Some plant species were already genetically selected for high yield by farmers and maxed out thousands of years ago. I can think of a few crops that haven't improved in yield for a looooong time. However, wheat has become so dis-similar from its pre-agricultural form that the older version of wheat is sold as "spelt," supposedly a low-protein ancient version that is easier to digest.
Farmers use evolution all the time. If you're gonna breed cattle, do you want the thin sickly ones to be parents? Probably not, if you plan to stay in business.
"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.
"Farmers use evolution natural selection all the time."