I asked chatGPT for an analysis of the links between Regeneration, Rejuvenation and Aging. This was the result:
Short answer: It depends on the animal.
Some species never seem to lose their regenerative super-powers, some keep them but the process slows with age, and in a few (including most mammals) the capacity is switched off very early in life.
1. Species that keep regeneration for life
| Group |
Typical examples |
What we know about ageing & regeneration |
Key references |
| Basal invertebrates |
Hydra (fresh-water polyp) |
Stem-cell–driven self-renewal is continuous; mortality and fertility curves stay flat for years, implying no age-related decline in regeneration at all. |
(PNAS, ScienceDirect) |
| Flatworms |
Planarians (e.g. Schmidtea mediterranea) |
Even “old” planarians still rebuild an entire body from a tiny fragment. Recent work shows that a round of regeneration can actually rejuvenate aging tissues. |
(Nature) |
| Urodele amphibians |
Mexican axolotl, newts |
Axolotls regenerate limbs, tail, spinal cord and even parts of the brain throughout a 10- to 15-year lifespan; repeated amputations in very old newts do not measurably reduce success, only slow the timetable a little. |
(Financial Times, PMC) |
2. Lifelong but slowing regeneration
| Group |
Example tissues regenerated |
Age-related changes |
|
|
Teleost fish (zebrafish) |
Fins, heart, retina |
Old zebrafish still regenerate but cardiomyocytes show replication-stress and the process takes longer. |
(Nature) |
|
Reptiles (most lizards) |
Tail |
Older lizards regrow tails more slowly and the cartilage tube is often thinner, but the capacity itself is retained. |
(PMC) |
|
Spiny mouse (Acomys) |
Skin, ear cartilage, skeletal muscle |
Adults of all ages regenerate with little scarring; very aged animals complete ear-hole closure more slowly and sometimes incompletely. |
(ResearchGate) |
Why the slowdown? Common themes are stem-cell DNA damage, epigenetic drift, and changes in the immune milieu that turn injuries from pro-regenerative to pro-scar-forming environments. (Nature)
3. Regeneration that is switched off early
| Species (mammals) |
What they can regenerate |
When the window closes |
|
| Mouse heart |
Full-thickness ventricular apex |
Day 1 neonates regenerate; by day 7 the same injury scars instead of regrowing muscle. |
(PubMed ) |
| Human fingertips |
Distal phalanx in children |
The ability fades around puberty; adults generally scar. (Clinical literature, no loss-of-function genes identified yet.) |
|
| Most other mammalian tissues |
Skin, liver, etc. |
Capacity declines steadily with age because resident stem-cell pools shrink and become senescent. |
|
Mechanistically, mammals restrict regeneration partly to guard against cancer: tumour-suppressor pathways (e.g., p16^Ink4a^) ramp up quickly after birth and curb the cell-cycle re-entry that true epimorphic regeneration demands. (PubMed )
4. Putting it together
-
No-loss species (Hydra, many planarians) couple continuous stem-cell cycling to strong genomic maintenance, so regeneration and “non-ageing” go hand-in-hand.
-
Slow-down species (zebrafish, lizards, spiny mice) maintain the genetic programmes but accumulate enough molecular and immunological “noise” that each round of repair is just a bit less efficient.
-
Early-loss species (most mammals) silence the programme entirely once development is complete, probably as an anti-cancer trade-off.
So the answer is not universal: whether a regenerating species loses that ability—and if so, when—depends on how its stem-cell biology, immune system and cancer suppression have been balanced over evolution.
The reason I think it is relevant is because I think regenerative abilities link to mitochondrial membrane potential.
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