To follow on from recent interest in the mechanism of longevity in naked mole-rats, here is a paper that looks at the biochemistry: "Underlying causes of species differences in maximum life span (MLS) are unknown, although differential vulnerability of membrane phospholipids to peroxidation is implicated. ... membranes of longer-living, larger mammals have less polyunsaturated fatty acid (PUFA). ... Both species had similar amounts of membrane total unsaturated fatty acids; however, mice had 9 times more docosahexaenoic acid (DHA). Because this n-3PUFA is most susceptible to lipid peroxidation, mole-rat membranes are substantially more resistant to oxidative stress than are mice membranes ... suggesting that membrane phospholipid composition is an important determinant of longevity." So there you go; mole-rats have just as many free radicals as their short-lived peers in other species, but may be vastly more resistant because their metabolism uses tougher biochemicals. Less damage means less aging - and thus a longer, healthier life.