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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Your question has pretty much been answered but as a general addition: Evolution doesn’t really care much for redundancy, and an orgasim won’t develop traits just because they *might* need it, they develop traits that are essential to survival.
There are vestigial traits, but those are only observed *after* evolution has done it’s job and the organism’s need for that trait has become unnecessary. At that point, if removing the trait isn’t necessary to the organisms survival, evolution won’t touch it and the trait is considered vestigial.
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