It seems that some animals possess biological immortality...at least in theory.
As they age, older lobsters become more fertile than younger lobsters. Lobsters, also, don't seem to die from old age, but due to being eaten by predators, or humans, or due to wasting by parasitic infestation. Scientists who study lobsters, do not have a way of working out the age of lobsters accurately, but it is believed that a lobster in the wild can reach a lifespan of 100 years. Lobsters when studied, show high levels of telomerase, an enzyme which repairs DNA sequences, and this seems to be their fountain of youth.
| Immortal Jelly Fish |
The immortal jellyfish, Turritopsis dohrnii, grows from a polyp into an adult and then it is able to reverse the cycle and become a polyp again. The jellyfish goes through the life cycle, growing into an adult, creating offspring, but instead of dying, it reverts back into a polyp.
Hydra
Hydra freshwater polyps don't appear to age and appear to be immortal. These tiny creatures do not mate but reproduce by budding; to do this they require a good supply of stem cells. The gene FoxO, which is also evident in humans, seems to be one of the important drivers of this continued renewal in the hydra and research on these creatures is providing important evidence about human ageing.
Planarian Flatworms
Scientists at the University of Nottingham have proved that these flatworms can regenerate indefinitely. Like the lobsters, the telomerase enzyme appears to be the important longevity factor. Of note, these creatures are hermaphrodites, possessing both testicles and ovaries. Also, if a worm is cut into pieces, they can regenerate into a complete organism. And if the head of a planariais is cut down the middle, the organism can grow two heads and continue living.
Tardigrade
Tardigrades which are known as waterbears, or moss piglets, can survive in very extreme conditions, withstanding water temperature from zero to well above the boiling point. They can be found in the deepest ocean and can survive the vacuum of outer space (taken on FOTON-M3 mission) and solar radiation, gamma radiation, ionic radiation, at levels hundreds of times that which would kill humans. They can also survive a decade without water, by entering a state called cryptobiosis. Their ability to withstand such extremes, which would kill other animals, is due to the use of trehalose, a nonreducing sugar.
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| Tardigrade |
However. tardigrades are only 1.5 mm long and they mostly spend their time sucking the juice out of moss and algae. To survive extreme conditions, these animals can slow their metabolism down to extreme levels called "Tönnchenform" and stay like that for decades. This has helped tardigrades, as a species, survive for 500 million years.
