Fundamental to evolutionary biology is the tendency for organisms to become progressively adapted to those environments to which they are most frequently exposed. Since background radiation is a universal component of our environment, radiation hormesis is an evolutionary expectation. Whole-of-life experiments and more numerous (and evolutionarily more artificial) shorter duration and higher dose-rate experiments are consistent with this expectation. Additional research is needed especially at the molecular level to search for underlying mechanisms, and implications for radiation protection guidelines need to be analyzed.