael Blowhard writes:

Dear Blowhards --

cochranharpending2.jpg.jpg

This week, 2Blowhards is celebrating the release of Gregory Cochran and Henry Harpending's bold and exciting new book "The 10,000 Year Explosion: How Civilization Accelerated Human Evolution" by interviewing Gregory Cochran. (Buy the book here; explore the book's excellent website here.) Yesterday we talked about the fact that human evolution didn't -- as we were once told -- stop 40,000 years ago. Today: Culture and its impact on evolution.

***

A Q&A With Gregory Cochran, Part Two

2Blowhards: We were all raised to laugh at the idea that acquired characteristics can be inherited. Yet now I learn from you and Henry that culture does affect evolution. What's the difference between Lamarckism and what you propose?

Gregory Cochran: Cutting off a dog's tail will not result in tailless puppies in the next generation (or the next, or the next): Lamarck thought so, but he was wrong. But if you cut off dog tails for a very long time, eventually a mutation might arise that creates a Manx dog -- and that dog might do better in life, if only because it would be spared dangerous trauma. Then the no-tail mutation would gradually become common and might eventually become universal in that breed of dogs.

We're saying that when people are subject to a new and different environment, gene variants that cause their bearers to have higher fitness (be better at surviving and having children) will gradually become more common. Given enough time (thousands of years, sometimes less than that) change can be substantial.

It is also the case that gene variants that already exist and are fairly common can also influence the fitness of individuals under selection. Since they start out with higher frequency, they can respond more rapidly to new circumstances. An example: a 5% edge can increase a gene's frequency from 40% to 60% -- a 20% increase in gene frequency -- in just a few generations. A completely new mutation starts out with a single copy and takes thousands of years or more to increase from near-zero to 20%.

2B: Is part of what enables us to think of culture affecting evolution the fact that we now know that evolution is proceeding rapidly?

GC: Yes. And because different cultures result in different selective pressures, sometimes quite strong ones.

2B: What should the interested Eng-Lit amateur make of the evolution-culture question? What picture could he carry around that would be useful and accurate-enough?

GC: He should remember that people can and sometimes have changed biologically over historical time, and that the changes have not taken the same course in every population. He should not expect events over a single generation to have much genetic effect. And he should, if all possible, try to remember that cicumstances over the past 70 years are different than those experienced over most of history: also that 70 years is not enough time for much change.

2B: Would we generalists be wildly mistaken if we were to think of a social-cultural milieu as an ecological niche? One that humans will tend to develop a fitness for?

GC: In the sense that a population in that milieu experiences a different mix of jobs, problems, diseases, etc -- yes. But that's not to say that blacksmiths in a particular population are a genetically separate group. They may be, on average, somewhat genetically different -- stronger, probably -- but they keep mixing with the general population. Unless you have a tight caste system of some sort.

2B: Because we create our own culture, and do so at least semi-consciously, this would all seem to imply that we have -- if only to a microscopic extent -- some semi-conscious influence over how we evolve. To what extent is that a fair or not-fair thing to say or think?

GC: I would say that many human genetic changes have been the result of culture innovations and choices, but it's hard to think of a change that anyone planned or intended. Other than the Illuminati, of course -- just one finger of the Hidden Way and the Rule that is to Come.

2B: How controversial would the thesis that culture influences evolution be among the general run of scientists? What kinds of scientists would try to take issue with you? On what grounds?

GC: On some points I think I'd get very little argument -- lactase persistence for example. On anything that influences personality or cognition, I think they'd hate it, but that kind of evolutionary change is bound to happen. The social world changed and we changed too. There's genetic evidence for it, and of course lots of evidence of psychometric differences.

2B: The main example you use to illustrate how cultural developments can influence evolution is agriculture. Why was the development of agriculture such a major event where human evolution was concerned?

GC: It increased human density by tens of times, which made a big difference in disease risks. It radically changed diet, and it dramatically furthered hierarchy and social complexity.

2B: You and Henry assert that populations that adopted agriculture were much influenced by the development, and in non-insignificant, deep-in-the-biochemistry sorts of ways. What would your favorite examples of those adaptations be?

GC: Metabolic/diet changes like lactose tolerance, many changes in genes involved with defense against infectious disease, many changes in genes that affect hearing and smell, changes in neurotransmitters and related genes that most likely influence personality, changes in genes involved with the regulation of nerve connections and brain growth.

2B: One implication would seem to be that there are striking differences between populations that developed agriculture long ago and ones that encountered it only recently. Fair?

GC: Yes. Peoples with short histories of agriculture have trouble with alcoholism, diabetes, and generally have a lot of trouble fitting into complex hierarchical societies.

2B: Can you tell us a bit more about all this? And can you explain why should we think of these differences as more significant than, say, hair or eye color?

GC: Eye and hair color are somehow involved with genetic changes that gave advantage -- Vitamin D looks to have been important, but I don't think we know the whole story on that. I tend to think things like vulnerability to diabetes or TB are important because they cripple and kill people: generally I'm against that.

2B: What are some other examples of differences between population groups that discovered agriculture long ago and ones that encountered it recently?

GC: Alcoholism is a biggie.

I suspect that people descended from peasants are somewhat better at living on a poor diet, but even if true, that wouldn't matter much in the US today. We'd hardly know if the Navaho were some worse at living on a low-vitamin diet or could only plow 90% as many acres per calorie.. not in a rich country like the US, where the problem is obesity. But it shows up a little: dark-skinned people here sometimes have a problem with rickets, many people are lactose-intolerant as adults and thus cannot fully enjoy ice cream, poor devils. There are probably some other undiscovered problems of this sort.

2B: How certain are these examples? On what bases would some scientists take issue with you?

GC: Some are quite certain, others are highly likely. A few are wild-assed guesses, but we tried to avoid those. Some scientists are, in my opinion, misled by the neutral theory of evolution. And a lot are viscerally hostile to the idea of ethnic and racial differences. I'd like to point that I'm not trying to create any. Although, come to think of it ...

2B: I notice, by the way, that one of your sources is Loren Cordain, known to health-eating-and-exercise buffs as one of the guys behind the "Paleo" diet. Cordain and others in his camp urge people to eat like a caveman; we're better adapted to a pre-agricultural diet than we are to an agricultural one. What's your own hunch about this? Might there be something to "Paleo eating"?

GC: The answer is probably different depending on your ancestry. But there ought to be something to it -- with the caveat that it's impossible to implement on a worldwide scale, because of economics.

2B: Do you see having-gone-through-the-leap-to-agriculture-or-not as one of the more fundamental ways in which population groups differ from each other? Or is it simply one that's graspable and apparent given what we know now?

GC: I think it's very important, and I think that a number of its effects are clear. Not all of them, by any means. Another important factor driving differences must be whether the population ever got big: Polynesians farm, but their populations have been always been small and isolated from each other -- that would make it harder for new favorable mutations to show up and to spread.

2B: What are some of the other cultural developments that might rank, if not entirely up there with agriculture, almost up there? And how might they or would they have influenced human evolution?

GC: The development of strong states probably limited local violence and thus upped the selective importance of food shortages and infectious diseases. In the past, good government, absent of rapid technological change, led to lower living standards.

The Ashkenazi Jews couldn't have gone down the path they did before the invention of writing and currency. You can think of them as a scribe caste. I can imagine a situation in which something similar happened in the past, well before the Ashkenazi Jews -- an enduring, reproductively closed caste of priests with strong selection for verbal intelligence. This could have happened in Egypt: if it had, selection could have operated for much longer than among the Ashkenazim, with more dramatic effects. Didn't happen, but it would make for an interesting story. I figure those priest-kings would be suckers for smoldering-eyed, sword-wielding barbarians.

2B: How do you expect that our understanding of history will be affected as we learn more and more about recent evolution and about the ins and outs of the genome?

GC: One hopes that it will make a bit more sense -- not so much lists of stuff that happened. I'm not expecting psychohistory any time soon, though.

2B: How about so far as our understanding of politics and economics goes?

GC: If a given institution or social patterns works in population A, I would say it's not guaranteed to be workable in another population with a very different evolutionary history. This is probably the case for cultural differences as well: they don't just automatically go away when you wave a magic wand. Although many institutions are transplantable: it would be just as silly to assume impossibility.

2B: Will future historians need to become a lot more familiar with, say, the way alleles can sweep through populations than they currently are?

GC: They could hardly be less familiar. I see interdisciplinary teams working these problems.

2B: One of my favorite moments in your book comes on the first page, where you write "Sargon and Imhotep were different from you genetically, as well as culturally." That certainly blows the idea that cultural differences are nothing but meaningless accidents of time and space out of the water. In other words, perhaps tastes differ from culture to culture not just because standard-issue Blank Slate people are responding to different environments but also because the people doing the encountering have preferences and penchants that are biochemically based. How would you expect the kind of knowledge and thinking that is now emerging to affect discussions of culture? And how would you like to see it do so?

GC: There's probably such a thing as "national character," at least when we're contrasting distant peoples, say Japanese and Irish -- even if they both have Oharas. The idea has fallen deeply out of fashion. I once tried to see if anyone on the net was thinking along those lines, and the closest I came was some idiot who wrote in French. After fighting my way through the language, I then found that he was insane, to the point of having been involved with both Lyndon LaRouche and the American Enterprise Institute. However, an idea being out of favor (and mainly held by lunatics) doesn't mean that it is necessarily impossible or wrong.

***

Henry Harpending's faculty page is here. Here's the Unofficial Gregory Cochran Site. Harpending and Cochran often make appareances at GNXP.

Here's a site that the authors made for their book. Be sure to visit it; the website provides an excellent overview of the book's contents and includes some well-worth-reading outtakes. Buy the terrific book here.

Some of the buzz around the web:

Back here and here, I interviewed Greg Cochran about the Iraq War.

Please leave comments and questions. As I mentioned above, Greg will respond to a selection of them on Friday. And please return tomorrow for Part Three.

Best,

Michael

posted by Michael at January 27, 2009




Comments

Everything old is new again.
I remember in the research for my Master's Thesis digging through some 30 odd file boxes filled with sociological research from the 1920s-1960s. The early stuff is just chock filled with notions of some sort of essential differences between ethnicities, which gradually move more and more to the idea of social construction as time passes.

It was all very interesting, if completely unrelated to what I was looking for in 99.9% of the time. The most interesting one was a student reporting on his grandfather, a Caucasian who had been adopted by his Chinese nursemaid after his missionary parents had died. Knew Cantonese, Fukkianese and Mandarin, hardly spoke any English.

I digress, so here's my question to Dr. Cochran:

The fall of the Blank Slate theory is being preceded by a swell of interest in various internet forums, some of which merely interested in the fact of matter, while others are much more interested in the social implications and what should be done. So, if the Blank Slate falls, so does the mindset that has been constructed around it, namely the basic mutability of human societies, in a basic civic progress upwards out of barbarism and into a sort of social parity across the board. If large groups of nations or groups within nations simply can't get to there from here, plainly speaking, then some sort mindset for global society will have to replace the blank slate one. On that note, I find most models to be either pie in the sky (cheap genetic engineering is just around the corner, soon all children will run like Usain Bolt and think like Richard Feynmann!) or frankly miserably dystopic (Eloi and Morlock wars in the streets of New York and Paris, Who Will Win this preordained battle?).
So, on that note, what's your opinion on the societal mindset that should be taken in regards to the changing paradigm?

Posted by: Spike Gomes on January 27, 2009 8:59 AM



Yes But it shows up a little: dark-skinned people here sometimes have a problem with rickets

It's nutritional rickets they get, UVR exposure has nothing to do with it

"cereals seem to increase vitamin D requirements by decreasing calcium absorption and by shortening the half-life of the main blood metabolite of vitamin D (Pettifor, 1994; see Paleodiet).[...]Undoubtedly, lighter skin allows more UV-B into the skin. As Robins (1991, pp. 60-61) notes, black African skin transmits three to five times less UV than does European skin. But is this a serious constraint on vitamin D production? Apparently not. Blood metabolites of vitamin D show similar increases in Asian, Caucasoid, and Negroid subjects when their skin is either artificially irradiated with UV-B or exposed to natural sunlight from March to October in Birmingham, England (Brazerol et al., 1988; Ellis et al., 1977; Lo et al., 1986; Stamp, 1975; also see discussion in Robins, 1991, pp. 204-205)."

Rickets is more common in sunny climes Rickets in Developing Countries

In practice, even for the very darkest of people living in Britain, it doesn't make much of a difference to their Vitamin D levels how dark their skin is.

A study under natural conditions in Birmingham, England, revealed comparable increases in 25-OHD levels after the summer sunshine from March to October in groups of Asians, West Indians and Caucasoids … This absence of a blunted 25-OHD response to sunlight in the dark-skinned West Indians at high northerly latitudes (England lies farther north than the entire United States of America except for Alaska) proves that skin colour is not a major contributor to vitamin D deficiency in northern climes.

Walk about in shorts in the British summer sun and you will shut of synthesis of 'Vitamin D'in 20 minutes. (Thats a give-away a vitamin that can be synthesized ?).You make 20,000IU in those 20 minutes by comparison the amounts from food or fish oil are so tiny as to be irrelevant. The sunny months provide huge amounts which can be stored and would have to see you through the UVR- less winter.

Africans have evolved to deal with all year rounds Vitamin D synthesis from the all year round UVR. After making 20,000 IU which takes them about 120 min. synthesis stops. Yes thats right an African's limit on making 'D' is the same as a North European's.

Question: if Vitamin D is so very good for you and northern Europeans have evolved where it is absent for half the year why do they shut off synthesis after this limit of 20,000 IU is reached? They ought to have evolved to make all they can while the sun shines and then store for the winter.

At the first step synthesis in the skin Vitamin the D is limited to 20,000IU The metabolism of this amount has been characterized thus

If one looks at the system of vitamin D metabolism in Figure 2 from the perspective of a system designed to control something, it becomes clear that this is a system better designed to cope with an abundance of supply, not a lack of it. The flow of vitamin D toward 25(OH)D is remarkably inefficient, with most bypassing it. Furthermore, there is no way to correct for deficiency of vitamin D, other than to redirect utilization of 25(OH)D toward 1,25(OH)2D production, which is the pathway most acutely important for life. That is, when supplies of vitamin D are severely restricted, its metabolism is directed only toward the maintenance of calcium homeostasis. To expand on the point that the system of vitamin D metabolism is effectively a designed for adjusting for higher inputs, not lower inputs, I offer the example of an air-conditioner system. Air conditioners are designed to compensate for excessive heat, but they are a useless way to compensate for a cold environment..

It will be pointed out that the basic metabolism of people in cold countries is still adapted to the high UVR environment where humans evolved, However, if true this ought to make the efficiency of the first step (synthesis in the skin) imperative for North Europeans in particular. They have to go 6 months without, so I'm left wondering.
If Vitamin D is so very good for you and northern Europeans have evolved where it is absent for half the year why do they shut off synthesis after this limit of 20,000 IU is reached? They ought to have evolved to make all they can while the sun shines and then store for the winter.

Posted by: Tod on January 27, 2009 2:25 PM



Blood metabolites of vitamin D show similar increases in Asian, Caucasoid, and Negroid subjects when their skin is either artificially irradiated with UV-B or exposed to natural sunlight from March to October in Birmingham, England

What about in January, when the UV input is not nearly so saturating? That's what matters. March to October doesn't.

If with respect to [calcidiol], dietary factors dominate the UV factor today at US/Euro latitudes - then how do you explain the circannual variation in [calcidiol], which IIRC shows a 2x difference from trough to crest?

If Vitamin D is so very good for you and northern Europeans have evolved where it is absent for half the year why do they shut off synthesis after this limit of 20,000 IU is reached?

For one thing calcidiol has a not-insignificant affinity for the vitamin D receptor - only about 40x lower than calcitriol's, according to one paper. Jack up [calcidiol] a lot and you may be running interference on the interaction between the triol and VDR. Would this happen, to an impactful degree, by dialing up the diol 4x? I don't know.

Fortunately there's a shortcut:

Vieth reports human toxicity probably begins to occur after chronic daily consumption of approximately 40,000 IU/day (100 of the 400 IU capsules).

The mechanism doesn't really matter.

Vieth is a D specialist and advocate who has vocally tried to dispel fears of toxicity at reasonable doses. Therefore if he says 40,000 IU a day is toxic I'm just going to assume it's probably roughly true, for at least some populations.

Posted by: Eric J. Johnson on January 27, 2009 5:49 PM



"I can imagine a situation in which something similar happened in the past, well before the Ashkenazi Jews -- an enduring, reproductively closed caste of priests with strong selection for verbal intelligence. This could have happened in Egypt: if it had, selection could have operated for much longer than among the Ashkenazim, with more dramatic effects. Didn't happen, but it would make for an interesting story. I figure those priest-kings would be suckers for smoldering-eyed, sword-wielding barbarians."


Has anyone done any studies on the archetypal "enduring, reproductively closed caste of priests," the Hindu Brahmins?

Posted by: SV on January 27, 2009 6:43 PM



@ SV -

There was a lengthy discussion of Indian IQ's at Steve Sailer's a while back. You should be able to find it at his site. As I recall it, the conclusion was that the Brahmins of South India (northern India is more mixed) have an average IQ just about that of the Ashkenazim.

Posted by: Peter on January 27, 2009 9:30 PM



Eric J. Johnson said

If with respect to [calcidiol], dietary factors dominate the UV factor today at US/Euro latitudes - then how do you explain...

You are right; dietary Vitamin D is not and never has been the decisive factor in the evolution of skin colour away from the hunter gatherer norm (light brown) anywhere in the world, ever. Moreover nor has UVR synthesised 'vitamin' D ever been a factor in the lightening of skin colour. The !Kung San in the extremely high UV environment of the Kalahari are a case in point.

What about in January, when the UV input is not nearly so saturating? That's what matters. March to October doesn't.

The availability of vitamin D synthesis from UVR where white skin evolved is the thing relevant to my argument and it is totally absent for months on end. Nobody can make Vitamin D for >4 months of the year in northern Europe. If white northern and eastern European's skin is adapted to maximizing vitamin D synthesis in the months when it can be made then they are also adapted to going without Vitamin D synthesis for a period of several months. Why then does their skin shut off that production of vitamin D after 20 minutes of summer sun have made 20000IU of D just like non-whites. Whites don't benefit from a day in the summer sunshine any more than the blackest of Africans. Surely the first thing to be selected for would be to increase the limit on the amount that can be synthesized in one go to cover the daily needs in the UVR-less months.

In whites the difference ought to be that selection for availabilty of vitamin D in the UVR-less months has resulted in the first step (synthesis in the skin) making far higher amounts than in other people because the limit on the amount synthesized in the sun would be higher.

If Vitamin D is so very good for you and northern Europeans have evolved where it is absent for half the year why do they shut off synthesis after this limit of 20,000 IU is reached?

They ought to have evolved to make all they can while the sun shines and then store for the winter if their light skin was an adaptation to a chronic lack of vitamin D combined with the recurring seasonal period of zero vitamin D from UVR lasting for months.

White people do not have any special adaptations to chronic vitamin D deficiency as can be deduced from the fact that if they did those living and sunbathing in the sunniest countries in the world like S Africa and Australia, would have developed vitamin D poisoning from decades of year round UVR and resulting in excess vitamin D storage. They haven't.


Posted by: Tod on January 28, 2009 8:46 AM



Nobody can make Vitamin D for >4 months of the year in northern Europe.

But summer doesn't yield instantaneously to winter, of course. What about the two weeks right before those >4 winter months, and the two weeks right after? Those are respectively your last chances to save up for winter and your first chance to recover from it. If lighter people make more D in those periods, the result will be a modestly less severe winter nadir in calcidiol levels.

If light skin is more permissible, it would seem there must exist be some range of UVR levels where light people have an edge in making D, even if there were no difference in July or in January. And the ambient irradiation must pass throught that range, because the circannual changes in cloud cover and sun angle are gradual.

Do you have any circannual data for dark and light people who are in the same small geographic area at high latitude?


Surely the first thing to be selected for would be to increase the limit on the amount that can be synthesized in one go to cover the daily needs in the UVR-less months.

That's impossible to judge - we don't know the pleiotropies of the mutations that would accomplish that, or how rare those particular mutations are.

We know the depigmentation mutations are loss-of-function, so we at least know there is a very large set of possible mutations that can provide the loss of function. Again we don't know the pleiotropies, but at least we know we won't be mutation-limited. Whereas if you want to raise your calcidiol stores by altering some function less destructively (let's say changing very precisely the various Kd's of vitamin D binding protein), and this can only be done by say changing 3 different nonconsecutive amino acids in the binding site - obviously that mutation may never be available in a reasonable amount of time.

Posted by: Eric J. Johnson on January 28, 2009 12:09 PM



What about the two weeks right before those >4 winter months, and the two weeks right after? Those are respectively your last chances to save up for winter and your first chance to recover from it. If lighter people make more D in those periods, the result will be a modestly less severe winter nadir in calcidiol levels

'D' Synthesis in the marginal UVB days at the begining and end of the high UVR period would be an excellent point if white skin maximized vitamin D production, but it doesn't. Huge amounts of Vitamin D are destroyed throughout the middle of summer in white skin. In practice white skin doesn't make more 'D' than in the blackest of skin). The tiny amounts that could be synthesised in the marginal UVB period are trivial by comparison and make no difference to vitamin D stores.

Do you have any circannual data for dark and light people who are in the same small geographic area at high latitude?
Data for the period where UVR is absent would show lower levels for all skin colours as the vitamin D is not synthesized in the UVB-less period. The important thing is that, as pointed out at the begining of my first comment, the white skinned do not make larger amounts of 'D' than the very blackest skinned because the single period synthesis limit beyond which whites destroy Vitamin D is just the same as blacks'.


I said Surely the first thing to be selected for would be to increase the limit on the amount that can be synthesized in one go to cover the daily needs in the UVR-less months.

That's impossible to judge - we don't know the pleiotropies of the mutations that would accomplish that, or how rare those particular mutations are.We know the depigmentation mutations are loss-of-function, so we at least know there is a very large set of possible mutations that can provide the loss of function. Again we don't know the pleiotropies, but at least we know we won't be mutation-limited. Whereas if you want to raise your calcidiol stores by altering some function less destructively (let's say changing very precisely the various Kd's of vitamin D binding protein), and this can only be done by say changing 3 different nonconsecutive amino acids in the binding site - obviously that mutation may never be available in a reasonable amount of time.

Raising the limit on the amount that can be synthesized in one go is not something that a load of rare mutations was needed to change, the 20000IU figure is an average, a few people make far more than this. Those higher limit people would have become the norm through natural selection acting on the existing variability if chronic vitamin D deficiency was ever a problem in northern and eastern Europe. They didn't so it wasn't.

Posted by: Tod on January 29, 2009 11:07 AM



'D' Synthesis in the marginal UVB days at the begining and end of the high UVR period would be an excellent point if white skin maximized vitamin D production, but it doesn't. Huge amounts of Vitamin D are destroyed throughout the middle of summer in white skin.

But - I'm not talking about the beginning and end of the high UVR period; I'm talking about an intermediate UVR period. There is not an instant binary transition from the high UVR period to the near-zero-UVR period; instead there is a smooth transition. My point is that white skin
could maximize production when the UVR dose is marginal. The fact that lots of D is destroyed when the UVR dose is blazingly high isn't relevant to this. My suggestion is that in London on September 20th, a white person and a black person who spend an average day together, including some time outdoors, might make different amounts: 15,000 IU for the white and 5,000 IU for the black.


Anyways - I'll have to admit, it's possible you might be right in part or in whole, and the orthodoxy ("pigment promotes D deficiency at high latitudes, and depigmentation evolved because of this") seems less clearly supported than I had blithely assumed. Nevertheless, I still think my position about light people making more D under intermediate UVR conditions in spring and fall might be right.

Your major source on controlled irradiation experiments on light and dark skinned subjects is "Evo and Proud," which cites the following in support of there being little difference in light people's and dark people's vitamin D photoproduction during irradiation:

1. Robins pp. 204-5
2. Brazerol 1988
3. Ellis 1977
4. Lo 1986
5. Stamp 1975


I'll address each:

1. Robins pp 204-5 underlines that asian Britons get rickets but afrocarribbean Britons rarely do, though they are darker than asians. Let's stipulate that Robins is probably right that the afrocarribbeans right that one factor is that the afrocarribbeans hang out outdoors more. Also I'll accept without reading it the data saying black USA infants have less sun exposure than white USA infants. Still, this doesn't prove that skin tone is irrelevant to D; only that cultural practices regarding sun exposure can have comparable magnitude. The other four citations all deal with irradiation.

2. Brazerol: Initial UVB dose was 5% below the minimal erythemal [sunburning] dose for the most sensitive skin, followed by 10% increase per exposure for 4 weeks. This sounds like a highish (summer-like) dose, very probably. I read abstract only.

3. Ellis - did not irradiate anyone; from the abstract it sounds like the subjects were merely asked about their general sun exposure levels. This is rather inexact. I read abstract only.

4. Lo: serum vitamin D concentrations of six Asians in response to 1.5 times their minimal erythemal [sunburning] dose (MED) of whole-body ultraviolet radiation - definitely a very high dose. I read abstract only.

5. Stamp goes so far as to point out himself that the UVR doses he used were high: While these changes [in 25-OH-D levels] may represent maximum stimulation of vitamin D synthesis, overcoming a partial pigment barrier, it is clear that even the blackest skin is far from an absolute barrier to vitamin D synthesis [emphasis added by EJJ]. The whole Stamp paper is free but I must point out I didn't read every word.

I conclude that you are right in part: the idea that europeans are white for the sake of vitamin D may not be conclusively supported, for all I can tell. Also that cultural factors (level of outdoor exposure to sun) are a likely major factor in rickets in Britain and elsewhere. But I don't think your information on high dose irradiation experiments excludes my idea that light skin could have evolved to exploit low doses of natural UVR in spring and fall at high latitudes. My prediction, again, is that white canadians or brits would produce more D in late Sept and early April and thus suffer a lower winter nadir. You suggest this is not enough to make a difference; I suggest otherwise. The data to decide our point of contention may not exist at present, and thus I would suggest that the vitamin D theory of light skin may not be totally decidable at present.


Raising the limit on the amount that can be synthesized in one go is not something that a load of rare mutations was needed to change, the 20000IU figure is an average, a few people make far more than this.

I would grant both points. But in the context of our discussion about evolution, it's only fitness-increasing mutations or sets of mutations that matter. It is not at all obvious that fitness increasing mutations or set of mutations that raise the limit above 20,000 IU are common in genome sequence space. The rare individuals who make far more than 20,000 IU may suffer from a subtle fitness deficit if and when their 25-OH-D stores go way above normal. They may well be D-intoxicated, considering that Vieth thinks toxicity begins around 40,000 IU a day. Even though it is probably easy (ie, not strongly mutation limited) for evolution to create much higher stores of 25-OH-d, it is not at all obvious that it would be easy for evolution to fix the body so that these high levels would no longer be toxic, which might be required in order for higher stores can increase net fitness.


Posted by: Eric J. Johnson on January 29, 2009 2:24 PM



The genitics is over my head I'm afraid, maybe you have a point.
the system of vitamin D metabolism ... from the perspective of a system designed to control something, it becomes clear that this is a system better designed to cope with an abundance of supply, not a lack of it. There is another mechanism in Europeans that is minimizing Vitamin D: tanning. By the end of summer exposed skin will be tanned reducing its capacity to make'D'.
Association between quantitative measures of skin color and plasma 25-hydroxyvitamin D

Exposed but not unexposed skin color was associated with better vitamin D status. Sun-exposure was more important than natural skin color in determining vitamin D status in our population.

Posted by: Tod on January 30, 2009 10:59 AM



But in the context of our discussion about evolution, it's only fitness-increasing mutations or sets of mutations that matter. It is not at all obvious that fitness increasing mutations or set of mutations that raise the limit above 20,000 IU are common in genome sequence space
Maybe so, genome sequence space is not my strong point.


My point is that white skin could maximize production when the UVR dose is marginal. The fact that lots of D is destroyed when the UVR dose is blazingly high isn't relevant to this. My suggestion is that in London on September 20th, a white person and a black person who spend an average day together, including some time outdoors, might make different amounts: 15,000 IU for the white and 5,000 IU for the black

Lets assume selection for getting through the UVB-less months was what the caused white skin to evolve (remembering Vitamin D is stored). Late Sept. cloudy weather means Vitamin D synthesis would be in doubt why not take the extra 'D' when it is certain by extending the limit on D synthesis in one period to 40,000, by the end of summer 'D' stores would be full. The lower limit means leaving to the last minute the topping up of the vitamin D stores and doubtless sometimes that intermediate period in (which ends earlier than late September in N.Europe) will not deliver the 'D, due to bad weather blocking UVB. I think natural selection would eliminate this set-up in favour of one that got the required amount into the body at the first and most certain opportunity and was less vulnerable to bad weather.


Nevertheless, I still think my position about light people making more D under intermediate UVR conditions in spring and fall might be right..
Yes you have a point, in those sub-optimal conditions whites probably do make more 'D'. (Especially in the spring).
Which brings me to yet another evolved mechanism to reduce vitamin D in north and east Europeans: tanning. By the middle of summer the exposed skin of whites has a tan which reduces their ability to synthesize vitamin D by about half (in the tanned skin). This gives me added confidence that Europeans' skin was not selected for any increase in vitamin D production.

Here is something I found all by myself
Association between quantitative measures of skin color and plasma 25-hydroxyvitamin D

Mean (SD) 25OHD was significantly higher in Europeans than Pacific People, 88 (31) nmol/L vs. 75 (34) nmol/L, respectively. Based on constitutive skin color, 35% of participants were very light, 45% light, 16% intermediate, 4% tanned, and 0% brown or dark. Skin color at the forearm but not constitutive skin color was a significant predictor of 25OHD. Each 10° lower skin color value at the forearm (more tanning) was associated with a 5 nmol/L higher 25OHD (P .
Conclusions Tanning but not natural skin color was an important determinant of 25OHD. Further study is needed in a population with a higher proportion of darker skin people.


(I think this is the correct explaination: SEXUAL SELECTION AND HUMAN GEOGRAPHIC VARIATION)


Posted by: Tod on January 30, 2009 12:52 PM



Interesting review of Paleo diet:

www.westonaprice.org/bookreviews/paleodiet.html

Posted by: Brad G on February 2, 2009 12:03 AM



Tod,

You said:
By the middle of summer the exposed skin of whites has a tan which reduces their ability to synthesize vitamin D by about half (in the tanned skin). This gives me added confidence that Europeans' skin was not selected for any increase in vitamin D production.

I'm from Ireland and get sunburnt in Spring in Ireland - same latitude as Northern Canada. I have 2 siblings that can NOT tan under any circumstances. So your comment above seems to be false.

Posted by: pconroy on February 2, 2009 5:22 PM



I'd like to hear the authors' thoughts on what the modern welfare state selects for.

It seems as if the best evolutionary strategy possible for a male is to get as many women as possible pregnant and have the state care for them. The kids won't have great lives but like everybody else they'll survive and have opportunities to pass on even more of these genes for promiscuity and parasitism.

It’s politically incorrect enough to discuss the past in these terms and it’s tempting to ignore the implications for the future, but they are frightening.

Posted by: Richard H on February 3, 2009 4:39 AM






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