Talk:Human skin color/Archives/2013/July

Dubious

I've marked recent additions about the speed and scope of human skin colour changes. These additions use a single ref, a story on the NPR website from 2009 based on a short radio interview with Nina Jablonski. Since the interview, Jablonski has published numerous papers on the topic in peer-reviewed journals since the interview, as well as a book, and none (at least that I can find) reiterate nor provide evidence for the claims made. Perhaps the interview was given at a time when a line of research looked promising, but then it never panned out and so was not included in her published work. Unless there is some more robust supporting material I suggest we remove these additions. Tobus2 (talk) 02:23, 11 July 2013‎ (UTC)

Tobus2 is referring to these changes that were made by Soupforone. I agree with Tobus2 about this. Since I've linked Soupforone's username in this paragraph, Soupforone will get a notification about this discussion via WP:Echo (assuming that he or she has not opted out of getting a notification when someone links to his or her username on a talk page). However, Soupforone might have this article on his or her WP:Watchlist and thus does not need the notification. Flyer22 (talk) 02:49, 11 July 2013 (UTC)

Thanks for cleaning up for me Flyer Tobus2 (talk) 02:24, 12 July 2013 (UTC)

You're welcome. I didn't mind signing for you, especially considering that you usually remember to sign. Flyer22 (talk) 02:39, 12 July 2013 (UTC)

Here is the transcript of the NPR interview. It's all in there. Jablonski also does not appear to have changed her research stance much if at all since then. She indicated more or less the same thing in an article that she wrote a few months ago for the AGEI's website, as an adjunct to her lecture at the AGEI's 2012 Darwin Seminars [1]: "From a genetic perspective, skin colour re-pigmentation and de-pigmentation evolved many times over, independently of other traits like eye and hair colour. So we can’t group people into genetically distinct groups based on skin colour." Soupforone (talk) 22:24, 11 July 2013 (UTC)

The link to the transcript is wrong - it's a link to a mobile-friendly version of the same story. The actual transcript is here. If you listen to the audio it's obvious that it isn't a genuine interview - it's a story with soundbites from Jablonski edited in to make it sound interview-ish. She doesn't actually say a lot of what's attributed to her in the story and we can't assume that any of her statements are actual responses to what the reporter just said. I don't think we should treat it as a reliable source.

Thanks for finding the 2nd link. It does refer to repigmentation and multiple independent evolution, but there is no support in there for two major claims in the first ref - that skin colour can change in 100 generations with no intermarriage and that South Asians/Sri Lankans were once lightly pigmented. I searched a bit deeper and found two papers in peer-reviewed publications which explain the 'repigmentation' as tanning ability and the 'many times over' evolution as the two known European and East Asian cases plus the possible Neanderthal one:

• "Depigmented and tannable skin evolved numerous times in hominin evolution via independent genetic pathways under positive selection" Human skin pigmentation as an adaptation to UV radiation (Supplement 2)
• "This has been proved by genetic evidence for selective sweeps having established depigmented integumental phenotypes independently in the ancestors of western Europeans and eastern Asians [10,11] and probably also in Homo neanderthalensis [12]. Dispersal of human populations into latitudes between about 23° and 46° was accompanied by the evolution of partially depigmented phenotypes capable of tanning [3]. Many such populations probably represent repigmented descendants of previously depigmented peoples—such as in the case of the indigenous peoples of the New World—but identification of candidate loci associated with evolution of secondary dark pigmentation is still in its early stages [13]." Human skin pigmentation, migration and disease susceptibility

We shouldn't be including the claims made in the NPR story unless there is some robust corroborating evidence.

Tobus2 (talk) 02:24, 12 July 2013 (UTC)

Unlike perhaps the authors of those other papers, Jablonski is clearly not referring to tanning when she speaks of "re-pigmentation" in her AGEI piece [2]. This is evident since she mentions re-pigmentation in conjunction with de-pigmentation, indicating that both "skin colour re-pigmentation and de-pigmentation evolved many times over, independently of other traits like eye and hair colour". In other words, Jablonski is referring to long-term directional changes in the skin color trait itself. That is why she concludes the passage with the caveat that "we can’t group people into genetically distinct groups based on skin colour." That is also why elsewhere she uses South Indians as an example of this process at work (please see below).

With regard to the NPR interview, it was evidently longer than what has been transcribed, and was edited down before publication. This is obvious since the NPR article on Jablonski quotes her saying things that aren't featured in the transcript of the final presentation of the interview. For example, her assertion that changes in pigmentation within a given lineage can happen in "a blink of an eye".

It is also apparent that the NPR interview was longer than what is included in the transcript since the transcript paraphrases some of what she says and then attributes those statements to her. In the process, it notes her responses to the interviewer Krulwich's own assertions. That includes the main points about how the ancestors of most people living today were likely a different color not that long ago and lived in a different part of the globe; how a lineage/family group can evolve a different skin color in as little as 50 to 100 generations (~2,500 years), with no intermarriage required; how populations in present-day South India are an example of this, as they "re-evolved dark pigment" after having migrated down from Central Asia; and how she and other researchers know all this through recent advances in genetic clocking technology.

From the NPR article [3]:

• ”that color, the one you have now, says Jablonski, is very probably not the color your ancient ancestors had — even if you think your family has been the same color for a long, long time.”
• ”Skin has changed color in human lineages much faster than scientists had previously supposed, even without intermarriage, Jablonski says”
• ”Recent developments in comparative genomics allow scientists to sample the DNA in modern humans. By creating genetic "clocks," scientists can make fairly careful guesses about when particular groups became the color they are today. And with the help of paleontologists and anthropologists, scientists can go further: They can wind the clock back and see what colors these populations were going back tens of thousands of years, says Jablonski.”
• ”She says that for many families on the planet, if we look back only 100 or 200 generations (that's as few as 2,500 years), "almost all of us were in a different place and we had a different color."”
• ”Over the last 50,000 years, populations have gone from dark pigmented to lighter skin, and people have also gone the other way, from light skin back to darker skin, she says.”
• "People living now in southern parts of India [and Sri Lanka] are extremely darkly pigmented," Jablonski says. But their great, great ancestors lived much farther north, and when they migrated south, their pigmentation redarkened. "There has probably been a redarkening of several groups of humans."

From the NPR transcript [4]:

KRULWICH: And I didn't know this, but there are also instances of lighter groups turning darker over time.

Dr. JABLONSKI: The people now living in southern parts of India are extremely darkly pigmented.

KRULWICH: But once upon a time, those same people lived in central Asia. And up north, there, they were much lighter, until they moved south, where new evidence suggests…

Dr. JABLONSKI: They re-evolved dark pigment.

KRULWICH: And they're not the only ones. Aboriginal Australians may have gone from light to dark, Pacific Islanders, the same.

Dr. JABLONSKI: There's probably been a re-darkening of several different groups of humans.

As the research findings are coming from Jablonski herself and have been attributed as such, the tags should be removed. Soupforone (talk) 21:31, 12 July 2013 (UTC)

Jablonski IS the author of those other papers. If you read her actual 'research findings' (ie her published works) instead of a radio DJ's interpretation of them, the 're-pigmentation' reference at AGEI can only be about tanning - she simply provides no other genetic mechanism for skin redarkening. She presents a theory that light skin evolved twice (possibly thrice if you count Neanderthals) as populations moved north and then tanning evolved (multiple times?) as light-skinned populations expanded south - that's what "skin colour re-pigmentation and de-pigmentation evolved many times over" is referring to. Her theory is dark->light->tanned, not dark->light->dark as the reporter seems to think. But don't listen to me, listen to the evidence: we have 2 peer-reviewed published research papers by Jablonski, both with sources and supporting data, saying 're-pigmentation' is tanning, compared with a single news item by a journalist who has edited her words to imply it's genetic evolution, with no sources or data. Which do you think is more reliable?

Don't get me wrong, I would love for the claims to be true. When I first read your additions I was very excited and went to look for the paper the story was based on. I wanted to see which new SNP's they've found for 're-pigmented' dark skin and was hoping to analyse the data showing populations which have migrated and changed skin colour within 100 generations. Unfortunately there is no paper, there are no new SNPs, there is no population data, there's not even Jablonski actually saying the things the journalist has implied she said. It turns out the NPR story is a beat up - it misrepresents and sensationalises Jablonski's theory, hence the 'dubious' tag.

I'm happy to remove the tags if you are able to find peer-reviewed published research which shows that:

1. South Asians were once light-skinned and independently evolved dark skin

2. Human skin colour can change in 100 generations with no intermarriage

If not then can you please remove these claims.

Tobus2 (talk) 03:11, 13 July 2013 (UTC)

Actually, it's indicated fairly conspicuously in the NPR article [5] that those are Jablonski's own words. It's her that asserts that most people living today were likely a different color not that long ago and lived in a different part of the globe; that a lineage/family group can evolve a different skin color through environmental adaptation in as little as 50 to 100 generations (~2,500 years), with no intermarriage required; that populations in present-day South India are an example of this, as they "re-evolved dark pigment" after having migrated down from Central Asia (she mentions the indigenous peoples of the New World as another example in her 2012 paper [6]); and that she and other scientists know all this through recent advances in genetic clocking technology. In a nutshell, this is what Jablonski means by re-pigmentation and de-pigmentation. That is why those assertions are annotated with phrases -- bulleted and italicized in my previous post above -- like “Jablonski says”, or “says Jablonski”, or “she says”. They're not the work of one over-eager NPR science writer's imagination, as you appear to be suggesting. That is also why this same NPR piece is cited as a reliable source on the Race (human classification) page (where I first got wind of it, btw). If it's good enough for use there, it should be good enough here too. Soupforone (talk) 22:05, 13 July 2013 (UTC)

Also note that repigmentation and depigmentation of global populations are things that Jablonski has been emphasizing for many years now. What's really novel is her estimate for how quickly skin pigmentation can change in a given lineage or family group. As recently as 2005, she was asserting that it took at least 15,000 years [7]. However, with the significant advances in genetic clocking technology, Jablonski and other researchers have now lowered that estimate to around 2,500 years. Soupforone (talk) 22:05, 13 July 2013 (UTC)

Thanks for the heads up on the other article using the same source, it's used much more accurately there but I've flagged it as dubious as well so the editors there can review it.

I've gone ahead and removed the claims I flagged as dubious, you haven't provided any reliable verification for them and despite looking I can't find any either. We can reinstate any claims with more appropriate wording if this discussion leads to some supportable facts. Jablonski is a prolific writer and her theories and ideas are very easy to find. If this NPR story is the only place she is reported as saying something, it's probably not something she says. The fact that neither of us can find any other reference to the claims in question is an indication that we shouldn't be repeating them.

I agree that the article indicates that those are Jablonski's own words, but because the claims differ from what she presents in her research I checked to make sure, and as I've already told you, most of them are not her own words. I really didn't want to get into a quote-by-quote analysis of the NPR "interview", but I will. The reporter takes short soundbites with no context and places them in his own context, without the original source there's absolutely no way of knowing what Jablonski was really talking about. For instance, you think "it's her that asserts... :

• that most people living today were likely a different color not that long ago and lived in a different part of the globe"

All she said was "Almost all of us were in a different place and we had different color." It could come from an introduction to an overview of OOA and mean "all Eurasians once lived in Africa and had dark skin". The fact that editor has placed it immediately after the reporter saying "if you go back not that many generations..." makes it sound like she means in recent times, but there's no way of knowing if that's what she was actually talking about.

• that a lineage/family group can evolve a different skin color through environmental adaptation in as little as 50 to 100 generations (~2,500 years), with no intermarriage required;"

What she actually said was "Our original estimates were that this occurred perhaps at a more stately pace, but now we think that that process of change may have had to occur much more quickly." and "We might be thinking let's say 50 to 100 generations…". Notably she doesn't mention "without intermarriage" and she's not definite about the timespan ("may have had to" and "might be thinking"). She also says "We're talking about the rate of change during the earliest parts of the human evolution when we would not have had the nice togas or clothing that the man in Greece may have had." which is in direct contradiction to the "not that long ago" the reporter is claiming.

• that populations in present-day South India are an example of this, as they "re-evolved dark pigment" after having migrated down from Central Asia"

She actually says "The people now living in southern parts of India are extremely darkly pigmented." and, in a separate soundbite that may have preceded the first one or come much later when talking about a different topic, "They re-evolved dark pigment". She does not say that South Indians migrated down from Central Asia. She also doesn't state that South Indians re-evolved dark skin, although the editing would make it appear so. Without the source context there no way to know if those two statements are about the same or completely separate topics.

• (she mentions the indigenous peoples of the New World as another example in her 2012 paper [17]);"

She does mention North Americans in her 2012 paper, but not "as another example" like you misinterpret. She mentions them as a 'probable' alternative/adjunct to tanning and then concedes that there is no actual evidence of a second evolution of dark skin:

Dispersal of human populations into latitudes between about 23° and 46° was accompanied by the evolution of partially depigmented phenotypes capable of tanning. Many such populations probably represent repigmented descendants of previously depigmented peoples—such as in the case of the indigenous peoples of the New World—but identification of candidate loci associated with evolution of secondary dark pigmentation is still in its early stages

In any case India covers latitudes 6° to 35°, so this would only apply to northern India, not to southern India and Sri Lanka which are the areas that we are discussing.

The article makes it look like it's Jablonski making the claims, but without the source context for her quotes it's impossible to know what Jablonski actually said and what is being extrapolated by the reporter and editor. The best we can do is to find corroboration in other publications and the best I've found there suggests she means tanning when talking about "repigmentation". I could find no mention of the "50-100 generations" claim in any of her other work. If the NPR story were a reliable source then it would be possible to find other publications that agree with it. If you have other sources that support the claims in the NPR story then please supply them, otherwise I'll consider the discussion closed.

Tobus2 (talk) 04:50, 14 July 2013 (UTC)

With respect, there's no sense in arguing that Jablonski did not make those statements since it's indicated in the NPR piece [8] that she in fact did. Those assertions are clearly attributed to her, not to the interviewer. Krulwich didn't, for example, come up with the 100 generations rate of change by himself. That is Jablonski's own new estimate, given the recent advances in genomic technology:

"Skin has changed color in human lineages much faster than scientists had previously supposed, even without intermarriage, Jablonski says[...] And with the help of paleontologists and anthropologists, scientists can go further: They can wind the clock back and see what colors these populations were going back tens of thousands of years, says Jablonski. She says that for many families on the planet, if we look back only 100 or 200 generations (that's as few as 2,500 years), "almost all of us were in a different place and we had a different color."

Jablonski explains further in a 2011 article of hers that such major skin color changes can occur in just a few thousand years through selective sweeps, which greatly accelerate populational shifts in pigmentation:

"Light skin is actually depigmented skin. When people started moving away from very sunny places with high levels of UVB to less sunny places with lower levels of UVB, those individuals who had lighter skin were able to stay healthier and leave more offspring. Evolution was at work again. The individuals with lighter skin had specific genetic mutations that resulted in their producing less eumelanin and so having less natural sunscreen in their skin. These new patterns of genetic variation were very successful. We see evidence, in fact, that “selective sweeps” – greatly accelerated periods of evolution by natural selection – led to genes for lighter skin becoming fixed in the population over the course of just a few thousand years."

This is what National Geographic means as well when it asserts that "scientists believe that major changes in skin color can happen in the relatively short evolutionary period of some 100 generations[...] notably, skin color can change from both dark to light and light to dark." Soupforone (talk) 21:41, 14 July 2013 (UTC)

I understand you have faith in the NPR reporter, but I'm highly sceptical. He makes claims that are outside the generally accepted consensus on the topic. He attributes these claims to one of the leading researchers in the field but they're not in any of her research papers. He quotes her multiple times - always agreeing with and supplementing the claims but somehow never actually saying them. It rings major alarm bells to me, made doubly strong by it not being from a particularly respected publisher and by it being presented in such a simplistic way. You may choose to take everything in the story at face value, but before I accept it as fact I want to see it confirmed somewhere else.

By contrast the other two sources you give are much more reliable, both are in publications with high editorial integrity and both make statements that are consistent with the scientific consensus. (I make particular note that neither mentions "without intermarriage" nor claims that South Indians once had light skin.) How would you feel about basing something on one or both of these sources instead of the NPR story?

Tobus2 (talk) 13:08, 15 July 2013 (UTC)

The Jablonski & NatGeo sources could work. Here is a summary of Jablonski and her husband Chaplin's current research, from the Orthomolecular Medicine News Service (January 17, 2013) [9]:

”Jablonski and Chaplin have published a series of papers on human skin pigmentation and its relation to solar ultraviolet radiation (UVR) [Jablonski and Chaplin, 2012]. Their primary thesis is that human skin pigmentation has adapted to UVR conditions where a group of people live for 50 generations, or about a thousand years. UVR from mid-day sunlight produces vitamin D, which provides important protection against many diseases, but sunlight also causes skin cancer and destruction of folate. Dark skin protects against free radical production, damage to DNA, cancer, and loss of folate. Thus, dark skin is best in the tropical planes regions while pale skin is best at high latitude regions. Those with skin adapted to UVB between 23° and 46° have the ability to tan, which is an adaptation to seasonal changes in solar UVB doses. However, in recent times, people have moved or traveled to regions where their skin pigmentation is not suited to the local UVR conditions. They discuss three examples: nutritional rickets, multiple sclerosis and melanoma. Their abstract concludes with this observation: "Low UVB levels and vitamin D deficiencies produced by changes in location and lifestyle pose some of the most serious disease risks of the twenty-first century."” Soupforone (talk) 21:21, 15 July 2013 (UTC)

This is not such a good source, Orthomolecular medicine is generally considered a pseudo-science and so being published in the "Orthomolecular Medicine New Service" doesn't give a ref much credibility. I'd be sceptical of anything that publication says unless it can be verified elsewhere. In this case it's verified by the Jablonski 2000 and the NatGeo refs you provided in your last post and since they are the more reliable publications you might as well just use those as refs instead.

I'm happy for you to add content back in that is supported by NatGeo and/or Jablonski's work, but not claims that are made solely in the NPR story. In particular this would mean not saying the speed is without intermarriage and not saying that South Indians were once light-skinned. It sounds like you are OK with this so perhaps we can agree and consider the matter resolved?

Tobus2 (talk) 00:47, 16 July 2013 (UTC)

The “without intermarriage” is inherent in Jablonski and Chaplin's thesis since the latter is centered on environmental adaptation. Given this, I guess the phrase could be left out. The repigmentation of South Indians as they first moved into the Indian Subcontinent from Central Asia must, however, be included. It serves as a real life example of the kind of major change in skin pigmentation that is possible in the given timeframe. In the NPR transcript, Jablonski also clearly states that South Indians “re-evolved dark pigment.” Soupforone (talk) 21:34, 16 July 2013 (UTC)

We can't include a controversial claim unless it's verified by a reliable source, and without confirmation the NPR transcript is not a reliable source. We've found two reliable sources that confirm that skin colour can, under strong selection, change within a few thousand years (although neither states "without intermarriage" as NPR claims), but the claims about South Indians re-evolving dark skin don't seem to be independently verifiable. Tobus2 (talk) 12:28, 17 July 2013 (UTC)

Jablonski states the same thing with regard to South Indians in another interview [10], this time with her alma mater Bryn Mawr College: "“Light skin evolved more than once in human history, in Western Europe and in East Asia,” says Jablonski. “Dark skin re-evolved once and perhaps twice in populations dispersing into Melanesia and the southernmost part of the Indian subcontinent.”" She also has an alumnus page there [11]. Soupforone (talk) 21:57, 17 July 2013 (UTC)

This is a more reliable source and one that I'm happy to take at face value. The sentence you quote is unusual because it's at odds with accepted genetic evidence that South Asians and Melanesians share the same "dark skin genes" as Africans. Rereading some of Jablonski's research papers it seems that her claim is a hypothetical extrapolation of the effect of UV on skin colour based on the evidence available at the time:

• After first discovering the association between UV and skin colour she says "Thus, it is likely that some human lineages through time may have gone through alternating periods of depigmentation and pigmentation (or vice versa) as they moved from one UVMED regime to another." [12]. This was in 2000 before there was any positive association with any skin depigmentation alleles.
• She states something similar in 2004 and suggests MC1R as the responsible gene: "The production of eumelanin is under strong functional constraint as a result of natural selection in regions of the world with high levels of UVR, and there is increasing evidence that at least MC1R variation is an adaptive response to selection for different alleles in different environments". [13] In the same article she goes on to say "it appears that populations of humans have moved in and out of regions with different UVR regimes over the course of thousands of years. This finding would suggest that natural selection would have favored the evolution of dark and light skin pigmentation in disparate places at different times, resulting in the independent evolution of dark and light skin phenotypes and possibly involving recurrent episodes of repigmentation and depigmentation." At this stage she had proven a correlation with UV and skin colour, there was a known association of constrained MC1R with dark skin and evidence of relaxed MC1R contraints outside of Africa, but still no positive identification of skin depigmentation alleles. Her paper fits with the expectation that the highly variant MC1R would turn out to be primary cause of depigmentation and, due to the range and number of MC1R variants, the possibility of skin colour changing rapidly and often would have seemed a certainty.
• Between 2005 and 2007 a number of genes were positively associated with skin colour. In 2006 the first evidence was found that SLC24A5 and SLC45A2 account for a significant portion of European depigmentation and it was proven that light skin evolved independently in European and East Asian populations, adding further support for the idea that skin colour was highly variable.
• It was at this time, and in this context, that she makes the claim (in the 2007 interview [14]) that "Dark skin re-evolved once and perhaps twice in populations dispersing into Melanesia and the southernmost part of the Indian subcontinent" after the populations left Africa and spent lengthy periods in lower UV environments some 50,000 years ago. She makes a similar claim including Australian Aboriginals this time in a 2008 talk [15] where she says "So deeply pigmented skin evolved in early homo sapiens and has been maintained very stongly in equatorial Africa, but it has also evolved and we can make an excellent circumstantial case for it having evolved at least twice more, perhaps even more, independently in the ancestors of Australasians and southern Indians". The NRP story came out shortly after in early 2009 with a similar claim.

It's worth noting that all these papers talk about the possibility of repigmentation (note the use of likely, may, possibly, suggest etc.)... she's aware there's no known genetic mechanism for it and no population studies that support it. But if you take the "circumstantial" evidence of populations moving though varying UV environments, combine it with a highly variable MC1R and add to that the plethora of studies discovering skin colour alleles in other genes and proving that light skin evolved multiple times, it's easy to see how she would believe that confirmation of her repigmentation theory was just a matter of time. Since then however, there have been a few studies reinforcing the known associations, but almost no new skin colour alleles have been found. Just about all the skin colour ranges on the planet have been attributed to admixture of the original darker "African" alleles and the lighter "European" or "Asian" ones. It has been shown that the relaxed MC1R variants aren't responsible for population-level skin colour and have not been subject to selection. As time goes on it becomes more and more accepted that the "multiple evolution" of light skin is just twice and no evidence for a re-evolution of dark skin has surfaced. Jablonski's later papers reflect this:

• In 2010 [16]she says "Evidence is mounting that darkly pigmented skin, or the potential for facultative development of dark pigmentation through tanning, evolved secondarily under positive selection in populations moving from low-to-high-UVR environments." - introducing tanning, the only proven mechanism for repigmentation. Later in the same paper: ""Hominins and modern humans dispersed independently many times into nontropical latitudes and evolved depigmented phenotypes by numerous and different genetically based means, some of which remain to be illuminated. It is important to stress that habitation of middle latitudes between approximately 23° and 46° involved the evolution of partially depigmented phenotypes capable of tanning."... the "repigmentation" idea is noticeably absent and has been replaced by tanning: ""Depigmented and tannable skin evolved numerous times in hominin evolution via independent genetic pathways under positive selection"
• Another 2010 paper confirms this shift to a dark/light/tanning theory: "The stable gradient of skin colors observed from the equator to the poles is the product of two conflicting clines operating over a spatially varying optimum of UVR distribution. One of these emphasizes photoprotection by dark pigmentation near the equator, and the other emphasizes photosynthesis of vitamin D facilitated by light pigmentation near the poles. Moderately pigmented skin, which can develop a tan in the presence of high UVR in the summer and then lose melanin pigment again in the absence of strong UVR in the winter, is a characteristic of humans inhabiting middle latitudes and experiencing seasonal UVR regimes" [17]
• And again in 2011: "As modern humans moved around the world in greater numbers and over longer distances in the time between 50,000 and 10,000 years ago, a lot of “fine tuning” occurred in the evolution of skin pigmentation. As populations moved to parts of the world with different UVR levels, they underwent genetic changes that modified their skin pigmentation. As people moved into the Americas from Asia, for instance, we see evidence that some populations entering high UVR environments underwent genetic changes which made it possible for them to tan easily. Tanning is the ability to develop temporary melanin pigmentation in the skin in response to UVR and has evolved numerous times in peoples living under highly seasonal patterns of sunshine" [18]
• Same thing in 2012: ""Members of the human lineage dispersed many times independently into non-tropical latitudes, and evolved depigmented phenotypes by numerous and different genetically based means, some of which remain to be illuminated. Habitation of middle latitudes between approximately 23° and 46° with seasonally high loads of UVB favored the evolution of partially depigmented phenotypes capable of tanning. [19]
• ... twice: "This has been proved by genetic evidence for selective sweeps having established depigmented integumental phenotypes independently in the ancestors of western Europeans and eastern Asians and probably also in Homo neanderthalensis. Dispersal of human populations into latitudes between about 23° and 46° was accompanied by the evolution of partially depigmented phenotypes capable of tanning." [20]

It's quite clear that the hypothetical idea of populations "re-evolving" dark skin based on circumstantial evidence disappeared after the initial rush of research in 2006-7, to be replaced by a concrete assertion of the proven evolution of repigmentation by tanning. It is interesting to note that in both the two 2012 papers she mentions the repigmentation idea as an unproved possibility in reference to New World populations, but there is no mention of South Indian or Australasians. She does mention India in the 2011 paper, but it's about "the dispersal of lightly and moderately pigmented “Ancestral North Indians” into high-UVR reaches of the Indian subcontinent", a clear case of admixture since there were already darkly-pigmented "Ancestral South Indians" living there. So, if you want to use this ref to mention the idea that South Indians were once light-skinned and re-evolved dark skin, you will need to make sure you put it in context and make sure it doesn't sound like a statement of fact. It's certainly a possibility, but at the present time it's hypothetical with no hard evidence or research to support it. Personally I think something like what the NatGeo says would be sufficient. Tobus2 (talk) 16:12, 18 July 2013 (UTC)

Thanks for this; quite informative. It would appear that Jablonski once theorized that Australian Aboriginals may have re-pigmented as well. Her specification on page 6 of the 2011 paper with Chaplin that Ancestral North Indians may have re-darkened does not, though, seem to be attributed to admixture with in situ Ancestral South Indians, but rather to a selective sweep once the ANI reached the high UVR areas of the Indian subcontinent [21]: "Evidence is mounting that darkly pigmented skin, or the potential for facultative development of dark pigmentation through tanning, evolved secondarily under positive selection in populations moving from low- to high-UVR environments. Pigmentary changes such as these appear to have occurred following the dispersal of lightly and moderately pigmented “Ancestral North Indians” into high-UVR reaches of the Indian subcontinent and in lightly and moderately pigmented east Asians moving into the high-UVR environments of Central and mountainous South America". Jablonski appears to be suggesting here that the ANI re-pigmented once they moved into southern India since that is the part of the subcontinent where her and Chaplin's UVA & UVB maps are at their most intense [22], [23]. Soupforone (talk) 23:28, 18 July 2013 (UTC)

I think part of the problem here is one of terminology, in particular "evolution" doesn't always mean a de novo mutation. For a population to undergo selection, the allele being selected for must already exist in the population, even if only in minor frequencies. In cases of new traits this is usually from a de novo mutation, but for traits that once existed in the population's ancestors the allele could still be present as a minor allele in a heterozygous population, and for traits that exist in other populations it can be introduced via admixture. So when Jablonski says "evolved secondarily under positive selection in populations moving from low- to high-UVR environments" this doesn't necessarily mean a novel mutation in a skin pigmentation gene.

In the case of the ANI migration into southern India, admixture is a proven source of the dark-skin alleles. Jablonski provides a reference for her statements about ANI, which says:

We analyze 25 diverse groups to provide strong evidence for two ancient populations, genetically divergent, that are ancestral to most Indians today. One, the “Ancestral North Indians” (ANI), is genetically close to Middle Easterners, Central Asians, and Europeans, while the other, the “Ancestral South Indians” (ASI), is as distinct from ANI and East Asians as they are from each other. By introducing methods that can estimate ancestry without accurate ancestral populations, we show that ANI ancestry ranges from 39-71% in India, and is higher in traditionally upper caste and Indo-European speakers. Groups with only ASI ancestry may no longer exist in mainland India. However, the Andamanese are an ASI-related group without ANI ancestry, showing that the peopling of the islands must have occurred before ANI-ASI gene flow on the mainland.[24]

So she is well aware that the ANI interbred with the ASI as they migrated south and that this would have provided plenty of dark-skin alleles for the UV selection to work with. On top of this she also states that the ANI where "lightly and moderately" pigmented, indicating that they were already heterozygous for dark skin to some degree. Even without the ASI admixture they would have not have needed a de novo mutation in order to undergo repigmention.

Also, I don't think this is the scenario Jablonski was talking about in her 2007-9 interviews/speeches. In those she talks about the proposed repigmentation affecting Melanesians and Australians as well as Indians. I think she's talking about the original populating of India (and then Melanesia and Australia) some 50,000 years ago during the initial Out Of Africa dispersal. She doesn't make it totally clear but there are a few clues here and there that I can dig up if you think otherwise. The main clue is that the ANI migration was only 3-4,000 years ago and she notes (in the NPR transcript) that she's talking about a time before clothing and housing, "when we were naked and moving". The currently favoured Coastal Migration Theory allows for the migration from Africa to India, Melanesia and Australia without the need to go much out of the tropics, but they weren't necessarily travelling in a straight line and I guess it's feasible that some groups may have ventured north and experienced periods of a reduced contraint for dark skin. It's highly unlikely however that any of these hypothetical groups that eventually made it to Australia would have gone far enough north to completely lose the dark alleles and become "fixed" for light skin as happened subsequently in northern Europe. There would also have been continual contact with the people "behind" them and so a link to dark alleles via admixture is also highly likely. So even if any of these early OOA groups did undergo some degree of depigmentation in lower UV environments, they would not have needed a de novo mutation to become repigmented when they returned to the high UV areas. In short, as the NatGeo page says, "skin color can change from both dark to light and light to dark" (and probably has done so within the same population) but this does not require a new genetic mechanism each time - admixture and/or selection in heterozygous populations can account for all of it by allowing the reuse of existing mechanisms. As it currently stands, the only proven new mutations for repigmenting light skin are those responsible for tanning.

Tobus2 (talk) 12:51, 19 July 2013 (UTC)

Although Reich et al. (2009) presents an admixture model between incoming Ancestral North Indians and in situ Ancestral South Indians, it doesn't appear that Jablonski believes that this is the particular mechanism through which the dark skin pigmentation that is present in modern South Indians evolved. She suggests instead that it may have been due to environmental adaptation. Hence, why she likens the re-pigmenting of ANI peoples in high-UVR Southern India to the re-pigmenting of East Asian migrants in high-UVR Latin America. This particular migration from Central Asia into the Indian subcontinent is indeed held to have happened relatively recently. With respect to the much older Out-of-Africa exodus (which I agree Jablonski was referring to in her pre-2009 works), Jablonski's thesis still seems to have involved the movement of depigmented peoples from the direction of Central Asia southward into high-UVR Southern India and Sri Lanka, where they subsequently underwent repigmentation [25]:

"Imagine, for instance, the populations that went from East Africa and slowly made their way into central Asia or northern Asia. These populations would have had to undergo quite extensive depigmentation in order to maintain enough Vitamin D synthesis potential in their skin. But imagine some of these populations that were eventually on their way into Southern India, or what is now Sri Lanka. Those populations that also originated, ultimately, in eastern Africa would have undergone some depigmentation as they moved out of the most intense UV of the tropics, and then they would have undergone repigmentation as they moved down, back into the intense ultraviolet regimes of southern India and Sri Lanka. This same pattern of intense pigmentation to start out with, followed by a period of depigmentation perhaps 10, 20, or 30 thousand years long, followed again by another period of repigmentation, I think has been followed by many different populations as they have gone from one part of the world to another. It's not a deterministic process; it's simply an adaptive process as these populations have changed from one area with one particular ultraviolet light regime to another." Soupforone (talk) 21:36, 19 July 2013 (UTC)

I'm not saying that the ANI/ASI admixture is responsible for the paticular degree of skin pigmentation in today's Indians, I'm saying that on a genetic level, the alleles required for such a repigmentation were provided by the ASI ancestors (and probably also present in heterozygous ANI ancestors) and were not a new mutation. Since it's been 3-4,000 years since the initial admixture, I'm happy to accept that the particular range of pigmentation today is caused by adaptation to UV, my point is simply that this is not (and Jablonski doesn't say it is) due to a "re-evolution" in the sense of a new genetic mutation. As I said in my last post, the initial OOA migration to India and Australasia could potentially have resulted in a repigmentation but it's highly circumstantial (note the "Imagine.." at the start of your last quote) and highly unlikely that any such hypothetical repigmentation would have needed a new mutation either. Tobus2 (talk) 13:50, 20 July 2013 (UTC)

Ok, but Jablonski does not appear to suggest that a mutation/polymorphism was necessary for the repigmentation of the ANI to have occurred. What she states is that they adapted long-term to their new high-UVR environment in South India. Soupforone (talk) 21:25, 20 July 2013 (UTC)

By the way, there was an error under the SLC24A5 gene. It stated that it is “fixed in European populations and absent from populations that have no European admixture”. While the mutation is of course at fixation in European populations, it is not restricted to Europe nor is its presence in most other areas due to European admixture. In all likelihood, the gene evolved in West Asia and dispersed from there to Europe, the Middle East, North Africa, the Horn of Africa, and South Asia, where it is today found at high frequencies. Soupforone (talk) 21:25, 20 July 2013 (UTC)

Can you please explain how they adapted without a mutation/polymorphism?

All those populations you mention have European admixture, so the text is correct.

Please also note that it's not the ANI that have repigmented. The ANI and ASI merged to create modern Indians and it's this merged population, "following the dispersal of" the ANI, that Jablonksi is referring to. Every modern Indian has at least one ANI and at least one ASI ancestor, it makes no sense to say their ancestors once had light skin and repigmented - would you say that Halle Berry's ancestors were once white but are now darker?

Tobus2 (talk) 13:18, 21 July 2013 (UTC)

I'm aware of the ANI/ASI dynamic; Reich et al. (2009) discuss it. Jablonski and Chaplin only mention the things in the post above from 23:28, 18 July 2013 (UTC). Anyway, here's the wikitext with the relevant links; please point out what exact phrase(s) you're referring to: More recent research has found that human populations over the past 50,000 years have changed from dark-skinned to light-skinned and vice versa.[26] According to specialist Nina Jablonski, head of Penn State's Department of Anthropology, darkly-pigmented modern populations in South India and Sri Lanka are an example of this, having redarkened after their ancestors migrated down from areas much farther north.[27] Scientists originally believed that such shifts in pigmentation occurred relatively slowly. However, researchers have since observed that major changes in skin coloration can happen on a much shorter evolutionary scale, in as little as 100 generations (~2,500 years) through selective sweeps.[28][29] Soupforone (talk) 21:58, 21 July 2013 (UTC)

Regarding SLC24A5 - the gene's presence in its high areas of concentration outside of Europe is not mainly due to European admixture. This was previously assumed to have been the situation, but now researchers have a better understanding of the gene's global distribution. West Asia instead seems to have been its center of evolution [30]. Soupforone (talk) 21:58, 21 July 2013 (UTC)

(Further discussion of SLC24A5 moved to own section Tobus2 (talk) 00:16, 23 July 2013 (UTC))

I was talking about the statements in your previous two posts: "she likens the re-pigmenting of ANI peoples" and "was necessary for the repigmentation of the ANI to have occurred". I let it go as a mistake the first time but after the second it was apparent you didn't understand that it wasn't the ANI who repigmented nor that ASI are as much the ancestors of modern Indians as the ANI are (in some cases more so). With this understanding now clear, the statement that you added to the article: "modern populations in South India and Sri Lanka are an example of this, having redarkened after their ancestors migrated down from areas much farther north", makes no sense. Tobus2 (talk) 11:45, 22 July 2013 (UTC)

What I indicated in the wikitext is what Jablonski actually states. She does not mention ASI. Anyway, if it's still uncertain what she means here, we can always email her for clarification. As a professor, I'm sure she'd be happy to oblige. Soupforone (talk) 21:34, 22 July 2013 (UTC)

What Jablonski actually states is:

"Evidence is mounting that darkly pigmented skin, or the potential for facultative development of dark pigmentation through tanning, evolved secondarily under positive selection in populations moving from low- to high-UVR environments. Pigmentary changes such as these appear to have occurred following the dispersal of lightly and moderately pigmented “Ancestral North Indians” into high-UVR reaches of the Indian subcontinent and in lightly and moderately pigmented east Asians moving into the high-UVR environments of Central and mountainous South America".

Your interpretation of this is:

" More recent research has found that human populations over the past 50,000 years have changed from dark-skinned to light-skinned and vice versa. According to specialist Nina Jablonski, head of Penn State's Department of Anthropology, darkly-pigmented modern populations in South India and Sri Lanka are an example of this, having redarkened after their ancestors migrated down from areas much farther north".

Note that Jablonski says:

• "evidence in mounting" whereas you say "research has found"
• "appear to have occurred" whereas you say "are an example of this"
• "following the dispersal of lightly and moderately pigmented “Ancestral North Indians” into high-UVR reaches of the Indian subcontinent" whereas you say "after their ancestors migrated down from areas much farther north".

Certainly you have caught the general gist of what she is getting at, but you have stated it as fact where she hasn't and you've made assumptions about both the ancestry and the distance which she doesn't say. If you take what she actually said with the known ANI/ASI admixture of today's southern Indians you'd have to say with something like "Jablonski suggests that repigmentation after the ANI dispersal may have occurred due to UV adaptation but genetic evidence shows significant and widespread admixture with an already dark-skinned population"... it'd better not to mention it at all IMHO, after all it's just something she suggested once.

So, you *could* email Jablonski to see what she meant, I'm sure she loves spending her time solving minor Wikipedia disputes, or you could just accept that the ANI example is a rather poor one and drop it.

Tobus2 (talk) 01:03, 23 July 2013 (UTC)

Actually, the 50,000 maximal date was taken from Jablonski's solo 2011 article [31], not from Jablonski and Chaplin's 2010 paper [32]. In any event, here is what I actually wrote:

More recent research has found that human populations over the past 50,000 years have changed from dark-skinned to light-skinned and vice versa.[33] According to specialist Nina Jablonski, head of Penn State's Department of Anthropology, darkly-pigmented modern populations in South India and Sri Lanka are an example of this, having redarkened after their ancestors migrated down from areas much farther north.[34] Scientists originally believed that such shifts in pigmentation occurred relatively slowly. However, researchers have since observed that major changes in skin coloration can happen on a much shorter evolutionary scale, in as little as 100 generations (~2,500 years) through selective sweeps.[35][36]

Here are each of those wikitext assertions, with the supporting statements from Jablonski and NatGeo below them:

• "More recent research has found that human populations over the past 50,000 years have changed from dark-skinned to light-skinned and vice versa."
  • "Similar skin colors – both dark and light – have evolved independently multiple times in human history[...] As modern humans moved around the world in greater numbers and over longer distances in the time between 50,000 and 10,000 years ago, a lot of “fine tuning” occurred in the evolution of skin pigmentation"[37]
• "According to specialist Nina Jablonski, head of Penn State's Department of Anthropology, darkly-pigmented modern populations in South India and Sri Lanka are an example of this, having redarkened after their ancestors migrated down from areas much farther north."
  • "Imagine, for instance, the populations that went from East Africa and slowly made their way into central Asia or northern Asia. These populations would have had to undergo quite extensive depigmentation in order to maintain enough Vitamin D synthesis potential in their skin. But imagine some of these populations that were eventually on their way into Southern India, or what is now Sri Lanka. Those populations that also originated, ultimately, in eastern Africa would have undergone some depigmentation as they moved out of the most intense UV of the tropics, and then they would have undergone repigmentation as they moved down, back into the intense ultraviolet regimes of southern India and Sri Lanka."[38]
• "Scientists originally believed that such shifts in pigmentation occurred relatively slowly. However, researchers have since observed that major changes in skin coloration can happen on a much shorter evolutionary scale, in as little as 100 generations (~2,500 years) through selective sweeps."
  • "Scientists believe that major changes in skin color can happen in the relatively short evolutionary period of some 100 generations. Notably, skin color can change from both dark to light and light to dark."[39]
  • "We see evidence, in fact, that “selective sweeps” – greatly accelerated periods of evolution by natural selection – led to genes for lighter skin becoming fixed in the population over the course of just a few thousand years."[40] Soupforone (talk) 22:22, 23 July 2013 (UTC)

Hang on a second, aren't we talking about the ANI dispersal ~4000 years ago? You're suddenly saying it's about the original OOA about ~50,000 years ago. Please make up your mind.

Still, you've clearly missed my point, even though I specifically highlighted the phrases I have issue with. I'll repeat, try to pay attention this time:

• You can't say "recent research has found" something unless some recent research has found it. The idea of repigmentation is a theory of Jablonski's not a proven fact in any peer-reviewed published research.
• You can't say "according to ..[A], [B].. is an example of this" unless A actually has said it's an example. Jablonski uses it as a hypothetical possibility based on circumstantial evidence, not as a concrete example of something that definitely happened.
• My third point is a bit moot now that you've changed the repigmentation event you are talking about, but note that "their ancestors migrated down from areas much farther north" is at odds with the leading theory on the route taken by the OOA migration which doesn't have the first south Indians coming from very far north at all - the coastal route would have them pretty much in the topics all the way to Australia.

You should note that I accept Jablonski's theory as a possibily (even a probability) and the claims that humans have repigmented and that pigmentation change can happen quickly are already discussed in both the lead and the evolution section. My issues with your most recent edit are: a) presenting a theory as fact, and b) singling out one population as an example when there is no concrete evidence that it actually applies to them. Tobus2 (talk) 10:11, 24 July 2013 (UTC)

The “more recent research has found that...” phrase can be changed to “scientists now believe that...”. Regarding the South Indian example, I suppose it could be somewhat confusing since Jablonski in different papers uses modern South Indians as an example of both older OOA-linked and recent ANI-associated repigmentation. Soupforone (talk) 21:28, 24 July 2013 (UTC)

... except that scientists don't "now believe that"... from the evidence we've seen, a scientist proposed a theory that it may have happened. Tobus2 (talk) 15:37, 25 July 2013 (UTC)

Per National Geographic, they do [41]: "scientists believe that major changes in skin color can happen in the relatively short evolutionary period of some 100 generations[...] notably, skin color can change from both dark to light and light to dark." Soupforone (talk) 22:24, 25 July 2013 (UTC)

OK, I'll accept that :) Tobus2 (talk) 06:58, 26 July 2013 (UTC)