There are organisms that use gamma radiation as an energy source. If we lived in an environment richer in naturally occurring radioisotopes, I think I'd expect to see more of this sort of thing -- maybe not up to the point of criticality, but maybe so.

Not much point in speculating, really; living on a planet that's better than four billion years old and of middling metallicity puts something of a damper on the basic biological potential of that pathway.