Theseus' Ship and Immortal Jellyfish: Whole Body Regeneration and Identity

Jellyfish rekindle age-old philosophical questions once more

The ability of metazoans (multicellular animals) to regenerate lost body parts varies greatly. Some animals can regenerate their whole bodies, including phyla Cnidaria such as jellyfish, Platyhelminthes, and Echinodermata, while others can only regenerate certain tissues or organs. Jellyfish have three life-cycle stages; larvae (planula), polyp, and medusa stage (the jellyfish we commonly recognize). Some types of jellyfish, such as Turritopsis dohrnii, are capable of reverting to the polyp stage and regenerating damaged and aged cells. Although they can still die from disease, predation, or unfavorable environmental conditions, without these conditions, they can be considered immortal species.¹

A jellyfish may live for hundreds of years, and even though its body cells regenerate several times, everyone still considers it to be the same jellyfish. The jellyfish's life is a real example of Theseus' ship. The Ship of Theseus is a thought experiment and a philosophical paradox that explores the nature of identity and change. Based on this thought experiment, as the ship ages, its wooden parts begin to rot and parts of the ship are replaced with new and identical materials. After all the original parts have been replaced, is the ship still the Ship of Theseus? No one is concerned about the identity of jellyfish; however, if we can remain immortal by the replacement of new tissues and organs, identity and consciousness will be a challenging question.

Assuming humans can live indefinitely like jellyfish, and considering the central role the brain plays in shaping our sense of self and identity, it is essential to investigate how potential brain regeneration may impact the current neural circuits. If the process of replacing neural cells occurs gradually and the neural networks remain stable, we can anticipate that the mind will remain unaltered. However, rapid replacement of brain tissue may disrupt feelings, mindset, and memory. The life of jellyfish prompts us to contemplate whether the concept of self and consciousness is linked to biological structures or exists as an independent entity, similar to the numbers prisoners receive when entering prison as a new identity.

A horrible science fiction scenario starring immortal jellyfish and hydra

Turritopsis dohrnii can also regenerate their bodies from a small number of cells. This ability is also found in other jellyfish and hydra (small organisms belonging to the phylum Cnidaria) although not to the same extent. These two species have exceptional regenerative abilities making it a subject of scientific research, particularly in studies related to stem cells, tissue regeneration, and developmental biology.

Let's imagine that in the far future, scientists have discovered a technique for whole-body regeneration in humans using just a few body cells or small parts of tissues.

It is not a matter of discussion what is scientifically possible to achieve whole-body regeneration in a complex species like humans; it is not an impossible assumption. It has been shown that most differentiated somatic cells have the capacity for division after injury. However, the accumulation of genetic errors in these cells predisposes them to becoming cancerous.² Although it may not be crucial for hydras and jellyfish, the potential identity of a human that could emerge from our cells during whole-body regeneration is an intriguing issue. Who is the individual formed from our cells? Is it me, or is it a copy identical to me, like a doppelganger? Does the consciousness of a dead person who has donated tissue before death transfer to a new body? If so, consciousness should either be encoded in genes or exist as an independent entity that can easily transfer between bodies.

The second scenario involves a copy that is identical to its template

Dolly was the first mammal cloned from a somatic cell taken from a sheep in 1996. She was completely identical to her cell donor. Since Dolly raised several ethical concerns about cloning techniques in humans, the cloning of humans was forbidden officially. When a person provides somatic cells for cloning, will the new clone be a new individual with a unique identity? When the clone is a new person, it means that genes probably do not affect self and consciousness. It seems that the new clone should start to experience a new life and then self-consciousness forms gradually.

These two scenarios raise the issue that creating a cell-by-cell identical copy of the body and brain could potentially result in a similar identity to the original template. It does not make sense that a new similar copy of the brain shows the same perceptions, memory, and personality as same old version. The new brain is further similar to buying a new mobile phone of the same model as the old one. They are alike but not one. If you have a Google account, it enables you to sync data across devices, such as contacts, emails, music playlists, photos, and app data, ensuring you have continuous access to vital information. Now, the new cell phone can function just like the old one.

Consciousness is defined within time and space. Any event, new experience, or environmental factors can influence our perception of ourselves in an online way. Therefore, our perception of self changes over time, even though the brain deceives us to think that our core self remains constant. A complete human body forming from a part of a finger, similar to a hydra or jellyfish, or a new clone derived from somatic cells, may not embody the identity of the original donor unless we acknowledge that consciousness flows in all cells and tissues. The copyable entities cannot recreate consciousness and self because the self is unique.