As super-powers go, living forever isn’t one of the flashiest nor is it all that original to the comic book genre. That said, there have been a number of memorable comic book characters that have immortality. The DC villain Vandal Savage was a caveman whose exposure to a radioactive meteorite made him an immortal jerk. He’s spent the last 50, 000 years trying to take over the world.
Vandal Savage (c) DC Comics, Mr. Immortal (c) Marvel Comics
On the other end of the serious spectrum, you have Marvel Comic’s goofy Mr. Immortal, the good-guy leader of the whimsical Great Lakes Avengers. He’s a mutant who can’t be killed but it isn’t entirely clear how he survives his fatal injuries. Where exactly is the immortality gene in humans? Nowhere, that’s where. However, there may be a biological explanation for immortality that we can torturously extract from the biology of a hydrozoan jellyfish. Let’s start by taking a look at its life cycle.
Colonial hydrozoan life cycle
When adult hydrozoan jellyfish (known as a medusa) aren’t busy stinging the bejillikers out of humans at the beach, they are busy floating in the ocean stinging the bejillikers out of small copepods and eating them. It’s a good life, but eventually the time comes to make babies. At this point, male and female jellyfish release eggs and sperm and then promptly expire. Meanwhile, the egg and sperm unite to form small, free-swimming planula larvae. The planula larvae settle on the ocean floor where they metamorphosize into a colonial polyp. The polyp is the juvenile stage and it looks like an inverted jellyfish, with tentacles sticking up rather than hanging down.
In this stage, the polyp can asexually create numerous small, jellyfish adults. This alone is quite a trick. In most cases (like you, for example), when a single egg fuses with a single sperm a single individual is formed. In the hydrozoan jellyfish, one sperm and egg can lead to a multitude of adult individuals because of the polyp’s prodigious cloning capacity.
Okay, now, for the immortal part. The adult jellyfish Turritopsis nutricula has found a way to cheat death.
After reproducing (and before expiring), Turritopsis nutricula shift their lifecycle into reverse and revert to the immature polyp stage. For this to happen, all of the adult cells have to revert into juvenile cells. The process of one type of specialized cell turning into another is called transdifferentiation and it usually only happens when some creatures regenerate organs. No other critter uses this trick to pull a Ponce de Leon and switch back into a kid. With the ability to transition back and forth between adult and polyp there is no limit to Turritopsis nutricula’s potential lifespan, because the adult stage need never die. And, even if some of the adult Turritopsis nutricula do die (perhaps eaten by some sea slug that will steal their stings), a zillion of their clones will endure elsewhere.
In fact, this jellyfish seems to have been using this remarkable super-power to avoid death and spread silently from its native Caribbean waters. Turritopsis nutricula has been popping up in oceans all over the globe, slowly inexorable taking over the world.
Vandal Savage would be proud.
Bavestrello, G. Sommer, C., and Sará, M. 1992. Bi-directional conversion in Turritopsis nutricula. In Aspects of Hydrozoan Biology. (J. Bouillon et al., editors). Sci. Mar. 56 (2-3): 137-140.
Piraino, S., Boero, F., Aeschbach, B., and Schmid, V. 1996. Reversing the life cycle: Medusae transforming into polyps and cell transdifferentiation in Turritopsis nutricula (Cnidaria, Hydrozoa). Biol. Bull. 90: 302-312.