From Veronique Greenwood at Nova Next:
In 1987, a group of researchers in France discovered something peculiar. When they protected single-celled organisms from background radiation—the sort that comes from cosmic rays and radioactive rocks—the creatures’ growth was stunted. Colonies that receive a background dose of radiation actually grew more quickly than their shielded brethren. That’s radiation—not vitamins, not nutrition, not anything people generally suggest you should get more of.
Was background radiation somehow required for life?
…
It’s a peculiar finding—why would being without radiation make cells more vulnerable? One theory is that very low doses of radiation can cause cells to keep their repair machinery switched on, and those without it are unprepared, like a runner who skipped one too many workouts before a marathon. But the answers are not clear yet. Satta says that the next step would be to try similar experiments with fruit flies, to get a sense of whether the effect occurs in more complicated creatures. “All this suggests that these experiments should go on,” he says, “but due to budget limitations, this plan is unfortunately not sure.” More.
See also: Researchers: Contrary to expectations, genes are constantly rearranged by cells
and
What we know and don’t know about the origin of life