(Well, you never answer this, but I'll try again...)
Why? Who asserts that "natural selection" is the mechanism of speciation? I'm not omnipotent, but I'm not aware of anyone who does. So why do you have this impression and keep saying this?
As I've noted previously natural selection can assist the process of speciation. For instance once there is reduced fertility between, say, two subspecies, there's an obvious selective advantage to adopting and then strengthening mate recognition mechanisms that reduce hybridization. But how would natural selection initiate speciation? Why should it? I can't think of any reason.
They keep track of "assists" in basketball.
Has something to do with "chain of causality".
Please, please don't make "Natural Selection" even more mysterious and metaphysical in nature than it already is. Demoting it from Godhead to godhead really doesn't avoid the problem you know.