eli5: If more melanin is advantageous in warm climates, why is less of it advantageous in colder climates? Wouldn’t darker skin still be most advantageous in cold climates where it might occasionally be hot?
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Melanin is useful for blocking against large amounts of UV radiation. It lowers chances of skin cancer from running around in the sun constantly.
But you need to take in *some* UV light to get vitamin D. If you live in someplace cold, you don’t go out much if you like having all of your limbs. That means you don’t get much sunlight, so you need to take in as much UV as you can so you can get your vitamin D.
TLDR:
Light Skin = All the Vitamin D. Good for minimal sunlight
Dark Skin = None of the Skin Cancer. Good for lots of sunlight
Humans need vitamins, basically. The more complex answer is, Humans synthesize Vitamin D using the ultraviolet radiation in sunlight, and melanin blocks that to help avoid skin cancers, because too much is also bad for you.
The advantages of melanin have nothing to do with heat and everything to do with UV exposure, it just so happens that places with more intense UV exposure also generally tend to be warmer (but not always).
Melanin protects the DNA in your skin cells from being damaged by UV light, that’s why people who evolved in sunny climates tend to have darker skin. The main disadvantage to having high melanin levels in climates with lower UV exposure is that it tends to lead to vitamin D deficiency as natural vitamin D production in the body is stimulated by UV exposure.
No.
It’s an adaptive advantage, and the lack of it is also an adaptive advantage. Skin with less melanin is more efficient at gleaning vitamin D from smaller amounts of sunlight, but is also more easily burned by prolonged exposure. This is why people who live closer to the poles tend to have less melanin. People with more melanin are more suited to sunnier climates and longer exposure to the sun, because their skin takes vitamin D in more gradually, and is less prone to burning.
Beyond that, and this is just anecdotal, but people with more melanin also seem to be more sensitive and uncomfortable with the cold. And people with less melanin seem to be more easily exhausted by heat.
Of course we’re all conscious beings and can take measures to adapt to wherever we find ourselves in, so it’s not that big of a deal in most cases, however people with darker skin ARE more prone to vitamin D deficiency in northern climates, which is actually a pretty big health issue. Not one that can’t be dealt with, but one that a lot of people just seem to be unaware of.
As a Scandinavian i can tell you that often even we need to take vitamin D. But culturally we are alot outdoor. Especially during summer. I wouldn’t be supprised if this is partly because of how much we can feel the vitamin D produced by the sunlight.
Melanin required resources to produce, and also does sloghtly reduce vitamin D production so in areas with less light, it was better to have less melanin and maximize vitamin D production. At higher latitudes, UV damage isn’t as much of a worry.
BUT this particular hypothesis on why skin color changes around the world is not definitive despite how popular the idea is. There are likely other interacting factors we haven’t worked out yet.
Melanin is useful for blocking against large amounts of UV radiation. It lowers chances of skin cancer from running around in the sun constantly.
But you need to take in *some* UV light to get vitamin D. If you live in someplace cold, you don’t go out much if you like having all of your limbs. That means you don’t get much sunlight, so you need to take in as much UV as you can so you can get your vitamin D.
TLDR:
Light Skin = All the Vitamin D. Good for minimal sunlight
Dark Skin = None of the Skin Cancer. Good for lots of sunlight
Humans need vitamins, basically. The more complex answer is, Humans synthesize Vitamin D using the ultraviolet radiation in sunlight, and melanin blocks that to help avoid skin cancers, because too much is also bad for you.
The advantages of melanin have nothing to do with heat and everything to do with UV exposure, it just so happens that places with more intense UV exposure also generally tend to be warmer (but not always).
Melanin protects the DNA in your skin cells from being damaged by UV light, that’s why people who evolved in sunny climates tend to have darker skin. The main disadvantage to having high melanin levels in climates with lower UV exposure is that it tends to lead to vitamin D deficiency as natural vitamin D production in the body is stimulated by UV exposure.
As a Scandinavian i can tell you that often even we need to take vitamin D. But culturally we are alot outdoor. Especially during summer. I wouldn’t be supprised if this is partly because of how much we can feel the vitamin D produced by the sunlight.
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