If you had been paying attention, you might have noticed there are other kinds and sources of genetic variation. Besides, how would you know if a variation is favorable? Is sickle-cell trait favorable? "Favorability" depends on environment, which changes over time.
If you had been paying attention, you might have noticed there are other kinds and sources of genetic variation.
There certainly are. Another example is the sun which causes cancer of the skin. What radioactive induced mutation shows is that changing the genetic arrangement of organisms at random is not good. This is what evolution is trying to sell the public and it is totally false.