I recall reading mold has a redundant set of DNA. For a mutation to happen, both sets need to have the same damage/radiation/etc happen at the same time. It's

I recall reading mold has a redundant set of DNA. For a mutation to happen, both sets need to have the same damage/radiation/etc happen at the same time. It's believed to be the reason why molds evolve so slowly and why they are so resilient to radiation damage.