Why are we different colors?

The most striking difference among human populations, or “races” (a loaded term that I discuss in WEIT), is skin color.  As we all know, and as the following diagram shows, populations from tropical areas have darker skin than do populations from higher latitudes:

Fig. 1.  Distribution of skin pigmentation among human populations (from Encylopedia Brittanica)

What causes this variation?  Various theories have been suggested, including sexual selection for different skin tones in different places, but because of the strong correlation between pigmentation and amount of sunlight, biologists have suggested that pigmentation differences are a result of natural selection imposed by different light levels in different places.  Here’s the amount of light (measured as total annual UV) in different areas of the world (note: the original figure that was here was incorrect: the source implied that it was yearlong UV incidence but it was actually for the month of November only, which accounted for its asymmetry around the equator).

Fig. 2 (from Jablonski and Chaplin 2010): Annual mean UVA (380 nm). Intensity is indicated by gradations from dark to light varying from 65 to 930 Jm−2 in 10 steps with oceans partially grayed-out.

The idea that pigmentation evolved as an adaptation to light levels is supported by the observation of facultative changes in pigmentation that occur with higher exposure, that is, tanning.  Light-skinned people get darker when exposed to more sun.

These differences among populations almost certainly represent more than one evolutionary event.  First, although we don’t have fossil skin from our African hominin ancestors like Homo erectus, it’s likely that they were dark, as are African populations now.  But even earlier ancestors may have been lighter. If you look at our closest relatives, chimps and gorillas, you see that their skin (at least those parts under the hair) is unpigmented.  Only the exposed parts are pigmented.  The ancestral color of humans, then, was probably light (but not as light as, say, Swedes) and then, as we became “naked apes,” evolved to a darker shade. (The evolution of hairlessness in our species is another matter, perhaps involving our ability to sweat.)

Then, as the presumably dark populations of humans moved into the Middle East and Europe, they evolved lighter skin color.  But when those populations colonized Australia, skin color got dark again. This almost certainly happened, too, when humans moved from northern Asia across the Bering Strait and down into the Americas: those populations that reached Central and South America likely re-evolved dark pigmentation.

What were the selective pressures that caused these changes?  For a long time I accepted the “classic” story that was taught in school:  populations getting more sunlight evolved darker skin as protection against UV-induced melanomas and the toxic effects of too much vitamin D3, which is produced only by sunlight striking the skin.  In low-light areas, skin evolved a lighter shade because we need fair amounts of vitamin D3 to build strong bones (without it, children get rickets, which is why foods like milk often have added vitamin D).  Thus, dark-skinned ancestors in the tropics would have reduced vitamin D toxicity and fewer melanomas, while lighter ancestors in the temperate zones would have stronger bones.  This could cause differential mortality or reproduction that would explain the differences in pigmentation.

The problem with this story is just that—it’s a story.  Although this scenario sounds plausible, there wasn’t much hard evidence supporting it, at least not when I was in school.  A recent paper in PNAS by Nina Jablonski and George Chaplin summarizes the latest evidence and comes to some different conclusions about the evolution of human skin color.  Their findings:

Why tropical populations are darker. Probably not because of melanomas. The authors dismiss this:

Sunburn and skin cancer have negligible effects on reproductive success (7, 18). Nonmelanoma skin cancers are common in older individuals from modern lightly pigmented populations inhabiting sunny climes, but they are rarely fatal or incapacitating (20). Melanoma afflicts younger individuals and is often fatal, but it is much rarer than nonmelanoma skin cancers.

They also point out that most human skin cancers result from light-skinned individuals moving to the tropics, something that wouldn’t have occurred in our ancestors.  They conclude that “the effects of skin cancers on reproductive success in humans today are modest, and were probably statistically inconsequential before rapid, long-distance travel and migration.”

Jabonski and Chaplin also criticize the idea that too much vitamin D was another selective force: they say that “overproduction of vitamin D was refuted as the primary cause of the evolution of dark pigmentation by the discovery that hypervitamosis D due to sun exposure is physiologically impossible because of photochemical regulation.”

This was all news to me, and I was glad to hear it.  I won’t be telling my students so much about melanoma and vitamin toxicity when discussing the evolution of skin color.

If it’s not skin cancer or hypervitaminosis, then, what were the selective pressures? Jablonski and Chaplin suggest that it’s the quantity of folate (folic acid), one of the B vitamins that plays a crucial role in biosynthesis, including DNA synthesis and repair. In a paper published in 2000 which I had not previously seen (citation below), the authors floated the idea that because folate can be destroyed by sunlight in the blood vessels of the skin, the skin evolved to be darker to keep folate from being destroyed.  In the present paper, they specifically mention that an absence of folate could cause neural tube defects (NTDs) in human embryos, serving as a potent selective pressure.

I find the evidence for this theory intriguing but a bit thin.  The authors say that there is evidence of a “protective effect of dark pigmentation against folate depletion,” but looking up the studies cited I see only a correlation between “racial” origin and NTDs.  This might be due to factors other than pigmentation.   The authors seem on stronger ground when claiming that folate protects against neural tube defects, several studies show that supplementing women’s diets with folic acid leads to a significantly lower production of NTDs in their offspring.

Why populations experiencing less solar radiation are lighter. Here the authors pretty much accept the idea that selection is based on the need for vitamin D3, which not only builds bones, but plays a role in the immune response, cell proliferation, and functioning of the brain, heart, and pancreas.  Since folate is produced in the epidermis and dermis, it seems plausible that the skin got lighter to ensure adequate amounts of this important vitamin.  But again the evidence is not conclusive.  The strongest, cited in the 2000 paper, is that recent dark-skinned migrants from tropical to temperate areas (Ethiopia to Israel, India to the UK) tend to suffer from vitamin D deficiencies.

Why there is tanning? Jablonski and Chaplin suggest that tanning was an adaptation that evolved not to protect long-distance human migrants (since they didn’t exist in our ancestors), but to protect populations at intermediate latitudes where there is much greater seasonal variation in the amount of UV.  Seasonally variable pigmentation would be useful in protecting against folate depletion in high-UV seasons while allowing vitamin D synthesis during periods of low UV.

The work of Jablonski and Chaplin is intruiging, I’ll certainly be telling my students about the “folate hypothesis,” as well as about the evolution of tanning.  But I’ll insist that these ideas are tentative.  Studying the adaptive significance of human racial variation is a difficult task for two reasons.  First, we can’t do experiments on humans, except for medically-related ones like giving pregnant women folic acid.  We certainly can’t move people wholesale from place to place and look at the connection between their traits and their fitness, though we can in some cases take advantage of fortuitous migrants. In fruit flies, which are larger in more northern areas than in tropical areas, we can actually do experiments, and show that large body size evolves in the laboratory when we rear flies under cold conditions.

The other problem is that traits distinguishing human populations evolved a long time ago (between 60,000 and 10,000 years ago, when humans moved out of Africa and colonized North America and Australia), and we can only speculate about selective forces that occurred so long ago. (That said, the geographic distribution of UV light hasn’t changed much since then!)

It’s curious, but understandable, that we know so very little about the evolution of population differences in our own species.  We do know a bit about skin color, but as for nose shape, hair texture, eye folds, and body build—the other traits that distinguish human populations—our ignorance is deep.

__________

Jablonski, N. G. and G. Chaplin. 2010.  Human skin pigmentation as an adaptation to UV radiation.  Proc. Nat. Acad. Sci. USA 107(supp.):8962-8968.

Jablonski, N. G. and G. Chaplin. 2000.  The evolution of human skin coloration. J. Human Evolution 39:57-106.

64 Comments

  1. Tim
    Posted July 20, 2010 at 7:15 am | Permalink

    This could cause differential morality…that would explain the differences in pigmentation.

    Just like the Lamanites in the Book of Mormon?

    (I know you meant mortality, though.)

    • whyevolutionistrue
      Posted July 20, 2010 at 7:30 am | Permalink

      Whoops! Corrected, thanks.

  2. Posted July 20, 2010 at 7:23 am | Permalink

    Facinating stuff. Excellent breakdown, Dr. Coyne!

  3. Tim
    Posted July 20, 2010 at 7:36 am | Permalink

    I don’t know much about the colonization of Oceania; how do we know that the original Australian colonists were derived from a light(er)-skinned population? Is it because the modern inhabitants of southeast Asia are relatively lighter?

    • jdhuey
      Posted July 20, 2010 at 11:50 am | Permalink

      I just watched a show on the Travel Channel last night call ‘The Human Journey: Australia’ that, while it was pretty lite on content and tended a bit for a sensational tone, it did seemed to be fairly science based. One of the things shown was a tribe of people in Malaysia that are much more darked skinned than the general population. The speculation was that these are the descendant of that original migration of people from Africa to India to Malaysia to Australia. The main idea is that this migration took place very rapidly. This would speak against the idea that the dark skinned Africans became lighter skinned Asians that then became darker skinned Australians.

  4. Tim Martin
    Posted July 20, 2010 at 7:43 am | Permalink

    They also point out that most human skin cancers result from light-skinned individuals moving to the tropics, something that wouldn’t have occurred in our ancestors. They conclude that “the effects of skin cancers on reproductive success in humans today are modest, and were probably statistically inconsequential before rapid, long-distance travel and migration.”

    I don’t understand the logic in this section at all. The potential for more melanomas comes when there is a mismatch between skin darkness and UV exposure (i.e. Lots of UV, but light skin). To say that this mismatch wouldn’t have occurred in our ancestors doesn’t seem to answer the Why question at all. Perhaps the mismatch didn’t occur because different populations evolved to fit their environments as they migrated.

    Someone help me out here?

    • Tim Martin
      Posted July 20, 2010 at 7:50 am | Permalink

      New thought: What about light-skinned people born in the tropics? Do they develop a semi-permanent tan from a young age that protects them from melanomas? I can’t imagine most Irish people getting a tan no matter how long they work at it.

    • Thanny
      Posted July 20, 2010 at 11:48 am | Permalink

      You don’t understand the logic because it isn’t there.

      It’s a colossal blunder, in fact.

      The fact that light-skinned people relocating to the tropics are more likely to get melanomas is strong evidence in favor of increased melanin concentration being adaptive for preventing said melanomas. It’s as you say – if your skin is too light for where you live, you or your offspring are going to die earlier than those with darker skin.

      It’s not the first time I’ve seen evolutionary biologists confuse current conditions with selective conditions of the past. I get the impression that some of them are so eager for data that they don’t stop to consider the logic first.

      • whyevolutionistrue
        Posted July 20, 2010 at 12:01 pm | Permalink

        See comment under #11 below. Yes, this is some evidence, but not as strong as people might think given that the ancestral condition in Africa was almost certainly not skin as light as that of northerners. The relevant question is whether the ancestors in Africa (who presumably had skin of some intermediate–i.e., chimplike–color were prone to melanomas and that the incidence of that cancer in reproductive age decreased as that intermediate-toned skin got darker.

        It is useful to remember that the incidence of melanomas in current migrants from the north might not be near as large as that occurring in ancestral populations. But you’re right–the authors dismiss this possibility too quickly.

  5. Rixaeton
    Posted July 20, 2010 at 7:48 am | Permalink

    Just throwing an idea off the top of my head, but seeing a person that has a tan gives the first impression that the person is healthy, but I don’t know why that is an automatic reaction, (or even if it is an automatic reaction)? Maybe tanning is just another way of advertising the health of the individual, and that would be enough pressure? To me, the average British tourist that has obviously just spent their first holiday day at the beach in Australia is not that attractive, and probably doesn’t feel that attractive the next day either :) However, a British tourist on a walking holiday from London to Sydney would change colour more gradually, and be less “unappealing”

    Ugh – I hate myself sometimes, but I can’t help it.

    • anthrosciguy
      Posted July 20, 2010 at 12:19 pm | Permalink

      Cultural. In another time pale skin would be considered a sign of healthy people.

  6. Posted July 20, 2010 at 8:04 am | Permalink

    Can someone explain to me why the peak UV distribution is centered on a sub-equatorial latitude? I would have expected it to be dead on the equator…

    • Bill
      Posted July 20, 2010 at 8:12 am | Permalink

      Yeah, I’ll second that question. In Africa, those from the west seem generally to be a lot darker-skinned than those from southern Africa, and groups like the Khoi-San who had southern Africa to themselves before the arrival of darker-skinned African groups are much lighter again – which definitely doesn’t reflect the peak UV distribution. Any ideas?

      • Rixaeton
        Posted July 20, 2010 at 8:19 am | Permalink

        From the Natural Frequency website “(the grey area indicates areas where no data was recorded). ”

        It looks like the data just was not measured for the northern hemisphere? It could also be due to levels of ozone, where ozone depeletion is one of the factors that gives Australia the worst levels of skin cancer incidents. But these are really guesses.

      • Posted July 20, 2010 at 8:40 am | Permalink

        @Bill: Some of that is explicable by migrations that took place in the past 8,000-10,000 years or so, i.e. too recently for natural selection to have altered skin color that much. Another example is that SE Asian skin color is not as dark as one would expected (certainly lighter than similar latitudes in Africa)

        @Rixaeton: Yeah, but even if we ignore the gray areas, there is a definite shape to the data that is there… and it peaks at around 15-20 degrees south or so.

      • steve oberski
        Posted July 20, 2010 at 10:05 am | Permalink

        The Earth currently has an axial tilt of about 23.5°

        • Posted July 20, 2010 at 10:16 am | Permalink

          And….?

          Yes, the axial tilt is what gives us seasons. But, all other things being equal, the average amount of sunlight amortized over a year should be at its maximum over the equator (I recognize that meteorological phenomena will alter this somewhat, hence the “noisy” image). This is true regardless of the axial tilt. Hell, a 90-degree axial tilt should still have that condition.

          It’s only explicable if the chart represents summer in the southern hemisphere.

          • steve oberski
            Posted July 20, 2010 at 11:00 am | Permalink

            If the intensity of UV (and light in general) received by the earth increases as the angle of incidence between a normal to the earths surface and received light approaches zero then the approx 23 degree axial tilt would explain why the UV seems to peak at 15 – 20 degrees from the equator in the graph.

            Visualizing 3D objects is not my strong suite but I’d think that a 90 degree axial tilt would result in maximum light intensity at one of the poles.

            • Posted July 20, 2010 at 12:21 pm | Permalink

              If the earth were stationary in regards to the sun, everything you say would be correct. But the earth ORBITS the sun. Like I said, the axial tilt (combined with the orbit, which I thought was implied) is what gives us the seasons. The axial tilt means that in the “winter” months, the southern hemisphere is pointed towards the sun, and in the summer months, the northern hemisphere is pointed towards it.

              If you had a 90-degree axial tilt, yes, one of the poles would get 100% of the sunlight — for one day per year. As the planet orbited around the sun, the location closest to the sun would shift in latitude until eventually, half-a-year later, the other pole was getting 100% of the sunlight.

              Again. If this graph is representative of a time period that is summer in the southern hemisphere, then all is explained by axial tilt (i.e. the seasons). If it is supposed to be amortized over a year — which will cause the axial tilt to be averaged out as the earth orbits the sun — then something is up.

            • whyevolutionistrue
              Posted July 20, 2010 at 12:31 pm | Permalink

              Yup, you’re right. See my comment higher up. The original figure was for NOVEMBER ONLY; I’ve replaced it with a year-round one.

    • Dominic
      Posted July 20, 2010 at 8:59 am | Permalink

      Could it have been taken in the southern hemisphere summer?

      Would the cooler climate & ‘invention’ of clothes mean that if you were paler your exposed skin, though less in area, would be as good at vitamin D production as a larger more darkly pigmented area of skin?

    • whyevolutionistrue
      Posted July 20, 2010 at 12:27 pm | Permalink

      Sorry about that–the source from which I took the figure implied it was year-round UV, but I got an email pointing out that that figure was for NOVEMBER ONLY. That accounts for the asymmetry you saw. I’ve replaced it with the correct figure (for UV A only), now taken from the Jablonski and Chaplin paper.

    • Torbjörn Larsson, OM
      Posted July 20, 2010 at 1:25 pm | Permalink

      It is explained at the Natural Frequency website, as Sky Illuminance is “the total amount of light coming from it [the sky]” after accounting for overcast and pollution.

      • Torbjörn Larsson, OM
        Posted July 20, 2010 at 1:27 pm | Permalink

        And yes, one month worth of data would make for an even larger asymmetry. :-D

  7. Thomas Huld
    Posted July 20, 2010 at 8:17 am | Permalink

    Not a major point, but I don’t think Fig. 2 shows the annual UV exposure. It looks very skewed towards the southern hemisphere and it’s more likely to be an average for a shorter interval, during the southern hemisphere summer.

    If you go to

    http://visibleearth.nasa.gov/view_set.php?categoryID=2360

    you can see similar images which are one-month averages. Confusingly, each one seems to be for different seasons, but only the year is given (for the ones that show the whole earth).

    • Posted July 20, 2010 at 9:23 am | Permalink

      Ah, that would be more in keeping with my understanding of the distribution of skin color anyway. For instance, I had been lead to believe that the presence of very dark-skinned Africans stretching all the way to the southern coast was a result of the Bantu expansion, i.e. a group of dark-skinned people from equatorial Africa engaged in a sustained southern migration/conquest, displacing or slaughtering the lighter-skinned native peoples (e.g. Khoi-san, pygmy) in very much the spirit of the colonization of the Americas.

      I had also been led to believe that the dark-skinned Australian and New Zealand aboriginees were more likely the descendants of people who had migrated from/been forced out of southeast Asia after a migration/conquest by lighter-skinned peoples living in what is now China pushed them out.

      The chart Jerry posted confused me meteorologically, astronomically, anthropologically, and evolutionarily. All of that confusion would be dispelled if we can just confirm, “Oh, that was taken in December.”

  8. FloM
    Posted July 20, 2010 at 8:41 am | Permalink

    I guess there would be two obvious places to look for effects of UV radiation on folate and NTDs: Australia and South Africa. Both places have high UV exposure according to the map and have been settled by ‘whites’ at slightly different times. Though of course there may be many other confounding factors, such as genetic effects (founder effects) and technology that protects these people from adverse effects of radiation (houses, clothing)…

  9. Posted July 20, 2010 at 9:14 am | Permalink

    Fascinating, but you still haven’t answered the real question at hand, “How can an African American person evolve from a white person… we are different skin?”

    • Notagod
      Posted July 20, 2010 at 9:32 am | Permalink

      Wellll, the answer is obvious, dark skin christians really are more intelligent than light skin christians.

  10. Delusional
    Posted July 20, 2010 at 10:13 am | Permalink

    Would ya look at that. I just got through reading something in the New York Times about recent evolution in humans, and it included this very topic.

  11. GM
    Posted July 20, 2010 at 10:28 am | Permalink

    I am similarly confused with Mr. Martin @ post #4.

    The incidence of skin cancer today being due to mismatches from globe trotters is seemingly irrelevant for why we changed from skin pigmentation similar to our closest ancestors to much darker skin. In fact, this mismatch between light skin and high UV exposure in our ancestors may be the reason more pigmented skin evolved. Specifically, lethal skin cancers could have been more prevalent with this original mismatch.

    While the folate argument seems interesting, I am dubious of the authors’ rejection of UV exposure.

    • whyevolutionistrue
      Posted July 20, 2010 at 10:37 am | Permalink

      Yes, good point, which had completely escaped me in my haste. But it depends on how pigmented our African ancestors really were. Presumably they weren’t as white as, say, Swedes, so we need to know what the incidence of melanoma was (and at what ages it struck) in ancestors that were presumably lighter than today’s Africans but darker than Europeans.

      • Posted July 20, 2010 at 1:11 pm | Permalink

        Interesting that twice on this page Swedes are brought up as examples of light-skinned people. While they are not black, they are not that fair either. While to some extent the contrast with blond hair might make them look a bit darker than they are, they generally tend to be quite dark (at least if they have a tan, which most do), much darker than the people in the British Isles. Same for Norwegians. Danes are a bit fairer, as are Fins. I was at a conference in Oslo once and noticed that several Norwegians (or pure Norwegian ancestry) were darker than a participant from Sudan (of pure Sudan ancestry).

        • Torbjörn Larsson, OM
          Posted July 20, 2010 at 1:33 pm | Permalink

          And then you have to figure in the native Sami population, which seems to derive of Berber origin (no, really; from genome data). They can get very dark, and can have very dark hair and eyes.

          That certainly help them, even if it is happenstance: during winter specular reflection in ice and snow gives one helluva UV exposure, during summer the long days do well too.

  12. mk
    Posted July 20, 2010 at 10:56 am | Permalink

    Is it the case that darker skinned humans from tropical areas are darker in Africa slightly lighter in Australia and lighter still in the American tropics due to the time spent adapting in these areas?

  13. Posted July 20, 2010 at 11:07 am | Permalink

    James, my guess is that because the Earth is closer to the Sun in southern summer/northern winter, this gives a slight southern bias to the annual UV data.

    • Posted July 20, 2010 at 12:23 pm | Permalink

      That’s a pretty good answer… I’m surprised it would be so significant though!

      • Posted July 20, 2010 at 12:42 pm | Permalink

        Ah, the new Fig. 2 doesn’t show any obvious southern bias. As Emily Litella might say, “never mind”.

  14. Torbjörn Larsson, OM
    Posted July 20, 2010 at 1:45 pm | Permalink

    My beef with the original map is that it was sky illumination, not actually exposure when adjusted for day length and environment. (I haven’t checked the new one.)

    As I noted in another comment, specular reflection from ice and snow (and likely sea, for fishing populations) seems to give a large UV exposure during winter. At least you can get a sunburn if not careful, and the native still outdoor living population around here [Sweden] can get fairly tan year round.

    Certainly the facility to tan is helpful to preserve fitness (less sunburn!) even at high latitudes. I’m not sure it explains, say, the British vs Swede facility to tan though, its origin is likely coincidental on population migration. But perhaps it is at least reinforced by the environment?

    • Hempenstein
      Posted July 20, 2010 at 3:04 pm | Permalink

      As to the British vs. Swedish facility to tan, does it seem to be easier to get a tan in Stockholm, vs, say, Bergen or Göteborg, thanks to the difference in amount of incoming cloud cover from the North Sea? At least, I’d expect that an expanded view of Scandinavia would show greater sunlight on the SE region, just like SE Greenland and England on the map above.

    • whrrr
      Posted July 20, 2010 at 3:17 pm | Permalink

      “…large UV exposure during winter”

      Yes, but only on the 1/10 or 1/20th of your exposed body during shortened daylight hours. Which, depending on region and diet, probably made it even more critical for northern people to absorb sunlight as much possible for vitamin D.

  15. Charlie Jones
    Posted July 20, 2010 at 1:57 pm | Permalink

    The thing that puzzles me is the following:

    While the tropics do get the most intense sunlight, they also tend to have extensive forests and lots of rain (and hence clouds). Why would people living in the forests of equatorial Africa, Indonesia, and Papua-New Guinea be as dark skinned as their subtropical neighbors? (The subtropics, of course, tend to be arid and thus feature sparse vegetation and little cloud cover.) Did ancient Africans, Indonesians, and Papua-New Guineans open up patches in the forests (for agriculture?), or were they taken over by subtropical groups, or is something else selecting for skin color?

    If the intensity of UV hitting the ground is the key, I’d think that the subtropical peoples would be the darkest skinned on Earth.

  16. littlejohn
    Posted July 20, 2010 at 3:00 pm | Permalink

    I am not a scientist, so please forgive any glaring errors in my reasoning, and please don’t hesitate to correct my mistakes.
    First, I agree with you that reproductive fitness is probably not important, at least with respect to skin cancer. The obvious evidence is that recently transplanted Brits in Australia, aside from having a deep tan, seem to be doing quite well.
    Second, I notice no one has mentioned a factor that seems obvious to me: Sexual selection. I dread getting politically incorrect, but it is a commonplace observation in the United States that dark-skinned men find lighter-skinned women more attractive. I can’t cite the study, but I know I’ve read it. At any rate, I listen to my black friends, and they agree. (I’m aware this may be cultural, but sexual preference is sexual preference, regardless of its source.) This might explain the variety of complexions across equatorial Africa. Occam’s Razor and all that.
    Third: Based on recent studies on vitamin B3, reports of overdoses would appear to be grossly exaggerated. These studies are recent, and perhaps you have not read them, but apparently unlike the other fat-soluble vitamins, such as A, it is damn near impossible to get too much D3, and given that most people have very recently gotten out of the sun and into air-conditioned buildings, many of us ought to be taking supplements. Every study I’ve seen has suggested the usual 1,000-2,000 unit dosage may actually be five to ten times too little for optimum health. I frankly can’t find any recent references to illness caused by excessive D3.
    At any rate, my education is in the liberal arts, so I’m over my head here. Does anyone have any thoughts?
    Thank you.

    • mk
      Posted July 20, 2010 at 5:25 pm | Permalink

      I dread getting politically incorrect, but it is a commonplace observation in the United States that dark-skinned men find lighter-skinned women more attractive.

      Please allow me to be the first to call bullshit. That kind of comment really does require a little more than “I read it somewhere.” Where did you read it? Who conducted the study? Was it a solid scientific study? How large a study was it? Etc.

    • Sven DiMilo
      Posted July 21, 2010 at 8:27 am | Permalink

      (I’m aware this may be cultural, but sexual preference is sexual preference, regardless of its source.)

      But if the preference is cultural, then it’s not subject to sexual selection.

      And, dude, if you dread being politically incorrect then don’t spew broadbrushed stereotypes without being able to remember where you might have read it and oh yeah some of your best friends are black.

      • Divalent
        Posted July 22, 2010 at 8:18 pm | Permalink

        “But if the preference is cultural, then it’s not subject to sexual selection.”

        Wait, wouldn’t that mean it is subject to sexual selection? When a culture values some physical feature, then that advantages those that have it. (e.g., if big noses are valued in a particular culture (perhaps because the warrior hero had a big nose), girls want to mate with big nosed boys, and perhaps boys want big nosed girls.)

  17. Brian
    Posted July 20, 2010 at 4:49 pm | Permalink

    One of the diagrams seems to indicate that indigenous Australians were uniformly dark. I recall a local (to Melbourne) aboriginal saying that it’s a common misconception that his tribe were dark like the tribes from the tropics. According to him, the locals skins were more of a golden hue. Don’t know how much that’s worth, but I’d find it odd if over 40,000 or so years aboriginals from several migrations were all exactly the same hue.

  18. littlejohn
    Posted July 20, 2010 at 6:24 pm | Permalink

    @mk: I simply don’t know what to say to you, sir. My degree is in journalism. And no, I don’t remember where I read those things. You seem remarkably rude. I was hoping for some of the science instruction here that I failed to get 35 years ago in college. What do you presume my hidden motive is? My name is John Anderson and you can find me on Facebook. I’m the one who went to Bethany College. I wouldn’t dream of calling you a liar.

  19. Jack Bentley
    Posted July 20, 2010 at 11:16 pm | Permalink

    An interesting anomaly in the ‘dark skin in tropics, lighter skin in higher latitudes’ observation is the aboriginal population of Tasmania. Isolated on an island 40 degrees south (about as far south as Switzerland is north)since the end of the Ice Age, the original population had very dark skins. Some sites in Tasmania have evidence of human occupation >30,000 years ago.

    • whrrr
      Posted July 21, 2010 at 2:47 pm | Permalink

      Eskimos/Inuit tend to have dark skin also, despite living in the arctic. However, it’s likely that diet could have removed the ‘pressure’ to evolve lighter skin. Fish are a natural source of vitamin D.

      • whyevolutionistrue
        Posted July 21, 2010 at 2:53 pm | Permalink

        Yes, especially because it’s cold up there and wearing clothes would further reduce the possibility of getting vitamin D from exposing your skin to the sun.

  20. Ant Allan
    Posted July 21, 2010 at 1:44 am | Permalink

    Is this rejection “the ‘classic’ story” a new idea?

    I recall a presentation by the astronomer Sir Fred Hoyle, with Chandra Wickramasinghe, at the University of Durham, UK, in the early 1980s, in which Sir Fred made exactly the same point as these authors, that “skin cancer [has] negligible effects on reproductive success” — essentially, that it generally occurs too late in life to have any influence on who passes on what genes to the next generation.

    Admittedly, a lot of Sir Fred’s other ideas had a high “woo” factor, and demonstrated an ignorance of, say, social anthropology greater than a physics student’s (well, mine!), but clearly he had been onto something with his doubts about the origins of variation in skin pigmentation.

    Were there evolutionary biologists advocating this idea at that time?

    • Ant Allan
      Posted July 21, 2010 at 1:46 am | Permalink

      ‘Is this rejection OF “the ‘classic’ story” a new idea?’

    • whrrr
      Posted July 21, 2010 at 3:04 pm | Permalink

      How late is ‘too late in life to have influence’? There is more to passing on genes than living long enough to have children, it also helps to be able to raise them.

      Also, modern people probably receive less exposure to sun than ancient people did, which delays the occurrence of this type of disease.

      • Ant Allan
        Posted July 21, 2010 at 4:00 pm | Permalink

        That is a good question.

        But I am neither of the authors of the article discussed here, nor am I the late Sir Fred Hoyle!

        I guess at least Jabonski and Chaplin have the data to support their conclusion & could answer your question for you!

        However, the truth (or falsehood) of this was not my point: Had other evolutionary biologists explored this issue since the early 1980s (or earlier) or was Sir Fred’s thinking original?

  21. MikeN
    Posted July 21, 2010 at 2:27 am | Permalink

    In reply to littlejohn, the obvious answer is that a dominant culture which constantly projects its own idea of beauty will tend to skew the tastes of minorities.

    • littlejohn
      Posted July 21, 2010 at 7:58 am | Permalink

      Thank you for a serious response to one of my questions. Also, thank you for not “calling bullshit.”
      I wonder if it has not occurred to mk that an apology is called for here, or is he in the habit of randomly insulting people?

      • Sven DiMilo
        Posted July 21, 2010 at 8:28 am | Permalink

        it’s the internet
        people are rude
        often much ruder than mk

        move on

        • littlejohn
          Posted July 21, 2010 at 9:23 am | Permalink

          I may not have taken many science courses, but I had a second major in philosophy.
          Surely you’re aware that what is and what should be are not the same thing.
          I’m not a young man, and maybe I’m just old-fashioned. If that sort of rudeness is now considered acceptable, I am very saddened.
          What disturbs me more is that mk himself has not responded. What sort of man could call someone a liar, be proven wrong, and feel no need to retract the accusation? I take such things seriously. Since religious people routinely accuse us of having no morals, one would think we would make some attempt to demonstrate they are mistaken.

          • mk
            Posted July 21, 2010 at 2:05 pm | Permalink

            Sorry, been away for a while.

            Little John,

            You’ll have to forgive me. Your statement sounded suspiciously like those of proto-racists. It appears sincere, but in reality it’s kind of ignorant. I take you at your word you meant nothing from it. Nothing hidden. Just genuinely curious. Even though it sounded very much like, as Sven said, a “broadbrush stereotype.”

            OK then. Sorry.

            • littlejohn
              Posted July 21, 2010 at 4:02 pm | Permalink

              You apology is, of course, accepted. By the way, I’m of mixed race.

  22. Posted July 30, 2010 at 7:39 pm | Permalink

    I liked your post and reposted on my blog. Someone left a comment, thought you’d be interested.

    http://blog.albertoconti.com/why-are-we-different-colors

  23. Posted January 3, 2012 at 3:33 pm | Permalink

    I have found that natural means tend to produce much more consistent results and I find that the majority of people are much happier in the end. In fact there are different ways to aquire fairer skin; lighten skin pigmentations; freckles; age spots; acne marks; lighten dark underarms; melasma; or lighten your overall skin tone. What are your readers thoughts and experiences?


2 Trackbacks/Pingbacks

  1. [...] science: what is behind the skin color in the skin that you show (excepting Rep. John Boehner)? It isn’t as easy a question to answer as you might think: These differences among populations almost certainly represent more than one evolutionary event. [...]

  2. [...] Coyne has just published an article on his web site, Why Evolution Is True, entitled Why Does Skin Color Vary Among Human Populations. The article talks about a paper published that puts forward other possible explanations. The [...]

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