But Turritopsis dohrnii and possibly some other jellyfish species too has a neat party trick: when it faces some kind of environmental stress, like starvation or injury, it can revert back to being a tiny blob of tissue, which then changes back into the sexually immature polyp phase of life.
It is a bit like a butterfly turning back into a caterpillar, or a frog becoming a tadpole again. They can still be consumed by predators or killed by other means. However, their ability to switch back and forth between life stages in response to stress means that, in theory, they could live forever.
Hydra look a bit similar to the polyp stage of a jellyfish which makes some sense, given that jellyfish and Hydra are grouped together in the phylum Cnidaria : a tubular body with a tentacle-ringed mouth at one end and an adhesive foot at the other. Their claim to immortality? This seems to be thanks to a particular set of genes called FoxO genes , which are found in animals from worms to humans and play a role in regulating how long cells will live for.
Lobsters also do not experience senescence. Normally, during the process of DNA copying and cell division, the protective end-caps on chromosomes, called telomeres, slowly get shorter and shorter, and when they are too short, a cell enters senescence and can no longer keep dividing. They produce lots of this enzyme in all of their cells throughout their adult lives, allowing them to maintain youthful DNA indefinitely. Telomerase is not unique to lobsters.
It is present in most other animals, including humans, but after passing the embryonic life stage, levels of telomerase in most other cells decline and are not sufficient for constantly re-building telomeres.
That takes a fair amount of energy. Lobsters do not die from old age but exhaustion as well as disease and New England fisherman. An embryonic jellyfish starts as a fertilized egg before hooking onto some kind of surface to then grow up. In this stage, they will stretch out to look like any other jellyfish. Eventually, they will break away from this surface to become a mature, fully developed jellyfish, which is in turn ready to reproduce.
So far, so normal. Yet Turritopsis dohrnii does something remarkable. But, their ability to change back to earlier forms of life, ones which are better adapted to certain environments or where there are fewer food sources, means that they could, in theory, go on forever. The more philosophical question, though, is why do we want to live forever? Yet, death serves a purpose.
As the German philosopher Martin Heidegger argued, death is what gives meaning to life. Having the end makes the journey worthwhile.
Being mortal in this world makes life so much sweeter, which is surely why lobsters and tiny jellyfish have such ennui. Jonny Thomson teaches philosophy in Oxford. He runs a popular Instagram account called Mini Philosophy philosophyminis. Jonny Thomson. But is this fun fact actually, well, fact? But like most decapod crustaceans , which also include crayfish and shrimp, they have indeterminate growth. By the time lobsters reach the age of seven, they molt once a year, and after that, once every two to three years, growing larger with each successive shedding of its exoskeleton.
The largest lobster on record, caught in Nova Scotia in , weighed 44 pounds, six ounces and measured 3. For lobsters, bigger bodies translate into more reproductive success: females can carry more eggs as their body volume increases, and they keep producing them until they die. Molting is a stressful process.
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