Two elderly residents of Sardinia, a certified Blue Zone. Photo: Claudine Doury/Agence VU’/Redux It is exceptionally hard to know how long long-lived animals endure. For the vast majority of species there are no growth rings to count, no blood tests to perform, no methods beyond marking time. The way scientists assess the longevity of wild animals is to tag them, go away, and hope to see them again. We know albatrosses live long lives because a 38-year-old ornithologist put a ring on a bird and