The thing is, there are so MNAY humans that any small advantageous mutations that would help us deal with increased UV radiation will be swamped out by the sheer size of our gene pool. Evolution tends to work fastest on small, genetically isolated populations. We really would have to mostly die out, or have some small subgroup be isolated on an island for a few hundred generations to see a truly distinct human species (home somethingorother as opposed to homo sapiens) emerge.
Species tend to be VERY stable over time, and only change if there is some kind of strong natural selective pressure. When such conditions arise, the change can be "rapid", although rapidity must still be measured in many thousands or millions of years. This is the heart of the idea of "puncuated equilibrium".
eye cint spil toody.