At the beginning of anthropologist Nina Jablonski's lecture yesterday at the Wagner Free Institute of Science, it appeared her audience of about 100 was composed of several different races. By the end of the free lecture, titled "The Evolution of Human Skin Color," the Pennsylvania State University professor had made a case that we are all just people with varying levels of melanin.
As author of the book Skin: A Natural History, Jablonski has studied all aspects of skin, perhaps none more important than why it appears in such a puzzling array of hues. It all comes down to the planet's uneven distribution of sunlight and the universal human need for two vitamins, she explained.
This knowledge was very recently acquired. "Only in the last decade or so has our data allowed us to crack open the mystery," Jablonski said as she began her lecture at the 152-year-old science museum near Temple University.
Nature has painted human skin using one major brown pigment, melanin, which evolved in many species. "It's a natural sunscreen," she said, which is important because humans have a troubled relationship with the sun.
Since we are relatively hairless creatures, our skin gets bombarded by ultraviolet light, which can burn us, destroy the DNA in skin cells, and lead to cancer. Hence an advantage of dark skin.
But there is more to melanin than protection from skin cancer and sunburn. Scientists recently realized that ultraviolet rays penetrating skin destroy the B-vitamin folate. With too little folate, or folic acid, men cannot make adequate sperm and women cannot start healthy pregnancies. So in very sunny places, any genetic mutations that created light skin would likely die out with their owners.
But with melanin offering so many advantages, the question was why anyone would evolve light skin.
Lighter shades came about because humans need some sunlight to penetrate skin and trigger a chemical reaction that produces vitamin D.
To illustrate the devastating effects of vitamin D deficiency, Jablonski showed slides of children with badly bowed legs and softened bones. In women, a lesser deficiency can lead to a narrowed pelvis, making childbirth impossible.
The original skin color was almost certainly very dark, since scientific evidence points to sunny Africa as the cradle of humanity. But once some branches of the human family starting moving north to Asia and Europe, the need for vitamin D gave those with lighter skin an advantage in absorbing the meager sunlight in winter.
Because vitamins lie at the heart of our color differences, locally consumed foods also play a role. Whales and fatty fish can give people some vitamin D, Jablonski said, so diet may explain why the Inuit, who live in Alaska and Greenland, are much darker than people from Northern Europe.
Recent findings from genetics labs show that there are many roads to what we think of as white and black skin - both of which, or course, are really shades of brown. In 2005, for example, scientists found that Europeans became light-skinned through a different combination of mutations than did Northern Asians.
Last year, scientists scraped enough DNA from the bones of a Neanderthal man to show that this extinct branch of humanity carried genes associated with fair skin and red hair.
Currently, Jablonski said, researchers are seeking genetic variants that led to dark skin in far-flung peoples - those from Australia, New Guinea and southern India as well as Africa.
While Jablonski hopes that examining skin through science can help defuse racism and racial tension, she said, she is also concerned with what she calls colorism. Colorism has more to do with perception of beauty, she said. Its primary victims are women.
With a slide of people frying on the beach and an advertisement for bronzer, she explained that colorism has white women thinking they look sickly without a tan. More dangerous still, dark-complexioned women in some countries are driven to use dangerous skin-lightening products, many containing arsenic, mercury and other poisons.
"Why are we always trying to change the way we appear?" Jablonski asked. "Skin color is a beautiful product of evolution. . . . We should revel in it."
Posts: 2595 | From: Vicksburg | Registered: Feb 2006
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posted
Nice article, explains the obvious which is: "It all comes down to the planet's uneven distribution of sunlight and the universal human need for two vitamins"
Everyone living close to the equator will become darker relative to their position, and those positioned remote of the equator will become relative lighter depending on their native habitat (excluding factors as diet as in the case of the inuits.)
Thats what makes all this talk of "black" and "white" people so nonsensical since populations positioned relative to the equator (and their development of/ or lack of melanin) doesn't take into consideration other variables that illustrates kinship more accuratly.
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I think we shouldn't spend too much time on colorism since we were all Black in the first place as indicated by the article, Europeans were Black, Asians were Black and Africans were all Black(not anymore for some groups)...one race ...one family...the human race...
Posts: 461 | From: Kilimanjaro | Registered: Jan 2008
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LOL. Note that Jablonski speculates that dark skin must have been the first because they came from Sunny Africa. and yet the Sandawe are one of the oldest populations od Sunny Africa in Tanzania and they were not as dark.
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^ Jablonski is not speculating but stating a fact as the genes for melonoderm Black denotes the original underived skin color condition of all humans.
Of course you know this, as Jablonski humiliated you on this issue before, so you appear to be venting your frustrations at her.
Better that you should get a girlfriend instead.
Sandawe Tanzania.....
dark skin is the original skin color condition of all humans - Nina Jablonski.
Igbo.... Nigeria:
quote:Habari: We were all Black in the first place as indicated by the article, Europeans were Black, Asians were Black and Africans were all Black(not anymore for some groups)...one race ...one family...the human race...
^ True. But Jamie is unable to cope with this reality, which apparently makes him a little crazy.... Posts: 15202 | Registered: Jun 2004
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quote:Originally posted by Chimu: LOL. Note that Jablonski speculates that dark skin must have been the first because they came from Sunny Africa. and yet the Sandawe are one of the oldest populations od Sunny Africa in Tanzania and they were not as dark.
She didn't speculate about anything, she plainly stated that the original humans were very dark, stop trying to twist things around with your double talk.
Posts: 2595 | From: Vicksburg | Registered: Feb 2006
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posted
Woooooops!!! There goes the Nordic idea of AE.
---------------------------------- But there is more to melanin than protection from skin cancer and sunburn. Scientists recently realized that ultraviolet rays penetrating skin destroy the B-vitamin folate. With too little folate, or folic acid, men cannot make adequate sperm and women cannot start healthy pregnancies. So in very sunny places, any genetic mutations that created light skin would likely die out with their owners. -------------------------------
Posts: 12143 | From: When you have eliminated the impossible, whatever remains, however improbable | Registered: Jun 2007
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Here is more – adding fuel to the flame. ---------------------------------------
Significant evidence for a genetic basis explaining variation in constitutive skin color exists on a molecular level. Various human pigmentation genes have been identified, such as tyrosinase-related protein family members, melanocyte-stimulating hormone, melanocyte-stimulating hormone receptor, and the melanocortin 1 receptor (D'Orazio et al., 2006). Tyrosinase-related protein 1 expression appears to increase tyrosinase activity, melanogenesis, and melanosome size, and causes the expression of substantially more protein in darkly pigmented African and Indian skin types than Caucasians. Such differences may explain why the same number of melanocytes in different skin types results in differential responses to UV light and injury. The intersection of pigmentation and immunology is likely to generate substantial future interest; already there are data that melanocyte-stimulating hormone appears to confer enhanced repair ability beyond simply increasing the sun protection factor by increasing the number of DNA repair proteins several fold (Bohm et al., 2005).
In terms of structure and function of the skin, an observed reduction in susceptibility to irritation in black and hispanic versus white subjects has been historically attributed to reduced permeability of the stratum corneum in the black population (Robinson, 1999).
In terms of structure and function of the skin, an observed reduction in susceptibility to irritation in black and hispanic versus white subjects has been historically attributed to reduced permeability of the stratum corneum in the black population (Robinson, 1999). Some studies suggest that Asian subjects may be slightly more sensitive than Caucasians, but the differences do not appear to be large (Robinson, 2002). Differences in skin resistance and other biophysical properties have also been noted. Epidermal structure and function, however, is also likely substantially affected by UV exposure, as the sun-exposed epidermis of lighter-skinned people shows more atrophy, cellular atypia, and disorderly differentiation (Taylor, 2002). Differences in the dermis have been described: in one small study, black women were found to have more and larger fibroblasts than white women, with a tendency toward multinucleation. In addition, collagen fiber bundles in black subjects were smaller, more closely stacked, and ran more parallel to the epidermis with a greater number of macrophages identified in the papillary dermis (Montagna and Carlisle, 1991). Taking an immunological perspective of barrier function, multiple studies have demonstrated an increased risk of developing a latex allergy among the non-white populations (Grzybowski et al., 2002; Zeiss et al., 2003), but patch testing studies have not shown a significant difference between black and white populations (Dickel et al., 2001; DeLeo et al., 2002).
Similarly, skin aging does appear to be delayed in darker skin types due to increased protection. In darker skin, aging tends to manifest as deepening folds (primarily naso-labial fold) rather than the fine lines and wrinkling seen in lighter skin.
Posts: 12143 | From: When you have eliminated the impossible, whatever remains, however improbable | Registered: Jun 2007
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quote:Originally posted by Chimu: LOL. Note that Jablonski speculates that dark skin must have been the first because they came from Sunny Africa. and yet the Sandawe are one of the oldest populations od Sunny Africa in Tanzania and they were not as dark.
She didn't speculate about anything, she plainly stated that the original humans were very dark, stop trying to twist things around with your double talk.
Stated based on mutations outside MCR1. Geuss what, even the KhoiSan are within the parameters of skin color of MCR1 try again.
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posted
Apparently that argyle guy loves men...he has a tendency to talk a lot about that kind of stuff...
Posts: 461 | From: Kilimanjaro | Registered: Jan 2008
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quote:Originally posted by rasol: ^ Jablonski is not speculating but stating a fact as the genes for melonoderm Black denotes the original underived skin color condition of all humans.
LMAO. That underived skin color condition claim is based on the same MCR1 gene existent in KhoiSan. Where is your evidenc eof a genetic mutation?
quote:Of course you know this, as Jablonski humiliated you on this issue before, so you appear to be venting your frustrations at her.
LMAO. Keep trying to project your frustrations on others. Can't ask Ausar to ban me on this forum. Jablonski seems to cater to whom she talk to. But all her quotes are valid and show that she is not certain.
posted
Chimu you were in a beauty contest and you wound up making it to the finals against one other competitor.
It was between you and the biggest, baddest Komodo Dragon in the country.
You won, but you really didn't win.
A panel of 10 judges gave you the victory by 1 vote. However one of the judges selected your name by accident and he couldn't make a correction because he had to abide by the contest rules.
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Still deluded into thinking your comedy is good. So long as the food stamps keep on working you are fine.
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I wonder if the hypertension theory is true?? See below
Climatic adaptation Early migration out of Africa exposed ancestral populations to colder environments, with less incident sunlight. The most obvious response is in pigmentation, due to the quantity, type, and distribution of melanin. Skin colour is strongly geographically differentiated, with darker-skinned populations concentrated in the tropics, and lighter-skinned populations in more northerly latitudes. In tropical climates the melanin in dark skins protects against sunburn by scattering and absorbing UV radiation; it may also limit photodegradation of nutrients such as folate. Where sunlight is low, depigmentation may be favoured because UV penetration is necessary for vitamin D synthesis (26). A balance between these factors can largely explain the global pattern of pigmentation (27). However, there are discrepancies: while these could be due to recent migration or admixture, an alternative view (downplaying the importance of light skin in vitamin D synthesis) suggests that they may reflect sexual selection, in particular male preference for light-skinned females (28). The last idea predicts that sexual dimorphism should increase with increasing latitude, but in practice this is not borne out (29). The genetic basis of pigmentation variation is complex (30). Candidate gene approaches based on information about melanosome development, abnormal pigmentation phenotypes and orthologs in other species, together with analyses of selection signals in HapMap, have identified a set of about twenty genes that are likely to play important roles (18,30–32). The finding of selection signatures in Europeans and East Asians suggests that there really is some selective advantage for light skin, and the fact that they are in different genes shows that evolutionary routes to similar phenotypes were distinct – convergent evolution (30,32,33). Residence of ancestral populations in tropical Africa also necessitated heat adaptation, including cooling through efficient sweating. The considerable salt loss, combined with low dietary salt availability, led to selection for salt retention; at the same time, there was likely selection for increased arterial tone and cardiac contraction force when blood volume was depleted by water loss. After migration into temperate climates, these adaptations became maladaptive, and may be responsible for increased blood pressure. In the CEPH-HGDP samples, the global distribution of the functional (heat-adapted) alleles of seven genes involved in blood pressure regulation shows a latitudinal cline (34) unmatched by neutral markers. Furthermore, a combination of latitude and the frequency of one of these alleles in the G protein ß3 subunit gene explains a remarkable 64% of global variation in blood pressure. Initially, heat-adapted African populations expanded northward, undergoing selection for cold adaptation. Subsequently, cold-adapted north Asians expanded southward into the Americas less than 20 KYA, undergoing selection for heat adaptation, so that Native Americans show similar salt retention and cardiovascular phenotypes to Africans living at the same latitudes. In more recent migrations, particularly that of Africans to the temperate climate and high-salt environment of North America (Fig. 1C), previously adapted genes may be particularly maladapted, leading to high frequencies of hypertension (35). Dietary adaptation The diversity of environments occupied by hunter–gatherer humans after the early migrations are mirrored by a diversity of diets. Early heterogeneity of resources may still have an impact today: for example, as judged by modern Y chromosome diversity (36), population expansions occurred earlier in the northern part of East Asia, probably because of the abundant megafauna of the ‘Mammoth Steppe’, but later in the south, due to poorer resources. In terms of influence on diet, the most important development in human prehistory was agriculture, beginning 10 KYA in the Near East, with distinct varieties emerging later in China, the Americas and West Africa (Fig. 1B). Increased population densities, reduced dietary diversity, sedentary lifestyle and exposure to animal pathogens together represented a major set of challenges. A common view is that post-Neolithic humans are adapted, through a ‘thrifty genotype’ (37,38) to a hunter–gatherer lifestyle of feast and famine (39), and that the arrival of agriculture signalled the start of an era of dietary maladaptation, leading to high incidences of type 2 diabetes. Later colonization events, like those of the Pacific islands (Fig. 1C), may have involved particularly strong selection for thrifty genotypes (40) – possibly causing subsequent extreme levels of diabetes. These views have not gone unopposed, however (41,42), and recent studies of diabetes susceptibility loci suggest that reality is not so simple. A variant in the transcription factor 7-like 2 gene (TCF7L2) is responsible for 17–28% of the risk of type 2 diabetes in Europeans (43), but, contrary to expectations of the thrifty genotype hypothesis, is associated with reduced body mass index (BMI) in diabetics (44). In the HapMap samples, the frequency of another variant of the same gene, associated with increased BMI, has been driven by selection to near fixation (95%) in East Asians, with lower frequencies elsewhere. The ages of the variant in the different populations correspond approximately to the times of origin of agriculture, suggesting that it conferred some advantage in the post-agricultural environment. However, the nature of this advantage is unclear. A clear example of genetic adaptation to cultural innovation is the selection of alleles of LCT permitting persistence of lactase expression into adulthood. This allows the drinking of milk without adverse effects, and the distribution of the phenotype correlates well with that of populations with a history of cattle domestication and milk drinking (45). In the HapMap samples (16), LCT in Europeans shows the strongest signal of positive selection, reflecting a powerful advantage that may have been more related to milk as a source of uninfected water than as a source of nutrition. Studies in European populations identified a causative regulatory variant 14 kb upstream of the LCT gene (46), with an estimated age of 2000–20 000 years (47). However, lactase-persistent populations elsewhere, including Africa, do not carry this variant. Studies of Tanzanians, Kenyans and Sudanese (48,49) reveal three further nearby variants causing lactase persistence. Examination of surrounding haplotypes show that the three African variants arose independently of each other and of the European variant (a further example of convergent evolution), within the last 7000 years. The known variants still do not account for all of lactase persistence; so further examples are likely to exist. Further dietary adaptations remain to be discovered, and signals of selection around genes involved in the metabolism of other carbohydrates, fat and alcohol (18) are interesting. Cognitive adaptation? While many factors have been crucial to the success of Homo sapiens, the defining innovation has been culture – the capacity to communicate and transfer knowledge, and to deal with novel environments by creating new technologies, including the development and exploitation of new food resources. Some have made the argument that the out of Africa migration entailed novel challenges that favoured the selection of enhanced cognitive ability, and have supported this using comparisons of IQ and brain size (50). However, it is unclear why the cognitive challenges in this gradual migration should be greater than those facing non-migrants subsisting in the diverse and changing environments of Africa. Genetic studies in this area differ from those in, for example, pigmentation, because the interest in a particular gene is stimulated not by any known phenotypic effect, but simply by its expression in the brain, and some unexpected pattern of population differentiation. The identification of an underlying selected phenotype may not be straightforward, or without controversy. Undoubtedly, brain size (and presumably associated cognitive capabilities) increased rapidly in the human lineage over the past 3–4 million years. A long list of functional candidate brain genes has been produced (51), though few have been studied. Most interest has focused on two genes that, when mutated, result in microcephaly – a small brain, but with normal neural architecture. Both abnormal spindle-like microcephaly associated (ASPM) and Microcephalin (MCPH1) show signatures of adaptive selection both during the emergence of the human lineage (52,53), and subsequently (54,55). Globally, both genes show young, high frequency haplotypes that are rare in Africa, and could reflect recent regional selection. There has been argument over whether these patterns could be explained by demographic processes rather than selection (56,57). Selection on these genes is expected to be through some aspect of intelligence, rather than brain size (58). However, the common derived alleles for both genes are unlinked to standard measures of IQ (59), suggesting either that the gene variants were not being selected at all, or that the selected phenotype is something other than intelligence, as measured by the simple single metric of IQ. Information about the transcript and protein expression patterns of the different allelic variants would be helpful.
Human skin pigmentation shows a strong positive correlation with ultraviolet radiation intensity, suggesting that variation in skin color is, at least partially, due to adaptation via natural selection. We investigated the evolution of pigmentation variation by testing for the presence of positive directional selection in 6 pigmentation genes using an empirical FST approach, through an examination of global diversity patterns of these genes in the Centre d'Etude du Polymorphisme Humain (CEPH)-Diversity Panel, and by exploring signatures of selection in data from the International HapMap project. Additionally, we demonstrated a role for MATP in determining normal skin pigmentation variation using admixture mapping methods. Taken together (with the results of previous admixture mapping studies), these results point to the importance of several genes in shaping the pigmentation phenotype and a complex evolutionary history involving strong selection. Polymorphisms in 2 genes, ASIP and OCA2, may play a shared role in shaping light and dark pigmentation across the globe, whereas SLC24A5, MATP, and TYR have a predominant role in the evolution of light skin in Europeans but not in East Asians. These findings support a case for the recent convergent evolution of a lighter pigmentation phenotype in Europeans and East Asians.
At OCA2 355, the derived allele (linked with lighter pigmentation) occurs at its highest frequencies across Europe and Asia but is also relatively common among Native American populations (18–34%) and is present at much lower frequencies (0–10%) among Bantu-speaking African groups. In contrast, the ancestral allele associated with dark pigmentation has a shared high frequency in sub-Saharan African and Island Melanesians. A notable exception is the relatively lightly pigmented San population of Southern Africa where the derived allele predominates (93%).
The photoprotective properties of a highly melanized skin and the recent African origin of modern humans suggest that the ancestral phenotype is one of the relatively dark skin (Jablonski and Chaplin 2000; Rogers et al. 2004).
Given the relatively recent arrival and divergence of humans in and across Europe and Asia, the most parsimonious evolution of light skin would involve such mutations arising in a proto-Eurasian population soon after humans left Africa. Consequently, these mutations should be shared between modern Asian and European populations.
Alternatively, if separate existing functional variants were driven to high frequency in East Asian and Europeans or independent de novo mutations arose and were selected in each population after the divergence of Europeans and Asians, then these would be obvious as high allele frequency differences between modern European and East Asian populations. Reduced levels of heterozygosity surrounding the SLC24A5 A111G polymorphism in the European, but not East Asian, HapMap populations support the latter hypothesis Posts: 15202 | Registered: Jun 2004
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quote:Originally posted by rasol: The photoprotective properties of a highly melanized skin and the recent African origin of modern humans suggest that the ancestral phenotype is one of the relatively dark skin (Jablonski and Chaplin 2000; Rogers et al. 2004).
Rogers: Over 1.2 million years ago, the human ancestors in Africa began to lose their hair and they came under increasing evolutionary pressures that killed off the progeny of individuals that retained the inherited whiteness of their skin. By 1.2 million years ago, all people having descendants today had exactly the receptor protein of today's Africans; their skin was black, and the intense sun killed off the progeny with any whiter skin that resulted from mutational variation in the receptor protein.
However, the progeny of those humans who migrated North away from the intense African sun were not under the evolutionary constraint that keeps human skin black generation after generation in Africa.
Jablonski: Dark skin evolved in conjunction with the loss of 'fur' and is the original condition of homo sapiens.Posts: 15202 | Registered: Jun 2004
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Brothers. About 10 years ago I started filing evidence away about the San and their lighter skin tones and accumulated a fair amount of material on this from different sources.
Then, in the last five years, I started to see pictures of San; and more-and-more of them. What surprised me was that the ones I saw (maybe not the same ones others saw) were not as light as I expected them to be: they were brown to dark brown and rarely ever yellow. Actually, I don't remember yellow San and I have a collection of maybe 18 to 20 photos.
I'm not saying that the researchers who wrote this fact are mistaken. But. Well, just food for thought.
quote:Originally posted by Wolofi: So what is the explanation for San having lighter skin?
There are two African allelles ASIP and OCA2 that have ancestral and derived versions.
The ancestral versions are more common in darker African populations - the derived version is more common in lighter African populations.
This has nothing to do with Khoi or San. All Africans have the same allelles which far predate the existence of non Africans, which is why they are found around the world.
Darker San and Bantu of Tanzania have more underived allelles, lighter San and Bantu of South Africa have more derived allelles.
All are equally AFrican and generally have melanin frequencies concordant to the AFrican latitudes at which the live.
The reason the darkest melanoderms [San and non San alike] have the most ancient allelles is because the original human poulations lived near the equator - before - migrating to southern Africa.
Europeans and some North East Asians have far more recent mutations on their skin color receptors which evolved -after- the split between Europeans and Asians, and so are not shared with either each other or any other peoples that do not have recent ancestry from these groups.
There is no skin color allelle specific to 'san', nor is there a melanin level specific to san. They share the same allelles as all other Africans, and Blacks of Asia and Australia.
The Sandawe of Tanzania.....
dark skin is the original skin color condition of all humans - Nina Jablonski.
quote:Originally posted by rasol: At OCA2 355, the derived allele (linked with lighter pigmentation) occurs at its highest frequencies across Europe and Asia but is also relatively common among Native American populations (18–34%) and is present at much lower frequencies (0–10%) among Bantu-speaking African groups. In contrast, the ancestral allele associated with dark pigmentation has a shared high frequency in sub-Saharan African and Island Melanesians. A notable exception is the relatively lightly pigmented San population of Southern Africa where the derived allele predominates (93%).
The photoprotective properties of a highly melanized skin and the recent African origin of modern humans suggest that the ancestral phenotype is one of the relatively dark skin (Jablonski and Chaplin 2000; Rogers et al. 2004).
LOL. Relative to what, is the question. Mark Shriver's study makes an assumption. That the derived OCA2 355, the derived allele is predominant in the San. But they never sampled the San. They based themselves on the assumption that lighter skin would have the derived gene. The important quote to read is this:
quote:The lightly pigmented hunter–gatherer San population of Southern Africa is exceptional in having a high frequency of the derived allele relative to geographically proximate and more darkly pigmented African populations (Jablonski and Chaplin 2000)
In other words, they did not do any sampling and made the assumption based on Jablosnski's reflectance study. NOWHERE in her study does she mention OCA2 355, or any derived gene, as her study was not genetic.
Jablonski has admitted to positive selection for darkness in the Bantu since their divergence with the Khoi San. She also has stated that she believes they were darker than the Khoi San. But she has never stated that her evidence gives an exact level of darkness between Khoi San to Bantu. Her belief is that the Sandawe were originally lighter because they migrated from the south. But she has never presented genetic evidence for this. Only speculation.
Rasol and all love to present pictures of present day Sandawe to indicate how dark they are. But then scoff at people who present pictures of present day Egyptians. The Sandawe show a high level of admixture with their surrounding Bantu neighbors. But the older literature always describes them as lighter.
So obviously to a person eyeballing back in the day, they were lighter than their Bantu neighbors.
I forwarded Frank Sweet's comments to Mark Shriver, the author of the study you quoted.
His answer?
quote:Thanks for your note. Frank has some good points. Clearly more work needs to be done on the variation within continents in particular Africa. We do have one recent paper that shines some light on these questions (The genetic architecture of normal variation in human pigmentation: an evolutionary perspective and model, McEvoy et al, 2006). Note that we did not find many genes with signatures of natural selection on the West African branch and thus no clear indication that the West Africans have gotten darker since their separation from the East Asians and Europeans. This fact, although interesting in and of its own, does not address the issue of the lighter skinned African populations. Good questions, clearly, but there is not data yet to even let us speculate intelligently.
Best Regards, Mark
That was on Fri 4/06/07 3:39 AM
quote:Originally posted by fsweet Comments on "Genetic Evidence for the Convergent Evolution of Light Skin in Europeans and East Asians" by Heather L. Norton, Rick A. Kittles, Esteban Parra, Paul McKeigue, Xianyun Mao, Keith Cheng, Victor A. Canfield, Daniel G. Bradley, Brian McEvoy, and Mark D. Shriver in Molecular Biology and Evolution (2007) 24(3):710–722.
We have obtained and made available here a pre-publication copy of what is by far the most comprehensive study to date of the genetic adaptations that have produced different skin tones in populations around the world. It shows that Europeans and East Asians both got paler after the Diaspora due to natural selection, but they did so by different independent adaptations. Readers interested in the subject are urged to read the study.
The following comments do not summarize the study. Instead, they focus on aspects of the study of that are of interest to subject at hand.
The study does not address the unique depigmentation of northern Europeans. The study's European reference sample was twenty residents of Valencia, Spain. Consequently, the study explains the evolution of the intermediate skin tones of Mediterraneans as well as those of East Asians. But it ignores the extraordinary depigmentation of people native to the region with 300 miles of the Baltic and North Seas and discussed in the essay The Paleo-Etiology of Human Skin Tone. This is a bit disappointing, but the study's authors may have had no choice. It would have been good to learn more about the evolution of the pink "Nordic" skin tone as well as that of the tanned beige "Spanish" skin tone. But one cannot identify the mutations that produced the former without first identifying those that produced the latter, since the former may well have evolved from the latter. Perhaps a future study will take the next step.
The study does not try to date the paleness mutations. Although the study does not speculate when the paleness adaptations took place, the time frame can be deduced. Given that Europeans and East Asians underwent different independent paleness mutations, the mutations must have happened after the two populations split around 40 kya. At the other extreme, classical Egyptian art from about 4 kya shows pink-skinned people (as well as brown- and black-skinned subjects). Hence, Mediterranean Europeans must have become pale sometime between 4 kya and 40 kya. Other evidence suggests a date of about 5 kya for the appearance of Nordic paleness, pushing the lower limit out by another thousand years. And Paleolithic cave art showing brown-skinned Cro-Magnons brings the upper limit in to about 12 kya.
The study speculates, but offers little evidence as to the skin tone of the Diaspora band. An often-discussed topic in the OneDropRule discussion group is the skin tone of the small group that crossed the Straits of Bab El Mandeb 75 kya to colonize the planet. The only pertinent evidence uncovered by the study is that the dark skin tone of Melanesians (Papua-New Guinea) and that of the darkest sub-Saharan Africans use the same genetic system. Hence, this system must be older than the European/East Asian split (older than 40 kya). At first glance, this seems to indicate that the Diaspora band was dark, and the study speculates that this is the case. The study then uses this assumption to suggest that the relatively light skin tones of some sub-Saharans (ancient Ethiopians, Khoi San) result from recent admixture.
The problem is that no evidence suggests that ancient Ethiopians and Khoi San (who are genetically closely related remnants of the hunter-gatherers who populated the continent before the Bantu agricultural expansion) are either admixed or recent adaptations. Indeed, there is much evidence that they are the oldest phylogenetic clade of H. sap. on the planet. Furthermore, the study found that the allele that makes these ancient sub Saharans paler than other sub Saharans (MATP C374G) is common in Europeans and East Asians but rare in other sub Saharans. Taking this into account leaves three possibilities:
(1) The Diaspora band were uniformly dark brown (like today's Bantus) by chance because they did not happen to include any ancestors of today's ancient Ethiopians or Khoi San with MATP C374G in their group. The MATP C374G that appears today in Europeans, East Asians, as well as in Khoi San and ancient Ethiopians must be explained by convergent evolution -- that two later independent mutations (in Europeans and East Asians) precisely re-created the ancient MATP C374G allele left behind in Africa (in the ancestors of Khoi San and ancient Ethiopians). This is exceedingly implausible.
(2) The Diaspora band were uniformly light brown (like today's Khoi San and Ancient Ethiopians) by chance, because they all happened to have MATP C374G. That Melanesians and Bantus today both have dark brown skin via the identical complex genetic mechanism must be explained by convergent evolution -- that Melanesians' dark brown skin tone uses the identical system as that of today's Bantus due to a later independent mutation that precisely re-created the ancient dark-brown system left behind in Africa. This is also exceedingly implausible.
(3) The Diaspora band comprised a mix of dark-brown, light-brown, and medium-brown skin tones due to a mix of the same light- and dark-skin alleles found throughout most of sub-Saharan Africa today. The light-skin alleles provided the variants (including MATP C374G) that mutated into European and East Asian traits, while the dark-skin alleles remained unchanged in Melanesia. This is the simplest explanation of the facts at hand.
The most praiseworthy aspect of the study is its meticulous attention to detail in avoiding misleading measurements. For example, if you want to measure the relative impact on skin tone of different alleles in an admixed population, you must use a population that is reasonably close to Hardy-Weinberg equilibrium. Testing random US Americans, for instance, would not give accurate results because US Americans have a notoriously bimodal admixture distribution due to the 300-year-old endogamous color line. And so the study's authors first made sure that their sample had a normal Gaussian distribution -- a vital detail that few other researchers would have taken the trouble to ensure. Another example is that as a backup sample of West Africans, the authors actually used subjects from the Geechee/Gullah population of the U.S. Sea Islands. This is because today's West Africans are more admixed with European and Middle Eastern genes than are the Geechee/Gullahs, who due to historical coincidences are still genetically 100 percent West African today.
The least justifiable conclusion of the study, contradicted by its own data, is its marginalizing the two most ancient populations on earth (Khoi San and Ancient Ethiopians). The study does this through circulus in demonstrando (circular argument). It says that most sub Saharans today are very dark (leaving out the two oldest populations). From this it concludes that extreme darkness must be adaptive in Africa. From this it concludes that extreme darkness must always have been adaptive. From this it concludes that the Diaspora band must have been very dark. From this it concludes that the presence of MATP C374G in the Khoi San and Ancient Ethiopians must be the result of recent European or East Asian admixture -- a conclusion contradicted by the fact that MATP C374G is identical in Europeans and East Africans, even though their paleness adaptations are independent.
All in all, this is a deeply important study by some of the most talented researchers in the field. It should be read by anyone interested in the evolutionary history of skin tone variation around the world.
quote:Mark Shriver's study makes an assumption. That the derived OCA2 355, the derived allele is predominant in the San. But they never sampled the San.
FIG. 3.— Distribution of allele frequencies in the CEPH-Diversity Panel for the 5 SNP showing elevated pairwise FST values for at least one population pair in our original population screen: (A) ASIP A8818G, (B) OCA2 A355G, (C) TYR A192C, (D) MATP C374G, and (E) SLC24A5 A111G. On all maps, gray shading corresponds to the frequency of the allele associated with lighter pigmentation. The numbered populations correspond to the following: 1) Biaka pygmies, 2) Mbuti pygmies, 3) Mandenka, 4) Yoruba, 5) Bantu N.E., 6) San, 7) Bantu S.E., 8) Bantu S.W., 9) Mozabite, 10) Bedouin, 11) Druze, 12) Palestinian, 13) Brahui, 14) Balochi, 15) Hazara, 16) Makrani, 17) Sindhi, 18) Pathan, 19) Kalesh, 20) Burusho, 21) Han, 22) Tujia, 23) Yizu, 24) Miaozu, 25) Orogen, 26) Daur, 27) Mongola, 28) Hezhen, 29) Xibo, 30) Uygur, 31) Dai, 32) Lahu, 33) She, 34) Naxi, 35) Tu, 36) Yakut, 37) Japanese, 38) Cambodian, 39) Papuan, 40) NAN Melanesian, 41) French, 42) French Basque, 43) Sardinian, 44) Northern Italian, 45) Tuscan, 46) Orcadian, 47) Adygei, 48) Russian, 49) Pima, 50) Maya, 51) Columbian, 52) Karitiana, 53) Surui.
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quote:Note that we did not find many genes with signatures of natural selection on the West African branch and thus no clear indication that the West Africans have gotten darker since their separation from the East Asians and Europeans
^ Exactly. Indeed, the relevant separation is not between East Asian and Europeans on the one hand and "West" Africa on the other, but rather between Africans and non Africans, and subsquently between East Asians and Europeans. European depigmentation is the recent adaptive response. Black skin is the original underived state.
quote:Good questions, clearly, but there is not data yet to even let us speculate intelligently.
^ NICE TRY, but you are misrepresenting again.
That is actually a response to Frank Sweets faulty assertion that West Africans grew darker recently, for which he begs for corroboration that does not exist.
"no clear indication that the West Africans have gotten darker" = no basis for Frank Sweets phony claims.
It is Sweets, and you, whose remarks are rooted in unintelligent speculation, and who are so debunked by the facts. As usual.
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quote:all in all, this is a deeply important study by some of the most talented researchers in the field.
translation: you and frank sweets are both debunked, and cannot refute the facts, you can only try to spin them to minimize the damage to your racist idiology.
By 1.2 million years ago, all people having descendants today had exactly the receptor protein of today's Africans; their skin was black, and the intense sun killed off the progeny with any whiter skin that resulted from mutational variation in the receptor protein. ^ case closed.
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quote:Mark Shriver's study makes an assumption. That the derived OCA2 355, the derived allele is predominant in the San. But they never sampled the San.
FIG. 3.— Distribution of allele frequencies in the CEPH-Diversity Panel for the 5 SNP showing elevated pairwise FST values for at least one population pair in our original population screen: (A) ASIP A8818G, (B) OCA2 A355G, (C) TYR A192C, (D) MATP C374G, and (E) SLC24A5 A111G. On all maps, gray shading corresponds to the frequency of the allele associated with lighter pigmentation. The numbered populations correspond to the following: 1) Biaka pygmies, 2) Mbuti pygmies, 3) Mandenka, 4) Yoruba, 5) Bantu N.E., 6) San, 7) Bantu S.E., 8) Bantu S.W., 9) Mozabite, 10) Bedouin, 11) Druze, 12) Palestinian, 13) Brahui, 14) Balochi, 15) Hazara, 16) Makrani, 17) Sindhi, 18) Pathan, 19) Kalesh, 20) Burusho, 21) Han, 22) Tujia, 23) Yizu, 24) Miaozu, 25) Orogen, 26) Daur, 27) Mongola, 28) Hezhen, 29) Xibo, 30) Uygur, 31) Dai, 32) Lahu, 33) She, 34) Naxi, 35) Tu, 36) Yakut, 37) Japanese, 38) Cambodian, 39) Papuan, 40) NAN Melanesian, 41) French, 42) French Basque, 43) Sardinian, 44) Northern Italian, 45) Tuscan, 46) Orcadian, 47) Adygei, 48) Russian, 49) Pima, 50) Maya, 51) Columbian, 52) Karitiana, 53) Surui.
My fault, misunderstood the second quote. But Frank addressed that as well.
quote:The least justifiable conclusion of the study, contradicted by its own data, is its marginalizing the two most ancient populations on earth (Khoi San and Ancient Ethiopians). The study does this through circulus in demonstrando (circular argument). It says that most sub Saharans today are very dark (leaving out the two oldest populations). From this it concludes that extreme darkness must be adaptive in Africa. From this it concludes that extreme darkness must always have been adaptive. From this it concludes that the Diaspora band must have been very dark. From this it concludes that the presence of MATP C374G in the Khoi San and Ancient Ethiopians must be the result of recent European or East Asian admixture -- a conclusion contradicted by the fact that MATP C374G is identical in Europeans and East Africans, even though their paleness adaptations are independent.
Now, what is the evidence that the OCA2 355 is more recent? Other than, as Frank points out a circular argument?
quote:Originally posted by rasol: [QB]
quote:Note that we did not find many genes with signatures of natural selection on the West African branch and thus no clear indication that the West Africans have gotten darker since their separation from the East Asians and Europeans
^ Exactly. Indeed, the relevant separation is not between East Asian and Europeans on the one hand and "West" Africa on the other, but rather between Africans and non Africans, and subsquently between East Asians and Europeans. European depigmentation is the recent adaptive response. Black skin is the original underived state.
Nice try. All he stated was that skin lighter than that of even the lightest Africans is a modern derivative. There are still a range of colors in Africa also present in Asia and the Americas. No evidence all are more recent adaptations.
quote:^ NICE TRY, but you are misrepresenting again.
That is actually a response to Frank Sweets faulty assertion that West Africans grew darker recently, for which he begs for corroboration that does not exist.
It is Sweets, and you, whose remarks are rooted in unintelligent speculation, and who are so debunked. As usual
Nice try again. As Frank never stated that Africans grew darker since the migration out of Africa. But the valid point is we do not know if lighter populations existed back then as they do today andf in the recent past.
quote:Originally posted by rasol: [QB]
quote:all in all, this is a deeply important study by some of the most talented researchers in the field.
translation: you and frank sweets are both debunked, and cannot refute the facts, you can only try to spin them to minimize the damage to your racist idiology.
Trying to project again? LOL Sorry He pointed what was not stated in the study, and it bugs the crap out of you.
quote:By 1.2 million years ago, all people having descendants today had exactly the receptor protein of today's Africans; their skin was black, and the intense sun killed off the progeny with any whiter skin that resulted from mutational variation in the receptor protein. ^ case closed.
As the Sandawe and the San did not die. Your conclusion is faulty. Skin is not just Black and White. Try again.
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quote:Originally posted by Chimu: [QUOTE]Skin is not just Black and White.
Evergreen Writes:
Chimu, please define in quantitative terms the melanin level that makes one Black or White?
Posts: 2007 | From: Washington State | Registered: Oct 2006
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quote:Originally posted by Chimu: [QUOTE]Skin is not just Black and White.
Evergreen Writes:
Chimu, please define in quantitative terms the melanin level that makes one Black or White?
LOL Throwing back my question? I already asked the same question when I stated Black and White were subjective. Obviously my beleif is it varies by perception. Now for those that claim Black and White are objective facts, they will have to answer your question (which I made as well).
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Understand this: You're and idiot who is too busy making stupid remarks to actually read the study or have any idea of what you're talking about.
quote:But Frank addressed that as well.
he's and idiot too, but not as stupid as you.
please bring him here so we can destroy him too.
quote:As Frank never stated that Africans grew darker since the migration out of Africa.
yes he did, actually. so you are now a liar as well as and idiot - trying to save Sweets from embarrassment by denying his statements.
^ Sweets made this dumb claim, and then attempted to beg the question to Shriver, who threw it back in his pathetic lying face.
thus no clear indication that the West Africans have gotten any darker
^ this is direct rebuttal your master's lying claims.
keep squirming chumpu.
you do realise you've humiliated yourself again don't you?
quote:By 1.2 million years ago, all people having descendants today had exactly the receptor protein of today's Africans; their skin was black, and the intense sun killed off the progeny with any whiter skin that resulted from mutational variation in the receptor protein.
quote:Originally posted by Evergreen: Chimu, please define in quantitative terms the melanin level that makes one Black or White?
Indeed the very idea that social ethnic terms can be quantified is silly.
But the real question for Chimpu is - tell us what 'spectrometer' level can delmit 'MIXED' as he advocates (??)
This is because it's his silly idea, and so for him to quantify, which of course he has no intention of doing.
Since no answer is forthcoming, then the notion that such can be quantified by spectrometer is mooted, and Chimus ongoing pleas for 'sympathy for his simple-mindedness' avails him nothing.
quote:Chimpu writes: Throwing my question back at me eh?
Yes because its your stupid question to begin with.
Either:
1) Provide and answer by quantifying "mixture" with a spectrometer and so prove the question isn't stupid.
or...
2) Provide no answer and admit to being stupid.
[by the way this question goes out to anyone who wants to take up Chimpu's position - calling you all out - IDIOT trolls asking senseless questions to hide from unpleasant truths]
Two choices - take one.
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quote:Rasol asks -> Chumpu: what 'spectrometer' level can delimit 'MIXED'? Do you even know what a spectrometer is, you idiot.
^ Deafening silence from the loudmouthed troll.
Don't come back to ES posting any more of your garbage, til you find and answer to your own stupid question.
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quote:Originally posted by rasol: Understand this: You're and idiot who is too busy making stupid remarks to actually read the study or have any idea of what you're talking about.
Oh please. I made an honest mistake. But contrary to you I can admit when I do one.
quote:he's and idiot too, but not as stupid as you.
The guy has ten times more brain than you and is not as immature.
quote:please bring him here so we can destroy him too.
LOL. Serious scholars don't come to this board. Only us who are bored. You are a joke without a life outside this board. He get's published, you just run around misinterpreting research in this wee lil world of yours.
quote:
quote:As Frank never stated that Africans grew darker since the migration out of Africa.
yes he did, actually. so you are now a liar as well as and idiot - trying to save Sweets from embarrassment by denying his statements.
Feel free to show any post recently where he has made that claim.
quote:Sweets made this dumb claim, and then attempted to beg the question to Shriver, who threw it back in his pathetic lying face.
Don't make me laugh. Mark and Frank are friends who have corresponded multiple times on various issues. They both would laugh at your pathetic attempts at misrepresentation of what they are saying.
Like I said. All you have is reposts and misdirection.
quote:Originally posted by rasol: But the real question for Chimpu is - tell us what 'spectrometer' level can delmit 'MIXED' as he advocates (??)
More silly strawmen. No such thing as a color for being Mixed.
quote:This is because it's his silly idea, and so for him to quantify, which of course he has no intention of doing.
As usual rashole is full of shyt. I never have mentioned any standard for Black or White. I call you guys hypocrites for making claims that there are objective standards for what is Black and then not being able to stick to your so called objective standards.
That is the true quandary, and the one Rashole stakes his measly internet life on. Because if he can't claim people around the world as Black, then he has no sense of accomplishment. He has to coattail.
Posts: 385 | Registered: Mar 2008
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quote:The guy has ten times more brain than you and is not as immature.
Megencephaly, enlarged brain, occurs in several acquired and inherited human diseases including Sotos syndrome, Robinow syndrome, Canavan's disease, and Alexander disease. This defect can be distinguished from macrocephaly, an enlarged head, which usually occurs as a consequence of congenital hydrocephalus.
Yes, he's a 'swell head' alright, and a coward too, so there's no chance of him showing up outside of his guilded cage forum for emotionally unstable 'kemophobic' mulattos.
And you're the fan-boy loser sniffing Frank's fecal material and repeating after his stench, but at much lower [if possible] intellectual level. Posts: 15202 | Registered: Jun 2004
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quote:Banned troll writes: More silly strawmen. No such thing as a color for being Mixed.
^ It's your strawman idiot. You just explained why 'mixed' cannot qualify color. Therefore your and Sweeets idiotic babblements about "mixture" are non-sequitur as qualifiers of color.
You continue to humiliate yourself.
You pose stupid questions and scream 'strawman' when you're asked to answer them.
What and idiot you are.
Posts: 15202 | Registered: Jun 2004
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quote:I never have mentioned any standard for Black or White.
^ We didn't ask you about black or white, idiot.
WE asked you about your standard of mixture.
You know, your pet term.
It's hilarious that you can't answer even the most basic questions pertaining to it.
You seem to be too afraid to even try?
{Is Greece mixed? Is Japan mixed? Is Swedan mixed? Is 'everyone' mixed, if yes, then 'what' pray tell does mixed qualify? If no then explain what "qualifies" mixed? If mixed means not 'black' and not 'white', then what colour is mixed? If mixed is not a colour then what relevance can it have for terms that denote colour?}
Your ridiculous query regarding qualification of ethnic color terms by spectrometer [repettition of Frank Sweets retardedness], requires that you supply a spectrometer value for mixed, since mixed is 'your preferred term', and spectrometer is your supposed method for denoting it.
If you can't answer these questions then your posts - all of them - are utterly pointless.
lol. Keep running you cowardly metizoo misanthrope, it's all you can do, since you never have any answers.
Maybe you should run back to Frank Sweets and sniff up some more troll responses - via his enlarged brain, or his rear end, *which-ever* end you sniff your silly troll replies from..
Lastly, I gather you want to take another beating on the topic of the meaning of Km.t [Rm.t] "The Blacks"?
quote:Originally posted by rashole: Yes, he's a 'swell head' alright, and a coward too, so there's no chance of him showing up outside of his guilded cage forum for emotionally unstable 'kemophobic' mulattos.
And you're the fan-boy loser sniffing Frank's fecal material and repeating after his stench, but at much lower [if possible] intellectual level. QUOTE] LOL. Your emotional outbursts and childish posts exemplify the reason why you can't be on a serious forum. You could never hang in a forum where only polite discourse, facts and evidence are required. You need a buddy moderator to coddle you. LOL
quote:Originally posted by rashole: [QB] [QUOTE]Originally posted by Chimu: Oh please. I made an honest mistake.
^ Get real. You're a miserable loser who spreads lies like a diseased hooker spreads stds.
Speaking about yourself again I see. LOL
quote:You just got caught, which is the only reason you own up to it.
Your wishful thinking is entertaining.
quote:"honest mistake" is the same excuse you made when you misrepresented the work of Jablonski.
No mistake there. My representation of Jablonski was quite accurate. The fact that you would only choose a set of quotes from her and ignore the others is an example of you misrepresenting her.
quote:Originally posted by rashole: It's your strawman idiot. You just explained why 'mixed' cannot qualify color. Therefore your and Sweeets idiotic babblements about "mixture" are non-sequitur as qualifiers of color.
You continue to humiliate yourself.
You pose stupid questions and scream 'strawman' when you're asked to answer them.
What and idiot you are.
More of your usual stupidity. While people of mixed heritage will usually show features that are intermediate between the two parent populations they span the whole spectrum. But when there are two populations involved with characteristic features and a third with intermediate features then py position and history you can predict admixture or clinal variation. Nice try at a strawman dumb ass. There is no color for Mixed. But if the color is intermediate between two populations being compared, yes admixture or clinal variation is probable.
Keep showing the moron you are.
quote:Originally posted by rashole: We didn't ask you about black or white, idiot. WE asked you about your standard of mixture.
Nice try nitwit. You guys are the idiots claiming that the terms black and White are biological realities. Mixture is a biological reality. And it is not predicated on a certain color, but color may be evidence of admixture. Mixture. When two separate populations encounter each other and offspring occur.
quote:Is Greece mixed?
Go look up the genetic studies. It will give you the level of admixture.
quote:Is Japan mixed?
Same thing.
quote:Is Swedan mixed?
Same thing.
Is the culture Mixed? Well it would depend on how much the admixture has led to a separate identity, marked difference in phenotype and if creolization of the culture has occured. In other words that the culture is not just one or the other of the parent cultures. I'd say Greece is more mixed than Sweden and Japan.
quote:If mixed means not 'black' and not 'white', then what colour is mixed?
Nice try again. As Black and White are adopted ethnic terms for many groups, Mixed would just indicate ancestry from two groups such as those. It is not a color. But colors, features, etc intermediate to two populations may be evidence of admixture.
quote:If mixed is not a colour then what relevance can it have for terms that denote colour?
Read above
quote:Your ridiculous query regarding qualification of ethnic color terms by spectrometer
LOL. Ridiculous because it would show the foolishness of yoursupposed ability to quantify what Blackness is.
quote:[repettition of Frank Sweets retardedness]
The only repetitiousness is in the tt in your typing.
quote:requires that you supply a spectrometer value for mixed, since mixed is 'your preferred term', and spectrometer is your supposed method for denoting it.
Nice try. Read above. The color variation is not the sole evidence of admixture. Genetics is. But the color variation seems to corroborate it.
quote:lol. Keep running you cowardly metizoo misanthrope, it's all you can do, since you never have any answers.
quote:As Black and White are adopted ethnic terms for many groups, Mixed would just indicate ancestry from two groups such as those.
This remark does not answer any question.
All Black and White groups have ancestry.
So what distinguishes 'mixed' from 'pure'.
Please provide a list of pure groups....
Please provide a list of mixed groups...
Explain what makes a pure group pure and a mixed group mixed.
Or...write a another reply that doesn't answer the question, which is what we expect from a conniving coward like you.
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