When Muller first tried exposing flies to X-rays, he killed them all. Frustrated, he lowered the dose—and found that he had now sterilized them. Rather than mutants, he had created vast flocks of dead, and then infertile, flies. In the winter of 1926, acting on a whim, he exposed a cohort of flies to an even lower dose of radiation. He mated the x-rayed males with females and watched the maggots emerge in the milk bottles.
