There was an essay by P.J. Plauger, I suppose collected into one of his "Programming on Purpose" volumes, talking about somebody he had worked with who was told to show off computers (then very new) to some biologists. He wrote a simple program that new how to generate itself to output (punched tape), and ran off copies. When the biologists arrived, he explained the program, and invited them to try creating mutations by punching extra holes. The usual result was a program that failed to run--call it sterility. Very rarely would a "mutation" occur and the program run to generate different output. I don't recall whether anyone managed to punch a no-op.