> But, in either case such selection is still evolution.  Evolution is change in response to a stimulus.  Nature can be the stimulus, but so can man.

OK, I see what you mean by that. Evolution includes artificial selection. Then, the distinction is between natural and artificial selection, and also the product. Natural selection produced what we call "nature," the nature that we wish to preserve, being as it is the product of 4 billion years. Mankind's hands are all over the planet now, so the distinction between nature and man-created may be subtle and vanishing.

* * *

We perceive today, as did Darwin, that natural selection is the environmentally
driven mechanistic process by which more advantageous
traits are, on the whole, passed on to succeeding generations more often
than less advantageous traits because of differential reproduction of the
individuals possessing them. Sexual selection is a natural process of intraspecific
competition for mating rights. 

Artificial selection, generally the motive force behind domestication, 
is often equated with selective breeding.

This often amounts to prezygotic selection (where mates are chosen
by humans) versus postzygotic selection (where the most fit progeny
reproduce differentially) as in natural selection. Although natural selection
plays a considerable role in the evolution of many traits (e.g., disease
resistance) during the animal domestication process, sexual selection is
effectively trumped by the human-imposed arrangements of matings
and often by the human desire for particular secondary sexual characters.

Artificial selection is a conscious, if unintentional, process, and therefore
is generally considered to be effected only by humans.

Driscoll, C. A., Macdonald, D. W., & O'Brien, S. J. (2009). From wild animals to domestic pets, an evolutionary view of domestication. Proceedings of the National Academy of Sciences, 106(Supplement 1), 9971-9978.

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