Here's a breakdown of the major themes in the Hacker News discussion about limb regeneration, supported by quotes:
Ethical Concerns and "Ick Factor" Regarding Organ Harvesting
A strong theme revolves around the ethical implications of growing human bodies for organ harvesting. "echelon" suggests a radical approach to solve the aging problem: "We should really just grow clones in labs and harvest them for parts. Remove the brains at week 16 through genetic and surgical means. Keep the rest of the body artificially alive...It's so simple and obvious, but nobody can get over the egocentric morality qualms and superstitious ick factor." They argue for overcoming moral objections to what they see as a practical solution, stating, "Our bodies are plants. It's our minds that are special. We should be able to transplant every other part." This highlights the tension between technological advancement and deeply held moral values.
Practical Challenges of Whole-Body Cloning and Transplants
Several commenters point out the significant practical obstacles to the "clone and harvest" approach. Specifically, "IX-103" notes, "I think the big factor there is that you'd have to wait over a decade for the transplant to be the correct size. I'm also not sure that we have the technology to keep a brainless body alive for such a long period - the brain is involved in a large number of processes that we don't yet have a way to replicate. And then you'd need a complex surgery to perform the transplant." "metalman" echoes the complexity, warning of "hugely complex surgeries that will take a long, realy long time, and there will be complications, so the risk to benifit ratio will only be good in a few scenarios....for which you need a wildly complex and expensive facility to prepare for many years in advance." These comments emphasize the technological hurdles that must be overcome before such a system could be viable. Furthermore, "jodrellblank" adds, "Saying 'it's so simple' doesn't make it simple."
Alternatives to Whole-Body Approaches: Pluripotent Cells and Organ Cloning
A counterpoint to whole-body cloning involves exploring alternative strategies for regeneration and organ replacement. "IX-103" advocates for using pluripotent cells, stating, "Pluripotent cells work fine in many animals with no apparent problems and avoid all of the issues with the clone approach. If pluripotent cells turn out to cause problems, then we could always engineer a kill switch to make sure they die off after the limb is regrown." "bitwize" highlights the potential of organ cloning: "I think that cloning individual organs is much more promising than cloning entire bodies and then harvesting. Much less work, you don't have an entire body you need to either upkeep or dispose of." These approaches are seen as potentially more manageable and ethically less problematic than growing entire bodies for parts.
The Role of the Brain and Nervous System in Regeneration and Body Function
The discussion delves into the intricate role of the brain and nervous system in the regeneration process. "v3ss0n" questions the idea of isolated limb transplants, asking, "Brain is necessary for growth, repair, and several immune responses. Do you want a zombie arm?" "ddingus" suggests a link between brain function and physical capabilities explaining "Ever notice as we age, get hurt, that table, network, updates?... And when I try and do it today, there is a very deep inhibition. My brain / body knows it no longer happens that way." "metalman" emphasizes that the nervous system of a "part" needs the brain in order to function. "jodrellblank" adds to this by pointing out that, "The gut has the enteric nervous system with half a billion nerve cells and a hundred million neurons. Where's the clear divide between 'brain' and 'everything else'?"
Regeneration in Other Species and Implications for Humans
The discussion frequently references examples of regeneration in other species, particularly salamanders and axolotls, to understand the potential for human limb regeneration. "alphazard" draws a parallel to limb development in utero: "We do grow limbs routinely, in utero. Typically 4 limbs per person. I would assume that we would be looking to activate the genes responsible for that same process." "sheepscreek" mentions, "From what I’ve read, Salamanders of all kind retain their stem-cell embryonic growth capabilities in their early life (after birth). But once they become adults, they become more mortal like the rest of us. But Axolotls for some reason never lose their ability." Several commenters discuss the idea that humans evolved through neoteny: "crazydoggers" posits, "There’s actually a theory that hominid ancestors at some point split off from other great apes by also not going through the typical great ape sexual maturity. For examples humans look a lot more like juvenile chimps that we do sexually mature chimps."
Bioelectric Fields and Non-Genetic Factors in Regeneration
The work of biologist Michael Levin, who studies bioelectric fields is discussed, focusing on the crucial role of bioelectric fields "oa335" includes a quote that details Levin's theories "Biologist Michael Levin posits that bio-electric fields, not simply genes, hold the key to limb regeneration." "cyberax" initially expresses skepticism: "This has always seemed like BS. There's just not enough expressiveness in electricity." However, "danwills" clarifies the concept: "I think people often hear 'bioelectric' and think it means electricity (electron flux) but what Levin's work is about is a pattern of voltage gradients (that cells maintain using electrically-non-neutral chemicals) that stores a pattern like a memory...of what to grow back into when the tissue is damaged." This explanation helps to clarify the more nuanced role of bioelectric signaling.