Most of the body doesn't regenerate because there was not enough evolutionary pressure. Even with regeneration you could still easily die from some severe injury, blood loss or disease. While salamander regeneration is impressive, it has its limitations. For example, no known adult salamander can regenerate an entirely removed eye. Also if you chop a salamander, it will not regenerate like a Planarian worm, it will just die. And a fun fact, Axolotls can regrow a limb yet cannot regenerate an adult eye lens.
Also, although the article is mostly true, there are some inaccuracies:
>> Neurons and cardiac muscle cells don't reproduce after childhood
There is some evidence showing a slow cell turnover in cardiac muscle, estimated around ~1% per year in young adults, falling toward ~0.5% in older people. Most neurons don't regenerate, but there an evidence that some parts of the adult brain (such as hippocampus) still produce new neurons, although the number is very low.
Liver regeneration is not perfect either: https://www.youtube.com/watch?v=rOv7Sr3X-eo .
I have an axolotl. They're really incredible creatures, with way more personality and interests than you would expect. They are really soft, and almost have the same density as water, so they can be neutrally buoyant and even swim rapidly like a fish. They're also very sensitive to sharp things; mine recently got a cut from an aquarium decoration, which healed fully over the course of a week. Her previous owner had neglected her and induced tail curl, which took longer to heal (a few months) but did fully heal. I have since adjusted her tank to give it all flat or smooth surfaces, with some variety.
https://ambystoma.uky.edu/teachers_materials/axolitbook/Axol...
Oh no! I read that one as a teenager. Hunting!
Actually I would argue that the evolutionary pressures run against it: if one generation dominates then the species can't evolve.
Regeneration is unlikely to warrant eternal life. In the wild, most animals die before even showing serious signs of aging. Even if regeneration increased lifespan, poorly adapted individuals would still die.
evolution doesn't act on the species or even individuals, it acts on the genes which is why it looks like evolution acts on the individual and its close family unit.
people have a hard time grasping this concept for some reason.
my favorite example to illustrate this is the trait of being poisonous. if evolution cared about species and then every single one would be poisonous and all predators would have to hyper specialize in prey (arms race between a particular poison and its resistance). it's precisely because it's so difficult to elicit a benefit from this strategy for the lineage that it's so rare. almost always a mutation in coloration has to happen to set the lineage apart from the others first. and then the lineage has to survive the disadvantage long enough.
The current model is that evolution acts on the molecular, cellular, and genetic level, and most importantly, at the population level.
https://en.wikipedia.org/wiki/Structural_inheritance
basically, the genes do not generally contain blueprints but rather processes utilizing existing cellular machinery. a "mutation" can occur in a machine which will allow a propagating difference.
and there is nothing special about populations. it's merely the only way to observe most changes. gene frequencies in gene pools.