New research reveals longevity gains slowing, life expectancy of 100 unlikely

We know it’s possible for living things to be functionally near immortal.

We also know germ line cells can give rise to new organisms which can give rise to germ line cells in an unbroken chain effectively forever.

This is quite far from making a human immortal but it shows that there appears to be nothing in physical law or intrinsic to biology that prohibits it. Therefore it is possible.

Star travel and terraforming Mars are also possible. Possible does not imply anything about difficulty. We don’t really know if radical life extension or borderline immortality are fusion hard, quantum computing hard, or starship hard.

> We know it’s possible for living things to be functionally near immortal.

Not in any sense that's applicable to humans.

The often-cited animal examples, like greenland sharks, tortoises, and lobsters, are slow-moving ectotherms with "cold" metabolisms. Adjusting for watts per unit mass of biochemistry, they might "live" less in all their centuries than you do in a single decade [0-3].

In that sense they're only "long-lived" in the same way a tree is long-lived. Yeah, it might not die. But it's also not doing much that produces wear and tear, misfolded proteins, scar tissue, plaque buildup, etc.

Microorganisms and cnidarians, which can be truly immortal, are even more divergent. For example a common form of "immortality" involves periodically regenerating body parts by reverting to stem cells. IIRC regeneration is ancestral to all animals, but mostly lost in mammals.

Humans can actually already regenerate to a limited extent [4]. But how are you going to regenerate an entire primate nervous system (which "immortal" animals don't have), without losing everything you are?

In fact, the use of regeneration to achieve "immortality", and even that only rarely and in very simple animals, suggests it may not be possible at all for living organisms to live indefinitely in the same body. Otherwise, why would evolution waste calories rebuilding a whole body?

I suspect some systems-theoretic effect like the Red Queen hypothesis [5], but on a micro scale. Change is the only constant, and immortality implies trying to stay the same when the only thermodynamically favorable options are to grow or decay.

  0: https://www.nature.com/articles/s41598-020-76371-0
  1: # Greenland shark metabolism over entire lifespan
     sh -c "units '((30mg/oxygen)*(mol/g))/hour/(1000/1000^0.84*kg) * (434kJ/mol) * 200year' MJ/kg"
  2: # Greenland shark lifespan metabolism, alternate estimation
     sh -c "units '192kcal/day*200year/126kg' MJ/kg"
  3: # Human metabolism over 1 decade
     sh -c "units '150W/100kg*10years' MJ/kg"
  4: https://en.wikipedia.org/wiki/Regeneration_in_humans
  5: https://en.wikipedia.org/wiki/Red_Queen_hypothesis

I don't think regeneration of bulk tissue is what people are generally talking about when they talk about immortality. Rather they talk about there being advanced homeostasis from yesterday, to today and to tomorrow under "normal" living condition. The point is not that you should be able to regenerate from blowing your brains out.

Yep. The point I'm making is that there is no precedent in nature for a complex animal maintaining homeostasis indefinitely like that (that doesn't rely on bulk regeneration). And given such immortality would presumably be highly evolutionarily advantageous, there is therefore no reason to believe it's possible at all, and many reasons to suspect it might not be (antagonistic pleiotropy, chaos theory, thermodynamics…).

Aren't some trees, some fungi, some sharks and some crabs basically exactly that? They are most certainly complex life. Sure you are right heir metabolic profile is very different.

But really the your argument is already shifting to "there is no life ver similar to humans that do it, so it must be impossible" which imo is a much larger stretch then assuming it's possible.

We aren’t much more complex than a crab, if we are at all. “Complexity” is not what makes us what we are. It’s that we went down an evolutionary path that heavily leveraged intelligence and social cooperation so we got a big hypertrophied brain. Our brain is like a cheetah’s musculoskeletal system or a rabbit’s reproductive system.

The OP is also massively underestimating plant complexity. We aren’t much more complex than a tree either.

We are higher metabolism than both though, and with that the OP has a point. We are already long lived for a high metabolism animal. Our metabolic rate makes it harder for our repair mechanisms to stay ahead of oxidative and radiation damage. That will make extreme life extension hard for us, harder than if we were reptilians or arthropods.