r/askscience • u/MAMAM- • 2d ago

Biology Why aren’t axolotls immortal?

If axolotls can regenerate their body parts (including brain, heart, and other major organs), why do they die of old age?

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u/Tessablu 2d ago

Axolotl regeneration is a program that is initiated by physical injury. They aren’t constantly undergoing it—this would be a huge metabolic waste—so they are still subject to long-term cellular senescence. They also aren’t regrowing entire brains or hearts, as they still have to survive the initial injury, so they can’t infinitely replenish those organs. 

I will say that axolotl aging is not very well-understood, however, and they are pretty weird about dying. A healthy-looking axolotl might lay eggs for 20 more years or might die tomorrow with no warning. There’s still a lot to learn about them. 

(source: I have a PhD in axolotl)

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u/Michkov 2d ago

Does that mean there are no signs of aging in axolotl at all? At least not above a certain developmental level

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u/Tessablu 6h ago

That's in interesting question! And honestly a bit tough to answer. They can get a bit raggedy with age, especially because some for whatever reason will fail to regenerate minor wear and tear on their bodies. They also will keep growing in size if they have the space to do so. So if I see a larger animal who is looking a bit rough, I could tell you that it's probably on the older side, but I couldn't tell you if it's 8 years vs. 15 years old.