Our closest worm kin regrow body parts, raising hopes of regeneration in humans | Hacker News Reader

Our closest worm kin regrow body parts, raising hopes of regeneration in humans

washington.edu

281 pointsawqrre156 comments

A lot of people are focusing on the mechanics, but it seems like humans don't generate body parts just like cells don't generate organelles. The entity is not _meant_ to exist by itself, but form a cohesive living group.

A cell doesn't need to repair itself, it can simply clone itself and then die. A human being doesn't need to regenerate itself because it can reproduce and be cleared away. Evolution evolved to ensure the survival of the species, not the individual.

The human being is constantly generating itself by multiplying cells. Similarly, the species is constantly generating itself by multiplying individuals.

> Evolution evolved to ensure the survival of the species, not the individual.

At some point in our evolutionary history the cells in our body made this choice. Evolution favors survival and potentially reproduction, because otherwise you are no longer in the game. So there was some evolutionary constraint that caused those genes not to regenerate parts.

It's possible we can change things so that those genes are active again. But we don't really understand these systems well enough to do that and won't anytime soon. But science carries on and I am sure you can make lab mice to test hypotheses of how this might work in mammals. And we probably will very soon, if not here then in China.

Evolution is perfectly fine even if you don't reproduce much, as long as you continue to survive in your environment. There are creatures out there that have changed very little and we know this because we have fossil records, and this is because they have been adapted to their environment and stayed adapted despite the environmental changes. And there are even immortal creature that die not because their bodies age and kill them but because they are eaten by other things, but still they don't change much over time. I guess you could say they are better evolved than other creatures that have to constantly change. They made better evolutionary decisions than other creatures very early on.

You don't have to regenerate parts to live long enough to have offspring. You can do it at like 15 years old. So evolution isn't going to help in that regard much.

Living for a long time after you have children is incredibly useful from the standpoint of genetic fitness. After all, grandparents play an important role in pretty much every human culture. And a grandparent with all their body parts is a whole lot more useful than one without.

There are plenty of species where the male dies during mating, and squillions more where the male isn't around after mating.

Evolution only requires that you get to reproduction, however that happens. It doesn't require that you're happy, sad, whatever, just that you reproduce.

> Evolution only requires that you get to reproduction, however that happens. It doesn't require that you're happy, sad, whatever, just that you reproduce.

It requires that your offspring actually survive as well. Humans are, at least historically, exceptionally well-equipped to influence the survival of their offspring.

Humans also take figuratively forever to be self-sufficient. Herd animals are born with the ability to walk, for example. Humans take about 10 years before they can be taught to be even somewhat self-sufficient, which is a ridiculously long time in comparison to others.

So, given that humans are sexually mature before they're fully self-sufficient, that enhanced ability to support their offspring is not all advantage - it's actually required for the propagation of the species. If older folks weren't taking care of the younger ones, none of them would reach reproductive age.

A 7 or 8 year old can hunt if you were to teach them to do so. An 8 year olds has conceived. So it's possible to do it at a much younger age if you have no choice.

While it may sound callous, if that 8-year-old did not produce viable offspring that could mature to reproductive age themselves, she is irrelevant to evolution. Conception is not synonymous with viable offspring.

As for the 8-year-old hunter, just how self-sufficient can they be? Procuring their own weapons, transporting their own carcasses, preparing healthy meals multiple times per day on an ongoing basis... the idea that you could just loose a 7-8 year old into the woods with a weapon and they'd survive in an ongoing sense is a bit far-fetched. Teaching someone to sneak, track, and point a gun is not the same as them being self-sufficient.

>Living for a long time after you have children is incredibly useful from the standpoint of genetic fitness. After all, grandparents play an important role in pretty much every human culture.

In the time scale that matters to evolution, grandparents played absolutely no role for the Homo Sapiens, and neither did culture.

I don't think that's at all likely. We've had fire and had the physiological adaptations enabling speech for well over a million years. We've been manufacturing complex tools such as spears with stone tips for about half a million years, to Homo heidelbergensis. Even Ergaster had lifespans allowing survival to an age where grandchildren could reach adulthood, allowing for skills transfer.

In many historic cultures, 'elders' were the ones who controlled the tribe.

Do you have children? Raising children is hard. And it's a lot less hard when you have other adults to help. Historically, those would be grandparents and aunts/uncles. But aunts/uncles would probably have children of their own.

"Historically" is the keyword here. Evolutionary timespans are much much larger than recorded history and human culture as we know it.

Nobody's saying that grandparents being alive are a prerequisite for grandchildren. But anybody with kids will tell you that grandparents are tremendously helpful in raising children.

Evolution is statistical in nature, not binary. Grandparents just have to be useful in raising grandchildren for them to be favored by natural selection. They don't need to be strictly necessary.

The counterpoint being that in resource-scarce evolutionary environments, every grandparent (or even parent) that stays around is consuming resources that could instead go toward creating+maintaining an additional child.

Often grandparents will starve to keep grandkids alive. Grandkids eat first.

That's assuming that they consume more resources than they extract from the environment. And then there's also that grandparents can use the power and influence they've accumulated to benefit their grandchildren.

I agree with you but don't forget the role of genetic drift.

It doesn't have to be all about the evolutionary fitness of regenerating limbs. I think it might just be that losing a limb (and having the opportunity/time to regrow it) may have been a fairly unlikely event. Possibly, those genes mutated and were broken, right around the same time that some other genetic advantage evolved that caused a huge gain in evolutionary fitness.

The ability to regenerate limbs could have been lost in mammals simply because some old pre-mammal who happened to have broken regeneration genes was smarter and much better at finding food than the rest, and went on to pass his/her genes to all of us.

Furthermore, the evolutionary advantage of regenerating limbs may not be much in most animals. It's something we really would like to have, But imagine that some ancient primate species was able to regenerate limbs. Under what scenario do primate lose limbs? When some tiger chews them off? If that was ever to happen to a primate, it was basically fucked. Even if the tiger didn't eat it, it didn't fare very well lacking an arm for several months. The primate that is better at spotting tigers and avoiding them has much higher evolutionary fitness.

Those mechanisms are good enough to have brought us to this point, but that has no bearing on what kind of future we choose to create for ourselves.

Metals rust and seep into the ground, but we dig them up and build spacecraft from them. Metals aren't _meant_ to do that, but we have some influence over our environment. We might end up having a similar influence over our cells.

This, to me, brings up the question of "where does myself ends and where does my environment begins?". I could change parts of my brain like I'm changing the environment around me, what would I be changing, the environment around me or myself directly? Both?

Classic greek Boaty McBoatface question I know. (cf Ship of Theseus)

> This, to me, brings up the question of "where does myself ends and where does my environment begins?".

Good question this! Until you find a conclusive answer, ie. until you clearly define/delineate "myself" & "env", you can ignore your follow-up question as irrelevant sophistry:

> I could change parts of my brain like I'm changing the environment around me, what would I be changing, the environment around me or myself directly

That question is exactly what I'm asking, what is "myself" and what is "the environment as defined around myself".

And I'm pretty sure there's no clear answer, but the question and reasonings ensuing are interesting.

By one definition, my possessions, my experiences, my social network would be part of myself. So changing my brain wouldn't be changing myself per se if those remained the same.

Another definition would be the strictly biological body, and of course changing the body would be changing the self.

But there's a fuzzier definition where something in the brain brings up "consciousness" and a sense of self, if I change something in the brain that isn't that particular part, the sense of self, have I changed the self or not?

(I can see my French high school teaching re-surging here...)

Self has no universal meaning robbing the question of any real value. You could include or exclude gut bacteria from you just as easily as you include or exclude identical clones, but that's just an outgrowth of your definition and says nothing about reality.

All abstractions leak eventually. You can't separate anything in the universe from everything else. To clone yourself perfectly (for all time-slices going forward), you'd have to clone the entire universe.

> Evolution evolved to ensure the survival of the species, not the individual.

Depending on which view you take, evolution can be seen optimized for the survival of individual genes, not species[0]. In Dawkins' book, bodies are portrayed as mere useful survival vehicles for various genes.

(I'm ignorant on this, would love to read counterarguments from someone better versed!)

[0] https://en.wikipedia.org/wiki/Gene-centered_view_of_evolutio...

Indeed virii are part of the evolutionary process and can insert genes into hosts from various species. Such genes can be successful from an evolutionary standpoint even if some of the host species disappear.

Not contradicting your core argument (though I'm sceptical about the significance in impact of this process), but you are certainly apt at mutating grammar: the plural of virus is viruses - not virii.

http://english.stackexchange.com/questions/3838/viruses-or-v...

ps: this is like kerning, you can't unsee it..

http://xkcd.com/1015/

Thanks :)

This idea can be applied to any species, and yet, there are animals who regrow body parts - octopus can regrow tentacles, crayfish and lobsters can regrow claws, salamander can regrow tail and limbs, etc.

The specie as the unit of selection is an idea that is very unpopular in the biological community. A lot of people believe instead that evolution works first and foremost at the gene level, and that gene selection is the driving factor for evolution.

https://en.m.wikipedia.org/wiki/Unit_of_selection

I think the difference in the 21 century is increased awareness of consciousness. Unconscious animals don't care about survival of their own self. They just reproduce.

Humans, since getting a bit of self-awareness have been fantasizing with the idea. Religion, and self-rebirth after death is an example.

Now they are getting more real and more practical. If you think about it, it makes more sense to increase your lifetime than make another person to carry-on your dreams.

Your emotions tell you otherwise, because you were made to reproduce. The brain is working something else. It's evolving and thinks that it can solve this problem and instead re-make the body.

Well, a plausible answer is that if we (or random mutations) re-enable those genes then the end result is simply a lot of cancer.

A reasonable default assumption is that each switch in our "genetic configuration" is set to a quite good value.

The only exception is if we see a feature that is beneficial at a high calorie cost - those features have been (reasonably) optimized away during our evolution, but would be useful in modern circumstances where food is not scarce anymore; this is a tradeoff where it would make sense to just turn the dial way to the right from where it had been throughout the last million years.

And perhaps some people might risk the chance of cancer to grow their body parts back.

Also with regeneration just cut out large chunks containing cancer and hope round 2 of your lungs is better!

Perhaps it could be turned on and off as needed: lose a finger in an accident, and take a drug to turn regeneration on. Grow your finger back in a week, and then take another drug (or stop taking the first drug) to go back to normal.

Your comment was either flagged or downvoted in to oblivion... I have vouched for it as I can't see any reason for either...

That's not how it works. For your finger to be capable of regeneration, the relevant genes would have to be in all your cells beforehand.

Advanced genetic engineering can be used to ensure that particular genes get activated only in the presence of some molecule that isn't naturally present in humans, so it would happen only if you take that particular drug; but it would still be applicable only to "newly built" humans e.g. as part of in vitro fertilization, not as something that can be applied to adults.

if you got cancer, just cut that piece off and eat more?

Yeah, just regrow that brain, liver, thyroid gland.

It could be those genes raise chance of cancer everywhere. Not just limbs.

I'd be willing to activate that feature if I was about to die.

Idea was not to activate ability. But to be born with it.

Are there animals that regrow their brain after a partial labotomy? In any case, humans can live with large chunk of brain removed, under the right circumstances.

The liver can regenerate. As little of 25% of the original liver mass can regenerate back to full size after either surgical removal or chemical injury.[1]

[1] https://en.wikipedia.org/wiki/Liver_regeneration

>Well, a plausible answer is that if we (or random mutations) re-enable those genes then the end result is simply a lot of cancer.

Interesting idea, but does the risk of cancer have that much selective pressure? It tends to be the "last thing that kills you", after you live long enough to survive everything else. So it seems like any increased risk of cancer would have to be pretty high before it traded off against injury recovery. Then again, "injury recovery" might not have been as beneficial either -- the time to regenerate would still leave you vulnerable, so adaptations favoring avoidance of that injury would have a leg up in selective pressure.

It's typically something that only hits you in old age because your body defends against it quite effectively.

For large animals, I'd believe that it's very rare to have non-fatal injuries that are large enough where regeneration would make a big difference to future life.

According to evolution (which hasn't yet noticed medicine), if something rips off your foot, that's not an injury, you simply bleed to death or die of infection even if you win the fight - unlike, say, various small regenerating lizards. What selective pressure could there be to regenerate feet if there were almost no (alive) people with missing feet until the last few hundred years?

However, risk of cancer is serious selective pressure even with short lives - e.g. https://en.wikipedia.org/wiki/Devil_facial_tumour_disease. Cancer tends to be the "last thing that kills you" exactly because so much of our biology is tuned to resist cancer. Also, all kinds of mechanisms causing our aging problems seem to be simply evolutionary adaptations to resist cancer by limiting cell division.

> if something rips off your foot, that's not an injury, you simply bleed to death or die of infection

That's a false premise.

Plenty of (four-legged) animals can survive just fine without a leg - in fact, it's often said that animals have a spare leg. Some animals might even gnaw their own leg off it's stuck in something and they can't get it out.

It's kind of correlated with size - the smaller the animal is, the easier it is to survive after losing a limb. For a horse, even a broken leg is likely to be fatal.

A missing foot is survivable for a lynx much more so than for a human in the absence of modern medical care.

The same applies for evolutionary pressure in the case of hypothetical regeneration. A lizard can take ~2 months to regenerate a limb, for a human it would take longer simply since the limb is larger and needs to grow more. Prehistoric humans and hominids were calorie limited - if an injured individual is capable and likely to (a) survive for e.g. half a year with the injury and (b) to obtain much more calories than normal to rebuild many pounds of tissue, then apparently there is no strong evolutionary pressure to favor regeneration it as he/she is capable of procreating almost as well even without this feature.

I see what you mean, but it still seems like cancer resistance is a bit "overengineered" relative to what you'd expect from selection pressures. If typical cancer onset were e.g. at age 50 rather than 70, I don't imagine that having much selective relevance in the human ancestral environment, as you'd have raised child-bearing children at that point (and you probably can barely carry your own weight at that point, metaphorically speaking).

OTOH, cancer rate is probably superlinear with respect to error rate, so a small loss of cell instruction robustness corresponds to a disproportionately shorter lifespan.

Cancer is probably selected against to a degree.

At least for most normal healthy males, not dying prematurely of cancer means you've got probably 50 or so years to pass on your genes. If a cancer causing mutation kills you at 30, you may still have the chance to pass on your genes, but you're still being outcompeted in the larger gene pool by those who don't die early and have more children than you. And if not you, then your children who die prematurely may not procreate. Evolution doesn't really have much noticeable effect at the scale of single generations anyways.

> Interesting idea, but does the risk of cancer have that much selective pressure? It tends to be the "last thing that kills you", after you live long enough to survive everything else.

You're assuming that's the default state, rather than the result of millions of years of cancer-preventing trade-offs. If e.g. being able to regenerate lost limbs gives you a 10% chance of dying of out-of-control cancer before reaching breeding age, that trait is going to be selected out fairly rapidly.

Cancer tends to be "the last thing that kills you" in much the same way your keys are always in the last place you look. A significant amount of cellular regulation is devoted to preventing runaway cell division, and sometimes in long-lived and large-bodied organisms those defenses eventually give way.

Most likely cancer as a disease will be a solved problem before we could enable this body part regeneration thing...if ever.

The ability to regenerate body parts and cancer are not inextricably linked. Take the axolotl. It has the ability to regenerate entire limbs. It's also estimated to be a couple orders of magnitude more resistant to cancer than humans.

Maybe that's the ticket? The cancer resistance is something that allows the axolotl to also keep regrowing limbs around in the genome?

There are also many animals who are long living, and immune to cancer (to varying degrees). Naked mole rats live up to 30 years and almost never get cancer (only one case formally verified so far).

Elephants have many more cells than us, and live to almost the same age, but only have a 5% chance of getting cancer, vs 10%-25% in humans. Lions have a 2% chance of getting cancer.

Out of curiosity, how do we know the cancer rates of various animals?

Someone would have had to examine a lot dead animals of various species to figure this out.

> Take the axolotl. It has the ability to regenerate entire limbs. It's also estimated to be a couple orders of magnitude more resistant to cancer than humans.

The lifespan of of the axolotl is 10-15 years. I'd love to see the cancer rates for 71 year old axolotls.

> A reasonable default assumption is that each switch in our "genetic configuration" is set to a quite good value.

I'd question that assumption-- each switch in our "genetic configuration" is set to a value, and it's set to one that results in survival often enough for the species to reproduce, but it's not necessarily the optimal value, or even a particularly good one. It's just one that happened to be able to survive under environmental pressures at some particular time.

To put this into a computer science context, genetic algorithms have the same problem-- they can find local maxima easily, but can have difficulty (depending on the nature of the search space) locating global maxima because they can't sacrifice short-term fitness to gain long-term fitness.

> A reasonable default assumption is that each switch in our "genetic configuration" is set to a quite good value.

Least awful sounds more correct.

Another exception would be if a limb has fallen off or otherwise failed.

Then it would be great to be able to turn regeneration on, for that limb only. Any added risk should be much smaller than the always-on version.

That's a bit much to expect out of evolution. First it needs a way to detect whether a limb has fallen off or otherwise failed. Then it needs to send a biochemical signal to the cells in the area iff the limb in the area failed. Then it needs to activate the regeneration iff the chemical signal is present. And each of these mutations has to be beneficial to the organism (or at least randomly there and costless). You can mush together the detection and signaling by having a local signal (like the biochemistry responsible for scabbing - iirc what happens is blood would do interesting chemistry while bleeding anyways, and so "turn into a scab when that chemistry is happening" is a worthwhile mutation), but still, it's a few too many steps.

I agree. What I was thinking (but didn't say) is that maybe we can make that happen with technology!

Maybe. The elephants being born without tusks due to ivory hunting pressures changing reproduction dynamics are likely at a disadvantage overall, but in the short term they will survive. Having tusks may be objectively better, but right now it'll get you killed.

From what I've understood from things I've read on the past, we do have pretty much full regenerative ability already. It is blocked by various things, such as the epidermis. If you chop off a finger, a blastula of stem cells will develop on the tip, at least until the skin grows over and stops it. If you could hold back the skin, then... well, you'd die of an infection in very short order. Waiting for regeneration is just not feasible in the natural world.

There's also the potential for cancer, of course, but personally I don't buy that objection. You can take cancerous cells and revert them to stem cells and they'll stop misbehaving (unless their genetic damage is very specifically triggering them to grow without bound, but I think this is rare. Usually it's a gene activation problem.)

And complexity of the regenerated part isn't much of a problem. You can reroute the nerves on a salamander to get a fully functioning arm poking out of its back. Some things can regenerate half their hearts fast enough to survive. I don't know exactly how the information is transmitted and expressed, but it's there.

No, I can't prove my assertions. They are based on half-remembered readings of the book The Body Electric from long ago, written by a guy who did experiments to back this craziness up. He was enough of a nutcase that not many people followed after, though his key findings were replicated. And he lost the thread at some point, going on a crusade against emf fields that didn't seem to be based on real science. So it goes.

As I understand it, scarring and regeneration are mutually exclusive. The advantage of regeneration is that you get the body part back. The advantage of scarring is that you don't bleed to death or get a fatal infection while waiting for the wound to close.

In larger animals, formation of scar tissue had a greater survival advantage. So humans scar instead of regenerating.

The regeneration capacity is probably all still there in humans, but it is never been observed in modern times, except after losing less than about 1 cm of fingertip. It may not be a matter of how to turn regeneration on, but how to turn scarring off.

Few years back I remember reading a story about the guy who lost his finger in an accident and then regrew it by dipping it into some kind of a powder.

Edit: found it!

>The magical formula to regrow a finger apparently includes a doctor, a pig, and some “pixie dust.” This is no fairytale, though; this is a medical breakthrough being explored at the University of Pittsburgh, Pa. In Science Channel’s video, “How to Grow a New Fingertip,” Dr. Stephen Badylak from the university explains regenerative medicine has the potential to grow a whole human body.

https://www.youtube.com/watch?v=DtBUM51t4iw

http://www.medicaldaily.com/pulse/magical-pixie-dust-pigs-bl...

Perhaps I'm wrong, but isn't this how scientists regrow organs? The matrix is used as the structure which gets implanted with the person's stem cells which activates growth. In the end the organ isn't even rejected by the body. However, growing limbs out of the same material is just mind-bending.

> In Science Channel’s video, “How to Grow a New Fingertip”

Just wow! This story is about actually regrowing a finger on the man's hand.

It's so incredible, I'd skeptical. Is this really correct? Why didn't they make a time lapse video of the man's finger regrowing -- even taking just one photo per day. That would have been the obvious thing to do, but they didn't do it (or didn't show it).

UPDATE: On further research, I guess it was just too good to be true. Here's one rebuttal to the claims from the exuberant video:

https://www.theguardian.com/science/2008/may/01/finger.claim

tl;dr: The finger was not so badly injured. It healed rather than regrew.

Here's some pictures of finger regeneration. DO NOT open these images if medical imagery bothers you. They're gruesome :)

http://www.mebo-international.com/sites/default/files/field/...

Page with a lot more pictures:

http://www.mebo.com/a/books/HUMAN/2011/0221/2934.html

These examples are from stem-cell activation therapy:

http://www.space-age.com/fingertipregeneration.html

The interesting studies are all in zebrafish and salamanders, not worms.

One of the more intriguing of the recent ones is this from last year, strongly reinforcing the theory that most species lost proficient regeneration due to evolutionary battles between cancer and aging. The greater question is perhaps why there are any proficient regenerators among the vertebrates rather than why we can't do it.

https://www.ucsf.edu/news/2015/11/251746/human-gene-prevents...

"Whether the regenerative powers of zebrafish and salamanders represent ancient abilities that mammals have lost, perhaps in exchange for advanced tumor-suppression systems remains an open question for biologists. Most tumor suppressor genes, being extremely useful for preventing cancer and for forming tissues during development, are broadly distributed and conserved across many different species. Recent studies, however, suggest that one, the ARF gene, arose more recently in the avian and mammalian lineage, and has no equivalent in the genomes of highly regenerative animals. To explore whether this gene might play a role in preventing tissue regeneration in humans, the researchers added human ARF to the zebrafish genome and assessed how it affected the fishes' normal ability to regrow damaged fins after injury. They found that human ARF had no effect on the fishes' normal development or response to superficial injury, but when the researchers trimmed off the tip of a fish's tail fin, the gene became strongly activated and almost completely prevented fin regrowth by activating a conserved tumor-blocking pathway."

That is sufficiently interesting to make me wish I could upvote it twice. But. What I really want to hear about is the opposite experiment. Take something that has ARF, and see what happens if you take it out.

I'm a huge believer that humans can cherry-pick the best traits of many different species and apply them to ourselves. It might sound like science fiction right now, bit give it time and we humans will have unlocked some crazy things that we claimed to be "impossible." It's always impossible until it's done. And to be honest, I think the second something is thought of, it becomes possible. I live for this shit.

Well, it depends what you consider to be "the best". If you have watched the olympics, you can see that different body types are better suited for different sports.

A basketball player playing ping pong or viceversa? probably not very successful.

But if that basketball player had super speed and agility, then he would be good at both sports. You're only thinking about what humans are like now. If we could freely add and take away genetic mutations, who knows what kind of freaky immortal animals we'll look like in the future. We may also not care about sports at that point.

Mechanically there's an advantage to shorter limbs for particular sports, that's just how physics works.

If a basketball player could be made super-human they might trounce ordinary ping-pong players, but a super-human ping-pong player would destroy them.

Plus there's more to these sports than any one aspect. It's never just strength or height or stamina, it's a complex of factors. Finding that optimal even given all the options might be difficult. There's intrinsic trade-offs.

For example, there's two kinds of muscle tissue, that better suited to fine motor skills and that suited to brute strength. Most animals are heavily stacked in the latter category, that's why a chimpanzee can tear you in half, but they lack the sorts of fine control that permits us to do things like type with agility and write precisely.

I meant things that pertain to longevity - like jellyfish that don't die but simply "restart" their lives, or regeneration. If you look at tardigrades, there is a lot that is possible that we cannot yet do. But yeah, I understand where you're going.

> Well, it depends what you consider to be "the best".

There are clearly traits that are best, bar exceptionally rare scenario e.g. regenerating a lost limb, improved hearing, or improved longevity. So while I understand your analogy will fit some option, it is limiting too assume there will always be a trade off.

Well, we do not regenerate limbs, we just reproduce and make more of ourselves. If one dies then other survive and keep multiplying. Same as with limbs but at a population level.

Yes. Currently, we rely on evolution by random mutation and recombining genes, which works in the long run, but has two problems: mutations are more likely to be detrimental than beneficial, and we have no way to appropriate the various advantages that non-human species have.

Deliberately cherry-picking traits seems like it could be quite a boon for the human race. (It would of course need to be done carefully and with proper ethical safeguards against careless experimentation.)

I don't think you're wrong, but I think there can be a lot of unintended, bad consequences. Especially if we start doing germline editing, where results might manifest themselves generations later when it's far too late.

It would be good to regenerate at least teeth.

that was my first thought as well ( I just had a bad dentist experience... )

I've read of a research to grow teeth from stem cells (but I'm not sure the sources of this info were reliable)

Teeth might also be a good area to look at in terms of figuring out how it works. Since most people already grow two full sets of teeth, and I believe there are numerous cases on record of people who have grown more than that, perhaps the regeneration genes are already partially activated in that region of the body.

I'm not a dentist, but I get the impression that milk teeth and adult teeth are different things, not a regeneration cycle?

Regenerating body parts doesn't happen because it is hugely expensive in terms of biochemical resources. Teeth are the most materially expensive parts of the human body. That is why teeth are often the most long lasting and best preserved human remains.

And yet, sharks do it. Also, the skeleton is similarly long lasting and that gets renewed.

So why not? Say a finger, which isn't too "expensive in terms of biochemical resources", why not regrow that? Take the acorn worm mentioned, in proportion to the worm regrowing itself must be really expensive.

I don't think this too expensive argument explains it.

It turns out that while sharks' teeth are functionally analogous to mammal teeth, they have an independent evolutionary origin - they are actually a specialized type of skin scale.

http://www.elasmo-research.org/education/white_shark/teeth.h...

It's apparently one reason why they can replace them constantly.

Shark also have rows of them.

http://www.dailymail.co.uk/sciencetech/article-3676060/The-e...

http://www.cda.org/news-events/learn-about-stem-cell-tooth-r...

I've spoken to Dr. Vining and it's probably about 50-60 years out in practice.

I believe the hairs within the ear also don't regenerate (leading to deafness when damaged through loud noises).

The "we have the same genes" argument is completely absurd. So alright, some set of DNA sequences in the context of a worm enable the regeneration of worm parts; does it follow that the same set of DNA sequences in the context of a human enable the regeneration of human parts? Of course not! In the same way that the knowledge of how fix a bike has little bearing on being able to fix a cellphone, or that the touchscreen drivers on said phone wouldn't provide a usable interface if loaded onto your gameboy. DNA is just data; its functional value is almost entirely dependent on its surroundings. For that matter, we're a bit physically different than worms; trying to port their mechanisms to human physiology is likely comparable to trying to graft wings onto your arms in order to fly.

Not to say that regeneration is implausible (after all, generation is possible), or that there's nothing to be learned from worm regeneration, but this article is fluff.

> does it follow that the same set of DNA sequences in the context of a human enable the regeneration of human parts? Of course not!

But that isn't really the argument. We know we can grow limbs because we've all done it once before.

There was an interesting Science Friday segment on this topic back in August 2016:

http://www.sciencefriday.com/segments/a-hand-a-fin-a-gene/

A couple of comments made by the guests during the discussion (from memory):

* there is a theory that humans/vertebrates actively repress regenerative abilities,

* children under the age of about five have the ability to regrow cut-off fingertips,

* the genetic instructions for growing a hand (or fin) consist of the thumb and little finger, and the rest get interpolated.

This is the type of research where I like to fantasize about the outcome. As a human race we've managed to basically cheat evolution with our advances in medicine and technology. If somehow we can stay alive as a species long enough we very well might be able to discover the secret to regeneration and immortality in some way.

> If somehow we can stay alive as a species long enough we very well might be able to discover the secret to regeneration and immortality in some way.

Hopefully we won't figure that out before we figure out how to not overcrowd Earth.

Forbid procreation for those who chosen immortality. If you decided to spawn children, then free space for them - die. (Or go cryopreservation and be kept in a small box occupying little space. In this case you and your decedents can live in turns: they live for one century while you sleep frozen; next century other way around).

You can't let people choose because even a small percentage of people choosing immortality a generation will end up overcrowding the planet given enough time.

This depends on the reproduction rate. If it's > 1 then you're right. BTW, controlling reproduction rate is a way to not overcrowd Earth.

> Forbid recreation for those who chosen immortality

How do you police sex in a democracy?

The same way you police it in a dictatorship, or any other form of government. Just do what China does for its one child policy, except that it would be a zero child policy. I doubt this is a good idea though.

> I doubt this is a good idea though

I agree. Overpopulation is an overstated problem [1]. Rich societies reproduce at below their replacement levels. Pursuing higher quality of life by expanding capability (including by tapping extraterrestrial potential) is more sustainable than by constraining population.

[1] http://www.nytimes.com/2013/09/14/opinion/overpopulation-is-...

But this happens because we don't live very long currently. So we prioritise using the time we have to build material resources so that when (if) we have a child we can maintain standard of living.

If you were assured to live even 100 years you could spend the first 50 creating a high standard of living and the next 50 raising children within that standard.

Just as an aside, the word you're looking for is "procreation" - "recreation" refers to leisure activities.

Thanks, fixed. (Although "re-creation" looked so right. Maybe I will use "reproduction").

May want to read "2 B R 0 2 B" by Vonnegut.

thanks for the reference

The processes that built us originally worked with much smaller versions of us. The techniques for constructing an arm that is a few cells wide may not work when the arm is millions of cells wide.

From another research done on mice, the answer is mainly scar tissue. https://www.ncbi.nlm.nih.gov/pubmed/12557217

About the evolution part: we have a higher change to live with scar tissue, then we have without (shorter chance for infections).

If this were possible, I wonder how our new limb would grow. Would it be a reconstruction of the structure of the old limb or would it grow like a child limb and take the same amount of years (18-20) to reach the adult stage of the limb?

Edit: replaced limb instead of member.

FYI, referring to a body-part like "his member" is often a euphemism for penis, so your post is (unintentionally?) amusing to read.

Unintentionally. In my defence I have to say that the term is correct but I get your point. I've replaced it for limb hoping the question will be taken more seriously.

We regenerate plenty. Our bodies are constantly regenerating. We keep growing new skin to replace old (dandruff is a simple example), damaged organs can recover (eg liver problems), and even exercising to increase strength involves regeneration (broken muscle fibres grow back stronger). We don't regenerate large external body parts in general, but we do regenerate some bits quite well - like the palms of our hands.

If you cut us, do we not bleed? Then clot? Then grow new tissue to heal the wound? Sometimes so that there is no evidence of a cut afterwards?

Sure, we have the genes to grow limbs while hibernating suspended in amniotic fluid and being fed intravenously. Maybe recreate those exact circumstances and we can regrow limbs.

"Why can't we break off half a microchip, and then rebuild the missing part so it works again? We have all the mask artwork and silicon wafers ..."

This doesn't strike me as a reasonable analogy.

1) Microchips don't grow autonomously in the first place, unlike organisms.

2) The article's point is that not only do humans have the "mask artwork and silicon wafers", but also the genes that other organisms use to regenerate portions of their body. A closer equivalence would be "the instructions on how to rebuild the missing half of the microchip from what remains".

Microchips grow autonomously if you regard the entire fab and its staff as a big organism.

And note that the blueprints for the chip do actually encode more or less what it looks like: as a genotype they resemble the phenotype. Yet such a repair is not feasible.

DNA genes do not encode an arm or a leg directly, but a convoluted process by which the structure develops.

> Yet such a repair is not feasible.

Well, we don't really know, because we've never bothered to build a chip/fab process with that capability. It's cheaper to just throw broken ones away (edit: plus, it isn't morally reprehensible to throw them away because they don't have consciousness... yet). I guess the other thing is that a CPU is pretty simplistic compared to a big organism.

We do bin products and then e.g. underclock or disable parts of them accordingly. So there's the start of an "injury"-sensing mechanism. But microchips still have a few thousand years to go in their "evolution" at least :)

The old UK sci-fi television series, Blakes 7, which aired in 1970's had this as one of their predicted technologies.

Entire portions of machinery would regenerate after being exploded in sabotage.

Grids of "radiation mine wire" would after being cut, would have the ends of the cable seek each other out and it would grow to join up again. The strategy to bypass this grid/minefield of interlaced wire, would be to fire the blaster across it clearing a path and then to run through it within 8 seconds before it regenerates.

While it was a bit fantastical for the time, I'm sure some hand-waving could justify nanotech as the way this TV tech might be realised.

It seems like the cells in a worm are relatively position-independent, so they can regrow using only local information.

If you lopped off your leg, a cell would need to know how much of the leg to regrow to get to the kneecaps, how much to grow to get to the foot, or more. If you chopped off a foot, it seems hard to know which parts need to be regrown and which don't. There's a lot of complexity in a foot.

This has to be a solved problem unless the womb offers some sort of telemetry.

In that case, the entire organism is forming. It can use techniques like forming the general structure before filling in the details. It could be that forming the general structure is carefully scripted by chemistry, while the details are mostly position-independent.

Bones can have their lengths determined by biological clocks that operate over years. Examples of clocks are hormone release cycles, which the rest of the body uses for signaling. But, a new leg wouldn't have access to the global clock, since it would've shut off if the affected parts are fully-developed.

Bones and muscles might have their final shapes partially determined by outside forces. The biggest one is gravity. It may be that people develop longer legs in space, or their spines don't develop correctly. A leg intended to be regrown on an adult might not have time to be shaped in this manner.

It's more than just worms that regenerate body parts. Some salamanders can regenerate whole limbs.

https://www.youtube.com/watch?v=EsCSwVx3GvA

I remember seeing a story on BBC a while ago about how one guy, who lost the top portion of his finger while operating a toy in his hobby shop, was able to regrow it completely. It only took 4 weeks to regrow, including the nails, fingerprints et al., exactly as it was before using extracellular protein from pig bladder. Here is a link to the story: https://www.youtube.com/watch?v=NEnLK0oJCa8

One answer I've read in The Spark In The Machine[1], is that our cells' organizational energies (or Qi in Chinese Medicine) is not strong enough as we grow older.

Only when someone is super young (when their qi is super strong) can they regrow body parts and very small ones (the tips of the fingers!)[2]

""" Doctors have seen the effect in humans without quite understanding how it happens. "Kids will actually regrow a pretty good fingertip, after amputation, if you just leave it alone," says Dr. Christopher Allan, from the University of Washington Medicine Hand Center, who wasn't involved in the research. """

EDIT: yeah i know its HN so i'll probably get downvotes, but as far as modern science is concerned we still know very little about embryology and what actually controls the beautiful orchestration of a single cell developing into a full human in 9 months. The idea of an organization energy that directs embryological cellular function is now starting to be investigated in western science [3]

[1]https://www.amazon.com/Spark-Machine-Acupuncture-Explains-My...

[2] http://www.npr.org/sections/health-shots/2013/06/10/19038548...

[3] https://vimeo.com/26761300

I am kind of doubtful about this Qi business. I followed the amazon link you gave and it made it even more doubtful.

Nevertheless, I gave you an upvote, because I had no idea fingertips could ever regrow; that's really cool!

I'm not sure what point you're trying to make with the third link. Are you saying Qi is electric?

Yes! the term "Qi" is just another way to denote the organizational electric energies our bodies use to orchestrate cellular function. This video does a way better job at describing it: https://vimeo.com/154294365 (2 minutes)

Okay, fine. Then what makes you say that children have more than adults?

Its more about the strength and quality rather than the quantity. As we get older the quality reduces with the rate depending on our genes, lifestyle, habits etc... Children in general, have better qi because they are 'new'.

I'm not going to go into the scientific details here and start listing off pubmed studies, but its all in that book if your interested (many references at the end of each chapter). I'm sorry the amazon link seemed to further dishearten you, I would love to know why!

> I would love to know why

Sorry for late response. The entire blurb on Amazon gives off a mildly pseudo-science vibe, but it is mild enough that I was willing to forgive it. But this I could not overlook:

"[...] how the hearts of two people in love (or in scientific terms `quantum entanglement') truly beat as one"

Just no. I don't know quantum mechanics, but I know enough to say that can't possibly be anywhere near right, or even vaguely plausible.

Ah yes, so, similar to how womens' periods synchronize up when they live together...Studies of couples show that when in a state of rapport, of emotional empathy, heart rates become matched and that they become mismatched when out of rapport: http://www.futurity.org/heart-beats-sync-up-in-romantic-coup...

Yeah I would probably not take that quote 'Truly beat as one' literally, I mean, I'm betting the heart rates in the study aren't as precise as to say... a distributed real-time system written in go /joke :)

It's not the "beat as one" I object to, it's the "quantum entanglement".

Oh, Rats! Well when speaking about quantum entanglement, we (as Naive realists on HN (see my profile)) should just ignore it for the next 2000 years, hopefully by then physicists will have a definitive yes or no answer for that domain. Like an unfortunate cardamon seed in our tasty sweet rice kheer, I guess just navigate around it and enjoy everything else presented in the book with a back-up-with-references-from-pub-meds-from-the-last-40-years format.

All right, all right :) I'm adding it to my list.

But when then if you cut of an arm - do the body then regenerate a new arm and the cut off arm a new body ?

Unless the arm managed to quickly generate enough organs to crawl around an feed itself, it would suffocate/starve before it could generate a body.

What about unwanted parts which are removed intentionally? Wisdom teeth and appendicitis come to mind. Or body parts intentionally modified by surgery. Basically, unless there is some control regarding which part to regrow, this might not always be desirable.

Watching axolotl regrow a full limb is quite exciting mentally. The thing reboots topologically and not 'linearly' like most wounds. The bioengineering if I may say so seems passionating.

If I could I'd go Inti embryology.

seems to me that when the original generation of organs, bones, and other structure is occurring, there is a chemical soup of proteins/hormones/etc that provides the right environment for a whole host of gene expressions not seen after the generation is done and the organism is more or less fully formed. recreating that environment seems challenging. it's like getting back to bios after you already booted the OS.

Lizards can regrow their tails.

https://www.google.com/amp/s/www.geneticliteracyproject.org/...

Imagine you chop off your head, give both your head and body necessary environment to regenerate. It'd be like cloning.

Although the head gets a brand new body that works just as good if not better, while the body gets a head that is completely blank. Sounds pretty unfair to the latter...

and supply the necessary materials to let it work.

That is the key.

We changed the URL from http://newatlas.com/human-body-regeneration-worm-genes/46670..., which points to this.

Do you know cancer? The cancer is the ability of regenerate from the very begin in human's history. But we lost the ability of control cancel cells and it became an illness.

What is this claim based on? This sounds like speculation.

Probably because limb regeneration wasn't a favored trait during our evolution. e.g: we managed to survive and be fertile without it.

Rather than limb regeneration we evolved pain and fear to prevent losing a limb in the first place.

A similar question would be why aren't fruit toxic so animals stop eating them? Because they pass their genes anyways. Rather than that, animals that were too good at eating fruit, destroyed their own food source and died.

Another interesting phenomenon are lemmings. Why lemmings kill themselves en-masse? Because they're too fertile. And as a population their own way to control their size is to mass suicide.

The hawk and dove model game in game theory attempts to explain a bit of this.

You are spot on correct. And regenerating lost body parts will require far more than just flipping the activation of a few genes.

Don't think that just because natural selection tended to favor a particular thing that it's necessarily a good thing.

Some sheep have the most ridiculous horns because of how they compete for mates. If, in some alternate world, those sheep became intelligent and lived in a civilized society where such a thing was no longer relevant the horns themselves might have little worth other than prestige. They serve no functional purpose.

Humans have survived in spite of our relative weaknesses. We've got a seriously screwed up head, nothing in there is oriented correctly, and parts of our body are on the verge of self-destructing even at the best of times. We were never intended by nature to live more than twenty years, everything past that is actually quite unnatural, as everything in your body starts falling apart at that point because from the perspective of natural selection taking place fifty thousand years ago you've either bred and done your duty, or you're dead weight.

There's a lot of mistakes in our DNA that time will correct, but we can always jump start that process by making a few tweaks today.

Fruit relies on being eating to assist in seed dispersal (notice how the seeds are usually cast aside?). Also, most of the fruit that you find in the supermarket are selectively bred to have quite a bit more flesh to them.

Oh, and lemmings don't mass suicide. That's a myth that came about cause of Disney.

The myth existed before Disney, but they did perpetuate it (and kill a bunch of lemmings).

http://www.snopes.com/disney/films/lemmings.asp

> Another interesting phenomenon are lemmings. Why lemmings kill themselves en-masse? Because they're too fertile. And as a population their own way to control their size is to mass suicide.

Lemmings don't commit mass suicide.

https://en.m.wikipedia.org/wiki/Lemming#Misconceptions

OK, fine. Disregard the lemmings.

They do die massively, but it's not intentional, I get it.

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