quote:But I don't see how something could be selcted for if it wasn't already present due to a mutation?
You are correct, it couldn't. Initially mutation provides variation and then natural selection gets to work, weeding out the useful mutations from the bad. I think perhaps your problem boils down to the fact that occasionally people use the term "natural selection" to refer to the process of evolution overall, missing out other important factors, such as mutation and genetic drift.
quote:Now my question appears sixth on a google search.
Don't you just hate it when that happens!
Mutate and Survive
"A curious aspect of the theory of evolution is that everybody thinks he understands it." - Jacques Monod