The only vertibrates I know of that can even regenerate spinal cord, so long as the injury does not kill the animal outright, are urodele amphibians. Maybe zebrafish can do this too, I’m not sure. I don’t think either has significant capacity to regenerate brain. You pretty much have to go down to the level of flatworms to get that kind of regenerative capacity, and they don’t have much of a brain, really, just bundles of nerve cells up under the eyespots.
But newts and salamanders and such are truly amazing, all the same. You can remove a cm of their spinal cord, and it will grow back, good as new. Cut off an eye; it grows back. They can regenerate portions of their hearts, entire limbs, things no other verebrates can do at all. Mammals don’t even have close to this regenerative capacity. Some scientists are studying newts and zebrafish to see if mamals could be given such regenerative potential, at least for some tissues, like the spinal cord or the heart. There are lots of approaches being explored now, usually involving stem cell therapies, or perhaps manipulating differentiated cells such that they aquire stem-cell-like properties, as newts do in the regenerative tissue known as the “blastema”. Mammals don’t make blastemas, anywhere, anytime. Beyond the fetal stage, we lose this capacity virtually completely. That goes for mice as well as men, no matter how comparitively primimitive they may seem. Mice are actually not all that distantly related to us, but I won’t go on that tangent. Suffice to say, all we mammals retain is a relatively pathetic pool of stem cells, derived either from the bone marrow or other places, like those regions of the brain I mentioned above. These stem cellss can do a little, but not a lot, to repair some tissues, like CNS, heart, etc. They perhaps allow us to cope with a low level of wear-and-tear, but they don’t do much for injury, and they certainly don’t make us immortal.
Truly, as you say, our ability to learn decreases with age. There is no universal rate at which this occurs, but it seems to be true of everyone to a certain degree. I’m sure neuroscientists would like to know what makes normal people endowed with great cognitive longevity so special. Could these qualities be enhanced, via drugs, cell therapies, gene therapy, or genetic engineering?
Again, who knows. These are the ultimate goals, though. It’s not a gross exaggeration to say that scientists are searching for the fountain of youth, so to speak. I doubt we’ll find it in any one place, or through any particular method. Purely speculating, I think its possible some day we’ll learn enough about human biology, and the biology of other creatures we hope to emulate to some degree, that its possible we may greatly enhance human longevity (as well as the quality of life during that span) in the not-too-distant future. Perhaps within a couple hundred years. It will be a huge challenge, and certainly will open up a host of ethical pandoras boxes, but everything is pointing in that direction. We want to live longer, be smarter, etc… We see, through animal experiment, that its possible to manipulate genetics to increase life span, enhance memory, and so on. If newts can do it, why can’t we? That’s a question being asked seriously by some very bright and accomplished people. The answer could well be, “We can!” Not “naturally”, but via drugs, other therapies, and, ultimately, changing our genetic makeup deliberately.
Human evolution may be at the cusp of an epoch of genetic self-determinism, driven largely by the dream of immortality. Hang on to your hats! It will be a wild ride for civilization, I’m sure.
