I don't completely agree, js1138. It seems to me that quite definitely selection is what ever shapes the direction of change. But, contrary to what you suggest, it must really make a difference what causes or produces the change, at least to a neo-Darwinist; for the neo-Darwinist insists that only “nature” – i.e., natural selection, understood as prompts coming in from the external environment – can be a source of selection pressure.
But it seems to me that in highly organized living systems, there are a whole lot of other “selections” that have to be made internally to the system, such that all the gadzillions of its constituting parts can operate together, cooperatively and synergistically, so as to maintain the conditions that can support biological life.
IOW, Darwinist evolutionary theory seems to account beautifully for selections made according to the external, environmental pressures, but is entirely silent about the internal, biologically- or organismically-driven ones. And for that reason I continue to suspect that the theory is somehow incomplete as a comprehensive theory of biological life. JMHO FWIW
Actually, Darwin had quite a bit to say about sexual selection. Descent of Man is mostly about sexual selection, not only in mammals generally, but also insects, birds, and man himself.
Your argument was quite effectly argued in 1802 by the Reverend William paley, in "Natural Theology". Darwin was quite familiar with this argument, as are all biologists.
The fact is that mutations are ocurring all the time without destroying life. In plants it is even common to have doublings of chromosomes (not theory, but observation). Life is tougher than you might imagine, and the "design" of living things has more slop and redundancy than you might imagine. Look at all the parts you can remove from a human an still have something that walks around.
Even the brain continues to perceive itself as whole when large chunks of functionality are distroyed by disease or accident.