Just remember if you argue that dog breeds are different species, especially the case of the mastiff and chihuahua, or the teacup yorkie and newfoundland, these different species are verifiably the result of intelligent design. Selection was involved, but not natural selection.
Only those who don't understand what an intelligent designer actually is, may make this argument. An intelligent designer creates from the top down. Meaning that all species were created in the form you see and can never deviate from that form. Evolution works the other way, from the bottom up. So the fact that there are different dog breeds at all, is evidence that species can change given the proper environment. Humans simply gave nature a little nudge. They would also be making a giant assumption that any human activity is "unnatural". Even if we are "chosen" in some sort of way by a silent intelligent creator, we still obey all the same laws that everything else does in nature. Also we didn't one day just decide to create a chihuahua from scratch, it took hundreds if not thousands of years of breeding. It could even be a possible, if not likely, that the first guy that started the breeding process didn't even know what the end result would be. Taking the whole intelligence part out of this equation.
God made the integers; all else is the work of Man. -- Kronecker