Evolution requires a process: Mutations occur; most mutations are harmful/detrimental, but a few are beneficial. Then, beneficial mutations are selected for.
It seems to me that there is a trade-off. Too much mutation, and too many individuals will get harmful mutations and die off, shrinking the population and increasing the likelihood of extinction. Too little mutation, and the species will not be able to adapt to a changing environment.
On Earth, all life has some mutation due to cosmic radiation, UV radiation, etc. There are also certain chemicals that can cause radiation. But many species have evolved DNA repair mechanisms to mitigate some of this mutation.
Is the mutation rate on Earth perfectly optimized? On a planet completely protected from all forms of radiation, would life fare better or worse? What about on a planet bombarded by very high levels of radiation?
What is the optimal rate of mutation to ensure both population growth and maximum adaptability?