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Wednesday, April 23, 2008
Vitamin D: bones, brains and skin color
It's been for long known that vitamin D is essential for good bone developement and that its lack causes rickets. Vitamin D can be obtained from some foods (fatty fish and mushrooms specially) but it's mostly generated in the skin photochemically, what requires some absorption of (otherwise dangerous) UV rays from the Sun. Therefore it has been considered for many decades a most important evolutive factor in the developement of low pygmented ("white" or "pale") skin type in West Eurasia and specially Northern Europe, where solar radiation is extremely low due to latitude and cloudiness. The rationale behind East Asians and, specially, Siberian natives not being generally as pale as Northern Europeans is because of their food habits: most often rich in fish (that is one of the main food sources of vitamin D).
Now a new study (see news article) suggests that it is also important for a correct brain developement function, with this vitamin being very active in our brains, and also acting as protection against autoimmune diseases.
In brief: vitamin D seems essential for correct human developement and, while in our original tropical latitudes we had no problem obtaining it directly from the Sun, rather needing protection against excess of UV rays (hence black or dark skin), when we entered the northern latitudes where the solar input is much smaller, we needed other strategies to adapt to this important bological conditionant. A fish-rich diet was one possibility but surely was not available for all. So light skin was a natural evolutionary goal, specially for those living in the darkest places.
There are indications that some of the genetic variants (mutations) involved in light skin among Europeans may have evolved quite recently, maybe as late as the Epipaleolithic, coincident with the colonization of Northern Europe after the ice shield melted out. The evidence is quite compelling anyhow in the sense of Eastern and Western Eurasian pygmentation genes having evolved separate but parallely (i.e. after both branches separated somewhere in southern Eurasia, maybe 50,000 years ago). Still, the genetics of pygmentation is poorly understood by the moment, as there may be dozens of different genes involved. In any case, it seems clear that evolutionary pressures related most specifically with vitamin D processing were central in this differentiation.
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Skin color and vitamin D
Proponents of the vitamin D hypothesis will point to the Inuit and say that non-Europeans get enough vitamin D at high northerly latitudes from fatty fish. So they don’t need light skin. In actual fact, if we look at the indigenous peoples of northern Asia and North America above 47º N, most of them live far inland and get little vitamin D from their diet. For instance, although the Athapaskans of Canada and Alaska live as far north as the Inuit and are even somewhat darker-skinned, their diet consists largely of meat from land animals (caribou, deer, ptarmigan, etc.). The same may be said for the native peoples of Siberia.
Conversely, fish consumption is high among the coastal peoples of northwestern Europe. Skeletal remains of Danes living 6,000-7,000 years ago have the same carbon isotope profile as those of Greenland Inuit, whose diet is 70-95% of marine origin (Tauber, 1981). So why are Danes so light-skinned despite a diet that has long included fatty fish?
Osborne et al. (2008) measured skin color and bone strength in a hundred white and Asian adolescent girls from Hawaii. Skin color was measured at the forehead and the inner arm. Bone strength was measured by section modulus (Z) and bone mineral content (BMC) at the proximal femur. A multiple regression was then performed to investigate the influences of skin color, physical activity, age, ethnicity, developmental age, calcium intake, and lean body mass on Z and BMC. Result: no significant relationship between skin color and bone strength. .../...'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'..../...Clearly, something other than solar UV has also influenced human variation in skin color ... and one may wonder whether lack of solar UV has played any role, via natural selection, in the extreme whitening of some human populations..../...Latitudinal variation in human skin color is largely an artefact of very dark skin in sub-Saharan agricultural peoples and very light skin in northern and eastern Europeans. Elsewhere, the correlation with latitude is much weaker. Indeed, human skin color seems to be more highly correlated with the incidence of polygyny than with latitude (Manning et al., 2004).
.../...Sexual selection of women was strongest where the ratio of unmated women to unmated men was highest. This would have been in the ‘continental Arctic’, a steppe-tundra environment where women depended the most on men for food and where hunting distances were the longest.../...The same area now corresponds to a zone where skin is almost at the physiological limit of depigmentation and where hair and eye color have diversified into a broad palette of vivid hues. This ‘European exception’ constitutes a major deviation from geographic variation in hair, eye, and skin color (Cavalli-Sforza et al., 1994, pp. 266-267).
Actually, at any given latitude, solar UV radiation is just as intense at ground level in Europe as it is in northern Asia and North America. (Jablonski & Chaplin, 2000; see also charts on: http://pages.globetrotter.net/peter_frost61z/European-skin-color.htm). At these latitudes, UV radiation is already weak, so a significant further reduction in solar UV requires continually overcast skies, such as exist only on the coastal fringe of northwestern Europe.
Moreover, it is doubtful that relaxed selection for dark skin could have diversified hair and eye color by allowing defective alleles to proliferate. Two papers have shown that such a scenario would have needed close to a million years to produce the hair-color and eye-color variability that Europeans now display, with the redhead alleles alone being c. 80,000 years old (Harding et al., 2000; Templeton, 2002). Yet modern humans have been in Europe for only 35,000 years or so.
Instead of relaxed selection for dark skin, perhaps there was increased selection for light skin, notably to boost synthesis of vitamin D. This hypothesis solves the time problem but does not explain the increase in the number of MC1R and OCA2 alleles. Natural selection would have simply favored one allele at the expense of all others, i.e., whichever one optimally reduced skin pigmentation.
We don't know the diet of ancestors. Fish may be important among some groups and not among others, at some times and not at other periods. In fact it's hard to imagine people hunting mammoths and bison in Russia or the Danub in the dephts of Ice Age and getting enough vit D from diet.
But maybe we should consider it as just a contributing factor and not a radical on/off switch. There's people with rather dark skin living in places like Sweden now and people with very light one living in Australia and other tropical areas. Most of them manage to survive and reproduce... but in the long run surely those lineages with the most adequate color will leave a signifcatively more extense legacy. A small adaptative advantage can be enough to drive a gene to fixation rather fast (somebody reminded me that the other day).
Actually, at any given latitude, solar UV radiation is just as intense at ground level in Europe as it is in northern Asia and North America.
That's quite obvious in the big picture (i.e. at the troposphere) but there are some differences caused by local climate. When you look at a map of solar radiation you see perfectly that the clines are not merely horizontal.In fact you see marked anomalies like large chunks of the tropics being relatively low insolated (because of tropical rainy weather) and you can also see that, in Eurasia, the stripes are pretty much more to the south in Europe: northern Spain has much lower solar radition than Beijing, in spite of being at the same latitude. When you compare those clines with actual population (that is largely a function of temperature, much warmer in Europe for the same latitudes, because of the Gulf Stream), you see that there's virtually no place in the world reciving the ultra-low insolaton of Scandinavia or Scotland and being inhabited by anything but a bunch of nomads (Alaska would be comparable but it's of very recent colonization).
You can't anyhow deny that over- or under-exposure to UV leads to some striking negative effects on health and that variations in pygmentation are directly related to the prevention of such diseases.
Moreover, it is doubtful that relaxed selection for dark skin could have diversified hair and eye color by allowing defective alleles to proliferate.
That's pretty much nonsense. While eye and hair color are not strictly related to skin color or among themselves, all seems to be mutually influenced by generic pygmentation genes (it's not a matter of just one or two genes in most cases but rather of many acting and compensating each other) and therefore there may be a correlation (i.e. maybe some blue eyes, not all, are all descendant of one single ancestor but it is also very possible that the gene that causes blue eyes may promote lighter colors in other organs). Hair color variation anyhow is probably at least as old as Eurasian humankind, as blondism is also found out of Europe (Oceania specially).
Two papers have shown that such a scenario would have needed close to a million years to produce the hair-color and eye-color variability that Europeans now display...
That's ridiculous. It is obviously not the case. Furthermore, we know that under similar conditions (Europe), Neandethals also evolved in the same direction but (very important) with different genes.
Theorizing with mathematical models is not the same as "demonstrating". Far from it.
Instead of relaxed selection for dark skin, perhaps there was increased selection for light skin, notably to boost synthesis of vitamin D.
More than just perhaps, I'd say. But I also think that before that positive selection for light skin and rosy cheeks arose, there was some major lost of function and also, importantly, minority founder effects that made sure that the West Eurasian genetic pool had the right materials to work with to eventually produce the results we see today.
This hypothesis solves the time problem but does not explain the increase in the number of MC1R and OCA2 alleles. Natural selection would have simply favored one allele at the expense of all others, i.e., whichever one optimally reduced skin pigmentation.
Only if the advantage of that one would have been decissive, what doesn't seem evident. These two genes are related with hair and eye color primarily anyhow, so they are essentially trivial for skin pygmentation (though they may influence it somewhat, at least MCR1). Skin color is (as ar as we know) primarily defined by other genes (tough there's still a lot of research to make anyhow).
Also both "famous" alelles of these genes (the one behind red hair and the one behind some blue eyes) appear to be clear founder effects (single common ancestor), what really makes all theories pretty much irrelevant as founder effects are essentially historical accidents. Blue eyes are relatively widespread, what to me mans that the common ancestor was surely some Cro-Magnon of Gravettian culture. Instead red hair is rare and the only exception to this rarity is with Scots and Irish, who probably also went through major founder effects at the colonization of these areas after the Ice Age.
If vitamin D played any part in the evolution of Europeans' white skin - why then do they have a mechanism for destroying vitamin D which kicks in after 20 minutes in the summer sun (10am-2pm)?
It seems to me that in northern Europeans evolution ought to have disabled this mechanism to a certain extent to optimize Vitamin D before evolving white skin. The excess Vitamin D being stored in the body for the winter.
...human skin color seems to be more highly correlated with the incidence of polygyny than with latitude (Manning et al., 2004). This second correlation is especially evident in sub-Saharan Africa, where high-polygyny agriculturalists are visibly darker than low-polygyny hunter-gatherers (i.e., Khoisans, pygmies) although both are equally indigenous. Year-round agriculture allows women to become primary food producers, thereby freeing men to take more wives. Thus, fewer women remain unmated and men are less able to translate their mate-choice criteria into actual mate choice. Such criteria include a preference, widely attested in the African ethnographic literature, for so-called 'red' or 'yellow' women — this being part of a general cross-cultural preference for lighter-skinned women (van den Berghe & Frost, 1986). Less mate choice means weaker sexual selection for light skin in women and, hence, less counterbalancing of natural selection for dark skin in either sex to protect against sunburn and skin cancer. Result: a net increase in selection for dark skin. Just as weaker sexual selection may explain the unusually dark skin of sub-Saharan agricultural peoples, stronger sexual selection may explain the unusually light skin of northern and eastern Europeans, as well as other highly visible color traits.
"The presence of Bougainville as a 'black spot' in an island world of brownskins (later called redskins) raises a question that cannot now be answered. Were the genes producing that darker pigmentation carried by the first Bougainvillain s when they arrived? Or did they evolve, by natural or by 'social' selection, during the millennia in which the descendants of those pioneers remained isolated, reproductively, from neighbouring islanders? Nothing now known about Bougainville;s physical environment can support an argument for the natural selection of its peoples' distinctively black pigmentation; therefore a case might be made for social selection, namely, an aesthetic (and hence reproductive) preference for black skin. This preference has, by the way, surfaced recently with added political meaning".
why then do they have a mechanism for destroying vitamin D which kicks in after 20 minutes in the summer sun (10am-2pm)
Where did you got that idea from? And why would a mechanism like that act only in the morning?
especially evident in sub-Saharan Africa, where high-polygyny agriculturalists are visibly darker than low-polygyny hunter-gatherers (i.e., Khoisans, pygmies)
Pygmies look very dark to me, honestly. Imposible to take apart from their Bantu neighbours merely on skin tonality. Khoisans are a different people from non-tropical Southern Africa.
Also archetypical Black people are not necesarily polygynic, in many societies they are even matrifocal (what basically excludes poygyny at all: if inheritance and family locality are dependant on the wife/mother, a man cannot be married to more than one woman at a time) and were probably that much more frequently in the past. Equally they do have a wide variety of tonalities, the darkest among all being the Dinka of Sudan, who I believe are not polygynistic.
As for Boungaville (right near New Guinea, right?) I have no good knowledge of the local variability, so I won't comment much. Just that Melanesians are called that way for a reason (i.e. evident elevated melanine levels).
I think that you're gathering a lot of incidental and somewhat dubious data and trying to create a theory out of that. I don't know who's that Manning guy but his hypothesis seems a lot far fetched, specially when the egenral correlation between skin color and latitude is so patently obvious.
Notice that family systems have varied a lot along ages, even wthin the same populations. Like all or most other cultural aspects there's no direct correlation between phenotype and such things. And it makes perfect sense that it is not that way at all.
Vitamin D Council
Studies show that if you go out in the summer sun in your bathing suit until your skin just begins to turn pink, you make between 10,000 and 50,000 units of cholecalciferol in your skin. Professor Michael Holick of Boston University School of Medicine has studied this extensively and believes a reasonable average of all the studies is 20,000 units. That means a few minutes in the summer sun produces 100 times more vitamin D than the government says you need! As discussed in other pages, this is the single most important fact about vitamin D.
The skin does another amazing thing with cholecalciferol. It prevents vitamin D toxicity. Once you make about 20,000 units, the same ultraviolet light that created cholecalciferol, begins to degrade it. The more you make, the more is destroyed. So a steady state is reached that prevents the skin from making too much cholecalciferol. This is why no one has ever been reported to develop vitamin D toxicity from the sun, though it is possible when taken orally.
The vitamin D is produced by the solar UVB wavelength which is strongest when the sun is closest, around midday in the middle of summer. If we assume white skin evolved during a time of less UVB due to ice age weather, people would have evolved to maximize vitamin D during the summer and store it for the winter,(vitamin D can be stored in tissues).
If the synthesis of Vitamin D was so difficult due to low levels of UVB why would there be a mechanism to restrict it after only 20 minutes
Vitamin D Wikipedia,
"Vitamin D3 is derived from animal sources and is made in the skin when 7-dehydrocholesterol reacts with UVB ultraviolet light at wavelengths between 270–300 nm, with peak synthesis occurring between 295-297 nm.[8][9] These wavelengths are present in sunlight when the UV index is greater than 3. At this solar elevation, which occurs daily within the tropics, daily during the spring and summer seasons in temperate regions, and almost never within the arctic circles, adequate amounts of vitamin D3 can be made in the skin after only ten to fifteen minutes of sun exposure at least two times per week to the face, arms, hands, or back without sunscreen. With longer exposure to UVB rays, an equilibrium is achieved in the skin, and the vitamin simply degrades as fast as it is generated.[1]
White peoples' metabolism of vitamin D shows no sign of having evolved in conditions where it was difficult to synthesize, in fact it is restricted. 20 minutes in the summer sun gives 100 times the recommended minimum
You can't anyhow deny that over- or under-exposure to UV leads to some striking negative effects on health and that variations in pigmentation are directly related to the prevention of such diseases
Khoisan "From the beginning of the Upper Paleolithic period, hunting and gathering cultures known as the Sangoan occupied southern Africa in areas where annual rainfall is less than 40 inches (1016mm)—and today's San and Khoi people resemble the ancient Sangoan skeletal remains. " it is odd they are so pale if they evolved in this high UV environment and tropical areas would have more tree cover which would reduce UV.
Khoi-San are not "pale" but their enviroment is not tropical Africa anyhow. It's more like, say, Arabia or even Italy.
There's more than just melanin in this matter anyhow. East Asian "yellowish" pigment is an excellent skin cancer protection (not as good as melanine but almost) and does not hinder so much vit D absorption. Skin Cancer in people of East Asian ancestry is extremely low, almost as low as among people of Tropical African ancestry. Maybe Khoi-San have the same pygment?
But skin cancer is very high among people of North European ancestry, specially those that live in tropical and subtropical areas (and in spite of all farmaceutical protectors available).
...
I did not know that issue with vit. D destruction. But still I don't think that matters, after all it's summer sun where? What happens in winter? What happens when it's all day long cloudy and rainy, and that way one day after the other, as we have to suffer every fall and winter and most of spring? What happens when people, as it's normal in cold climates, only expose their faces to the weather most of the time and never use bathsuit or equivalent? Going to the beach to get a tan is a very modern hobby.
You have suggested sexual selection but people with very pale skins are somewhat repulsive, IMO. I don't know if in some areas that is considered a beauty trait but, if so, it's probably because it favors health in such enviroment. This applies at least to other traits, like female proportions, specially hip width... natives of the amazons happened to have the same "ideals" as westerners in this regard and that's because it's a matter of health (regarding maternity in this case).
And the polygamy issue makes no sense in any case, no matter how you look at it.
"What happens when it's all day long cloudy and rainy, and that way one day after the other, as we have to suffer every fall and winter and most of spring? What happens when people, as it's normal in cold climates, only expose their faces to the weather most of the time and never use bathsuit or equivalent? Going to the beach to get a tan is a very modern hobby.
a few minutes in the summer sun produces 100 times more vitamin D than the government says you need! As discussed in other pages, this is the single most important fact about vitamin D.
It is exactly my point that
UVB is not strong enough in north Europe during the winter to make Vitamin D; therefore the storing of the Vitamin D synthesized in the body to tide one over the winter would seem to be logical.
My point is why would there be a limit on the manufacture of vitamin D in this brief period of high UVB?
The cloud and rain for much of the year you mention makes me wonder. Why have a mechanism to restrict UVB manufacture of Vitamin D, couldn't that excess be used in the winter?
I conclude that if Vitamin D manufacture was curtailed by this evolved mechanism then shortage of UVB manufactured vitamin D was never a problem in northern Europe. "What about rickets?" I hear you say, this has been due to cereal agriculture not lack of sunlight 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).
Vitamin D is toxic at high levels (most vitamins are in fact, so you should never take too much). Storing it doesn't seem viable, otherwise I guess Nature would have found the system to do it.
That element of cereals (thanks for your interesting inputs, btw) might explain maybe why some of the alelles related with extreme light pygmentation appear to have evolved quite recently. Though it's hard to be sure if this was caused by the needs of living in higher latitudes (Epipaleolithic colonization of Northern Europe) or by the modified diet of Neolithic. Maybe both?
here
OVERVIEW OF THE SYSTEM OF VITAMIN D
METABOLISM, AND ITS REGULATION.
Administration of vitamin D (cholecalciferol) is unusual
in pharmacology or in endocrinology, because this
molecule is two metabolic steps away from the
biologically active agent, 1,25(OH)2D. Furthermore, the
laboratory test to monitor dose is the concentration of a
metabolite, 25(OH)D. Figure 2 illustrates the metabolite
“compartments” occupied by vitamin D after ingestion or
exposure to sunshine. Less than the 25 percent of vitamin
D that enters the body actually becomes 25(OH)D. More
than 75 percent of vitamin D entering the circulation
bypasses what we recognize as the vitamin D endocrine
system. Instead, most vitamin D entering the circulation
is excreted and/or metabolized by other routes not shown
here, and most likely, excreted into the bile.
Figure 2 consists of two panels to illustrate the
metabolic adaptations that exist so that the vitamin D
endocrine system can accommodate to a wide range in the
substrate concentration. The vitamin D system is
optimized to maintain plasma 1,25(OH)2D levels
according to the requirements of calcium homeostasis.
The earliest compromise to progressive restriction in
vitamin D supply is a diminished capacity of non-renal
tissues to produce 1,25(OH)2D. This compromise at nonrenal
tissues is illustrated in Figure 2 by the greater height
of one of the valves representing the 1-hydroxylase on the
“pail” that represents the 25(OH)D compartment.
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.
The environment under which human vitamin D
metabolism was effectively designed was for people
without clothing, living at latitudes where UVB intensity
was always enough to produce a relative abundance of
vitamin D. In contrast, most modern humans cover close
to 95 percent of skin surface and avoid sunshine. The
vitamin D endocrine/paracrine system is not designed to
cope with the lack of vitamin D created by our modern
culture of clothing and sun-avoidance. Inadequate
supplies of vitamin D limit the paracrine control that
many tissues need so they can function properly. As a
result, it is possible that what we regard as a modern
“normal” prevalence of some of the diseases listed in
Table 1 could be reduced substantially if we were to
increase our intakes of vitamin D (44-47).
Control of metabolism in the vitamin D
endocrine system is very different from the way other
steroid hormones are regulated. For conventional steroid
hormones, the concentration of substrate (cholesterol) is
far higher than the substrate in the vitamin D system.
Figure 3 illustrates the effective in-vivo Km of 1-
hydroxylase, in relation to the physiological concentration
Harvard Public Health Review spoke with HSPH Professor of Nutrition and Epidemiology Edward Giovannucci.
Q: What are the best sources of vitamin D?
A: The sun is the most potent source. When the sun’s ultraviolet rays hit the skin, the skin makes the vitamin, which is rapidly absorbed in the blood and can be stored for several months, mostly in the blood and fat tissue. This is why it’s hard to figure out how much supplemental vitamin D people might need.
If you spend a fair amount of time outdoors, you probably don’t need a vitamin D supplement. A light-skinned person living in Boston who takes walks in the summer with the face, neck, and arms exposed for 15 minutes gets enough. A 30-minute, full-body exposure to summer sun at noon without any sunscreen protection triggers the release of about 20,000 IU into the bloodstream. Most of that is stored.
Vitamin D and skin color.Is white skin an adaptation to the cereal diet that Europeans have been consuming for the past five to seven thousand years?
The vitamin D hypothesis also implies that European skin turned white almost at the dawn of human history. Cereal agriculture did not reach northern Europe until some 5,000 years ago and, presumably, the whitening of northern European skin would not have been complete until well into the historical period. Is this a realistic assumption, given the depictions of white-skinned Europeans in early Egyptian art?
Map of skin hue
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.
Like sweating or lacking body hair the overall human metabolism is tropical. Without our ingenuous nature and all the artificial things we create we could not live in Europe at all (even in the Mediterranean winters can be really cold) or even almost anywhere out of the tropics.
So, well, no surprise here: sunshine is rather aboundant in those areas, specially the drier ones (savannah ecosystem) where it's likely our species arose and became specialized.
The environment under which human vitamin D
metabolism was effectively designed was for people
without clothing, living at latitudes where UVB intensity
was always enough to produce a relative abundance of
vitamin D. In contrast, most modern humans cover close
to 95 percent of skin surface and avoid sunshine. The
vitamin D endocrine/paracrine system is not designed to
cope with the lack of vitamin D created by our modern
culture of clothing and sun-avoidance.
Ditto.
What the article doesn't deal with is with the fact that, at cold latititudes (so-called "temperate" often - lol how can be temperate for humans a place where you can hardly live without clothes?) everybody covers the body and has been doing it since probably the times of H. erectus. Additionally, with a harshest (cold, stormy) climate out of the shelter, staying for as long as you can inside and along the fire only makes a lot of sense.
So the easiest way to adapt our tropical vit D skin absorption metabolism to cold climates is to lighten the skin and develope rosy cheeks - as the face is the main area exposed to the Sun.
The vitamin D hypothesis also implies that European skin turned white almost at the dawn of human history.
That's obviously wrong (as it's "history" in the sense of written history, not archaeological history). But it's not any assumption of the vit. D hypothesis overall. Obviously there are several, probably many, genes involved in skin pygmentation and some of them, likely most of them have been changing since early on in the Eruasian colonization process, what can mean as much as 130,000 years (at least 60,000 years).
In some documentaries I have seen black people playing archaic Europeans of the Aurignacian times. That is obviously an extreme exaggeration. Eurasians, must have lost the extreme pygmentation of the tropics as soon as they did not need it anymore (lack of function), specially when there was another pressure (vit. D) pushing in the opposite direction.
It is possible that Aurignacian Europeans were still "moreno" (light brown) but hardly "black" (dark brown). But it's also possible that they'd be even lighter (not the extreme cases you find in some areas of Northern Europe yet anyhow: they were able to tan back then for sure).
Then it follows some 30,000 years of Paleolithic. Considering the archaeological evidence two regions were most important: Franco-Cantabrian in the West and Dniepr-Don in the East. Additionally there were some less influential Mediterranean regions (Iberia, Italy) and Central Europe (Rhin-Danub). This one appears to have gone not fully but almost deserted in the LGM but it may have been important as craddle of Northern Europeans overall, specially in Magdalenian and Epipaleolithic times. European N-DNA structure appears to support a cluster of such Renano-Danubian origin extending also into Northern Europe nowadays, cluster that is distinct from those of Basques or Iberians.
But Basques, for instance, have nearly null imput from that Central-North genetic pool and yet show relative aboundance of fair types (extreme Nordic blonds are not found though). Much of the same can be said of non-Basque Iberians, where the typical "moreno" type (not dominant at all, here called often "mediterranean") rather seems a Neolithic introduction from outside Europe or at least the Balcans.
So my guess is that at least as early as Magdalenian times, and possibly even as early as the Gravettian age (necesary to explain blondism in North Africa), fair types existed in the European population to a variable ammount. Maybe not so much because of dire need of vit. D but also because of founder effects and loss of function of darker pygmentation types. As Europeans moved to the north, first to Central Europe after the LGM and then to Northern Europe in the Epipaleolithic, such lighter types may have been selected for, becoming more aboundant and even extreme in some cases. Still typical Nordics can tan, only extreme Nordics can't.
Only the extreme pale types can be claimed to be Epipaleo-/Neolithic, IMO and are basically a "radicalization" of pre-existent fair types that can be as old as Europeans and maybe West Eurasians as a whole. I'd think that the extreme paleness of such types (my Northern Italian grandfather for instance - well, my mother too to an extent) must be caused by accumulation (addition) of several genetic loci and not just one gene. When "remixed" they tend to create less markedly pale/blond types (i.e. fair types) or even "revert" to brunette types of somewhat daker (yet clearly white) skin type. In some cases they can even become "moreno" types more proper of North Africa or Arabia, as hidden genetic baggage becomes more dominant in recombination events (I'm thinking in one cousin of mine who looks pretty much transmediterranean, while all his brothers are blond and light eyed - ironically he's the neonazi of the family).
Enjoy.
The environment under which human vitamin D
metabolism was effectively designed was for people
without clothing, living at latitudes where UVB intensity
was always enough to produce a relative abundance of
vitamin D. In contrast, most modern humans cover close
to 95 percent of skin surface and avoid sunshine. The
vitamin D endocrine/paracrine system is not designed to
cope with the lack of vitamin D created by our modern
culture of clothing and sun-avoidance.
Ditto.
White skin is new so there was a strong selection pressure in Europe for white skin.
If white skin is an adaptation for getting enough Vitamin D (which is only possible for a few months in the summer) then the system of Vitamin D metabolism would have been under selection for maximizing the vitamin's production and storage in white people
So north Europeans should have a significantly higher threshold for the breakdown of Vitamin D. Moreover they should store it in vast amounts (to tide them over the UVB/Vitamin D- less winter), and should be vulnerable to vitamin D poisoning when they are exposed to high UVB year round in Australia or South Africa.
>The skin does another amazing thing with cholecalciferol. It prevents vitamin D toxicity. Once you make about 20,000 units, the same ultraviolet light that created cholecalciferol, begins to degrade it. The more you make, the more is destroyed. So a steady state is reached that prevents the skin from making too much cholecalciferol. This is why no one has ever been reported to develop vitamin D toxicity from the sun, though it is possible when taken orally.
It ought to have been reported in some sunbathing white people if they have been under selection for making and storing Vitamin D from scarce UVB
The illnesses that Vitamin D is said to be efficacious for are things like some cancers, heart disease, psoriasis, Crohns disease which are said to be a result of excessive immune system activity which is itself said to result from modern overeating and obesity. Vitamin D is believed to modulate the overactive immune system, damping down this inflammation. These are diseases of the affluent and are very recent.
Rickets is found in Black Africans in Africa Nutritional Rickets in Nigerian Children
So why has their skin not lightened in Africa ?
Black Africans do not get rickets in the UK.
Why are Black African agriculturists darker than the Bushmen hunter-gatherers if nutritional rickets is a factor in skin colour.
Sexual selection- Wikipedia
Charles Darwin conjectured that the male beard, as well as the relative hairlessness of humans compared to nearly all other mammals, are results of sexual selection. He reasoned that since, compared to males, the bodies of females are more nearly hairless, hairlessness is one of the atypical cases due to its selection by males at a remote prehistoric time, when males had overwhelming selective power, and that it nonetheless affected males due to genetic correlation between the sexes. He also hypothesized that sexual selection could also be what had differentiated between different human races, as he did not believe that natural selection provided a satisfactory answer.
White skin is new...
No. It's old. Only some specific genes that apepar (all very diffuse) to be related to the extreme untanneable pale skin of some Northern Europeans apear to be new, i.e. Neolithic or Epipaleolithic.
... so there was a strong selection pressure in Europe for white skin.
There was some selection and also lost of pressure. Not just in Europe but in all West Eurasia (Saddam Hussein was white, wasn't him?) an in other parts of Eurasia (Eastern Asians are also quite white, if we don't use that name it's because of other differences mostly unrelated with skin pygmentation)
Anyhow, you first have o clarify what the heck means "white skin" for you? It's a very ambiguous term as there's no such thing as "Pantene white" and "black" skins, all are brown-beige shades.
I see that white (rather depygmented) skin is widesepread in Eurasia and it must have been around since people began to move out of the tropics - or soon after.
And that super-pale skin found among some Northern Europeans may be a more recent developent and I tend to consider it a mild form of albinism (and in fact it has some of the same negative effects). If you want to call "white skin" to this last developement, it's up to you, but be specific becuase there's a whole scale of tones.
My white skin type (rosy light beige in winter, nicely tanned in summer, maybe the more widespread in Europe) is old. Andy Warhol's extremely pale skin may be Epipaleo-/Neolithc and is just a radicalization of the other type.
Many genes are involved anyhow: so far we only know genes that are said to be responsible of maybe 25% of skin pygmentation. There's a lot of research to do.
he illnesses that Vitamin D is said to be efficacious for are things like some cancers, heart disease, psoriasis, Crohns disease which are said to be a result of excessive immune system activity which is itself said to result from modern overeating and obesity. Vitamin D is believed to modulate the overactive immune system, damping down this inflammation. These are diseases of the affluent and are very recent.
Vitamin D is essential for a proper brain developement and health, and also for the bones and many other issues (read the article that triggered this post, please).
Rickets is found in Black Africans in Africa...
Again read unprejudicely. It says:
Conclusions Nigerian children with rickets have a low intake of calcium and have a better response to treatment with calcium alone or in combination with vitamin D than to treatment with vitamin D alone.
So vitamin D is not the problem here but low calcium in their diets (calcium is hard to get and keep balanced unless you take many dairy products or figs). But this is another problem that has nothing to do with skin color. It may relate to another issue: lacose tolerance (a rather rare paedomorphic trait that allows adults to digest milk). Lactose intolerant peoples can take milk in form of cheese or yogurts anyhow but calcium may be hard to get for peoples that have little or no access to cattle products.
So why has their skin not lightened in Africa ?
Because it would be of no help, as vitamin D is not the problem there. Cancer and sunburn may be instead.
Why are Black African agriculturists darker than the Bushmen hunter-gatherers if nutritional rickets is a factor in skin colour.
Again mixing apples and oranges. Khoi-San peoples live in a climatic area comparable to the Mediterranean. They are probably the oldest distinct human population and they may have their own (not researched, AFAIK) pygmentation system.
Nutritional rickets have nothing to do with vitamin D and therefore skin tone.
You know that. Why do you insist?
OK you got me
Yah, you had not made your basice homework, so to say. :P
There is evidence for Vitamin D deficiency as a factor in schizoprenia
Now you are bringing here really valuable info I was ignorant of. If lack or excess of vit. D cause major defects in newborns and as intake from the Sun is the safest way (because all excess is removed, no overdose is possible)... then we have a very neat explanation, way beyond the mere rickets, for differences in pygmentation and the fundamental need of sun-produced vit. D.
Surely the first change under conditions of low UVB such that vitamin D would not be able to be synthesized for most of the year would be to the mechanism that broke down the day to day excess in the middle of summer.
In the tropics it's "summer" (so to say) all year round. And most of Human existence (unlike that of Neanderthals) happened there (or not too far away). The first AMH are estimated to be some 200,000 years old (and their likely predecessors, H. heilderbegensis were also of Tropical lifestyle). The first humans known significatively north of the tropical belt, in Central Asia probably, are surely not much older than 50,000 years ago, though some lived maybe 130,000 years ago in Palestine, where the word "winter" does makes some sense (but it's, today, Mediterranean climate and close to the subtropical deserts, with high solar input in any case).
... however 20 minutes summer sun sythesizes 20,000IU then it shuts off leading to deficiency in the winter; thousands of years of low UVB winters is not enough time for natural selection to work towards the simplest solution ?
I think you got it wrong: the vit. D processing happens all the time, but the excess is destroyed immediately. In summer (or near the tropics) it's easy to synthetize all needed vit. D (which is toxic in excess) as you say. But in winter, specially with the skin covered by clothes, it demands a much increased ability of processing such limited input, more perfected as you move farther north. This is what caused depygmentation in both West and East Eurasians, though in the East it's often not as extreme (for whatever reasons, like a fish-rich diet or mere evolutionary accidents).
"The typical African diet is rich in grains..."
In fact nearly all Neolithic diets are. Only those peoples that are specialized in cattle or fishing may escape this dominance. In Medieval Europe for instance bread (and other cereal based meals like muesli) was the staple food, even in areas where it's not eaten so often nowadays.
Anyhow, I have read others who argue that vegetal foods are more balanced for this calcium issue and that are meat-based diets which are terribly bad for calcium (meat, fish included, is specially high in phosphorus, and the body needs a P-Ca balance), unless milk and daries are also present or calcium is taken in some other form (like directly from pulverized bones and eggshells, or from the few fruits like figs that are high in calcium).
-If UV radiation D is a significant factor in black African skin melaninisation that might lead one to expect that their skin would be under selection for lighter skin to let more UVB in and generate increased vitamin D to counter the rickets and osteomalacia inducing effect of thier diet.
Again this is mixing apples and oranges. If their problem is lack of calcium, no increase in vit. D will help. They need calcium supplements, cheese, yogurth, dry figs.
"Khoi-San peoples live in a climatic area comparable to the Mediterranean".
Worldwide, the highest rates of skin cancer are found in South Africa and Australia, areas that receive high amounts of UV radiation check out the SA UV Index
Ahem. That map is for today: and now it's Summer in the southern hemisphere. I was kinda flippant when I saw all the northern hemisphere in the dark (so to say), even the Sahara being "green".
Along the year, Southern Africa is like the Mediterranean areas of Africa and Asia (check the radiation map I posted before). In fact South Africa, California and an area of Chile are the only Mediterranean climates outside of the Mediterranean basin as such.
Anyhow, I insist, the Khoisan pygmentation system has not been researched and their skin appears to have a similar yellowish tinge to that found in East Asia, which is a separate pygment, unexistent in Caucasoids, that is an excellent cancer protection (not as good as high "black" melanine but almost).
Regarding supposedly high rates of skin cancer in South Africa and Australia.
I could not find in your link where it says that and the article seems extremely biased towards the problems of white people: "for example, skin cancer is more common in Texas than it is in Minnesota". Sure for the same skin type and ancestry. But probably the cancer rates are much higher in Texas than in Mexico, and in both than in Haiti or Jamaica, where most of the people have very dark skin, even if these islands are further south well in the tropical belt.
Australia has certainly a mostly tropical/subtropical climate but the majority of its population is of NW European ancestry. So no wonder you have high skin cancer rates there. South Africa instead is mostly of Tropical African ancestry, so the rates should not be so high, in spite of the Boers. it may still have high rates for the white fraction of the population, but hardly overall (whites are like 20% only).
Would it have been colonized by the Portuguese instead of the Dutch, surely the South African cancer rates among whites would be much lower (Iberians generally tan pretty well - even if there is variation, the extremely pale types of the far north just do not exist).
I wasn't factoring in the southern summer, does it make a difference to the point at issue?
As far as I can see it means that Khoi-San people have evolved where UVB is strong enough to make Vitamin D all year and in their summer, they would, as hunter gatherers, have been exposed for much of the day to the very highest levels of UV radiation All forms of UV radiation are reduced by cloud cover. Persistent lack of cloud cover in some regions (e.g. Australia and South Africa) increases the danger from UV radiation compared to similar latitudes in the Northern Hemisphere.
If north Europeans were transplanted to S. A. and led a hunter-gatherer life for hundreds of generations would their skin darken? Quite possibly, however the argument has nothing to do with the case. It is the existence of the darkest skinned people in the world in west Africa where the UV is effectively lower than one would think from its latitude, as pointed out in the link above, that requires explaining, if UV is a strong selective force. Those who evolved where a lot of the UV gets through the relatively cloudless sky (i.e. the Koi-San) do not have skin anything like as dark as the UV selective force for skin melanization theory would predict.
South America also has extreme UV at the earths surface but no very dark skinned people live there. (Bush removed climate monitoring from NASA's remit now it's back) NASA map showing where more or less UV radiation reaches the surface.
If UV is the main factor in the evolution of west African's very dark brown skin then of course you must be right in speculating that
Khoisan pygmentation system has not been researched and their skin appears to have a similar yellowish tinge it to that found in East Asia, which is a separate pigment, unexistent in Caucasoids, that is an excellent cancer protection (not as good as high "black" melanine but almost).
But Khoisan pigmentation has been researched pigmentation gene alleles Norton doesn't seem to think they have especially effective UV protection.
West Africans have a high incidence of polygyny and the darkest skin.
Here is the commonly accepted story The evolution of human skin coloration it suggests that darker skin protects Folic Acid from destruction. Wrong as shown by this These observations suggest a new role for reduced folate in protection from ultraviolet damage and have bearing on the hypothesis that folate photodegradation influenced the evolution of human skin color
Schizophrenia is more common in winter and (like homosexuality) in those born in cities, it is probably due to an infection of some kind A New Germ Theory
North Europeans would be going several months of the year without any Vitamin D from UVB, where is the adaptation to this putative selection pressure to be found.
Black Africans do not get rickets in north Europe except formerly which was nutritional rickets (that whites also used to get) with the same diet.
(Define white? - well you look like a 'typical white person' to me.)
As far as I can see it means that Khoi-San people have evolved where UVB is strong enough to make Vitamin D all year and in their summer, they would, as hunter gatherers, have been exposed for much of the day to the very highest levels of UV radiation All forms of UV radiation are reduced by cloud cover. Persistent lack of cloud cover in some regions (e.g. Australia and South Africa) increases the danger from UV radiation compared to similar latitudes in the Northern Hemisphere.
It's not likely that the Khoisan evolved in the deserts specifically, but rather in more favorable areas from where they ahve been displaced by Bantu expansion recently. By "no cloud cover" you obviously mean the dry deserts of the world - and very few people live or used to live in such extreme regions. So ignore them, ok?
Anyhow we are merely speculating about the Khoisan because no specific pygmentation or cancer-rate research among them has been done ever. In Australia certainly Aborigines are very dark in general. and I have even read the opposite argument: why Tasmanian Aborigines were not white?
Obviously evolution is not so simple and lineal.
If north Europeans were transplanted to S. A. and led a hunter-gatherer life for hundreds of generations would their skin darken?
Definitively yes, even without any admixture. Just in the mid-run the darker individuals and those who can tan with greater ease and effectivity would have somewhat higher survival rates and overall better health and therefore would be the most succesful in reproduction. In the 60s at least it was claimed that in just 50 generations (like 1000 years) the pygmentation of a population should significatively evolve to adapt to local climate. Though becoming black out of white or vice versa surely needs more time. But sould be enough time to get people to appear more neutrally "brown" (milk coffee color instead of chocolate or vanilla ones).
It is the existence of the darkest skinned people in the world in west Africa...
Actually the Dinka of East Africa are probably the darkest people in all Earth. Some Eurasian tropical peoples are also extremely dark (Tamils, Papuans).
Africans in general anyhow had a more diverse founder genetic pool to pick genes from - and they probably evolved specially in Savannah conditions. The colonization of West Africa and specially of the jungle regions (excepting Pygmies) is quite recent.
Jungle anyhow has advanced and retreated at different periods. But humans and proto-humans evolved specifically in Savannah conditions particularly.
South America also has extreme UV at the earths surface but no very dark skinned people live there.
Native Americans come from Siberia/Beringia and only "recently" arrived to that area. They have darkened but not blackened - they did never have time (nor surely the genes in their pool) to go that far. Also "brown" skin colors manage pretty well under most conditions anyhow.
Btw, the extreme area in coastal South America is mostly the desert.
NASA map showing where more or less UV radiation reaches the surface.
UV-B only. It's somewhat different from the general Wikipedia "insolation" map. Tropical jungle areas still are very high in NASA map.
The only place where there is enough non-tropical landmass to justify widespread "whitening" is in the Northern Hemisphere. And there is precisely where we find the lightest types.
Notice please how Mongolia has about the same radiation levels as the sunniest areas of the Mediterranean (yet Mongols have often rosy cheeks and quite light skin). Most of Europe has conditions not found almost anywhere else on Earth, where people lives in sufficient numbers. It is a most special climate (relatively warm and yet very low in radiation levels) and this is even more extreme in the far North.
That alone should be enough explanation for the very light pygmentation found in Europe.
But Khoisan pigmentation has been researched pigmentation gene alleles. Norton doesn't seem to think they have especially effective UV protection.
There's only one brief mention in that article to Khoisan, specifically to San (Bushmen). It says they have greater ammount of the derived alelle OCA2 than Black Africans (and "black" Tropical Asians/Oceanians).
There's no further research in any Khoisan-specific alelles that may exist, like the ones that do exist among East Asians and that do offer a high skin-cancer protection. Khoisan are a very ancient branch of Humankind and they may have their own pygmentation genetics, maybe not shared by anyone else. These hypothetical specificities are what I say has not been researched. I believe they must exist anyhow as they are a locally very well adapted people in general.
West Africans have a high incidence of polygyny and the darkest skin.
Other peoples also have high inccidence of polygyny - so what? Polygyny is certainly not any African-specific phenomenon and in fact it may be a relatively recent introduction.
Here is the commonly accepted story The evolution of human skin coloration it suggests that darker skin protects Folic Acid from destruction.
I did not find that part (folates are anyhow taken in food) but in any case it does ratify the widespread understanding that skin pygmentation is basically a function of insolation levels:
Wrong as shown by this These observations suggest a new role for reduced folate in protection from ultraviolet damage and have bearing on the hypothesis that folate photodegradation influenced the evolution of human skin color
The issue of vitamin D alone is enough to justify pygmentation evolution. While this issue of folates may be another piece of the puzzle, it is not necesary to explain anything.
Schizophrenia is more common in winter and (like homosexuality) in those born in cities, it is probably due to an infection of some kind A New Germ Theory
Well...
In any case vit. D is necesary for so many things, including embrionic developement and nerve/brain proper formation, that human biology has found it very necesary to make sure it is incorporated in sufficient ammounts even in the darkest of climates.
North Europeans would be going several months of the year without any Vitamin D from UVB, where is the adaptation to this putative selection pressure to be found.
What?! In their extremely light skin. They are the most efficient processors of vit. D from the Sun anywhere on Earth. Additionally fish-rich diet allows for a very decent vit. D intake.
Please stop this circular reasoning. We don't need to go over this again and again.
Black Africans do not get rickets in north Europe except formerly which was nutritional rickets (that whites also used to get) with the same diet.
Not sure. Nowadays almost every food is fortified with vitamins, including maybe 100% the recomended intake of vit. D. I can imagine that dark skinned peoples living in high latitudes are somewhat concerned about such issues and make sure that they take enough vit. D in their foods.
Rickets, as discussed already, is not the only problem caused by low vit. D levels - and surely not the main one either.
(Define white? - well you look like a 'typical white person' to me.)
So would I say. But some people seem to reserve that for extremely pale Nordic types, while others would extend the concept to all Caucasoids, including southern Indians and maybe even Ethiopians. So it's a very slippery term.
Anyhow, what matters in this sense is the different types of skin coloration found among West Eurasians. I'd say these can be roughly (and somewhat arbitrarily) described as three: light brown (found specially among Mediterraneans, specially in North Africa and Arabia peninsula), basic white/beige (the most common one in West Asia and Europe) and extreme white/creamy (found specially in Northern Europe but only in some areas being really dominant). This last type is the one I think is most recent, maybe even as late as Neolithic. Instead the "basic white" type should be much older and represent the general adaptation to the insolation conditions of Europe and the Mediterranean (but excluding the extreme conditions of Northern Europe, then still under a thick layer of ice).
Of course this typology of just three types is somewhat simplistic and some greater variation must have existed all the time, as it does now.
It's not likely that the Khoisan evolved in the deserts specifically, but rather in more favorable areas from where they have been displaced by Bantu expansion recently.
You mean the Bantu expansion out of west Africa (of people who just happen to be agriculturist and polygynists, tall, powerfully built, and er.. 'black') displaced the Khoisans (who just happen to be hunter-gatherering, largely monogamous, very short and weakly built and er ...a far lighter shade of brown)
Whatever line of evidence you go by Khoisans are an older population - skeletal remains
From the beginning of the Upper Paleolithic period, hunting and gathering cultures known as the Sangoan occupied southern Africa in areas where annual rainfall is less than 40 inches (1016mm)—and today's San and Khoi people resemble the ancient Sangoan skeletal remains. The Khoisan people were the original inhabitants of much of southern Africa before the southward Bantu expansion — coming down the east and west coasts of Africa — and later European colonization. Both Khoi and San people share physical and linguistic characteristics, and it seems clear that the Khoi branched forth from the San by adopting the practice of herding cattle and goats from neighboring Bantu-speaking groups.
Prefer mtDNA evidence? The Dawn of Human Matrilineal Diversity"
To shed light on the structure of the mitochondrial DNA (mtDNA) phylogeny at the dawn of Homo sapiens, we constructed a matrilineal tree composed of 624 complete mtDNA genomes from sub-Saharan Hg L lineages. We paid particular attention to the Khoi and San (Khoisan) people of South Africa because they are considered to be a unique relic of hunter-gatherer lifestyle and to carry paternal and maternal lineages belonging to the deepest clades known among modern humans. Both the tree phylogeny and coalescence calculations suggest that Khoisan matrilineal ancestry diverged from the rest of the human mtDNA pool 90,000150,000 years before present (ybp)
Khosians evolved in a high UV environment, I think the NASA site shows much of SA is extremely high UV. It is reasonable to say Khoisans are well adapted in the amount of UV protection from melanin that they have.
http://www.lewrockwell.com/miller/miller25.html">In Seattle (47° N) and London (52° N), from October to April UVB photons are blocked by the atmosphere so one’s skin cannot make vitamin D. (The half-life of circulating vitamin D is approximately one month.)
Africans in Britain do not have lower levels:-
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.
That's right, the most efficient processors of vit. D from the Sun anywhere on Earth. don't have higher levels than blacks in the summer, in Britain .
It is important to understand that the amounts available from food are tiny -"In the United States and Canada, for example, fortified milk typically provides 100 IU per glass, or one quarter of the estimated adequate intake for adults over the age of 50.[1]
Fatty fish, such as salmon, are natural sources of vitamin D.Very few foods are naturally rich in vitamin D, so much vitamin D intake in the industrialized world is from fortified products including milk, soy milk and breakfast cereals or supplements.[1] Natural sources of vitamin D include:[1]
Fish liver oils, such as cod liver oil, 1 Tbs. (15 mL) provides 1,360 IU (one IU equals 25 ng)
Fatty fish species, such as:
Herring, 85g (3 oz) provides 1383 IU
Catfish, 85g (3 oz) provides 425 IU
Salmon, cooked, 3.5 oz provides 360 IU
Mackerel, cooked, 3.5 oz, 345 IU
Sardines, canned in oil, drained, 1.75 oz, 250 IU
Tuna, canned in oil, 3 oz, 200 IU
Eel, cooked, 3.5 oz, 200 IU
One whole egg, provides 20 IU
Beef liver, cooked, 3.5 ounces, provides 15 IU"
How much fish liver oil would one have to drink to get the 20,000IU that even the blackest black Africans get after one and a half hours in the British summer sun in shorts, then the body shuts off production (just like in white people after 20000IU/20 min.) because a higher dose becomes deleterious if it mounts up.
Easy to understand why Africans are shuting off synthesis to avoid storing say 100,000IU of Vitamin D . Every day is at least as strong as British summer sun in Africa so they would be poisoned after a few years.
My point is why do the whites do the same thing. Evolution should have selected for those who did continue to synthesize 'D',
The fact that blacks can get through to winter fine because vitamin D is not required in the astronomical amounts that in theory could be made from the UV in northern Europe, even dark skinned will get enough in summer to see them though the winter , the trivial amounts available from food are irrelevant, brown skinned people have always been able to get through the year fine in nothern Europe. Lack Vitamin D is not what led to Europeans becoming white. Lack of UV may explain the resource poor environment and hence sexual selection's special focus.
UV exposure may damp down immune sytem over-activation and hence inflammation, it may prevents more cancers than it causes.
Multiple sclerosis (MS) is a neurologically devastating disease that afflicts people with low vitamin D levels. Its victims include the cellist Jacqueline Du Pré, whose first symptom was loss of sensation in her fingers, and some 500,000 Americans who currently suffer from this malady. MS is an autoimmune disease, where the body’s immune system attacks and destroys its own cells. With multiple sclerosis, T cells in the adaptive immune system, Th1 cells (CD4 T helper type 1 cells), attack the myelin sheath (insulation) of the axons (nerve fibers) that neurons (brain cells) use to transmit electrical signals. The Vitamin D hormone system regulates and tones down the potentially self-destructive actions of Th1 cells. These cells make their own 1,25-dihydroxyvitamin D if there is a sufficient amount of vitamin D (25-hydroxyvitamin D) circulating in the blood. Researchers have shown that the risk of MS decreases as the level of vitamin D in the blood increases (JAMA 2006;296:2832–2838). People living at higher latitudes have an increased risk of MS and other autoimmune diseases. Studies show that people who live below latitude 35° (e.g., Atlanta) until the age of 10 reduce the risk of MS by 50% (Toxicology 2002;181–182:71–78 and Eur J Clin Nutr 2004;58:1095–1109).
In a study published earlier this year, researchers evaluated 79 pairs of identical twins where only one twin in each pair had MS, despite having the same genetic susceptibility. They found that the MS-free twin had spent more time outdoors in the sun – during hot days, sun tanning, and at the beach. The authors conclude that sunshine is protective against MS (Neurology 2007;69:381–388).
New research suggests that influenza is also a disease triggered by vitamin D deficiency. Influenza virus exists in the population year-round, but influenza epidemics are seasonal and occur only in the winter (in northern latitudes), when vitamin D blood levels are at their nadir. Vitamin D-expressed genes instruct macrophages, the front-line defenders in the innate immune system, to make antimicrobial peptides, which are like antibiotics (Science 2006;311:1770–1773). These peptides attack and destroy influenza virus particles, and in human carriers keep it at bay. (Neutrophils and natural killer cells in the innate immune system and epithelial cells lining the respiratory tract also synthesize these virucidal peptides.) Other vitamin D-expressed genes rein in macrophages fighting an infection to keep them from overreacting and releasing too many inflammatory agents (cytokines) that can damage infected tissue. In the 1918 Spanish flu pandemic, which killed 50 million people, of which 500,000 were Americans, young healthy adults (as happened to my 22-year-old grandmother) would wake up in the morning feeling well, start drowning in their own inflammation as the day wore on, and be dead by midnight. Autopsies showed complete destruction of the epithelial cells lining the respiratory tract due, as researchers now know, to a macrophage-induced overly severe inflammatory reaction to the virus. These flu victims were attacked and killed by their own immune system, something researchers have found vitamin D can prevent (Epidemiol Infect 2006;134:1129–1140).
Randomized clinical trials need to be done to test the vitamin D theory of influenza. With what we know now, however, perhaps an annual shot of 600,000 IU of vitamin D (Med J Aust 2005;183:10–12) would be more effective in preventing influenza than a jab of flu vaccine....There is now strong scientific evidence that vitamin D does indeed reduce the risk of cancer. Evidence from a well-conducted, randomized, placebo-controlled, double-blind trial proves beyond a reasonable doubt that this is the case, at least with regard to breast cancer. A Creighton University study has shown that women over the age of 55 who took a 1,100 IU/day vitamin D supplement, with calcium, and were followed for 4 years had a highly statistically significant (P <0.005) 75% reduction in breast cancer (diagnosed after the first 12 months) compared with women who took a placebo (Am J Clin Nutr 2007;85:1568–1591).
Some of the genes vitamin D activates make proteins that halt cancer by inducing apoptosis (programmed cell death), which destroys aberrant cells before they become cancerous, like adenoma cells in the colon and rectum. Others promote cell differentiation and reining in of out-of-control growth of cancer cells (like prostate cancer cells). Vitamin D-expressed genes inhibit angiogenesis, the formation of new blood vessels that malignant tumors need to grow, as studies on lung and breast cancers show. Other genes inhibit metastases, preventing cancer that arises in one organ from spreading its cells to other parts of the body, as studied in breast, and prostate cancers.
Vitamin D also expresses genes that curb cardiovascular disease. One gene controls the renin-angiotensin system, which when overactive causes hypertension (high blood pressure). Others stifle the immune system-mediated inflammatory response that propagates atherosclerosis and congestive heart failure (Curr Opin Lipidol 2007;18:41–46).
John Manning has done work on 2d4d ratios Hands up! How your fingers reveal so much about you...
Here is his take on polygyny's conection to skin colour Second to fourth digit ratio, sexual selection, and skin colour . He thinks the higher testosterone levels in black Africans predispose them to infections (testosterone lowering immunity)therefore black skin as barrier to infection evolved in polygynous Africans.
The Antimicrobial Properties of Melanocytes, Melanosomes and Melanin and the Evolution of Black Skin
Black Africans are not massively polygynistic as you claim. In fact Black Africa is a region where you can find many matrifocal societies that, by their very nature, are not polygynistic (only patriarchal societies are).
Make your anthropological homework, please.
Regardng Khoisan pygmentation, I insist that it has not been sufficiently researched, if at all. They do not appear to have any sort of hugh incidence of cancer, hence they must have a solution for that problem, whichever it is.
They are not pale in any case.
We suggest that polygynous populations incur selection for high prenatal testosterone and low prenatal oestrogen because of competition among men for wives. Such groups have low 2D:4D, and high susceptibility to sunburn and skin infections which may result from the immunosuppressive effects of prenatal testosterone.
Honestly it looks to me a weirdo fantasy and nothing else. In Patriarchal plygynistic cultures, men get more women based on their wealth and not skin color. The competition among men in such societies is one of power and property, not one of beauty.
(Do) your anthropological homework, please.
OK, will this do:- Pebley, A. R., & Mbugua, W. (1989). Polygyny and Fertility in Sub-Saharan Africa. In R. J. Lesthaeghe (ed.), Reproduction and Social Organization in Sub-Saharan Africa, Berkeley: University of California Press, pp. 338-364.
In non-African societies in which polygyny is, or was, socially permissible, only a relatively small fraction of the population is in polygynous marriages. Chamie's (1986) analysis of data for Arab Muslim countries between the 1950s and 1980s shows that only 5 to 12 percent of men in these countries have more than one wife. … Smith and Kunz (1976) report that less than 10 percent of nineteenth-century American Mormon husbands were polygynists. By contrast, throughout most of southern West Africa and western Central Africa, as many as 20 to 50 percent of married men have more than one wife … The frequency is somewhat lower in East and South Africa, although 15 to 30 percent of husbands are reported to be polygynists in Kenya and Tanzania.
Taken from Polygyny or patrilocality?
In fact Black Africa is a region where you can find many matrifocal societies that, by their very nature, are not polygynistic (only patriarchal societies are).
I looked up 'matrifocal' Wiki Anthropologist R. L. Smith (2002) refers to 'matrifocality' as the kinship structure of a social system where the mothers assume structural prominence.[14]
I did some real homework and turned up this The Maternal Uncle, or nijaay in Wolof, often helps to settle family disputes. He may also be expected to help his sisters in times of need when the parents are no longer able. Among many groups in Senegal, a prefered marriage for a man is to his nijaay's daughter. So the mother, or mother's side of the family at least, has a special importance. This is very interesting (and relevant to studies like Hammer et al) but I don't see how it excludes polygyny.
Regardng Khoisan pygmentation, I insist that it has not been sufficiently researched, if at all. They do not appear to have any sort of huge incidence of cancer, hence they must have a solution for that problem, (whatever) it is
A large body of evidence indicates that sunlight does not cause the most lethal form of skin cancer, malignant melanoma. A U.S. Navy study found that melanoma occurred more frequently in sailors who worked indoors all the time. Those who worked outdoors had the lowest incidence of melanoma. Also, most melanomas appear on parts of the body that are seldom exposed to sunlight (Arch Environ Health 1990;45:261–267). Sun exposure is associated with increased survival from melanoma (J Natl Cancer Inst 2005;97:195–199). Another study showed that people who had longer lifetime exposure to the sun without burning were less likely to get melanomas than those with less exposure (J Invest Dermatol 2003;120:1087–1093.)
The rise in skin cancers over the last 25 years parallels the rise in use of sunscreen lotions, which block vitamin D-producing UVB radiation but not cancer-causing ultraviolet A radiation (UVA). (Newer sunscreen lotions also block out UVA.) Each year there are 8,000 deaths from melanoma and 1,500 deaths from nonmelanoma (squamous and basal cell) skin cancer. Surgical excision of nonmelanoma skin cancers cures them, except in rare cases where the growth has been allowed to linger for a long time and metastasize. Dr. John Cannell, Executive Director of the Vitamin D Council, makes this point: 1,500 deaths occur each year from non-melanoma skin cancer, but 1,500 deaths occur each day from other cancers that vitamin D in optimal doses might well prevent.
It is probably true that sunbathing while covered in 'sunscreen' lotion is far more dangerous than exposure for the same amout of time without 'sunscreen' lotion. Moreover untill recentlly the sunscreens blocked UVB (responsible for the burning sensation) while letting UVC through and hence those using 'sunscreen' were likely to stay longer in strong UV without feeling the effects the greater UVC damage possiblly resulting in skin cancer.
In the past UVA was considered less harmful, but today it is known that it can contribute to skin cancer via the indirect DNA damage (free radicals and reactive oxygen species). It penetrates deeply but it does not cause sunburn. UVA does not damage DNA directly like UVB and UVC, but it can generate highly reactive chemical intermediates, such as hydroxyl and oxygen radicals, which in turn can damage DNA. Because it does not cause reddening of the skin (erythema) it cannot be measured in the SPF testing. There is no good clinical measurement of the blocking of UVA radiation, but it is important that sunscreen block both UVA and UVB. Some scientists blame the absence of UVA filters in sunscreens for the higher melanoma-risk that was found for sunscreen users.[12]
Ultraviolet
In an experiment that was published in 2006 by Hanson et al, the amount of harmful reactive oxygen species (ROS) had been measured in untreated and in sunscreen treated skin. In the first 20 minutes the film of sunscreen had a protective effect and the number of ROS species was smaller. After 60 minutes however the amount of absorbed sunscreen was so high, that the amount of ROS was higher in the sunscreen treated skin than in the untreated skin.[13]
Modern rates of skin cancer in Europeans are due to Western lifestyles that arose very recently. Natural sunlight does not induce skin cancer to the extent one would think when extrapolating from modern 'white' rates. Therefore it was not much of a factor in the evolution of the populations who have darker skin than the Khoisans.
Many Europeans have been exposed to extremely high UV on holiday, which their skin was not prepared for by gradual tanning in a similar climate.
Many users of the old home UV lamps have inflicted severe UV damage on their skins
Using a sunbed once a month or more can increase your risk of skin cancer by more than half.
Obesity triggers, restricted-calorie diet inhibits skin cancer
Smoking Triples Risk Of A Common Type Of Skin Cancer
...I don't see how it excludes polygyny.
When the husband goes to live to the wife's village (matrilocality, normally associated with matrifocality and sometimes confused with the non-existent "matriarchy"), the polygynic family cannot be formed. Polygyny in Africa (and elsewhere) requires the wifes to go to live to the husband's place, normally with this one having to provide a separate home for each wife.
Matrifocal/-local sosieties are certainly not polygynistic. Also it is generally accepted that partiarchy and polygyny are relatively recent inputs in most Black African societies, that the remaining matrifocal societies, and the often prominent role of women even in patrairchal ones, are only the tip of the iceberg of a much more generalized historical pattern.
This basically subverts the hypothesis of family type having any relation with skin color, IMO.
The rise in skin cancers over the last 25 years parallels the rise in use of sunscreen lotions, which block vitamin D-producing UVB radiation but not cancer-causing ultraviolet A radiation (UVA).
I always suspected that sunscreens are just another scam of the pharmaceutic industry. I never use them (but I can tan properly). They do prevent sunburn to an extent anyhow, right?
Modern rates of skin cancer in Europeans are due to Western lifestyles that arose very recently. Natural sunlight does not induce skin cancer to the extent one would think when extrapolating from modern 'white' rates.
It depends at what latitudes. One of the issues with "whites" worldwide (normally meaning people of NW european origin, that are typically even paler) is that they have colonized areas that are rather high (USA) or even extremely high (Asutralia) in solar radiation for what their genetics would recommend.
Also the fashion of beach vacations and, worse maybe, artificial tanning under UVA machines, obviously increase the rates. Nevertheless, UVA machines users are still a minority: working class people basically don't use them at all (like golf and other abusive fashions, it's restricted to the affluent sectors or at most the wannabees).
Therefore it was not much of a factor in the evolution of the populations who have darker skin than the Khoisans.
Hmmm. Don't think so. Attending to the data that you have posted here, ancestral humans (but Khoisan, who probably branched out before) appear to have been black (i.e. middle/dark brown) and only when they expanded into higher latitudes they seem to have become lighter pygmented (in two separate processes: one in West Eurasia and another in East Asia).
So I guess that the ancestral human population living probably somewhere in East Africa (from Kenya to Sudan, including The Horn) found in high melanin production an easy way out of the problem of high insolation (sunburn, potential cancers). This is somewhat logical as the abilty to produce melanine and therefore rather black skin is present among our closest relatives: chimpanzees, bonobos and even gorillas. Only the more distant orangutans are "white" (so-to-say) in adulthood (and redhaired, btw).
So probably not just AMHs but maybe our Erectus/Ergaster ancestors were rather black. And this is without doubt the genetics and phenotype that the people migrating OOA carried originally with them in any case.
But surely it's not the only possible biological solution to the problem: all such problems have many possible solutions and occasionally several different ones are found and tested.
By the way Nina G Jablonski;George Chaplin say "Populations
believed to have inhabited their current area of distribution for 10–20,000 years (e.g.,Spanish Basques) conform most closely to
predicted values for skin reflectance.
In a later (2002)Scientific American article Nina G Jablonski and George Chaplin address the objection that Khoisans are native to sub-Saharan Africa but do not have very dark skin
"A number of the earliest movements of contemporary humans outside equatorial Africa were into southern Africa. The descendants of some of these early colonizers, the Khoisan (previously known as Hottentots), are still found in southern Africa and have significantly lighter skin than indigenous equatorial Africans do -a clear adaptation to the lowerlevels of LTV radiation that prevail at the southern extremity of the continent
However, they are simply wrong about the amount of UV at the earths surface in south Africa
Distribution of UV radiation at the Earth's surface from TOMS-measured UV-backscattered radiances
In the equatorial regions, ±20°, the UV exposures during the March equinox are larger than during the September equinox because of increased cloudiness during September. Extended land areas with the largest erythemal exposure are in Australia and South Africa where there is a larger proportion of clear-sky days. The large short-term variations in ozone amount which occur at high latitudes in the range ±65° cause changes in UV irradiance comparable to clouds and aerosols for wavelengths between 280 nm and 300 nm that are strongly absorbed by ozone.
Remember South Africa ties with Australia for the highest levels of erythemal UV at the earth's surface of any extended landmass in the world.
Even if this is supposed to mean Khoisans stuck to the southernmost tip of south Africa, (they didn't), they would still be exposed to erythemal UV comparable, if not greater, than equatorial Africa.
To my way of thinking this is a very telling piece of evidence that white skin as well as red and blonde hair are the result of strong sexual selection.
We've always known that people with fair skin and light hair have a greater chance of getting skin cancer from the sun than people with darker features. We simply assumed that people who did not tan lacked the protection that natural pigment provides in response to sun exposure.
Dr. Brash's study is very important because it explains in more detail how people with fair skin and light hair are at greater risk for skin cancer.
Type of melanin is a co-conspirator in causing skin cancer
Now we understand that it's
the type of melanin that
blondes and red-heads
have—pheomelanin—that seems to be important in skin cancer risk. This type of melanin acts as a co-conspirator in causing a person to be more at-risk for developing skin cancer. People with the other type of melanin—eumelanin—have darker hair. Interestingly, while dark-haired people with eumelanin can be fair-skinned, they don't burn as readily as a blonde or a red-head.
Dr. Brash found that the type of melanin that causes blonde and red hair actually increases the risk for cell death such as seen in sunburn . Blondes and redheads have what is called pheomelanin. People with darker hair have eumelanin.
If pheomelanin increases the risk of UV induced skin cancer how could it become widespread in northern Europe under selection for protecting the skin from UV induced cancer?
Yes, it is a very interesting piece of research, thanks. :-)
If pheomelanin increases the risk of UV induced skin cancer how could it become widespread in northern Europe under selection for protecting the skin from UV induced cancer?
Because there was no such selection anymore. In Northern Europe skin cancer is not really a problem (too low insolation) but it can be for people of Northern European ancestry in other areas of the world.
But this is not anymore a matter of just skin color, but mainly of hair color. And hair color doesn't appear to have been favored by any selective pressure, at least not any that would be a mere mater of health. Hair color (not the default black) is either favored by social aesthetic selection (including sexual selection) or just accidentally accumulated (by founder effects or drift).
Another possibility is that eumelanin bearing people may have on average an even lighter type of skin that favors best the processing of vitamin D in low insolation areas. In that case (a serious possibility, I'd say) blonds (and to a lesser extent redhairs) would have been selected for, not for their hairs but their particularly fair skins.
Cancer seldom happens at young age, anyhow. Defense against cancer would be secondary and a valid sacrifice if that would secure enough vitamin D for survival and succesful reproduction. Advantages are not always clear cut, they often come at a price.
That may also explain why there are still some brunettes in Northern Europe - many in some areas. It would be a situation of unstable equilibrium, where both alternative phenotypes have something to offer (and something to lose).
Another possibility is that eumelanin bearing people may have on average an even lighter type of skin that favors best the processing of vitamin D in low (UVB radiation )areas. In that case (a serious possibility, I'd say) blonds (and to a lesser extent redhairs) would have been selected for, not for their hair but their particularly fair skins.
It is natural to assume that, in the form it is found in Europeans, blonde hair has the effect of making the skin white or whiter. Rather surprisingly this is not the case. Alleles that lighten skin color, are specific to European populations, and appear to have been under positive selection, i.e., the "redhead" MC1R alleles, the derived SLC24A5, SLC45A2, and AIM1 (MATP) alleles, and possibly DTNBP1, EDA, OCA2, KITLG, MYO5A, HPS7, and TYRP1 variants (McEvoy et al. 2006; Sturm and Frudakis 2004).
It is true of red hair or the "redhead" MC1R alleles that they make the skin lighter.
If we examine the many homozygous and heterozygous combinations of MC1R or OCA2 alleles, most have little visible effect on skin pigmentation, except for the ones that produce red hair or blue eyes (Duffy et al., 2004; Sturm & Frudakis, 2004 so redhead alleles would give an advantage over other colours in putative UVB environments where chronic Vitamin D deficiency exerts a strong selective force for making Vitamin D from UVB (and presumably protection from skin damage is less necessary).
My objections
1)
Why are redheaded people not common in Finland, why are the Sami not rich in redheads? Red hair alleles are much older than the others so why did they they never become the norm or close to it in any part of northern Europe.
Blond hair does nothing for Vitamin D production while increasing the risk of cancer so why are there no northern European countries where red hair was selected for to the extent blond hair was selected for in Sweden (which is 40% blonde). The redheadeds seem to have lost out just where they should have an unbeatable advantage.
2)
The amount of vitamin D available in food is tiny the British recomended daily intake for children is 1000iu, In the United States milk is fortified with 10 micrograms (400 IU) of vitamin D.
Over half a gallon of milk, (which many black people find distasteful), who drinks that?
Sunshine is the main source. Britain has a very cloudy climate and, compared to other countries, it is true Britain has the least UVB.
But that relatively low amount of UBV supplies 20,000 IU in 20 minutes in shorts. A hour or so summer walk in a t-shirt would see white's 'D' synthesis shut off. Even thoough they must have been selected to get though the UVB-less north European winter, British whites get too much in the summer, too much even though they can store it, vitamin D from the sun and so they shut off production. Black people do not have lower vitamin D levels than whites in the British climate, (rickets is really a nutritional disease remember).
3) If we consider the estimated time of origin of these color traits, at least two of them seem to have appeared long after modern humans had entered Europe's northern latitudes about 35,000 years ago. The whitening of European skin, through allelic changes at AIM1, is dated to about 11,000 years ago (Soejima et al., 2005). No less recent are allelic changes at other skin color loci and at the eye color gene OCA2 (Voight et al., 2006). Did natural selection wait over 20,000 years before acting?
4)People with the other type of melanin—eumelanin—have darker hair. Interestingly, while dark-haired people with eumelanin can be fair-skinned, they don't burn as readily as a blonde or a red-head.
To me this means there is no advantage even in the putative marginal UVB environment (which doesn't exist) for redheads over dark haired and fair skinned whites.
Why are redheaded people not common in Finland
From a variable pre-existent stock some phenotypes we more at hand. This is anyhow not just a matter of selection, specially when we talk of such a secondary element as hair color, but also of founder effects (i.e. what was available). Red and yellow hair are just alternative possibilities but I'd think that overall blondes are more adaptative to varied conditions (less extremely "albinistic", except for some particularly light shades maybe).
why are the Sami not rich in redheads?
No population outside Ireland and Scotland is rich in redheads. They are rare to very rare in fact and this strongly suggest a marked founder effect in the Epipaleolithic first colonizaton of those countries, quite remote areas back then.
Blond hair, much more widespread would appear to offer the same advantages as red hair and maybe less disadvantages. It may also be older, at least if we consider its much larger distribution.
Sami are in any case also a small population (extremely small even today) with their own founder effects. It does not seem like red hair has ever been common in Eastern Europe anyhow.
Blond hair does nothing for Vitamin D production while increasing the risk of cancer...
Well the basic hypothesis I reached in the previous post is that blond hair and its eumelanin type also lightens the skin somewhat. In fact, I have not noticed that lightening as much in redhairs (rare here) as in blond and fair haired people. Just compare my brother and I: we are very much alike physically (except surely in body shape: he's shorter and stockier, while I'm rather average) but I'm brunette and he's blond. His skin is also lighter than mine, even if it's just a matter of degree: I'm more reddish/brownish, he's more pinky/creamy - just a degree.
Your link above mentioned the same pheomelanin for both red and yellow haired people, a type that could favor skin cancer when under the wrong conditions. It did not make any difference between both types and that's why I'm considering them here to be "convergent" in evolutionary terms: two alternative, parallel, adaptations for the same circumstance.
so why are there no northern European countries where red hair was selected for to the extent blond hair was selected for in Sweden
1) Consider always founder effects.
1a) If you compare Denmark and Sweden, for instance, they have two very different, even if related colonization processes. Swedish blood must have come largely from Ukraine via the Baltic, while that influence is minor in Denmark, which had alaready a dense agricultural population when Eastern migrations arrived. Therefore the resulting phenotipes should also be somewhat different, as Danes are mostly Western, while Swedes are more mixed (and even largely Eastern probably). Sweden also must have suffered more marked founder effects (and drift, which would increase selection in adaptative traits) because it's farther north, colder...
1b) In a different context, Ireland and Scotland were also remote, cold and rather unhospitable and therefore founder effects and drift also happened there.
So you probably have a Central European UP populaton where blonds are somewhat aboundant already, where redhairs also do exist in some ammounts. And then small groups founding colonies further North. Blonds were surely also common in Eastern Europe (so they probably existed in Gravettian times) and they reinforced that trend. But redhairs were surely nonexistent back then in the East (and probably also rare in Central Europe and the West, much as they still are now).
The amount of vitamin D available in food is tiny the British recomended daily intake for children is 1000iu, In the United States milk is fortified with 10 micrograms (400 IU) of vitamin D.
I have in front of me a Bayer can of vitamin pills that reads: "vitamin D3 - 5 micrograms - 100% DRA". So your data and mine are contradictory in this.
Black people do not have lower vitamin D levels than whites in the British climate, (rickets is really a nutritional disease remember).
Are you sure? Unless they are taking their vit. D from diet (mostly fish) they should, specially in winter.
Vit. D generation from sunlight is also "nutrition" (as it's basically that or take it from food).
If we consider the estimated time of origin of these color traits, at least two of them seem to have appeared long after modern humans had entered Europe's northern latitudes about 35,000 years ago.
First, and this goes also for your friend Evo, these are not "traits" but genes, genes that are part of the overall pygmentation genetics but not the only element in them. They may account for a fraction of it, just that.
Second, as it seems that you insist on following Evo in his speculations, he says that Natural selection would have simply favored one allele at the expense of all others, i.e., whichever one optimally reduced skin pigmentation. And he's bluntly wrong in that.
This is not any "finished" and totalistic selection (i.e. there are still many brunettes in the far north, for example). Selection is not just a matter of black and white extremist categories, it's about diversity. If one trait favors this often does at the expense of that, so unless the "this" is extremely more important than "that", selection will naturally tend to keep the diversity and not restrict it as radically as he assumes.
Also it's a relatively recent process that has happened along a mostly constant population expansion (first colonization of the far north, then agricultural revolution/s, then civilization/s). Without malthusian conditionants putting really extreme presure to select only the "best", selection will naturally remain incomplete. Such a totalist selection process would need a massive bottleneck... or much more time than it had till now.
And finally, if two or more solutions happen to satisfactorily solve any given problem, they are likely to co-exist, moreso when they have different geographic distributions to some extent. It's not a single process in a small community but many process in many, interconected but distinct, communities.
Your and Evo's perception of the issue is too extremist.
The whitening of European skin, through allelic changes at AIM1, is dated to about 11,000 years ago (Soejima et al., 2005). No less recent are allelic changes at other skin color loci and at the eye color gene OCA2 (Voight et al., 2006). Did natural selection wait over 20,000 years before acting?
These are just guesstimates. Ignore them unless you have aDNA research to prove it. It's an erudite guess, nothing more.
To me this means there is no advantage even in the putative marginal UVB environment (which doesn't exist) for redheads over dark haired and fair skinned whites.
Maybe not. I was just hypotesizing, I don't have a firm opinion on that. Maybe it's just a matter of lower selective pressure against them. Or maybe also parallel processes of convergent evolution.
Evo and Proud is part of the website of Canadian anthropologist Peter Frost. His perception of the issue is too extremist? Yeah, like Darwin's!
And he is not the first to doubt the 'white skin for vitamin D from scarce UVB' theory (that, to be fair, I'll concede was not available to Darwin) either.
The evolution of human skin coloration mentions this weighty effort Biological Perspectives on Human Pigmentation By Ashley H. Robins
Loomis’s central hypothesis concerning depigmentation of the integument of humans living at high latitudes as a requirement
for adequate vitamin D synthesis has been most strongly challenged by Robins (1991). Robins’ main points are that early Homo at high latitudes was exposed to the full impact of the natural environment. Even when clad with animal skins and furs, he claims that enough of the body’s surface would be exposed to permit synthesis of
adequate amounts of previtamin D3. While he admits that winters in Europe during glacials would have been particularly cold and dim, he indicates that the late spring and summer would have afforded good opportunities for hominids to expose their skin to UV radiation. According to Robins (1991), the long, dull winters would not have triggered widespread hypovitamosis D and rickets because vitamin D can be stored in fat and muscle (Rosenstreich et al., 1971;
Mawer et al., 1972). He suggests that vitamin D deficiencies are a product of ‘‘industrialization, urbanization and overpopulation’’
(Robins, 1991:207) and supports
his claim by pointing out that the
majority of modern human populations that suffer from such problems are urban dwellers,
deprived of natural sunlight and the opportunity to synthesize previtamin D3. According to Robins, dark-skinned human
populations living under conditions of low annual UV radiation do not suffer from
vitamin D deficiencies that can be attributed to lack of sunlight.
I keep mentioning this next point, 'going round and round', because I lead with my strength and it is unaswerable once grasped.
Spelling it out, why it is it significant that 'blacks' don't get rickets' in Britain or have lower vitamin D levels than whites?
The relatively small amounts in food are available to whites as well remember, so if blacks are at a disadvantage in synthesizing vitamin D from UVB in Britain then whites food intake of vitamin 'D' added to their synthesis of vitamin D from UVB should give them far higher vitamin D levels in this lowest of UVB environments. Well when studied they don't have higher levels.
Second, as it seems that you insist on following Evo in his speculations, he says that Natural selection would have simply favored one allele at the expense of all others, i.e., whichever one optimally reduced skin pigmentation. And he's bluntly wrong in that.
What Controls Variation in Human Skin Color?
Independent of phenotype, a gene responsible for selection of different skin colors should exhibit a population signature with a large number of alleles and rates of sequence substitution that are greater for nonsynonymous (which change an amino acid in the protein) than synonymous (which do not change any amino acid) alterations. Data have been collected only for MC1R, in which the most notable finding is a dearth of allelic diversity in African samples, which is remarkable given that polymorphism for most genes is greater in Africa than in other geographic regions (Rana et al. 1999; Harding et al. 2000). Thus, while MC1R sequence variation does not contribute significantly to variation in human skin color around the world, a functional MC1R is probably important for dark skin.
Blondes and redheads not only are more susceptible to skin cancer, but the source of their skin and hair pigmentation, melanin, actually magnifies the damaging effects of ultraviolet (UV) rays, according to a study published online this week in the Proceedings of the National Academy of Sciences.
Melanin filters out UV radiation, but the melanin in hair follicles, particularly in light hair, actually increases the sun damaging effects of UV rays and causes cell death in the hair follicle, said Douglas Brash, principal investigator and professor of therapeutic radiology, genetics and dermatology at Yale School of Medicine.
So it is not just a case of reducing the amount of melanin. Dark haired people can get all the vitamin D from UVB they need , as much as blonds or redheads, just by getting paler and without increasing their skin cancer risk. (Will an allele with a small risk won become common if it brings zero benefits?)
'Parallel evolution', this would be parallel drift in fact if these alleles for light hair colours and redhead skin have no selection related to UV acting on them. That's unlikely IMO.
If pheomelanin increases the risk of UV induced skin cancer how could it become widespread in northern Europe under selection for protecting the skin from UV induced cancer?
Maju replied
Because there was no such selection anymore. In Northern Europe skin cancer is not really a problem (too low insolation) but it can be for people of Northern European ancestry in other areas of the world.
Biological Perpectives On Human Pigmentation. Page 59 states
The Republic of Ireland has the third highest death rate from skin cancer in the world cancer (next to Australia and South Africa), even though it is located between 52 degrees N and 54 degrees N
Northern Europeans would have been under selection by skin cancer. Yes, as you say it would strike the older people. Men over 45 in most cases will not be fathering children but a few would be. There would still be enough of a reduction in fitness for the redhead and blond genes to become increasingly rare (over many generations), certainly enough to stop them becoming more widespread by drift if they offer no compensatory advantage over dark haired fair skin.
More recent data
melanoma mortality rates in the mid-1990s (1993–1997) are highest in Nordic countries and lowest in southern European populations, such as Greece, Spain and Portugal
Australia and New Zealand have the highest incidence and mortality rates of melanoma in the world, according to Australia's Department of Health and Aging. In those two countries, the risk of developing melanoma before the age of 75 is 1 in 24 for males and 1 in 34 for females.
Northern Europeans would have been under selection by skin cancer. Yes, as you say it would strike the older people. Men over 45 in most cases will not be fathering children but a few would be.
But no women certainly. And in any case, when the overall life expectancy was probably under such ages... it was not any issue. Another thing is that it would have just killed people in their teens or 20s. Then it would be a real problem.
A issue with some kind of diseases, those that only or mostly affect elderly people, is that they just don't matter re. selection. As someone said, in the end the death rate is always 100%, no matter the cause of your death. But it matters when it affects halth or even life expectancy at young age. Then it is an evolutionary disability.
There would still be enough of a reduction in fitness for the redhead and blond genes to become increasingly rare (over many generations)
Why? You claim that these alelles have no advantages but I can see how they help to produce vit. D and that, in some circumstances, they may even be favored in sexual selection (birds like red and yellow in their mates, why not humans? Or some argue that rare colorations are favored over common ones. Others that redhaired women are hot, men not so much it seems). Whatever the case, we also have to consider that the genes involved in red hair will in most cases yield just black hair, because they are recessive (at least Rs1805007 is, though it only increases the chance of red hair, it does not detrmine it). Recessive genes and such genes as Rs1805007 that do not even determine hair color themseleves alone, can perfectly exist without selective pressure against them being really effective, as happens with the albinism gene.
Just let it stay like it is now. You are not going to persuade me that vitamin D processing is irrelevant (it's not, it's actually essential to prevent severe malformations in the new borns, like schizophrenia and many others) and that it has nothing to do with pygmentation variability. You are not going to persuade me on fallacious reasoning (like claiming that Black Africans are somehow naturally polygynistic, a false assumption in itself) of such rather weirdo alternative hypothesis as the ones you have posted in this thread.
We can agree to disagree, I guess.
We can agree to disagree, I guess.
Sure, thanks for taking an interest and spending so much time on this.
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