How an immortal jellyfish could end evolutionary theory as we know it
Almost all organisms grow old (i.e. physically deteriorate over time), a process that eventually results in death. Biologists call this age-related decline ‘senescence’. We know only a few exceptions. The ‘immortal’ jellyfish Turritopsis dohrnii periodically reverts to an earlier stage in its life-cycle, like a butterfly turning back into a caterpillar.