How/when did humans evolve to become white?

Discussion in 'Human Science' started by skaught, Dec 5, 2010.

  1. skaught The field its covered in blood Valued Senior Member

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    Is it known how, where, and when humans skin color started to lighten? Dowe know what the contributing factors are?
     
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  3. arfa brane call me arf Valued Senior Member

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    It isn't known exactly, but the loss of pigmentation in human skin started when populations migrated from equatorial regions to higher latitudes, and started wearing more clothing.
    Near the equator, most indigenous people (who didn't migrate) still have high levels of natural 'sunscreen' for obvious reasons, and you don't see people in these regions wearing clothes to keep warm, but for cultural or tribal reasons--for identification mostly.
     
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  5. jmpet Valued Senior Member

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    Humans are dark-skinned. Being white is the exception.
     
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  7. kurros Registered Senior Member

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    I thought that the reason was vitamin D. Someone told me one time that the only thing white skin is better for is helping produce vitamin D, dark skin is better in every other way. I.e. when light levels drop enough that not only do we not need so much protection from the sun but we start to have problems producing vitamin D then it becomes beneficial for skin to be lighter.
    I have nothing solid to back that up though

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  8. granpa Registered Senior Member

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    became white or became caucasian?

    Its naive to assume that early humans were not white
    chimpanzees are born white and become black as they age.
    http://en.wikipedia.org/wiki/Neoteny

    One would therefore expect that early hominids were composed of 2 groups
    1. one group that were born white and became black over time
    2. one group that were born white and stayed white

    Since modern blacks are born black and stay black I expect that they are descended from group 2
    certainly black skin appears to have evolved from white skinned caucasians in india.
     
    Last edited: Dec 6, 2010
  9. Fraggle Rocker Staff Member

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    Skin color is one of the most ephemeral of human traits, and also one of the most important in relation to environment.

    Melanin, the primary pigment that makes skin appear dark, is a natural sunscreen. Before the diaspora out of Africa 60KYA, and before the invention of the technology of clothing 70KYA (that's when body lice speciated from head lice) humans needed that sunscreen to prevent skin cancer. Other primates don't need it because their skin isn't exposed to the sun.

    However, by blocking the absorption of solar radiation, melanin also greatly reduces the amount of Vitamin D that sunlight catalyzes in human metabolism (sort of our version of photosynthesis). So as humans moved north they began to suffer from Vitamin D deficiency. This is a deadly condition that will quickly result in natural selection for less melanin.

    This effect occurs rapidly. The dark-skinned Bengalis and the light-skinned Lithuanians are closely related populations separated by only about three thousand years of migration in opposite directions from the Pontic Steppe, the original homeland of the Indo-European people. That's only about 150 generations, not a very large number of breeding cycles.

    Today light-skinned people who live in the tropics can wear long sleeves and sunglasses and put lotion on their faces to avoid melanoma. Dark-skinned people who live in Alaska can take Vitamin D supplements to avoid rickets and osteomalacia. So there is no longer any environmental pressure for skin color to change over time.
     
  10. S.A.M. uniquely dreadful Valued Senior Member

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    You are correct. 1,25 dihydroxycholecalciferol which is the active form of vitamin D in the body is required for very important stuff like gene expression and cellular differentiation. It is "manufactured" under the skin through a process which requires UVB rays. The amount of vitamin D produced is related to the angle of the rays, the amount of exposure and the level of melanin in the skin [melanin acts as a filter for UVB rays]. UVB is easily filtered, available less when the skin is covered, when the earth is angled away from the sun and above the 37th parallel

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    Seasonal changes in vitamin D levels in the blood:

    http://www.ajcn.org/content/vol85/issue3/images/large/znu0030743810001.jpeg

    The gradual adaptation to lower UVB and lesser melanin would be a perfectly rational explanation for the evolution of white skin. You can also see how this effect can cause rickets or other bone diseases in those dark skinned people who migrate to the cooler climates and skin cancer in those light skinned indivduals who migrate closer to the equator.

    source:Addressing the health benefits and risks, involving vitamin D or skin cancer, of increased sun exposure
    http://www.pnas.org/content/105/2/668.full

    see also: Deficiency of sunlight and vitamin D
    http://www.bmj.com/content/336/7657/1318.extract

    Time for more vitamin D
    http://www.health.harvard.edu/newsweek/time-for-more-vitamin-d.htm
     
    Last edited: Dec 6, 2010
  11. skaught The field its covered in blood Valued Senior Member

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  12. arfa brane call me arf Valued Senior Member

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    A comment on the title of this thread: loss of skin pigmentation is an adaptation, not really an evolved trait.
    As someone else may have pointed out the pigmentation gene is dominant--it's why a 'mixed' marriage always results in dark-skinned children. And sometimes fair-skinned couples produce dark-skinned children for the same reason.

    Adaptation is evolutionary, but in the case of human adaptation to lower levels of UV it hasn't resulted in populations that can no longer interbreed.
     
  13. iceaura Valued Senior Member

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    There's a complication, in that dietary Vitamin D is available in some fish and other foods available to early human migrants - who mostly followed coastlines.

    So the adaptation is not only to latitude, but to hunting, herding, or farming life inland. The areas opened up are the vast and rich interiors of the major continents at higher latitudes.
     
  14. Emil Valued Senior Member

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    But the yellow people?
    Do not say it has something like jaundice!

     
  15. S.A.M. uniquely dreadful Valued Senior Member

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    The highest dietary sources of vitamin D is cod liver oil which is about 1000-1400 IU per serving [1 tbs]. It is followed by salmon which is around 400 IU per serving [around 3 ounces]

    Compare that to 15 minutes in full sunlight without sunblock on arms and legs which results in ~20,000 IU of vitamin D. 90% of vitamin D is obtained through non-dietary sources

    Michael Holick is a fairly well known authority on vitamin D requirements.

    http://chetday.com/vitamindchronicdisease.htm
     
  16. quadraphonics Bloodthirsty Barbarian Valued Senior Member

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    That's only if you're a white person and it's either summer time or you are close enough to the equator that it doesn't matter. A person with what I imagine your skin tone is will not make any significant vitamin D from sun exposure for the majority of the year if you are more than about 35 degrees away from the equator.
     
  17. spidergoat Valued Senior Member

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    There is no such thing as white people.
     
  18. quadraphonics Bloodthirsty Barbarian Valued Senior Member

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    Tell that to my sunburn.
     
  19. EmptySky Banned Banned

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    Human skin has never 'changed color' and anyone who tells you that it has is only trying to mitigate the importance of the subject in accordance with the liberal dogma which determines contemporary Western culture and scientific thinking.

    Primates have different skin colors under their fur, therefore, applying Occam's Razor, it is logical to conclude that our ancestors had the same. When a combination of evolutionary factors begun to occur, such as the loss of body hair and the movement of homonids out of the jungles their skin became more exposed to the sun, resulting in a dramatic fall in the quality of life for those with pale skins. At this early stage of human evolution there was no clothing or houses or sun screen or parasols to protect those with pale skins from the sun yet emergence from the jungle was essential for our continued evolution. Hence, a strong environmental pressure existed for whites to leave Africa and find cooler climates.

    Eventually, ALL paler skinned humans migrated out of Africa and into more northern climates. Tellingly, the small groups of blacks that did migrate out of Africa travelled directly along the equator and into Australasia forming todays Aborigines. Obviously they felt no pressure or need to go north. Why would you go north anyway to face freezing winters and a scarcity of fruit and vegetables unless you were forced to and had the intelligence to cope with it?

    Ironically, rickets is known as the English disease. You won't find any notable difference between dark and light skinned people suffering from it in northern climates.

    Skin color is only one variable in the subject of race, there are others which are more important in determining the quality of a race.
     
  20. Fraggle Rocker Staff Member

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    Different species within a genus are commonly capable of interbreeding, at least among mammals and birds. They will often do this in the wild under environmental pressure (the black-headed and rose-breasted grosbeaks are the poster children for this phenomenon among North American birds; the wolf and coyote among mammals), more often in captivity when they become artificially socialized, and between species whose courtship rituals are incompatible it can in many cases still be accomplished by AI.

    Besides, evolution first creates subspecies before they diverge into completely different species. Subspecies are always capable of interbreeding and commonly do when whatever environmental or artificial barrier that keeps them separate is breached, e.g., dogs and wolves.
     
  21. S.A.M. uniquely dreadful Valued Senior Member

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    Huh? That is patently false, rickets is seen to a much higher degree in dark skinned children in northern climates

    In fact, historically, dark skin is one of the significant features associated with nutritional rickets in northern climes

    source: Nutritional Rickets with Normal Circulating 25-Hydroxyvitamin D: A Call for Reexamining the Role of Dietary Calcium Intake in North American Infants
    Quality of race? What is that?

    One of the mechanisms by which rickets would aid in evolution of white skin would be by reducing reproductive fitness. Women with soft bones would not have healthy children or easy pregnancies. Loss of teeth, fragility of bones [there are case studies of women with rickets so severe their wrist bones snap if they lean against the wall] etc would further undermine fitness and reproduction
     
  22. Emil Valued Senior Member

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    I vote for the red skin.

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  23. S.A.M. uniquely dreadful Valued Senior Member

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    I was looking for generic information from the American Academy of Pediatrics and found this article:

    Without adequate supplementation from infancy, children at higher latitudes would suffer from impaired growth and development with dark skin, which through eventual natural selection would lead to progressively whiter skinned individuals having the advantage over them.

    see also:

    This is one of the reasons why women in Arab countries where veiling is common have inner courtyards or roof top courtyards where sunbathing is possible
     

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