High mutation rates in Escherichia coli can either help or hinder evolution. Researchers studied E. coli with different mutation rates for 3000 generations in the lab. They found that moderate increases in mutation rates led to faster adaptation and better growth in new environments. However, very high mutation rates caused reduced adaptation and poor growth in all tested environments. This shows that the balance between harmful and beneficial mutations changes with mutation rate, with a tipping point at moderate rates.