Who Wants to Live Forever?

That's roughly the title of an article I came across in the newspaper over the weekend:

Want to Live Forever?

Disappontingly, the article doesn't offer the secret to immortality. It suggests three main ways of extending one's lifespan, two of them rather mundane: Vitamin B12 as an aid to physical and mental health in aging; maintaining optimal sleep rhythms; becoming a Greenland shark. Found to live two centuries or more, Greenland sharks have "evolved resilience to molecular and tissue damage over time."

Here's the Wikipedia page on the longest-lived known species in various categories:

List of Longest-Living Organisms

Even not counting colonies, clones, microbes, or creatures such as the "immortal jellyfish" (reverting to a larval stage and cycling through repeated growth phases), it's worth noting that almost all the extraordinarily long-lived species -- those that exceed the normal human lifespan -- aren't mammals. Some trees are 4000 years old or more. The glass sponge can reach 10,000 years. Another type of sponge is known to live to 1550 years, while tubeworms may reach 1000. One particular Greenland shark may be over 500 years old, the longest living vertebrate. Giant tortoises' lifespans have been estimated at approximately or, in at least one case, beyond 200 years. Bowhead whales may reach two centuries, making them the longest-lived mammals. Some birds live to over 100. Virtually all the other animals on the list capable of outliving us aren't warmblooded. Moreover, many of them dwell in cold environments, particularly aquatic. Is there something about cold water that promotes longevity?

Judging from the known record-holders among humans, our maximum lifespan peaks around 120. Therefore, Robert Heinlein's fascinating life-extension project, as described in METHUSELAH'S CHILDREN and related works such as TIME ENOUGH FOR LOVE and TO SAIL BEYOND THE SUNSET, simply wouldn't work the way it's portrayed. If the genetically determined limit on our lifespan is set at 120, no amount of concentrated inbreeding among individuals with genes for longevity would produce descendants surviving for multiple centuries. The breeding project couldn't create new genes. A mutation would be needed; in the introduction to TIME ENOUGH FOR LOVE, it's explicitly stated that Lazarus Long, born near the beginning of the multigenerational project and practically immortal (although even he, like everybody else, requires artificial life-extension treatments to go on surviving indefinitely), owes his phenomenal age and perpetual youth to a mutation. In much later generations, after he has spread his genes throughout the network of "Howard Families," it would be plausible for all their offspring to live for centuries without aging beyond maturity. But not at the time of METHUSELAH'S CHILDREN.

Anyway, as the theme song to the TV series HIGHLANDER puts it, who wants to live forever? One society in Jonathan Swift's GULLVER'S TRAVELS includes a subset of immortal people. They do grow old, however, and they have an unhappy lot in other ways. Senility inevitably creeps up on them. Well before that, at a certain point in their lives they are declared legally dead, their possessions transferred to their heirs. Classical mythology features a similar cautionary tale, about a goddess who petitions endless life for her lover but forgets to include endless youth. Even if immortals remained in the prime of perpetual health, would they really want to outlive their mortal loved ones? Boredom with deathless existence appears frequently in vampire stories, leading to suicide by daylight (in the case of those vulnerable to the sun). TIME ENOUGH FOR LOVE starts with Lazarus Long trying to kill himself out of boredom. Endless extension of earthly life as we know it doesn't sound too appealing. Linear survival in "chronos" -- ordinary clock time -- wouldn't be the same as eternal life in "kairos," a richer, multidimensional mode of life.

Margaret L. Carter

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

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