"The fact that one species may evolve more than another within the same family, or in a different way, does not change anything about that family of species because ducks are still ducks."
By the exact definitions of species that you base your belief system on, Mallard and Blacks (interbreeding) are 'micro-evolving' whereas Mallards and Teal (non-interbreeding) are not 'macro-evolving'.
So you see, the common definition of species that you seem to put so much value on is pretty silly when applied to something as simple as 'if it looks like a duck, quacks like a duck, then it is a duck'.
You need to read the definition again and pay attention to the bold print:
A common definition is that of a group of organisms capable of interbreeding and producing fertile offspring of both genders, and separated from other such groups with which interbreeding does not (normally) happen. Other definitions may focus on similarity of DNA or morphology. Some species are further subdivided into subspecies, and here also there is no close agreement on the criteria to be used.
Because there is variation we are going with the "common" definition. In the "common" definition there are "norms" of breeding. This allows for variation from the norms within the same family. The family is divided into subspecies which show variations within the same family. One family of species does not evolve or interbreed with another family of species.
