What are the advantages of light skin, and why is it selected for at higher latitudes?
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Vitamin D production; as well as less energy spent on melanin.
Basically, the same way plants use sunlight to make sugar in their leaves; humans use sunlight to make vitamin D in our skin. But that happens deeper in the skin than melanin; and melanin blocks out the light that is needed for Vitamin D production. Which means that dark-skinned people need to be in the sun for longer to make the same amount of vitamin D.
Not having enough Vitamin D is linked to rickets (a disease where your bones are weaker and malformed) and other bone problems. Basically, it’s important to turn calcium from food into bones; so if you don’t get enough of it, you get bone problems. Before we learned to make Vitamin D artificially and put it in foods, people who weren’t outside enough had bone problems. And darker-skinned people need more time outside in the same location.
The second reason – a much, MUCH smaller one – is that melanin does take energy to make. It’s not a lot – it might be a few meals over a lifetime – but it does mean you have slightly more energy to do other things if you don’t need to produce as much of it.
But the main reason is “bone problems from not enough Vitamin D”
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