Ageing versus immortality Ageing

immortal hydra, relative of jellyfish

human beings , members of other species, animals, experience ageing , mortality. fungi, too, can age. in contrast, many species can considered immortal: example, bacteria fission produce daughter cells, strawberry plants grow runners produce clones of themselves, , animals in genus hydra have regenerative ability avoid dying of old age.

early life forms on earth, starting @ least 3.7 billion years ago, single-celled organisms. such organisms (prokaryotes, protozoans, algae) multiply fissioning daughter cells; not age , innately immortal.

ageing , mortality of individual organism became possible evolution of sexual reproduction, occurred emergence of fungal/animal kingdoms approximately billion years ago, , evolution of seed-producing plants 320 million years ago. sexual organism henceforth pass on of genetic material produce new individuals , become disposable respect survival of species. classic biological idea has been perturbed discovery bacterium e. coli may split distinguishable daughter cells, opens theoretical possibility of age classes among bacteria.

even within humans , other mortal species, there cells potential immortality: cancer cells have lost ability die when maintained in cell culture such hela cell line, , specific stem cells such germ cells (producing ova , spermatozoa). in artificial cloning, adult cells can rejuvenated embryonic status , used grow new tissue or animal without ageing. normal human cells die after 50 cell divisions in laboratory culture (the hayflick limit, discovered leonard hayflick in 1961).