The idea of living forever has fascinated humanity for centuries, but one tiny creature may hold the key to immortality. Meet Turritopsis dohrnii, a jellyfish that, when faced with life-threatening challenges, has an extraordinary ability to reverse its life cycle and return to its youthful state. This jellyfish was first discovered in the Mediterranean in the 1880s, but it wasn’t until the 1990s that scientists fully realised its impressive survival capabilities.

Unlike most organisms that follow a linear life cycle, this species can essentially age backwards. It starts life as a larva (known as a planula) and eventually becomes an adult jellyfish, or medusa, after passing through various developmental stages. But here’s where it gets fascinating—when Turritopsis dohrnii encounters stress, whether due to injury or starvation, it reverts back to its early polyp stage. This reset process can theoretically go on indefinitely, making it biologically immortal.

Standing at just 4.5 mm in diameter, with its transparent bell and striking red stomach, this jellyfish may be small, but its impact on the scientific community is enormous. Its ability to “start over” comes from a cellular process called transdifferentiation. Through this process, adult cells, which are already specialised for a particular function, can transform into completely different cell types. It’s like a brain cell deciding to become a skin cell, for example.

Scientists are intrigued by this ability because it has potential medical applications, especially in the field of regenerative medicine. The idea of being able to convert one type of specialised cell into another could revolutionise how we treat conditions where cells have been damaged by disease. Imagine being able to regenerate heart tissue after a heart attack or repair damaged brain cells!

Yet, Turritopsis dohrnii isn’t just a marvel in the lab. It’s also spreading across the globe. Marine creatures have long hitched rides across the oceans via ships, and this jellyfish is no exception. It has been spotted all over the world, from the Mediterranean to the Pacific, thanks to its hardy nature and ability to thrive in various environments. Researchers have found genetically identical jellyfish spread across the globe, leading to a fascinating question: if an organism’s cells are completely replaced, is it still the same individual?

While humans are far from cracking the code of eternal life, this jellyfish offers a glimpse into what might one day be possible in the realm of longevity science. We may not be ready to turn back time just yet, but Turritopsis dohrnii shows us that nature already has some incredible tricks up its sleeve.