Robins’s (2008) [sic] opening quote from Huxley is an interesting 1870 antecedent of Popperian scientific philosophy. From a Kuhnian perspective (Kuhn, 1962), it does not apply very well to the paradigmatic role of vitamin D in the evolution of human skin pigmentation, because anomalies alone are insufficient to overthrow a paradigm without an alternative competing paradigm. As to the observation of a singular, linear correlation of skin pigmentation to UVB in the winter, the vitamin D hypothesis still holds explanatory scope and predictive success. Whatever be its specific actions, vitamin D is the only agent that can account for the observation that light skin is actively selected in areas where UVB is seasonal, absent, or more variable. In areas where UVB is strong and unwavering, dark skin is positively selected.Related:
- Skin color evolution in Europeans and Social skin color vs Disease in Puerto Ricans
- The Evolution of Human Skin and Skin Color
Vitamin D and the evolution of human depigmentation
George Chaplin, Nina G. Jablonski
Abstract
In his recent commentary, Robins (2009) disputed the
role played by ultraviolet radiation (UVR), namely, the
vitamin-D-producing wavelengths of ultraviolet B (UVB),
in the evolution of human skin. He questioned the
theory that reduced levels of pigmentation in human
skin were selected to facilitate absorption of UVB. He
provided evidence to support his idea that people can
produce enough vitamin D in their skin, regardless of
pigmentation, if they are not pursuing a modern lifestyle.
He asserted that, within his framework, rickets
was the only selective force that could have influenced
the evolution of light pigmentation because other detrimental
effects of vitamin D deficiency are unproven. As
rickets is increased by industrialization, Robins concluded
that ‘‘. . . vitamin D status could not have constituted the
fitness differential between lightly pigmented and darkly
pigmented individuals at high latitudes that favored the
evolutionary selection of the former’’ (Robins, 2009).
In this article, we examine the current evidence for
what has been termed the ‘‘vitamin D theory,’’ and highlight
the importance of UVB penetration in the evolution
of human skin. We begin with an overview of the solar
processes involved in cutaneous vitamin D synthesis, followed
by a discussion of causal arguments and causation
in the context of the vitamin D theory, and conclude with
a review of physiological mechanisms and their evolutionary
significance.
Link
Vitamin D is fundamental for the correct developement of the brain. Whoever that is still arguin on the grounds of mere rickets and osteomalacia is pathetically obsolete. Guess that's what the authors of this reply argue but I can only imagine.
ReplyDelete18 months ago the Canadian Cancer Society started recommending that everyone take vitamin D to prevent cancer but few appear to know about this. Take a look at www.vitaminD3UK.com for some good summaries of the data. The site also has a good newsletter
ReplyDelete5-Methyltetrahydrofolate inhibits photosensitization.
ReplyDeleteHere is confirmation of that Serum folate levels after UVA exposure: a two-group parallel randomised controlled trial
“Our data suggest that both single and serial UVA exposures do not significantly influence serum folate levels of healthy subjects. Therefore, neural tube defects claimed to occur after periconceptual UVA exposure are probably not due to UVA induced folate deficiency.”
That destroys the UV explanation for black Africans ( i.e. melanin protects from the destruction of Folic Acid by UVA). Frank Sweet is at least aware that rickets is a nutritional disease, which Nigerian children get by the way.
Loren Cordain: It is thought that the high levels of phytate in unleavened whole grain breads cause a zinc deficiency which in turn is responsible for hypogonadal dwarfism, along with other health problems associated with zinc deficiencies. In Europe, where immigrant Pakistanis consume high levels of unleavened whole grain breads, rickets among their children remains a problem.
Robert Crayhon: So this is rickets that has nothing to do with vitamin D deficiency, but with mineral deficiency?
Loren Cordain: No, both. Cereal grains seem to have a simultaneous influence on vitamin D and Ca metabolism.
Robert Crayhon: How do they alter vitamin D metabolism?
Loren Cordain: Epidemiological studies of populations consuming high levels of unleavened whole grain breads show vitamin D deficiency to be widespread. A study of radio-labelled 25 hydroxyvitamin D3 (25(OH)D3) in humans consuming 60g of wheat bran daily for 30 days clearly demonstrated an enhanced elimination of 25(OH)D3 in the intestinal lumen. The mechanism by which cereal grain consumption influences vitamin D is unclear. Some investigators have suggested that cereal grains may interfere with the enterohepatic circulation of vitamin D or its metabolites, whereas others have shown that calcium deficiency increases that rate of inactivation of vitamin D in the liver. This effect is mediated by 1,25 dihydroxyvitamin D (1,25(OH)2D) produced in response to secondary hyperparathyroidism, which promotes hepatic conversion of vitamin D to polar inactivation products which are excreted in bile. Consequently, the low Ca/P ratio of cereal grains has the ability to elevate PTH which in turn stimulates increased production of (1,25(OH)2D) which causes an accelerated loss of 25 hydroxy vitamin D.
Robert Crayhon: So it doesn’t get activated by the kidneys if there are a lot of cereal grains in the diet? The hormone version of vitamin D doesn’t come into existence if people are eating 70-80% of their diets as cereal grains?
Loren Cordain: The mechanism still is unclear, however, the clinical response remains the same (overt rickets) in animal and human models. Here are some of the references if you are interested: (1. Batchelor AJ, Compston JE: Reduced plasma half-life of radio-labelled 25 hydroxyvitamin D3 in subjects receiving a high fiber diet. Brit J Nutr 1983; 49:213-16. 2. Clements MR, Johnson L., Fraser DR: A new mechanism for induced vitamin deficiency in calcium deprivation. Nature 1987; 325: 62-65. 3. Dagnelie PC et al. High prevalence of rickets in infants on macrobiotic diets. Am J Clin Nutr 1990; 51: 202-8.)
Which makes this less surprising
Know Your Pathology: Osteomalacia and Rickets
“Evidence has been found in Neolithic skeletons from Denmark and Norway, and more plentiful evidence comes from Hungary in the Roman period. However, the rarity of this disease in the past is attested by the few cases described even in exhaustive studies of human remains prior to the Medieval period.”
Some say that ”for dark skinned people to colonize a low UV environment they need to either eat a lot of fish (Eskimos) or lighten up. Only fish and dairy can provide adequate amounts in a low UV environment.”
However, see Tauber, H. (1981). 13C evidence for dietary habits of prehistoric man in Denmark. Nature, 292, 332-333.
“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?” and by the way “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.”
Calcium isn’t ‘D’
Milk’s got calcium but is fortified for ‘D’ Vitamin D Office of Dietary Supplements National Institutes of Health
Salmon, cooked, 3.5 ounces gives 90% of the ‘daily value’ 360IU. Even a tablespoon of cod liver oil gives only 1360IU
Compare this with Northern Europe where UVB is strong enough to reach the 20000IU of ‘D’ that ‘D’ synthesis is limited to (by skin heating) in under a hour for a San type skin. How much cod liver oil to match a hour outside.
In Europe ( that is where we are talking about) people just went out in the sun in the summer got a huge amount most which was stored for the UVB-less months and they were sorted for vitamin D.
North Europeans do not make any more ‘D’ with prolonged intense UVB exposure than those who evolved where the sun is strong enough to make vitamin D every day of the year. This limit would have been the first thing to be altered by natural selection if ‘D’ was wanting over a year in northern Europe. It should be remembered that north Europeans evolved where there is no UVB to provide skin synthesis of vitamin D for several months at a time. It should be obvious that the supply of vitamin D from synthesis in the sun was was always more than ample in Europe because Europeans have a mechanism that limits the amount that can be made at one time, a limit that kicks in with a mere 20 minutes European midsummer sun.
Obesity in Europeans may be reducing 'D' levels Body fat and vitamin D status in black versus white women. "In conclusion, the serum 25(OH)D-%BF relationship in women varies both by race (stronger in whites than blacks) and age (stronger in younger than older persons). This complex relationship may explain why differences in obesity do not appear to play a major role in explaining variation in serum 25(OH)D by race." Real ill effect may be due to the obesity, not the lower 'D' levels it causes.
It should be remembered that north Europeans evolved where there is no UVB to provide skin synthesis of vitamin D for several months at a time.
ReplyDeleteThis is not correct. Such thing only happens north of the Arctic Circle. North Europeans (excluding Saami) evolved much farther South.
It should be obvious that the supply of vitamin D from synthesis in the sun was was always more than ample in Europe because Europeans have a mechanism that limits the amount that can be made at one time, a limit that kicks in with a mere 20 minutes European midsummer sun.
This is misleading. The mechanism is not exclusive of North Europeans (obviously) but common among humans. But specially, what happens in midsummer is trivial, what happens in the depths of winter is what really matters, especially under a the ehavy clothing needed at such cold latitudes (which is why rosy cheeks exist, obviously).
And also one should not focus in adults as much as in children. An adult can get alzheimer because of lack of vitamin D but that's rather unimportant as his role in life is mostly done, what matters specially is what happens to pregnant mothers and children, and this is the critical issue because lack of vitamin D causes severe damage to the developing young brain, being behind diseases such as autism and schizophrenia, for instance (see above). This may also be a reason why children (and to some extent women) are somehwat lighter pygmented than adult men, for whom the vit. D need is not so critical.
Jablonski (p12)
ReplyDelete"In the tropics, the zone of adequate UV radiation throughout
the year (Zone 1) is delimited by bold black lines. Light stippling indicates Zone 2, in which there is not sufficient UV radiation during at least one month
of the year to produce previtamin D3 in human skin. Zone 3, in which there is not sufficient UV radiation for previtamin D3" synthesis on average for
the whole year, is indicated by heavy stippling."
Zone 3 covers northern Europe. Here's the same map on GNXP Potential for Vitamin D synthesis That's fudging the way the data are presented,it passes over the fact that the UVB making 'D' is so abundant in the summer that there is no need to change the synthesis limit. It does make the point, if you think about it, that several months of the year in northern Europe must be without suficiently intense UVB.
On GNXP you said Scandinavia and Scotland have historically been very marginal areas (and the more nortwards you go, the more preipherical from a historical and prehistorical viewpoint Yes, agreed.
I strongly think the basic pygmentation variant evolved not so far north but in continental Europe probably, though it was even more extremely selected as the far north latitudes were colonized in the Epipaleolithic and later on. Right about continental Europe being where the selection took place. Wrong about selection as proved by the complexion od Scots. Look how far north Scotland is. Now are Scots light enough compared to Danes to have been extremly selected for light pigmentation? The Picts were mainly blonde/redheaded?
"In a few places in Sweden, Britain, and France people have been noticed who show characteristics of the skull and face that remind one of late-Paleolithic man: these people are usually darker, in hair and eyes, than their neighbors; sometimes they even have swarthy skins. [...]. The many stories of golden hair and blue eyes suggest that sexual selection may have helped the change." Fleure, H.J. (1945).
Why are these hold outs found where the ongoing selection for depigmentation is the stongest according to the vitamin D/ latitude theory? The reason is that (as you have peceptivly pointed out) these are marginal areas.
The selection was in continental Europe, as you suggested, it just has nothing to do with vitamin D.
"before 10,000 BP, [...](T)he last ice age. At that time, the tundra ecozone ran further south in Europe than in Asia, having been pushed down on to the plains of northern and eastern Europe by the Scandinavian icecap. The lower, sunnier latitudes created an unusually bioproductive tundra that could support large herds of game animals and, in turn, a substantial human population—but at the cost of a recurring shortage of male mates. Among present-day hunter-gatherers, similar environments raise the male death rate because the men must cover long distances while hunting migratory herds. The man shortage cannot be offset by more polygyny, since only a very able hunter can provide for a second wife (tundra offers women few opportunities for food gathering, thus reducing their self-reliance in feeding themselves and their children). With fewer men altogether and fewer being polygynous, the sex ratio is skewed toward a female surplus.
In this buyer’s market, men will select those women who look the most feminine. Since human skin color is sexually dimorphic (women are the ‘fair sex’), this sexual selection would eventually whiten the entire population. Where pigmentation has no female-specific form, as with hair and eye color, sexual selection would favor women with color variants that stand out by their novelty, the outcome being an increasingly diverse polymorphism.
It's the diversity that's the unusual thing about Europe.
SEXUAL SELECTION AND HUMAN GEOGRAPHIC VARIATION And I should make clear that I don't dispute that vitamin D is important and vitally necessary for survival and reproduction, for brain development and in a miriad of other ways. I do insist that it was available just by going outside where, as you pointed out, people spent much of their time untill recently.
You may have a point about how modern lifestyles reduce sun/UVB exposure . Personally I think the increase in obesity and maybe even refined carbohydrates reduces vitamin D levels. Decreased bioavailability of vitamin D in obesity
The lower, sunnier latitudes created an unusually bioproductive tundra that could support large herds of game animals and, in turn, a substantial human population—but at the cost of a recurring shortage of male mates.
ReplyDeleteThat last is just a fancy idea. Why would there be any shortage of male mates?
Also the "southern-driven" tundra was not as sunny though I'd guess it was wetter because of the Oceanic influence, so I suppose a rather dense cloud cover over the year (much as today). It is not as much that the European climate was odd in the Ice Age but actually it is odd now: with ample areas of relatively warm climate where anywhere else is frozen as Dante's 7th hell. This is because of the Gulf Stream, our particular post-glacial advanced heating system. Nowhere else on Earth there is such a huge area of temperate climate so far north able to support such large populations. This just was not true in the Ice Age, when Europe was more standard. But I presume that the dominant Atlanic winds and their insistent storms, definitory of most European climate today, were also active at that time, at least to some extent.
Ecological zones of Europe at last glacial maximum, c. 18,000 BP Primary source material? A GIS-based Vegetation Map of the World at the Last Glacial Maximum(25,000-15,000 BP)."Ice sheets covered northern Europe and Scandinavia. Most of the rest of northern Europe resembled semi-desert, with a mixture of tundra and grassland elements (steppe-tundra). In southern Europe, vegetation resembled a semi-desert steppe,
ReplyDeletewith scattered pockets of trees in moist areas."
Desolate Landscapes: Ice-Age Settlement in Eastern Europe
By John F. Hoffecker
New Brunswick, Rutgers University Press: 2002 Reviewed by Peter Frost "As humans spread out of Africa, they entered new environments, including one that no longer exists. The loess-steppe covered the East European Plain off and on during successive ice ages until 10,000 years ago. Quite unlike today’s northern barrens, it combined Arctic tundra with fertile loess soil and low latitudes―the Eurasian tundra belt having been pushed far to the south by the Scandinavian icecap. Long intense sunlight favoured a lush growth of mosses, lichens, grasses, and low shrubs that fed mammoths, reindeer, bison, and horses. Despite this high bioproductivity, the loess-steppe confronted humans with a number of adaptive challenges. Winter temperatures averaged from -20 to -30 °C in exposed conditions with little natural protection. Wood was scarce for fuel or shelter. Finally, almost all of the biomass suitable for human consumption was in the form of large migrating mammals."
They hunted on foot, the main prey animal Reindeer travel farther than any other land mammals. "Biologists have discovered, by using satellites to track caribou, that the herds actually travel much farther than the straight-line distance between summer and winter ranges would indicate. They move to and fro over a wide area, adding many miles to their journeys. Porcupine Caribou herd animals, for example, have been observed to travel over 3000 miles per year".
Clearly extremely long distances in would have to be covered in sub-zero temperatures by a hunter, He would have a shorter distance return trip, it being straight home, but think of the carcass weight to be carried. Moreover reindeer are excellent swimmers. So the men died of exposure, exhaustion, falls, immobilizing lower body injuries, starvation, and drowning.
The ones who hunted caribou, you mean...
ReplyDeleteVery speculative in any case: obviously people would use hunting strategies that granted survivability, not outright suicide.
In my area they hunted bison, horse, auroch, deer and goats mostly, probably depending on the season. I did not even heard before of caribou at all in relation with European UP (unless it's the same as reindeer). In general they are thought as being semi-sedentary, based on actual archaeological data, with hunting grounds of maybe 100 km radium at most.
(Sorry, the information on them covering 3000 miles per year was from Canada where Reindeer are called Caribou although they're the same species). Cold -adapted Reindeer would take the place of horses towards the north. The excerpt fom 'the 'Desolate Landscapes' reveiw above does mention " mosses, lichens, grasses, and low shrubs that fed mammoths, reindeer, bison, and horses" so yes horses were about.
ReplyDeleteWhat they were hunting is really a side issue I brought up. You're right would depend on the area they were in, one would assume that horses, not being cold adapted, were more common in the south and less present in the northern area.
You can see a map of the the ecological zones of Europe at last glacial maximum, c. 18,000 BP- here (scroll down) At that time the Basque country was in a slightly (but not completely) different ecological zone namely Park_Tundra.
The steppe-tundra zone overlaps with maps of where the greatest diversity of hair and eye colour is found today (and the whitest skin although that's got lighter rather than diversifying) Ecological zones of Europe at last glacial maximum, c. 18,000 BP for comparison with areas of diversified hair and eye colour The more northern areas require more ground to be covered because:-
"Hunter-gatherer diet is strongly influenced by latitude and temperature. To begin with, energy demands increase significantly in cold climates and caloric intake in arctic environments may be as much as 30 percent higher than it is in tropical regions. The percentage of meat and fish in the diet of recent hunter-gatherers increases as temperature, moisture, and primary productivity decline, and equals or exceeds 80 percent among most peoples who live in areas with an effective temperature of 10 degrees C or less. …
The high protein-fat diet and hunting and fishing subsistence of hunter-gatherers in northern environments has major implications for foraging strategy. Although cold maritime settings often provide rich concentrations of aquatic resources that require limited mobility, hunter-gatherers in northern continental environments who subsist on terrestrial mammals must forage across large areas in order to secure highly dispersed and mobile prey. Among peoples who rely primarily on nonaquatic foods, there is a correlation between temperature and the average distance of residential moves and a related correlation between the percentage of hunted food in the diet and territory size. Another consequence of low temperatures and a high meat diet is that males procure most or all food resources, generating a more pronounced sexual division of labor" Hoffecker (2002, pp. 7-8):-
Sexual selection and Arctic environments"First, hunting distance increases with decreasing numbers of game animals per square kilometer, thereby increasing male mortality"
Second, food gathering decreases with longer winters, thereby increasing women’s reliance on men for provisioning and increasing the costs of polygyny for men. It is this combination of higher male mortality and limited polygyny that intensifies sexual selection of women."
I have my own anotations on paleolithic climatolgy and certainly most of what is called "tundra" there was more a mixture of steppe and semiforested areas. A cold savannah, so to say.
ReplyDeleteThe tundra in Europe extended in the strip just south of the ice sheet, then there was the taiga (wich is forested) and then, where most archaeological findings we have, there was steppe.
Notably what you call "loess tundra" was in fact loess steppe in the Rhin-Danub and Dniepr-Don areas. This area was apparently very rich as it was rather densely inhabited, except probably in the coldest periods of the LGM.
Then in Northern France and most of the Balcans there was a continental steppe that was not that much productive, as it has yielded many sites.
And then in Aquitaine there was a steppe-prairie-forest climate that certainly was anything but reotely close to tundra.
The Mediterranean was then largely forested surely, less productive than the Aquitanian mixed area maybe but still much more productive than the tundra or the continental steppe it seems.
Excepting some rare sites in Russia I know of no humans living in tundra conditions back then. Loess steppe yes: many, but not the extreme taiga probably (at least not documented).
Additionally UP maps typically depict the LGM extension of the Ice Sheet but that was not a static situation at all: most of the time the ice sheet was smaller and the climatic strips were somewhat displaced northwards. Check for instance Don's Maps: ice maps.
In any case Palelithic Europeans were people of the steppe, not the tundra - at least for the most part.
The steppe-tundra zone overlaps with maps of where the greatest diversity of hair and eye colour is found today.
What do you call "greatest diversity"? It's a B/W bidimensional graph that cannot have greatest diversity anywhere: all that is not 100% one of the extremes is equally diverese. I don't make any sense of that claim.
As for the rest: do you have any factual evidence that actually people like Swabian Aurginacians or Moravian Gravettians moved thousands of kilometers in fact? Or does the archaeological evidence rather supports a more stable way of life?
The archaeological findings tend to be concentrated in certain areas, which were surely the richest ones in terms of game and other resources (they also ate rabbits, fish and a variety of plants - believe me). Those people had dogs but had no horses yet (at least that's the mainstream opinion) so they could only travel that fast and that far behind the reideer, bison or whatever they wanted to hunt. Like North American Natives before the horse they were reliant on bison arriving to them and they could not effectively follow the bison everywhere. When their game migrated they would have to survive on dried meat and/or other produce (fish, goats, veggies).
There no surviving steppe hunter-gatherers anymore of that style. The closest we can think of are the North American Natives of the great plains before the arrival of the horse. Evn for those, our documentation is limited because the horse was introduced early on with Castilian colonization. But in any case, it doesn't look like they could effectively follow the migrating herds for the many thousands of kilometers you mention. Not at all. They would rely on their seasonal return and on alternative resources for the meantime.
Erratum: "as it has yielded many sites" should read "as it has yielded NOT many sites".
ReplyDeleteAlink brief description of Steppe-tundra and the forms it took.
ReplyDeleteA GIS-based Vegetation Map of the World at the Last
Glacial Maximum (25,000-15,000 BP). says
"Steppe-tundra A vegetation type
widespread during the Last Glacial
Maximum, which combined plants of
tundra and steppe environments.
Probably around 50% ground cover
by plants; bare ground abundant but
patchy. No Olson analogue" and that
"Ice sheets covered northern Europe and Scandinavia. Most of the rest of northern Europe resembled semi-desert, with a mixture of tundra and grassland elements (steppe-tundra). In southern Europe vegetation resembled a semi-desert steppe, with scattered pockets of trees in moist areas".
It was variable over time I grant you.
The actual straight line distances that reindeer migrated were less than a tenth of the ground they covered. Maybe they didn't follow them throught the year as you say, and there were other things to hunt.
Sexual selection and Arctic environments "Among caribou-dependent Inuit, “at least 1 period of hunger or starvation is part of the normal annual cycle” (Burch, 1972, p. 350). In good times, caribou herds do provide a bountiful food source, but at the price of continual camp moves and extensive reconnoitering on foot. This is the real man-killer in Arctic groups that have not yet domesticated reindeer, as Krupnik (1985, p. 126) notes when explaining the Chukchi’s low ratio of men to women:Among the Inuit the men of tribes who were hunting on foot did suffer a high mortality rate
Maybe they didn't follow them throught the year as you say, and there were other things to hunt.
ReplyDeleteWould not make any sense: travelling 3000 km per year means almost 100km every single day. That is not something we humans can do, certainly not on foot.
Some notes on the paper:
- Areas that are moistier now were also relatively moistier then, even if drier and colder than now (There's no explicit Oceanic/Continental distinction anywhere in the maps though)
- Finer subdivisions were not mapped as they think there's not sufficient evidence. We can assume that the steppe-tundra area actually had three main subareas: (1) steppe, (2) taiga and (3) tundra. Steppe was surely the dominant one even in the coldest period.
Anyhow, nearly all Europeans (excepting Eastern ones) at the LGM lived south of that steppe-tundra area or at the southernmost parts of it, like Dordogne, wich would be clearly steppary.
Survival in Central Europe at that time would be linked to patches of semi-wooded land, like the one believed to have existed at Moravia (not mentioned in this paper). In any case, all the area was recolonized after the LGM from SW Europe in the context of Magdalenian culture, though guess there were also some local survivors.
Also, if you want to discuss the processes going on in Central Europe in the Paleolithic, you probably have to adress that region either before (Aurignacian, Gravettian) or after the LGM (late Solutrean of Hungary, Magdalenian). Not in its coldest and more desertic period.
Anyhow, sexual selection means selection based on pscyho-sociological preferences of attractiveness (i.e. selection of the beautiful - whatever beautiful means in each cultural context), not gender-biased mortality (which would select the fittest, not the prettiest). Anyhow we know of no groups in Europe, much less mainstream ones, who were doing that Inuit-like pattern of activity following on a dog-pulled sledge reindeer through the tundra. There may have been some but doesn't look like the archetypical European was doing that at any time, the same that the archetypical Native American was not doing it either.
Some clarifications are in order
ReplyDelete1)The extreme arctic Inuit are not a model for the steppe tundra hunters, they don't cover as much ground hunting as those to the south in the 'continental arctic':-
"Hunting
distance peaks in the continental Arctic, where almost all potential food is in the form of
wide-ranging and highly mobile herds (Hoffecker, 2002, p. 8). It then decreases further north
in the extreme Arctic, where hunters cover shorter distances in pursuit of solitary game, fish,
and seals (Kelly, 1955, p. 129)." (Frost 2006)
2)It is suggested the steppe-tundra men suffered high mortality from covering long distances on foot, not that they used dogs or any other animal for transport. The examples given were of high mortality for those on foot.
SEXUAL SELECTION AND HUMAN GEOGRAPHIC VARIATION" reindeer hunters regularly move their camps and do extensive
reconnoitering on foot (Burch, 1972, pp. 347, 349-350)".
3)The Map was 18,000 BP . That is not the suggested date for the hunters to have been active in north Europe, 18,000 BP is to early, as you say. The following is in line with the later time frame for hunting on the steppe-tundra in the later time frame and with reindeer being hunted.
A prehistory of the north: human settlement of the higher latitudes (2005)
By John F. Hoffecker [p101]
"Climates ameliorated rapidly after 16,000- 15,000 years ago and new changes began to sweep across western Europe. Sites reappeared in northern France, Belgium, northwest Germany and southern Britain between 15,500 and 14,000 years ago. Although many of them are considered late Magdalenian, other industries emerged in the northern areas containing distinctive curve-back and tanged stone points. An emphasis on reindeer hunting persisted through a cold oscillation during 13,000-11600 years ago (Younger Dryas event). Deglaciation resumed after this cold event..."
I think the main point is that there's no such thing as "steppe-tundra" ecosystem, neither in the past nor today. This is just a catchall term for a range of actual ecosystems of which different varieties of steppe were dominant, south of a strip of taiga forest, in turn south of a tundra area, probably desertic or nearly so at the time.
ReplyDeleteThe maps are said to cover the LGM "sensu lato", mentioning a range between 25-15,000 years ago, when the low temperatures were more or less stable. The LGM "sensu stricto" was 18,000 carbon-years BP but that is actually 20-21,000 years ago after calibration. In that period, anyhow, the signs of habitation of Central Europe are very limited.
Europeans had dogs 15,000 years ago, though we do not know if they used them for transport or just as hunting hounds. Some have argued that they also had domestic horses by that time (based on carvings like this and this), though most people flatly reject the idea without further consideration.
If they had transport they could follow herds much more efficiently but anyhow it doesn't seem to me that they were so much nomadic: after all most sites or groups of sites seems to indicate year long habitations, with very limited migrations within the area. Maybe this was different in Central Europe, but I still don't grasp you hypothesis of supposed high male mortality affecting the color of skin at all. It just doesn't seem to have any relation at all.
But infant mortality and correct mental developement would be a strong influential factor and that is largely dependent on vit. D, so the further north, the better for women and kids (and by extension men too) to have a lighter pygmentation and rosy cheeks.
I think the main point is that there's no such thing as "steppe-tundra" ecosystem, neither in the past nor today. This is just a catchall term for a range of actual ecosystems... I wouldn't argue with that.
ReplyDeleteAll terms are catch-all terms if you look hard enough.
The maps are said to cover the LGM "sensu lato", mentioning a range between 25-15,000 years ago, when the low temperatures were more or less stable...Agreed. I believe 15,000- 10,000 years ago is suggested to be a time frame for skin lightening by sexual selection. This is far closer to the the estimated dates for the various European specific alleles of hair skin and eye colour genes , which range from 12,000BP to 3,000BP.
But infant mortality and correct mental developement would be a strong influential factor and that is largely dependent on vit. D, so the further north, the better for women and kids (and by extension men too) to have a lighter pygmentation and rosy cheeks.If rosy cheeks are so good for you in the north why do the aforementioned European lightening alleles not date to about 30,000 years ago when modern humans entered northern Europe?
Europeans had dogs 15,000 years ago, though we do not know if they used them for transport or just as hunting hounds. Some have argued that they also had domestic horses by that time (based on carvings like this and this), though most people flatly reject the idea without further consideration.Wolves are capable of coordinating deceptive tactics and the staging of ambushes, they have special calls to announce their arrival at an ambush site. The wolf would easily adapt to driving game towards a hunter. Dogs are a special case of 'domestication' they had social hunting adaptations. . Until recently I was under the impression that due to their modification by man dogs, but not wolves, are able to realize where a food token is hidden if a human points or just looks ( chimpanzees usually can't do this ). Seems like that's wrong, they can do this better than dogs. (M.A. Udell, N.R. Dorey and C.D. Wynne, Wolves outperform dogs in following human social cues, Animal Behaviour 76 (2008), pp. 1767–177). 'Taming' wolves to hunt involved little modification of their natural instincts apart from fear of man. Using them as transport must have been a tall order without far more profound changes.
If they had transport they could follow herds much more efficiently but anyhow it doesn't seem to me that they were so much nomadic:[...] But I still don't grasp you hypothesis of supposed high male mortality affecting the color of skin at all. It just doesn't seem to have any relation at all.An interesting fact is that the Gray Wolf is the most effective natural predator of adult reindeer. Reindeer travel the furthest of any terrestrial mammals." "When hunting wolves have an actual travel rate of about 50km (30mi) a day". (Wolves: Behavior, Ecology, and Conservation 2003) Hunting reindeer on foot would entail some very long distances to be covered and there was an emphasis on them 13,000-11600years ago,(along with other herbivores).
But infant mortality and correct mental developement would be a strong influential factor and that is largely dependent on vit. D, so the further north, the better for women and kids (and by extension men too) to have a lighter pygmentation and rosy cheeks.You would think so from reading about all the problems putatively associated with vitamin D 'insufficiency'. Those having the very darkest of skin and living in a northern country should have increased rates of actual medical problems. All I can say is it just doesn't work that way. Black Africans living in Sweden or Scotland do not suffer from higher rates of brain developmental disorders or infant mortality.
... why do the aforementioned European lightening alleles not date to about 30,000 years ago when modern humans entered northern Europe?.
ReplyDeleteWho says they do not? What you have read is just a TRMCA estimate (and anyhow refers only to one gene that may affect only like 25% of the color variation between the gulf of guinea and the arctic). You are taking a hunch, an educated guess, as factual data and generalizing what is said of one single gene for the whole array of genetic and possibly epigenetic factors affecting skin color.
Black Africans living in Sweden or Scotland do not suffer from higher rates of brain developmental disorders or infant mortality.
Don't know the actual data but nowadays vit. D is everywhere (at least in the north): in milk, cereals, margarine and of course supplements. So it's not really comparable because we are distributing the equivalent to a tablespoon or two of "cod liver oil" in everybody's daily diet. Still the most directly affected should be infants. Adults are a lot tougher and are already developed.
And really, I don't get your explanations for why would skin color have anything to do with any sort of nomadism or whatever.
The red hair mutation is thought to be 80,000 years old. I think the others are estimated as I said. If you know different I am very interested in a reference.
ReplyDeleteThe theory you hold to is that of Nina G Jablonski and 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.
10-20,000 years is only enough to 'conform most closely? I would have thought Basques would be dead on the correct skin reflectance for their UV exposure by now. That sounds like a very weak form of selection to me, (I do think it exists but it's very weak).
If the Basque's skin is just about right for the amount of UV they get their constitutive skin color, that is their natural skin color, ought to require less adjustment when exposed to the sun. Basques living in their homeland and working outdoors should have a sun induced sun-induced skin color should be little different to their natural skin. In other words farmers ect should not be noticeably tanned compared to those who don't work outside. So is that true or is the situation as it is in the UK- anyone who works outside has a conspicuously tanned appearance.
"When researchers went to an Italian nursing home, they found that 99 of 104 residents had no detectable vitamin D in their blood,"
Bad news for these people ?
All of the 104 resident were over 98 years oldI hate to think how old they would have lived to if they'd kept their vitamin D levels 'normal'.
Here is evidence how abundant UVB is in the summer "Dr. Turnbull, working with Dr. Kimlin in Australia, showed that UVB light in the shade is strong enough to activate vitamin D production in the skin. Think of UVB as a ping-pong ball. It bounces off lots of things. When you go into the sun—if the sun is high enough in the sky—UVB light comes through the atmosphere and then starts bouncing around. It bounces at you from the ground, buildings, cars, and even the bottom of clouds. Sitting under a shade tree delivered about half as much UVB as sitting in the direct sun. Furthermore, the damaging UVA radiation under direct sun was three times more than under the shade tree. Sitting in the shade in the summer (and the winter in subtropical and tropical latitudes) is a good way to get vitamin D."
... anyone who works outside has a conspicuously tanned appearance.
ReplyDeleteDon't know: the last Basque monolingual I know has been living with his sheep in the western Pyrenees for 80 years and has conspicuous rosy cheeks (and this is a common trait among peasants and others, even in old age - my granpa and great-grandpa too). These things vary on individual complexion anyhow though, of course, the more you are outdoors, notably in summer, the more you tan (or take a reddish wannabee tan hue).
You're arguing about such things like if they were a simple mathematical formula with two lineal variants but the fact is that there are as many variants as individuals (depending on their individual meiotized ancestry - and noticed I say "meiotized" because syblings are on average 50% distinct, what is a lot: I tan a lot easier and much better than most of my relatives for example).
In both the British and Basque case there have been small but important arrivals of "new" genes from the Mediterranean since Neolithic. These have altered the overall looks of the people somewhat (and you can see clear geographic patterns as well), in general in favor of a somewhat darker skin tone. There has been some flow from Eastern Europe (where people are rather blondish) but that has not have such great impact, at least among Basques (maybe in Britain, mediated by Northern Europe - unsure).
...
Nature doesn't care about "old farts" nor longevity is the issue here (or in any other selective pressure): what matters is vitamin D among young ones, wether babies, children and teenagers can grow up properly.
...
It bounces at you from the ground, buildings, cars, and even the bottom of clouds. Sitting under a shade tree delivered about half as much UVB as sitting in the direct sun.
Cars? Are you telling me that natural structures are as reflective as cars, glass or tarmac? In fact they are not.
One exception though: snow and water. In fact insects seem attracted to tarmac because they suspect it being water. It could well be argued that ice reflectivity in the near-arctic enviroments acts at least slightly as opposite force to latitude. Nevertheless, I have never read anything confirming this suspicion of mine.
This logic could also explain why peoples traditionally living in jungles are dark skinned anyhow. But I'd argue that it should be fine-tuned not in regard to the lives of modern Australian cities but in regard to what we actually find in Nature.
Nature doesn't care about "old farts" nor longevity is the issue here (or in any other selective pressure): what matters is vitamin D among young ones, whether babies, children and teenagers can grow up properly.That is very true, and it means that all the discussion about diseases linked to low vitamin D levels is irrelevant (to the evolution of skin colour) if those suffering the diseases are over 45 years. Are there any reports of young men and women failing to to reproduce because of low 'D' levels?
ReplyDeleteOver time evolution perfects and polishes to the nth degree, but white skin is far from pefectly adapted to the amount of UV encountered in Europe if European's faces get reddened and sunburnt. And none of the European specific skin lightening alleles date to humans (archaic or not) entering Europe or northern Europe).
It shows how abundant UVB is if it bounces off clouds and hits you in the shade in European summer as the man said. (Water only reflects as much UVB as grass).
"It could well be argued that ice reflectivity in the near-arctic enviroments acts at least slightly as opposite force to latitude."
That is an excellent point; when snow is on the ground the intensity of UV would be increased. The UVB intensity at ground level would be increased by reflection. That (and the altitude) explains the 'Skiers Tan'. And helps explain why sun induced skin cancer occurs in northern Norway. Biological Amplification Factor for Sunlight-induced Nonmelanoma Skin Cancer at High Latitudes "Sunlight appears to be the main cause of basal cell carcinomas and squamous cell carcinomas even at the high latitudes of Northern Norway"
Understanding UVA and UVB
"UVB, the chief cause of skin reddening and sunburn, tends to damage the skin’s more superficial epidermal layers. It plays a key role in the development of skin cancer and a contributory role in tanning and photoaging."
The only scarcity of vitamin D synthesis in northern Europe is during the months when UVB isn't strong enough. So much UVB is available in the Summer that the body breaks Vitamin D down to prevent more being synthesized and stored, (as most Vitamin D is). As Europeans have to go several months without any vitamin D fron the sun it must have been the vitamin D stored in bodyfat that supplied the need for 'D' thorough the winter. The 'D' would be released as the fat was broken down in the winter months when animals and untill recently humans suffer a shortage of food and lose weight. So the fact that people don't lose weight in the winter any more would explain an increase in vitamin D related disorders.
In the summer vitamin D synthesis shuts off on exposed skin to limit 'D'. Natural selection has set this mechanism to synthesize and store the optimum amount for north Europeans to deal with the UVB-less months. It does not make the maximum amount of 'D', it limits it. One has to assume that there is a reason for this limit and that greater amounts of vitamin D are not needed. Cetainly altering this limit would be easier than evolving white skin.
Like you say Nature doesn't care about anything but continuing reproductive success.
Are there any reports of young men and women failing to to reproduce because of low 'D' levels?.
ReplyDeleteRead this article please. Excerpts:
"In fact, over 900 different genes are now known to be able to bind the vitamin D receptor, through which vitamin D mediates its effects. In addition to protecting against rickets, evidence now strongly indicates that a plentiful supply of vitamin D helps to protect against bone fractures in the elderly. Evidence also continues to accumulate suggesting a beneficial role for vitamin D in protecting against autoimmune diseases, including multiple sclerosis and type I diabetes, as well as some forms of cancer, particularly colorectal and breast".
(...)
"McCann & Ames point out that evidence for vitamin D's involvement in brain function includes the wide distribution of vitamin D receptors throughout the brain. They also discuss vitamin D's ability to affect proteins in the brain known to be directly involved in learning and memory, motor control, and possibly even maternal and social behavior. The review also discusses studies in both humans and animals that present suggestive though not definitive evidence of cognitive or behavioral consequences of vitamin D inadequacy".
References at the bottom of the article.
In other sites I have read that lack of vitamin D in early development stages can cause autism and schizophrenia. It may be possible for some to survive and even reproduce with low levels of vitamin D but it is also quite clear that there is a strong selective pressure in favor of effective vitamin D production.
... but white skin is far from pefectly adapted to the amount of UV encountered in Europe if European's faces get reddened and sunburnt.
ReplyDeleteThis extreme type (which is certainly not the dominant through Europe, not even in Northern Europe probably) probably evolved only in the North, where sunburn is hardly any risk, and may be the one favored by most recent selection in that area. You do find blonds, redhairs, blue eyed and pinky-skinned people in Southern Europe but almost never the extreme ultra-white non-tannable type, that would not be viable. This is a peculiar subtype of the North with all likehood.
The only scarcity of vitamin D synthesis in northern Europe is during the months when UVB isn't strong enough.
In Bilbao (and all the Cantabrian strip in Northern Iberia) winter is also pretty dark. Cloud cover really denies the sun for maybe 2/3 of the year. My English apartment-mate was surprised that here it rains and the sky is covered by clouds much more than in London. Temperatures are indeed somewhat nicer because of latitude but even in summer it's typical that we have storms every other day.
This is certainly not Marbella nor Cannes: in most aspects it resembles much more the climate of Ireland or Cornwall. In Galicia, that is even more exposed to the Atlantic storm fronts, they say that "when it doesn't rain, it's sprinkling". And the typical plumby cloud cover certainly filters sunlight a lot, including UV. Not sure if this could apply to UP climatic conditions or how much though.
This doesn't mean that there is not more scarcity of solar induced vitamin D in Northern Europe, of course, but the winter scarcity certainly begins at much lower latitudes. And not just in the Atlantic: have you ever crossed Northern Italy in winter? Typically it's all covered in a thick mist that makes driving very hazardous.
Much of these wintery limitations can even be extended to the more strictly Mediterranean regions too, even in Asia and North Africa. Obviously the conditions that apply to the tropical strip and produce there "black" skin do not apply north of it, what causes a gradual, even if somewhat irregular, lightening of pygmentation.
You say that the conditions only apply to Northern Europe but the USA (excluding Alaska) is at the latitude of Southern Europe and even the people of NW European origin seem to have vitamin D deficiency there to some extent.
So much UVB is available in the Summer that the body breaks Vitamin D down to prevent more being synthesized and stored...
It cannot be effectively stored in fact, it seems (possibly because our species evolved in the optimal sunlight conditions of the tropics). So it's trivial what happens in summer conditions, what really matters is what happens through the whole year, notably in the worst conditions (winter). Surely a few days without vitamin D intake don't make a difference but weeks or months, specially in pregnant women and children, certainly do.
Like you say Nature doesn't care about anything but continuing reproductive success.
Well, I maybe overemphasized. Certainly aged adults do have an important role in the human reproductive process, even if not that central as parents and children themselves. It's been argued that our comparative longevity after menopause is a mechanism that ensures the help of the elderly (notably women) in rearing children of younger people. Also in pre-modern times cultural wisdom was stored in the minds of the elders. But sure: they are not as important as the younger members.
Bruce N. Ames authored one of the studies that discredit the idea that folic acid is destroyed by UVA .
ReplyDeleteThe link does not answer my call for examples of actual disorders caused by vitamin D insufficiency beyond rickets bone fractures and 'possibly' cancer. Here's why Vitamin D discovery outpaces FDA decision making
"For half a century, medical science has been noting the
association between vitamin D serum levels and disease.
What developed has been a concept of ‘vitamin D deficiency’
based solely on the assumption that low vitamin D serum
levels somehow cause disease processes. [...]
that the observed serum levels are modified by disease processes—is far more plausible than the currently accepted ‘vitamin’ pragma—that the lower levels observed in sick individuals are indicative of a nutritional deficiency. [...]
What is a ‘natural’ homeostasis of
vitamin D synthesis?
It is thus very difficult to find a population which can be studied in order to ascertain what the level of natural metabolic homeostasis for 25-D might actually be. These studies show a wide variation in levels of 25-D being generated by populations whose diets have probably not yet
been significantly altered by ‘The Sunshine Vitamin,’ indicating
that the unsupplemented metabolic homeostasis is probably in
the range 23–60 nmol/L, and that it falls with advancing age.
.[...]
Surely we are being naive if we expect the exogenous
modulation of a metabolism that is responsible for the
expression of over a thousand genes to provide a simple
go/no-go result?"
It cannot be effectively stored in fact, it seems (possibly because our species evolved in the optimal sunlight conditions of the tropics). So it's trivial what happens in summer conditionsNo Maju it's perfectly true; Vitamin D can be stored The Pharmacology of Vitamin D, Including Fortification Strategies"During summer, we accumulate vitamin D3 and store it, so that supplies for vitamin D do not become completely depleted during the winter months. Within three days of a dose of vitamin D3, very little of the original vitamin D is detectable in plasma of rats (101) or humans (102). Most vitamin D entering the circulation appears to be excreted unmetabolized into the bile.[...]
If 30,000 years after entering northern Europe natural selection hasn't changed this (as it easilly could). I wonder if the reason isn't that the Vitamin D requrements are met, and then some, by North European sunshine.
"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 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."
This points towards a natural homeostasis of vitamin D synthesis and storage in northern Europe that has not modified from the one evolved in Africa because it's still dealing with an excess.
Too much Vitamin D is deadly. Those vitamins are a two edged sword.
ReplyDeleteDark skin may help limit too much Vitamin D being produced and the reason that the olive skin colour is so common in the temperate world of the mid latitudes is that is is the best solution to getting the right amount of Vitamin D converted from the precursor, beta carotene, found in the skin, and UV exposure.