Here is something that sounds like science fiction but is a biological reality: There is a jellyfish called Turritopsis dohrnii that is biologically immortal.
When this jellyfish becomes physically damaged, starving, or reaches the end of its natural life cycle, it doesn't die. Instead, it undergoes a process called transdifferentiation.
It essentially hits a "reset" button on its cells. It pulls its tentacles in, loses its ability to swim, and sinks to the ocean floor. From there, it transforms its mature cells back into their earliest, stem-cell-like state and reverts into a tiny, polyp-like blob (the jellyfish equivalent of a baby). From that polyp, it buds off new, genetically identical jellyfish clones.
In theory, it can repeat this cycle indefinitely, meaning it never has to die of old age. Scientists haven't found a "shelf life" for them yet—they only stop existing if they are eaten by a predator or succumb to a disease.
Here is something that sounds like science fiction but is a biological reality: The Greenland shark is the longest-living vertebrate on Earth, and some individuals alive today may have been born before the signing of the Declaration of Independence.
Here are a few fascinating details about them:
- They are incredibly slow: They grow at a rate of less than one centimeter per year. Because they live in the freezing depths of the North Atlantic, their metabolism is glacial.
- They don't reach maturity until they are about 150 years old. This means a shark that is 100 years old is essentially still a "teenager" in terms of reproduction.
- They live for centuries: Scientists have used radiocarbon dating on the lenses of their eyes to estimate their ages. The oldest specimen ever found was estimated to be between 272 and 512 years old.
- They are mostly blind: Most Greenland sharks are hosts to a specific type of parasite (Ommatokoita elongata) that attaches itself to the shark's cornea and eats the tissue, eventually rendering the shark partially or completely blind. However, this doesn't seem to bother them much, as they rely on their keen sense of smell to navigate the dark, deep waters.
So, while you are reading this, there is a massive, slow-moving creature swimming in the dark ocean that might have been born in the 1700s, never having seen the world in high definition, just drifting through the cold for hundreds of years.
Here is something that sounds like science fiction but is a biological fact: There is a species of jellyfish that is biologically immortal.
The Turritopsis dohrnii, often called the "immortal jellyfish," has a unique survival mechanism. When it becomes physically damaged, starving, or reaches the end of its natural life cycle, it doesn't just die. Instead, it undergoes a process called transdifferentiation.
It essentially hits a "reverse" button on its life cycle. It absorbs its own tentacles, closes its bell, and settles onto the ocean floor, transforming itself back into a tiny, sexually immature polyp—the earliest stage of its life.
From that polyp, it then buds off new, genetically identical jellyfish. Because it can repeat this cycle indefinitely, it is theoretically capable of living forever, barring predation or disease.
In simple terms, it’s the biological equivalent of a butterfly turning back into a caterpillar, and then back into an egg, over and over again.