Pre-Birthday Contemplation of Mortality

"First discovered in the Mediterranean in the late 19th century, Turritopsis dohrnii is believed to be the only species capable of aging backwards—reverting, in dire circumstances, from a mature adult medusa to an infant polyp. Theoretically, it can do so over and over again, effectively rendering itself biologically immortal. Unfortunately, no evidence has been found, in the laboratory or in the wild, to prove T. dohrnii has ever managed that trick."

(From "Difference Engine: Facebook for the dead")