Originally Posted by Xaccers

Melanin helps protect against UV light causing cancers etc, but it makes skin more reactive, scratches, burns, marks will be more pronounced in high melanin skin, hence why scarring is used in some tribes in a way tattoos are used.
Melanin also reduces the skin's ability to produce vitamin D.
With the reduced levels of UV, vitamin D production would be even lower, so melanin levels reduced to compensate.