I don't see how you arrive at that conclusion. You are in the same family, primates, as a gorrila, and you may very well look like a gorilla, yet still be gentically distinctive. Corn is in the grass family, but corn is not the same as fescue or bermuda or other grasses.
Differintiation within species isn't a problem, neither is differentiation within a family. Its when you have a species mutate to the point of being a totally new and separate phylum where you run into the fallacy of Darwinism.
So an elephant can evolve into a cat? (same phylum)
A moment ago you argued that resistant bacteria were the same species as bacteria, so no evolution had occurred. Now you acknowledge that my garden and my lawn are different species, but you still claim that no evolution has occurred because they are the same family. Suppose someone did run a lab experiment where they grew fish that breathed air and walked on land. Would that prove evolution, or would you then claim that until it put down roots and drank water from the soil evolution is still false?
Anyway, continuing to claim that evolution doesn't exist doesn't tell me why you feel the need to claim it doesn't exist. What verse of the Bible says no fish shall ever grow legs, nor the lizard grow feathers, nor the monkey build a house?