I hesitate to wade in, particularly since both Hooberus and Sea Breeze seem resistant to information that does not align with their beliefs, but here goes...
The selection in "natural selection," does indeed refer to existing traits. Natural selection in and of itself does not bring about anything "new;" rather, you have mutations to thank for that (among other things). A trait, of course, has to exist in order to be selected. "Selection" simply refers to the advantage that a member of a species has as a result of a particular trait over other members of the species who lack such a trait. How is it that traits appear in one member of a species but not others? Mutations constantly create variation in the DNA, the vast majority of which are neither beneficial nor harmful but silent. However, from time to time, variation does crop up that helps a member of a species survive in the face of new or changing environmental conditions. It is the combination of environmental variation with trait variation that creates the right setting for selection.
But natural selection is NOT the only force at work in evolution! Researchers now know (and have observed) a variety of other factors that also play a role. I should add-Prothero's book was an eye-opener for me. I highly recommend it.