It's an interesting thought, although that would mean the species opted out of having a working problem-solving mechanism. This is probably not associated with

It's an interesting thought, although that would mean the species opted out of having a working problem-solving mechanism. This is probably not associated with long-term survival. There are several reasons why genomes remain more stable than others, including - as you stated - replication accuracy (which can nevertheless not be 100%), but also survival chances of random mutations, and environmental factors that make deviations from the plan unfit for survival. Yet, bacteria in general show tremendous genetic mobility. They're easily the most promiscuous lifeform on the planet, considering the fact they have evolved a P2P genetic data transfer mechanism that doesn't require procreation. So, all things being equal, the rate of genetic change is expected to vary a lot. It's also worth considering that just because ancient versions are still around, that might still mean there are diverse offspring which are also doing fine. It's not automatically the case that earlier versions get replaced. > I'd be willing to bet that there is a healthy species of bacteria that has stopped evolving It sounds weird, but that's mostly a matter of definitions. If a species has stopped evolving, let's say because it developed a 100% accurate replication mechanism, that species will have trouble surviving changing environments. Sooner or later there will be a virus or something else that just wipes it out.