Animal Immortality

Some animals with amazingly long lifespans compared to ours, including one that can survive potentially forever, the "immortal jellyfish":

Animals with the Longest Lifespans

The most incredible is the glass sponge, possibly living up to 15,000 years. Corals and giant barrel sponges are not far behind. Other animals on the list, while impressive, fall within more imaginable ranges, e.g., Greenland sharks (400), ocean quahogs (225), and giant tortoises (possibly up to 250). It's noteworthy that all the most long-lived creatures aside from the bowhead whale (200) are invertebrates or cold-blooded vertebrates. What stops us from attaining such venerable ages? Elephants, at the bottom of the page, have about the same maximum lifespans as humans.

The Wikipedia article on the glass sponge goes into great detail about its biology and ecology but doesn't speculate why it can live so much longer than most animals:

Hexactinellid

"Biological immortality" enables some rare species to avoid aging and thus theoretically live forever. In practice, though, they're not truly deathless, since they can succumb to disease or predators.

Here's a page about the jellyfish with that extraordinary gift:

Immortal Jellyfish

In response to stress, it can hit a "reset button" and revert to its immature polyp stage. The regenerated polyp grows into an adult genetically identical to its previous incarnation. This process of "transdifferentiation," in which "an adult cell, one that is specialized for a particular tissue, can become an entirely different type of specialized cell," is being studied by scientists in search of new ways to "replace cells that have been damaged by disease." Suppose a sapient creature had a similar life cycle? If we did, would we recognize it as a type of "immortality" we'd want? Would memory and learned skills carry over from one phase of the cycle to the next? Bacteria, reproducing by fission, are technically deathless, but if they had individual identities, would that individuality be preserved through their descendants? In musing on the immortal jellyfish, the article raises the question, "If all of an organism’s cells are replaced, is it still the same individual? The genes are the same, of course."

If we consider the issue from that angle, however, almost all the cells in our bodies get replaced throughout a lifetime, too, many of them over and over. Nevertheless, we think of ourselves as the same persons, with continuity of memory, experience, and identity.

Margaret L. Carter

Carter's Crypt

The Wonders of Jellyfish

If possible, pick up a copy of the October NATIONAL GEOGRAPHIC and contemplate the dazzling photos in the article on jellyfish. Typical jellyfish (not all of which are related to each other; the general name is popularly applied to different groups of creatures) have a complicated life cycle. The adult stage, the parachute-like shape with tentacles that we're most familiar with, is called a medusa. Medusae reproduce sexually, releasing eggs and sperm into the water. The larval stage, known as planula, anchors itself on a rock or the sea bottom, where it becomes a polyp. Polyps reproduce asexually, budding off multiple clones called ephyra, which grow into new medusae.

The highly toxic Portuguese man-of-war illustrates a transitional phase between a colony of separate organisms and their union into a larger, more complex creature. What looks like an individual is "technically a colony that developed from the same embryo."

The oral arms—the tendrils that sweep food into the mouth—of some jellyfish have mouths on the streamers themselves, a feature that sounds like a model for a Lovecraftian eldritch monster.

One species has a unique, almost unbelievable ability to revert to the polyp stage and start life over when confronted by environmental stress such as near-starvation or severe injury, sort of like reincarnation. By producing clones of itself that become medusae, which in turn transform back into polyps, and repeating the cycle, it effectively never dies (at least from "natural causes") or grows old.

The Immortal Jellyfish

Understanding this process of "cell recycling," called "transdifferentiation," could make a vital contribution to stem cell research.

If an intelligent species with an alternating sexual-asexual and mobile-stationary life cycle existed on some alien planet, it would surely have a social structure very different from ours, especially if it followed the jellyfish pattern of producing myriads of offspring with every instance of sexual reproduction. Of course, such alien sapient beings couldn't be jellyfish as we know them, which have no brains. It's also hard to imagine an r-selected species, one that engenders huge numbers of fast-maturing young in hopes that some may survive, evolving intelligence. It wouldn't have the long childhood and parental care that we assume to be essential to intelligence as we know it. What about intelligence not-as-we-know-it, though? Could animals similar to jellyfish, given some sort of neural network, develop a hive mind? After all, in one phase of their life cycle, they're clones, so they might conceivably have a shared consciousness. Genetically identical "immortal jellyfish" have been discovered in widely scattered parts of the Earth. Might similar organisms on another planet belong to a worldwide group mind? If so, what would they think of us as solitary individuals?

Margaret L. Carter

Carter's Crypt