One of the recent "Ask the Expert" pieces at InfoAging features Steven Austad: "The one thing that seems to hold across species is that animals that are long-lived are better at repairing their DNA. That seems to be something that's pretty general because we find it across a whole range of species. One generality - that animals with high metabolic rates live shorter lives - has actually turned out to be untrue. It was a reasonable assumption because the very processes that make energy in an organism's cells produce free radicals that can cause damage. If those internal processes occur at a faster rate, it seemed logical to assume that they caused more damage. It was really quite a surprise - and exciting - to find animals with high metabolic rates that are such dramatic exceptions."