"Farmers use evolution all the time."
Genetic selection (for desireable traits) is used in agriculture.
The gene pool stays the same, just certain traits are selected for and expressed.
Actually when farmers do it, it's called artificial selection. I know if you want to get technical, natural & artificial selection are't proven to create new species (since the process would take a lot longer than human science has existed) but the example of the difference between the wheat of today and spelt still stands. The gene pool DOES change, you simply can't get spelt to produce wheat in a single generation when it took 10,000 years of intentional selection to make it happen.