There is always a certain amount of background radiation present, for example due to ionizing radiation from the sun and other stars. Also certain materials like granite may emit relatively large amounts of radiation.
Ionizing radiation may cause mutations in the DNA (Gevertz et al, PNAS 1985). Mutations, in turn, may lead to altered phenotypes. Altered phenotypes and survival of the fittest are key to evolution and formation of new species.
What is the (relative) contribution of background radiation on the formation of new species?. In other words, is background radiation a critical component in evolution and would the course of evolution have changed substantially when there would be no such background radiation?