Jose Fly
Fisker of men
So a mutation is only beneficial if it confers a fitness advantage in every possible environment?Every mutation is harmful... I doubt you realize that the mutation that made E coli able to process citrus without oxygen also made it so it can't survive on anything else....
There is no such thing as a purely beneficial mutation.....
They mutated Fruit Flies and got bigger and stronger Fruit Flies, but they didn't complete the mating process as often as the unmutated ones. Not to mention not a single one of any of the mutated flies can survive outside of the favorable conditions of the laboratory.....