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This a proposed task for future genetic engineers.
As you know, when human skin is exposed to ultraviolet light, it generates some protective compounds and changes color. There are two primary compounds, melanin (in the "black" and "brown" branches of humanity) and carotene (in the "yellow" and "red"
branches of humanity).
Organic compounds being quite versatile, it is not unreasonable to think that a similarly protective UV-blocker could exist that is white in color. While I'm sure every "white supremist" on Earth would want such a thing as "white melanin" --which actually wouldn't be melanin, of course-- their opinions have nothing whatsoever to do with the rationale for this Idea.
Basically, white substances can reflect other colors of sunlight. So, imagine some "white" person walking across the Sahara Desert, and catching a lot of sunshine in the process. If that person's skin could make a protective pigment against UV that happened to be white, then the skin becomes better at dealing with HEAT, not just UV. Because any color of light that is absorbed instead of reflected becomes heat, after all! And white reflects all colors.
Nanoparticle sunscreen
Nanoparticle_20titanium_20sunscreen
[bungston, Sep 02 2012]
[link]
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It's not clear that darker skin necessarily causes you to absorb more
heat than lighter skin. It would logically seem to be the case, but a
quick Google search of the question indicates that the answer may not
be so simple. As best I can tell, there's reasonable evidence that dark
skin doesn't actually make you hotter than light skin, but nobody is
exactly certain why that would be. |
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This is purely speculation, but I wonder if it may actually have
something to do with the heat absorbing/radiating properties of
melanin. Since melanin converts UV light to heat, perhaps it's the case
that the amount of heat energy given off by this conversion is greater
than the energy in the UV light, which would explain why melanin is
dark—to absorb the additional heat necessary for this conversion to
take place. So with a white “melanin”, you'd actually be losing heat
at a substantial rate while in direct sunlight (assuming the “melanin”
could absorb enough body heat to maintain the conversion). The net
result is that your internal temperature would increase to compensate
for the heat loss, actually making you feel hotter. |
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It is possible that both melanin and carotene have a decent amount of reflectance for infrared "colors". Nevertheless, humans have more sweat glands per square centimeter of skin than any other mammal, primarily to be able to dump heat better. And so I continue to think that if we could improve upon melanin (or carotene), to also reflect most ordinary visible light, then that would be a boon to a human body's overall cooling systems. |
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And remember, colder climates are generally cold because they receive less sunlight. Not to mention people tend to wear more clothes in those places. A white melanin would not be a disadvantage there. |
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I might mention that one other thing that human skin does with UV light is manufacture Vitamin D. It is known that dark-skinned people have trouble making enough when they move to high-latitude places. Their "default"/normal amount of melanin interferes with production of the vitamin. |
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Light-skinned humans are adapted to those high-latitude places; they have light skin exactly because of the need to make Vitamin D. The problem these people have is when they go to low-latitude places; their skin can't really make enough melanin or carotene for proper protection. I would hope that any genetic engineers who actually manage to get human skin to make a white UV-blocker could also enhance the ability to make it in quantities appropriate for the latitude! |
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Some shaky physics tells me that black bodies (in
the sense of 'black body radiation') radiate heat
better. So a white pigment may not help you stay
cooler. Of the people who live in hot, dry climates,
I think as many wear black clothes as white. |
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Also, is it possible to make a white pigment? (Yes, I
know titanium dioxide is white, but that's small
crystals as opposed to a soluble, biofriendly
pigment.) |
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I wonder if psoriatic skin would be more UV resistant. Lots of creatures in heavy UV environment cope by producing an external layer that is dead / dispensible. One could engineer humans to do this by making their skin hyperkeratotic. |
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They would not be pretty, these desert dwellers. |
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[MaxwellBuchanan], plenty of natural organic substances are white, and not just because of lack of other colors of pigments. A white flower petal, for example. The white parts of of the skin of a killer whale, for another. And this Idea doesn't ask for perfect white, leaving room for various reasonably effective (more reflective than melanin, at least!) off-white shades. |
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[bungston], titanium dioxide may be a bad idea, to mix it with organics. Remember that UV activates it such that it promotes chemical reactions with oxygen.... |
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//Also, is it possible to make a white pigment?// |
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Definitionally, no. But I guess it depends on what
exactly you mean by “pigment”. If you're talking
about a chemical that dyes some other substance
white, the closest I can think of would be bleach (sort
of a “negative pigment”, if you will). There probably
could be some sort of natural bleach that could be
genetically engineered, at least in principal. |
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//And remember, colder climates are generally cold
because they receive less sunlight. Not to mention
people tend to wear more clothes in those places. A
white melanin would not be a disadvantage there.// |
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Not much of an advantage either, though. The
decreased sensitivity to sunlight on exposed skin
might well be offset by the increased propensity
towards frostbite. |
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// a chemical that dyes some other substance
white, the closest I can think of would be
bleach// |
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Bleach is not a dye, and it works by destroying
pigments (which are generally full of vulnerable
double bonds). |
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//Plenty of natural organic substances are white,
and not just because of lack of other colors of
pigments// I disagree. Teeth are white because
they are made of microcrystals of transparent
minerals. Flower petals are white because they
lack chlorophyll or other strong pigments. |
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