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: <a href="https://www.youtube.com/watch?v=rOv7Sr3X-eo" rel="nofollow">https://www.youtube.com/watch?v=rOv7Sr3X-eo .
> Most of the body doesn't regenerate because there was not enough evolutionary pressure.
All basal metazoan branches (ctenophora, porifera, placozoa, cnidaria) have species that are capable of whole body regeneration, so this trait was likely lost on the bilaterian branch (which includes chordates like ourselves). If anything, there are evolutionary pressures to loose this trait.
For example, consider how frequently people lose a limb, and further consider the ratio of survival to death for injuries in that general ballpark. Then balance this quality of life improvement, for those who survive, for those injured in the first place, against the fact that all people with such a biological capability will almost certainly experience a significantly higher rate of cancer. Because in a nutshell cancer is uncontrolled proliferation while regeneration is controlled proliferation. (It would be very interesting to know the rate of incidence of various cancers in axolotls if they lived anywhere near as long as a human.)
Yes, that was my point. Amputations are quite uncommon, they usually lead to death (blood loss / infection, starvation, vulnerability to predators, etc) For relatively intelligent species they are even more avoidable. Regeneration would add very little benefit from natural selection point of view. Most body parts are durable enough for survival and reproduction.
senfiaj · · focus · HN ↗
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: <a href="https://www.youtube.com/watch?v=rOv7Sr3X-eo" rel="nofollow">https://www.youtube.com/watch?v=rOv7Sr3X-eo .
burning_hamster · · focus · HN ↗
All basal metazoan branches (ctenophora, porifera, placozoa, cnidaria) have species that are capable of whole body regeneration, so this trait was likely lost on the bilaterian branch (which includes chordates like ourselves). If anything, there are evolutionary pressures to loose this trait.
fc417fc802 · · focus · HN ↗
bondarchuk · · focus · HN ↗
senfiaj · · focus · HN ↗