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........

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