Ayooshi Mitra, Amity University Kolkata
Immortality is defined as eternal life i.e. being untouched by death, also acknowledged as eternal existence. Why do living beings gradually decay when they grow older? Senescence is the steady degeneration of cells or more appropriately of the entire organism ultimately.
Organismal senescence leads to an increase in mortality rate with increasing age, mainly in the final stage of an organism’s life cycle. As of now, there are only one known species referred to as biologically immortal’: the jellyfish– Turritopsis dohrnii. This small, transparent animal lives in oceans around the world and can turn back time by returning to the earlier stage of their life cycle.
Jellyfish, the next ‘Ashwatthama’?
A new life of a jellyfish starts with a fertilized egg, which grows into a larval stage called a planula. Soon, it develops into a polyp that gets trapped in a place for a certain time, developing into a small colony of polyps that share feed tubes with one another. Ultimately, it forms an outgrowth called ‘bud’ which breaks away from the rest of the colony. This process is responsible for the next stages of the life cycle of the jellyfish: the ephyra (a small jellyfish) and the medusa, a fully formed adult stage capable of sexual reproduction. This stage is the ‘end of the line’ for most jellyfishes.
But Turritopsis dohrnii has a unique ability: when faced with any type of environmental stress such as starvation or injury, it can return to being a tiny blob of tissue that changes back to the sexually immature polyp phase of life. It’s a bit like a butterfly turning back into a caterpillar, or a frog becoming a tadpole again. Although, Turritopsis dohrnii cannot be called ‘immortal’, since they can still be devoured by predators or killed in other ways. However, their ability to transfer back and forth between life stages in response to stress implies that, theoretically, they could live forever.
What is the secret to Hydra’s longevity?
Another species that comes to mind when talking about immortality is the Hydra. It may seem that they do not go through senescence at all. Instead of slowly deteriorating over time, the stem cells of Hydra have the ability for unbounded self-regeneration. This is due to a specific set of genes called FoxO genes, which are found in some animals and play an important role in regulating the life span of the cells.
For Hydra’s stem cells, there seems to be a surplus of FoxO gene expression. When scientists prevented FoxO genes from functioning, they found that Hydra cells began to show signs of aging and would no longer regenerate as they did before. It is still unknown as to how it works, but we do know that these genes have an important role to play in preserving Hydra’s never-ending youth.
Likewise, Water Bears or Tardigrades may be the toughest animal on the planet. These creatures, though very small, can survive extreme conditions such as boiling, cutting, drying, or even being if they’re put in outer space! Astonishingly, they can tolerate extreme radiation and can stop their metabolism for a long time and “come back to life” when they come into contact with water.
Funerals are grave affairs!
The transience of life and the grief caused by death may explain why human cultures around the globe had produced elaborate rituals to deal with it. From ancient Egyptian mummies in pyramids to Incan mummies to the modern American funeral homes, there is copious evidence to show that humans have a unique association with the dead. Since times immemorial, human beings have wanted to attain immortality. This effort includes the search for the so-called “Fountain of Youth” and even the freezing of corpses in the hope of preserving and bringing them to life in the future. Seemingly, there is already several plant and animal species that seem to evade death for a very long time.
Also read: Multisystem inflammatory syndrome associated with SARS-CoV-2
References:
- Petralia, R. S., Mattson, M. P., & Yao, P. J. (2014). Aging and longevity in the simplest animals and the quest for immortality. Ageing research reviews, 16, 66-82.https://www.sciencedirect.com/science/article/pii/S1568163714000622
- Kubota, S. (2015). Will Human Dreams of Immortality Come True Through Jellyfish Research?: Biological and life science studies of immortal and ephemeral jellyfishes.https://repository.kulib.kyoto- u.ac.jp/dspace/bitstream/2433/198671/1/RA2015_5(1)_25.pdf
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