All animals – with the exception, perhaps, of the seemingly immortal little sea creature known as the hydra – have a shelf life. They may live shorter or longer spans in captivity, in times of feast or famine, or in different habitats. But eventually, even with all the resources and coddling the world can possibly provide, a species will reach the limit of its natural life span. Even the most beloved, pampered pet pooch cannot live forever. According to a new study, humans are no exception to