Many animals, notably salamanders, axolotls, octopuses and starfish (etc) are able to regrow limbs (and other body parts) which have been lost through accidents or disease. Although mammals can regrow various tissues - notably skin, liver and tail tips - there is no ability to regrow limbs etc.

Some research groups suggest that the capacity for mammals to regenerate is genetically 'turned off'. If regeneration could somehow be 'turned on', it would be of huge benefit to amputees, and those with damage to other organs etc.. At present the biological mechanisms which control for regrowth are unknown.

Regeneration remains one of nature’s most exciting mysteries.Several organisms can regenerate diverse parts of their bodies with different efficiencies. Although important progress in the understanding of this phenomenon has been made in the last decades, the precise spatio-temporal cellular dynamics of the regenerative response remains an unresolved puzzle."

Source : Developmental Biology, Volume 461, Issue 2, May 2020

Several versions of 'Regenerative Medicine' are currently under development - with various drugs being tested for their potential to induce regrowth. None is as yet in routine use. See: Wikipedia

It has recently been suggested that salamanders - which have a record-breaking genome sizeplugin-autotooltip__plain plugin-autotooltip_bigGenome size

The size of the genome (the amount of DNA in an organism's genes) varies enormously from one species to another. The smallest sizes, for viruses, ranges from around 2 thousand base-pairs to over a million.

Humans have about 3 billion (forming around 19,000 genes *) - but some plants have more than, and very slow development - may have a predominance of stem-cells in their bodies, making it easier to generate new, specific cells, as required. See : Junk DNA Deforms Salamander Bodies Scientific American, Feb 2022.

Also see : Neural regenerationplugin-autotooltip__plain plugin-autotooltip_bigNeural regeneration

It's known that neural tissue can routinely re-generate in several species. The subject is intensely researched because of its potential to re-grow neural tissue which has been damaged, either due to disease (e.g. Parkinson's disease, Multiple sclerosis , Poliomyelitis etc), or by physical injuries.