Dogs have been bred for thousands of years. What dog breeding shows is that you cannot change a species by selection, whether natural or selected. In fact, the more selection, the less viable a species becomes:
However, inbreeding holds potential problems. The limited genepool caused by continued inbreeding means that deleterious genes become widespread and the breed loses vigor. ...
The ultimate result of continued inbreeding is terminal lack of vigor and probable extinction as the gene pool contracts, fertility decreases, abnormalities increase and mortality rates rise. ...
Inbreeding holds problems for anyone involved in animal husbandry - from canary fanciers to farmers. Attempts to change the appearance of the Pug in attempts to have a flatter face and a rounder head resulted in more c-sections being required and other congenital problems. Some of these breeds are loosing there natural ability to give birth without human assistance. From: Problems of Inbreeding
So selection really leads to the destruction of species.
Aside from the fact that all anybody ever got from breeding dogs was dogs (no goats, birds, or horses...), you can take any collection of danes, shepherds, and poodles and turn them loose in the wild and, after five generations, all that will be left alive is your ordinary, universal, fifty pound wild dog.
Dogs have been bred for thousands of years. What dog breeding shows is that you cannot change a species by selection, whether natural or selected. In fact, the more selection, the less viable a species becomes:
That shows that you have no understanding of what speciation is. For starters, plenty of species can interbreed; old scientific definitions make this mistake, but they are woefully out of date, and simply repeating them as dogma does not make them true. One can have two different species that are capable of interbreeding (lions and tigers, for instance). Man cannot breed dogs into seperate "species", by which you mean, groups incapable of interbreeding with each other, because it is not the difference in appearance which makes species unable to breed with each other, but rather genetic drift and mutation, which takes place over millions of years. Given enough time, if these man made dog "species" were kept from breeding with each other, they would develop into species incapable of breeding with each other. But in the short term, speciation is accomplished simply by selecting which features get passed on to the next generation - either by natural selection, or by man made selection. Whether we call these species "species", or something else, is a matter of semantics, not science. But then, the anti-evolutionary crowd has always been big on semantics and weak on actual science.