Some species do not age in any easily detected way - lobsters, for example. Others are just far more resilient to the passage of years than we humans, living longer or losing little of their vitality over the course of their lives. What can be learned from a study of their biochemistry? "The first photo is from 1973, when a dark-haired and spry Nisbet was banding chicks of the small sea bird off the rocky Cape Cod coast. The second photo was taken 33 years later and shows a grizzled, silver-haired Nisbet holding a 29 year old tern, one of the oldest on record. Nisbet's body shows common signs of wear and tear - gray hair, wrinkles, achy joints. The tern, however, shows none of these outward signs, despite being the equivalent of a human centenarian. ... Terns don't even demonstrate diminished physical abilities as they age. They aren't the only animals that have combined a long lifespan with minimal signs of aging; other seabirds, alligators, crocodiles, and some tortoises also seem to sip from the Fountain of Youth. Although medical advances have extended the human lifespan, these same advances haven't been able to prevent the inimical onslaught of old age. Scientists hope that by studying the secrets of ageless critters, humans will one day be able to pause the hands of time. ... The main difference between humans and organisms like common terns is how growing older affects the risk of dying. ... In some animals, like freshwater hydras, risk of death remains pretty constant during life. For other animals, like the tern, the risk of death actually decreases with age. It seems almost counter-intuitive: an older tern is less likely to die than a younger one. 'My 29-year-old tern was still breeding,' Nisbet said. The oldest terns produced the healthiest offspring and were actually more likely to survive the year than younger terns."