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

A Plant-Animal Hybrid?

Here's a Wikipedia entry about the emerald green sea slug, a mollusc living in marshes, pools, and shallow creeks, which feeds on algae and incorporates their chloroplasts into its own body. It thereby not only turns green but gains the ability to nourish itself with sunlight:

Elysia Chlorotica

The slug can "capture energy directly from light, as most plants do, through the process of photosynthesis." Once it has established a stable population of chloroplasts, this creature has "been known to be able to use photosynthesis for up to a year after only a few feedings." Some research suggests that a slug may "possess photosynthesis-supporting genes within its own nuclear genome."

An article discussing its biology in less technical language:

The Green Sea Slug Steals Photosynthesizing Power from Algae

The caption on that page declares the emerald green sea slug a true "plant-animal hybrid."

Could a human being -- maybe a superhero mutant -- live on light by photosynthesis, like a tree? I've read this wouldn't be physiologically feasible because that lifestyle requires a mainly stationary existence of standing around exposing a large amount of surface area to the sun for many hours per day. Elysia Chlorotica, however, seems to live like an animal and yet derive nourishment from the sun. Suppose a larger creature with intelligence comparable to ours could do that? Wouldn't that make a cool alien species?

Margaret L. Carter

Please explore love among the monsters at Carter's Crypt.

Quest for Longevity

The cover story of the January 2023 NATIONAL GEOGRAPHIC, a 35-page article titled "The Science of Living Longer and Better," explores several different approaches, both theoretical and practical, to the goal of extending the human lifespan. The genetically programmed maximum age for us seems to be around 120 years. However, very few people make it that far.

Numerous drugs enable mice to live as much as 60% longer than normal. Why don't they work on people? Why do certain animals such as naked mole rats and some bats live significantly longer, in proportion to their size, than we do? Why do Greenland sharks live at least 250 years, maybe longer? Altering a single gene in a certain species of roundworms doubles their lifespan while keeping them youthfully energetic, but we're more complicated than worms. Why do people in some societies tend to enjoy longer, healthier lives than the average? Environment? Diet? Exercise? Other lifestyle factors? Some scientists have tried promising drug therapies on themselves, with mixed results. Animal studies show life extension outcomes from severe restriction of calorie intake, but, again, such a regimen hasn't produced similar effects on human subjects. Anyway, personally, if I could lengthen my lifetime by a decade or two that way, I wouldn't bother; adding on years of semi-starvation would be no fun.

Stipulating the natural human upper age limit as about 120 years suggests that the Howard Families project in Robert Heinlein's METHUSELAH'S CHILDREN couldn't work the way the novel portrays it. By the date of the novel, the 22nd century, the typical Howard Families member lives to 150, retaining the appearance and vitality of a person in the prime of life. This situation exists before rejuvenation therapies are invented later in the story. Simply interbreeding bloodlines of naturally long-lived people couldn't extend their maximum ages past the 120-year limit if genes for such extension don't already exist. Moreover, real-life super-centenarians, however vigorous, still look their age, not so youthful they have to adopt new identities to avoid unwelcome attention. The only way the "Methuselahs" of Heinlein's novel could survive and remain young-looking to the age of 150 would be if Lazarus Long had already spread the mutated gene responsible for his apparent immortality through most of the Howard population. (Given the character of Lazarus as portrayed in the later book TIME ENOUGH FOR LOVE, that hypothesis seems not unlikely.) That explanation wouldn't work for the early generations such as Lazarus's own mother and her contemporaries, though. There's no plausible way mere selective breeding for a century or so could produce human beings who live over 100 years with the appearance of well-preserved middle age.

So if we want lifespans like Heinlein's characters, we'll have to develop futuristic technologies similar to those speculated about in the NATIONAL GEOGRAPHIC article. Even so, surpassing the natural limit of 120 years would seem to require something radically beyond those techniques, maybe direct alteration of DNA—such as the hypothetical "cellular reprogramming" mentioned in the article.

Margaret L. Carter

Carter's Crypt

A Taste for Blood

This week I donated blood, and as usual in that situation, I thought about vampires. (Doesn't everybody?) If vampires have razor-sharp teeth that painlessly produce tiny incisions in the skin, maybe with anesthetic in their saliva like vampire bats, they wouldn't need to leave conspicuous twin fang marks that the donor has to cover with a scarf. (Vampire bats, by the way, make incisions, not punctures.) The puncture produced by the blood donation needle, at least in my experience, is so minute that it's hardly noticeable after the bleeding stops. Usually it has almost disappeared by the next day. The procedure typically extracts a unit of blood in less than ten minutes. Afterward, the donor isn't prostrated from blood loss; the worst I ever feel is thirsty and slightly tired for a couple of hours at most. So much for the dramatic image of a victim languishing on the verge of imminent death.

That's if the vampire takes only "as much as would fill a wineglass," like Chelsea Quinn Yarbro's Count Saint-Germain. He's a supernatural vampire, though. For those creatures, we can postulate that they're really nourished more by the life-essence than by the physical components of blood, so they don't need to ingest a large volume of it. Likewise, the absurd movie scenes in which a vampire grabs a victim, bites his her or neck for a couple of minutes, and leaves a body completely drained of blood could be handwaved as magic. No awkward questions as to where all that liquid fits into the monster's body. But suppose vampires evolve naturally and have to conform to the limits of biology? As the vampire Dr. Weyland in Suzy McKee Charnas's THE VAMPIRE TAPESTRY rhetorically asks, "How would nature design a vampire?"

How do vampire bats cope with a diet high in protein and minerals but not much else, including a potentially toxic level of iron? This article explains how vampire bats' digestion and physiology have adapted to make them the only mammals able to survive entirely on blood:

Why Do Vampire Bats Have a Taste for Blood?

For one thing, they live in symbiosis with gut microbes that synthesize nutrients not found in their restricted diets. They have other fascinating adaptations for their predatory lifestyle as well, including anticoagulants as well as painkillers in their saliva and the heat-seeking ability to perceive infrared radiation marking hot spots on the bodies of their prey. We could give our naturally evolved humanoid vampires these traits. My own fictional vampires get their bulk nourishment from animal blood and milk rather than feeding heavily on human donors, whose life-energy they need to remain healthy. Still, I fudge the total amount they require with discreet handwavium. Weyland in Charnas's novel gets "good mileage per calorie," and I tacitly assume any natural vampire would have to operate that way.

Unfortunately, in real life vampire bats suffer from an inconvenient drawback as models for romantic haunters of the night. So much blood volume consists of water that the bat has to consume half its own weight to ingest enough calories to support life. Then, of course, it has to get rid of that excess liquid just to reduce its weight enough to be able to fly. Therefore, during and after feeding the bat urinates copiously. Not glamorous at all, alas. So the writer inventing a naturally evolved humanoid vampire typically avoids discussing that problem. (In THE VAMPIRE TAPESTRY, the blood-heavy bat's plight is mentioned, but that unsavory topic isn't covered in the explanation of how Weyland feeds and digests.)

I'm currently reading a Japanese novel titled IRINA THE VAMPIRE COSMONAUT, set in an alternate-world version of the 1960s space race. Members of Irina's species have fangs, rely mainly on milk for nourishment, have superhuman senses of smell but can't taste most foods, are sensitive to sunlight but not destroyed by it, lead a nocturnal lifestyle, and can endure cold better than humans but are more vulnerable to heat. They drink blood on ritual occasions but don't seem to require it for survival.

The ways authors rationalize science-fiction vampires fascinate me. Some striking examples include, besides THE VAMPIRE TAPESTRY, George R. R. Martin's FEVRE DREAM, Jacqueline Lichtenberg's THOSE OF MY BLOOD, Octavia Butler's FLEDGING, and S. M. Stirling's Shadowspawn trilogy (A TAINT IN THE BLOOD and two sequels). I analyze these and many other works in that subgenre in my nonfiction book DIFFERENT BLOOD: THE VAMPIRE AS ALIEN.

Different Blood

Margaret L. Carter

Carter's Crypt