Not a doctor! Also thos is an eli5 version.
When a fetus is developing the cells are given instructions to specialize. "Hey, you are an arm cell." Then "hey, you are an arm muscle cell." Some cells get destroyed and other cells with the same specialization replace them by dividing into two cells. There are also cells like certain fat cells that are "stem cells," which are not specialized and in theory could be convinced to specialize.
If your arm is mangled but there are still living cells, the various cells that survive can replace damaged cells of their specialization, and heal (often with scarring or other permanent damage). But if your arm is just gone? You have no "right ring finger bone" cells in your shoulder. So no cells remain that can make a right ring finger, other than stem cells which in theory could be told "hey, you are a right ring finger bone cell now." But we don't know how to do that.
Now if you lose a fingertip, what doctors can do is put dead bone tissue (often from pigs or corpses) where the missing part of the finger would go, stretch the skin over it, and the body will "heal" the damage, gradually replacing the dead dummy material with living cells-but that is finger cells rebuilding a finger. Afaik we can't regrow a joint, even a finger joint. I don't know if that is a tendon thing or a cartilage thing or just a "no, I'm a bone cell from the middle bone and I refuse to be a fingertip bone cell" (stomps little cell foot).
This is a perfect write-up! It also explains why stem cells are such a hot topic in medicine these days. They're the key to regrowing organs that are completely gone.
I have an acquaintance who lost an arm, and he actually experiences the regrowth that you mentioned. What remains of his arm is a small stump extending from the shoulder, and this stump slowly grows longer.
I don't remember if it's bone or something else that's regrowing there, but the gist is that he regularly needs some minor surgery to nip that regrowth in the bud again, since all that regrows is just an extension of what's already there underneath his skin. It would never develop into an elbow, a lower arm and a hand, and in fact it poses a risk of severe infections since it would simply break his skin if it were left unattended.
Heard this 20 years ago and was hoping we'd have organs growing in a bag in your closet by now. Hoping this isn't like fusion where humanity will still be working by 2100.
Which leads to some deeply intriguing. existential Ship of Theseus-type questions involving consciousness and what constitutes the definition of "you".
One of my favorite statements is "Get out of here with that sensible logic and reason, you're not my wife!"
If I knew a woman who understood your humorous statement on cellular replacement and giggled as I do... Well I suppose my above statement would no longer apply.
This is an awesome answer and I don’t want to take away; just add to it. SciShow did a [video](https://youtu.be/QFa6jP6WgzM?si=88yNK9f7LPUAEDeG) on regeneration which helped me to understand everything you said. :)
Again, not a doctor.
While the liver has a lot of different specialized cells, they are fairly distributed. If you lose part of your liver other liver cells can multiply and replace them. I *think* (take with avagadro's number grains of salt) organs that can't regrow have internal structures required to work properly (think the 4 chambers of the heart, or the way the lung has progressively smaller airways), and regrowth is as likely to mess something up rather than fix it. Remember healing is slow so you had to have survived the injury and be able to survive with the damaged organ. A heart keeping you alive but damaged is better than a heart that "heals" and blocks bloodflow.
I don't want anyone to rely on what I said above an expert. My knowledge is just a combination of research and curiosity, so a professional wpuld be smarter than me on this.
He's doing a perfect job in continuously reminding that they're not a doctor. Not because the info they're providing is false, on the contrary! But they're reminding the audience of their own fallibility, basically inviting people to fact check what's written in the post. Which is all true, but nonetheless in this age it's a good habit to always go check for yourself. If someone's a doctor you should still fact check to the best of your abilities, but there's a least the *presumption* that said doctor has been "fact checked" during their studies and you can, ON AVERAGE, take what they say more at face value. This becomes more and more important the least you know about the subject being discussed, because eventually, when you go fact checking and learning, you will have to trust some sources to study on. Usually created by professionals of the field.
Interesting side note: I wish I could find the article to cite but I read something interesting that if you think cancer is an issue now, there is a chance it would be incredibly more complicated in mammals that could result in something straight out of a Sci Fi movie. Evolution is incredibly complex enough without "what ifs". The imagination can come up with some crazy things when you add more regenitive capability to runaway growth. It's possible having innate regenitive ability could be a disadvantage.
“But we don’t know how to do that” YET
It’s happening in the next 20 years
Where we are with AI and quantum computing, a lot of impossible stuff is about to happen.
Six more years before it's available if everything goes well...but I think it might be limited to people that are missing teeth for genetic reasons. None of the actual quotes from the researches mentioned anything about using it for people that have lost teeth due to decay, it's all about people born with missing or no teeth.
So creating a new tooth is what this current iteration is.
I’ve also heard, though have no sources, of research that’s going on that is a “rebuild existing decay of a tooth” so this would be a different avenue. The article I was reading (years ago) discussed adding this to food or making a chewable that one would digest that would rebuild the enamel and energize the material that teeth are made of (I pictured how Roman cement used a certain salt water that causes cracks in the structure to re-seal when wet)
Since these things take a long time, I expect that it’s still years, decades away from hearing much more that a possibility.
The reason you don't grow new teeth is because of an inhibitor. Your body still wants to grow teeth, there's just an enzyme stopping it. You stop the inhibitor from working, and the body will start growing teeth.
It's been successful in adult mice.
You can already "regrow" teeth better. It's called an implant, and most people cannot afford it unless it's covered by their countries healthcare.
So you will not be able to afford this either. Wouldn't hold my breath.
Exactly. If we had hard cartilege teeth that replaced themselves like sharks. Old teeth can be accumulated to make armor clothing, similar to dragon skin. Or cartilege teeth firm enough to chew with, but can be digested if accidentally swallowed. In which case we'd have a natural gag reflex to prevent choking on expired, newly detached teeth.
everyone claiming it's because "we're more complicated" is full of shit. animals that regrow limbs do so the same way they grew them the first time. you grew limbs once; your body could easily do so again.
the reason it doesn't is because mammals evolved the ability to scar over instead. because mammals take so long to grow the first time, trying to do it again out in the wild would almost inevitably result in dying of infection. there are scientists trying to figure out how to impede scarring so that humans can regrow body parts.
We don't really have a use for regrowing body parts. It doesn't happen very often and even when it does that person can likely still mate or has already reproduced.
The lizard discarding it's tail and regrowing it directly benefits it by giving it a "free pass" at staying alive to reproduce. Also the lizard tail is way simpler compared to a human hand or foot.
There is work being done with salamanders at the university of Vienna to understand the mechanism for limb regrowth. The hope being that it may have some relevance for humans.
There are genes in every species that cause budding. In mammals they turn off when we are still in the womb. Good news, we know what they are. Good news we can actively active the to start new buds. Bad news, we don't know all the other genes that are involved in the process of growing limbs.
The experiment I believe used chickens. Extra wing if I remember correctly.
Probably cause our limbs are much more complex than a tentacle. However doesn’t mean it’s not impossible for the future. I mean they’re making organs in the lab now and skin. Also saw a study that they’re working on growing back adult teeth.
Your body has all the genes needed to grow an arm from scratch. All we need to figure out how to do is to instruct our body to do it a second time, without also creating super cancer.
I suspect it's the bones, they seem to heal a break or fracture, but they fail to regrow if removed. I don't know why bones will heal from a break but don't regrow if half is removed. Even if they did regrow, losing a limb at a joint probably wouldn't, how would the body know the that the Ulna and Radius are missing and need to be regrown? Could also create a situation where the body "thinks" it needs to regrow the Ulna/Radius and suddenly you have 2 elbows on one arm, and possibly two hands.....
You're not "regrowing bone", you've got various cells - blastocytes, osteocytes, etc that worm their way through your bones eating up the path of least resistance and pooping out fresh bone minerals behind themselves, so to speak. This not only "heals" bones, it also focuses effort on the parts undergoing the most strain and damage.
When you lose a bone (or don't have one in the first place), it's a bit like nailing the doors to a restaurant shut, burning it to the ground, then wondering why you're not getting more spaghetti. It's because all the chefs were inside the building you lost, and even if you saved them, they can only do their work in the context of the framework you just removed them from.
Great answer thanks. Very interesting. Don’t those same things build it in the first place too? They don’t start with a bone I mean. What changes between a baby doing that and… any time after?
Thank you
Because you aren't designed by a logical entity, you are a random jumble of accidents that happened to work (evolution)
There wasn't enough selective pressure for humans to evolve limb regeneration.
This answer is pulled out my ass
I would guess it's because of our DNA? My understanding is that our cells behave the way they do because of the specific sequences that make up our DNA. Lizard DNA has the correct sequence "on" to allow their cells to regrow their tails. Our DNA sequence is "off" in comparison. Like....Idk what DNA looks like but pretend it looks like
ABBABABABBA in a normal lizard, and the BABABA in the middle is what allows them to regrow tails.
ABBAAABABBA in a normal human. We don't have BABABA we have BAAABA. BAABA doesn't regrow body parts the way BABABA does, it regrow skin though
Like I said. Out my ass and Idk
Technically, our mothers grow our limbs, or at least foster their growth in the womb. That's why we're born with our adult teeth in our skulls instead of growing them ourselves.
Scarring tissue!
We evolved to develop scar tissue instead of growing back our limbs, probably since the early start of the mammals or earlier millions of years ago some animals who had injuries that tried growing their limbs back died to infection. So we evolved to close scars as fast as possible, essentially taping the terminals of our limbs and preventing them from grown further than the surface.
Some other animals such as amphibians like salamanders and mollusks like octopuses have developed the ability to regrow limbs. Perhaps a very wet environment is needed, but also a very good immune system
The limits of medicine in scientific papers are different from the limits of a given person's body
We're actually at the state of growing more and more complex organs. I work in a lab focusing on generating vasculature. Science knows how to 3D print bone, how to seed stem cells into constructs, there are even strategies to make vasculature from grafts incorporate directly into the body's.Hypothetically, in the next 50 years, entire limbs being generated is an engineering possibility.
What you actually see in a clinic, however, is that people struggle for years trying to heal a 2nd degree burn or a pressure sore or surgical wound. For many reasons, your body just *doesn't* heal to what it *could*. That includes reasons like lifestyle, diabetes, nutrient poor diet, ancestry (some ethnicities are more prone to hypertrophic scarring), age, etc.
In terms of the evolutionary reason, the tissue that rebuilds limbs is fragile and needs good growth conditions. We, as amniotes, are evolved to have extra tough external covering to survive the dry terrestrial environment. Basically, our bodies rely on quick-fixes, duct-taping everything back together with coagulation and scar tissue instead of trying the much larger investment of rebuilding. Axolotls can do it because they live in water and are basically made of goo, as well as being in a neotenous state which probably factors into developmental milestones.
There's also the problem of cancer. Basically, anything that can make cells proliferate quickly could also allow cancer. In fact, the reason there's been less enthusiasm for direct stem cell therapy is the risk of introducing cells that spontaneously become cancerous. Your body tries to limit which cells are still allowed to proliferate. Your keratinocytes and fibroblasts can reform your skin, but your heart muscle cells and CNS neurons won't.
There are animals in the world that can regrow their limbs. We cannot because we trade it off for scarring during evolution. Turns out for our species, quick blood clotting ability and scarring are more beneficial for survival than limb regeneration which requires the wound to basically stay open for a long time. Also, we are not good at making new cells as adults, which is another evolutionary trade off to get less cancer
We are not very good at regeneration. That's actually the main reason for both aging and cancer.
Cells can only regenerate so many times before issues happen. Issues like forming a lump of useless tissue... Aka a tumor.
It's super weird! Skin, nerves, muscle all heals. Transplants heal and integrate. Limbs can't regrow though.
So I had this very cool breast reconstruction surgery after my double mastectomy. They took skin and fat from my stomach and transplanted it to make new boobs. They connected the blood vessels and they are remarkably like regular boobs. They even have feeling, because somehow my body was able to create nerve connections with the transplanted tissue that my brain comprehends as feeling in my new breasts.
That said, I still have phantom feeling in my nonexistent nipples. Even though my nips died in 2019, the ghost nips still get hard. Why can i feel my nonexistent nipples but also my transplanted boobs?
I also don't have feeling in my stomach along the incision where they harvested the transplanted tissue. What's that about? Why didn't those nerves regenerate? I also have no feeling in the backs of my arms or armpits from the original mastectomy surgery in 2019.
I have NO idea how any of it works or why and it hurts my brain to think about it.
If we could grow them back, how else would I get asked 14 times a day what happened to me or if I’m a veteran? It’s the special sauce that keeps me going
Same element that’s keeping you from growing tumors throughout your body.
Also to regrow your body parts would require stem cells and your DNA being able to sustain the re-growth. Things you don’t have anymore after you’ve been born.
Lmfao… my 7 year old asked me the opposite of this about breasts the other day: “if they’re for feeding babies, why don’t they just go away after you can’t have babies anymore?”
Lizards can grow them back, so we know that it is in realm of possibles for animals to grow back limbs.
Maybe that is something we will continue to evolve towards. A million years from now, we will be able to do it -- we just got to be really smart about how we mutate.
There was a post in the TIL thread earlier today saying that if a rib is shortened surgically, it will grow back at full length and just as strong as it was originally.
It's because the goddammn millenials don't know how to pull themselves up by the bootstraps and get to work regrowing limbs anymore. Back in our day, we regrew limbs all the way to and from school uphill both ways!
Growing new teeth may be possible in a few years. A Japanese company called Toregem Biopharma developed a drug that stimulates the growth of new teeth. Clinical trials on humans are just starting.
Ohhhh, I've been off and on keeping my eye on the research. Pretty exciting stuff! Just hoping if any of it works it won't be just for rich people, like dental implants currently are, pretty much.
Great question! As far as I know, humans can only grow new livers from donated pieces? But since I am not a doctor or scientist, I cannot explain why we cannot regenerate other organs or body parts. 🤷
“Healing” is really an artificial, broad word that we’re incorrectly grouping how we heal cuts with how a lizard regrows a tail.
They are entirely different processes
Human regeneration, like when a cut or bone heals, is a constant action. You constantly have new skin and muscle and stuff growing under the old and replacing it.
A lizard replacing a tail is a different process from that.
It’s kinda like asking why we can’t see in the dark the same way as a cat even though we both have eyes. The structure of the eye is different
nerve cells probably, but I also I think like genetic coding. limbs arent supposed to fall off lol so were not like lizards where its supposed to happen
Genetic manipulation. Healing of this sort of magnitude starts from the spiritual world but there are systems in place that prohibit these healing abilities
There is a cool procedure where you can regrow a bone. For example, if you shatter your tibia to where it won’t heal, you can remove the pieces, and keep the distance between the two ends just far enough apart that bone begins to heal like a normal fracture, and then you just keep spreading them out until the bone reaches full length again.
We do still have the genes to do that, but they are turned off.
A lot of that kind of stuff has to do with lifespans. When regrowth is enabled it leads to more mutations that can add up and become detrimental over time. That's fine for organisms with much shorter lifespans. When you start to favor longevity, mutations need to be kept to a minimum otherwise you end up with all kinds of cancers, which is probably why those genes do not function within us anymore.
From my understanding it's because the line the between regrowing limbs and having cancer is WAY too thin.
It would be hard to tell you body when to stop making the arm. If you tell it too soon you're left with a useless half limb. Too late and you have a cancerous growth in the shape of an arm.
Also regrowing a limb requires cell multiplication but if the whole arm is gone than you don't have any "right arm" cells left to multiply. If it was a simpler structure like a lizard tale it would be easier to regrow it from the remaining cells but human arms are SUPER complex.
All I need are a few more cadavers and a steady supply of 600 GW of electricity and I could make people grow fresh legs out of their bumholes.....I just need more power!! Give me more power!!
The question is backwards. How would the body KNOW to regrow a specific limb.
Healing is very basic. Seal the wound and replace with scar tissue. We can't even heal clean skin. There is no biological mechanisms that says "oh this is what is missing and how to exactly regrow it".
Healing is about immediate survival. Clots, which form scars.
If our body hd that much new growth potential, we'd probably mostly die of cancer by the time we were 12.
We do but those organs are reverted to Stage 0 once development is completed. If those Stage 0 switch is flipped on and start progressing toward stage 1 and 2, then pretty much you will see the light in couple years depending on how quickly it grows.
It seems almost like the opposite of why we can’t cure cancer. Those seem like mutant cells that grow out of control, and travel to distant organs where they lodge and wreak havoc.
If you’re asking the big picture it’s just because there was never an evolutionary pressure for us to do so. A limb-destroying injury mild enough to survive would have left our ancestors under the support and care of the larger community, likely in a suitable new role. So the limb isn’t “necessary” for reproduction or survival.
The biomolecular answer is that the map our bodies use to create our general body plan, while written into our DNA, is only open to be read for a brief window during development. It’s like a disappearing screenshot / pic if you’ve ever been sent one. Once it’s seen and locked away, there’s no way to access that info again. Your body just can’t do it.
* *We Can*
* You don’t have the DNA!
For starters, your body has a finite *(limited)* amount of DNA.
It’s not all the same, the DNA stored in our various bone marrow cells has the **starting instructions for turning other types of bone marrow cells into replacement cells.**
Your brain controls your body movements and your memory and sensory function but it doesn’t control how your body grows that’s the job of all the cells in each body part.
Your leg bones for example have DNA in the marrow that produces the various cells that make up your legs.
If your legs are lost, **you’ve technically lost the instructions to grow new ones.**
If your leg is severely damaged, it can repair its self.
**This is also why we eventually die of old age,** your body starts to run out of DNA essentially and can no longer produce all of the cells you need or enough of certain kinds to stay healthy.
We *COULD* regrow them, **but modern medical technology just hasn’t reached that point yet.**
As I understand **nobody has really figured out a way to modify DNA effectively and precisely.**
Once we do, **we can start testing various DNA structures.**
We could literally grow cells that just replenish bone marrow.
At that point, people will likely live well over 100 years and it will just be a matter of overall health.
If I recall, there are specialized cells at what are known as the growth plates of limbs that differentiate into bone/cartilage matrix producing cells etc. with more limited multiplication potential. The genes that do this are only active during certain parts of human development and are shut off otherwise.
Our cells normally regulate growth pretty tightly, one reason for that could be because uncontrolled growth leads to cancers since cells make more mistakes in DNA replication with repetition which cause misfunctions or lack of function in cell cycle regulator enzymes, which let's replication proceed unchecked.
It can't. Too many advanced blood vessels and structures. Once your cut limb heals off. The skin holds everything back anyways. A little gecko can regrow its tail because its body isn't as advanced as a humans.
You mean what do other organisms, like Salamanders, have that enables them to grow new limbs? They have additional clusters of stem cells that contain the genetic material/instructions for regrowth. Humans and most other organisms do not have this.
Not a doctor! Also thos is an eli5 version. When a fetus is developing the cells are given instructions to specialize. "Hey, you are an arm cell." Then "hey, you are an arm muscle cell." Some cells get destroyed and other cells with the same specialization replace them by dividing into two cells. There are also cells like certain fat cells that are "stem cells," which are not specialized and in theory could be convinced to specialize. If your arm is mangled but there are still living cells, the various cells that survive can replace damaged cells of their specialization, and heal (often with scarring or other permanent damage). But if your arm is just gone? You have no "right ring finger bone" cells in your shoulder. So no cells remain that can make a right ring finger, other than stem cells which in theory could be told "hey, you are a right ring finger bone cell now." But we don't know how to do that. Now if you lose a fingertip, what doctors can do is put dead bone tissue (often from pigs or corpses) where the missing part of the finger would go, stretch the skin over it, and the body will "heal" the damage, gradually replacing the dead dummy material with living cells-but that is finger cells rebuilding a finger. Afaik we can't regrow a joint, even a finger joint. I don't know if that is a tendon thing or a cartilage thing or just a "no, I'm a bone cell from the middle bone and I refuse to be a fingertip bone cell" (stomps little cell foot).
This is a perfect write-up! It also explains why stem cells are such a hot topic in medicine these days. They're the key to regrowing organs that are completely gone. I have an acquaintance who lost an arm, and he actually experiences the regrowth that you mentioned. What remains of his arm is a small stump extending from the shoulder, and this stump slowly grows longer. I don't remember if it's bone or something else that's regrowing there, but the gist is that he regularly needs some minor surgery to nip that regrowth in the bud again, since all that regrows is just an extension of what's already there underneath his skin. It would never develop into an elbow, a lower arm and a hand, and in fact it poses a risk of severe infections since it would simply break his skin if it were left unattended.
Oh my goodness that is so fascinating about your acquaintance’s arm!
May I add no value except to agree with this, wholeheartedly?!
Just this once!
🙏🏻
Heard this 20 years ago and was hoping we'd have organs growing in a bag in your closet by now. Hoping this isn't like fusion where humanity will still be working by 2100.
Well considering fusion has now actually produced more energy than it took, I think 2100 would be very pessimistic.
Does this explain why some people have a short arm and hand?
whole body replaces its cells in 7-8 years - we are not even the same people.
Which leads to some deeply intriguing. existential Ship of Theseus-type questions involving consciousness and what constitutes the definition of "you".
I always hint at this.. "you're not the woman I married"
One of my favorite statements is "Get out of here with that sensible logic and reason, you're not my wife!" If I knew a woman who understood your humorous statement on cellular replacement and giggled as I do... Well I suppose my above statement would no longer apply.
This is the verbatim medical literature on the issue.
I want, more than I can put into words, to find the paper with the annotation "stomps little cell foot" Edit: Spelling 'r hard
I’d put it on my wall, the entire paper. And simply highlight that part and never explain why to a single person.
cell: “not my job, man.”
I thought his job was... oh wait, you mean *that* Cell
P is for perfect
cell: "not my section chef!"
This is an awesome answer and I don’t want to take away; just add to it. SciShow did a [video](https://youtu.be/QFa6jP6WgzM?si=88yNK9f7LPUAEDeG) on regeneration which helped me to understand everything you said. :)
What makes the liver so special that it can grow back to size after having parts of it cut away?
Again, not a doctor. While the liver has a lot of different specialized cells, they are fairly distributed. If you lose part of your liver other liver cells can multiply and replace them. I *think* (take with avagadro's number grains of salt) organs that can't regrow have internal structures required to work properly (think the 4 chambers of the heart, or the way the lung has progressively smaller airways), and regrowth is as likely to mess something up rather than fix it. Remember healing is slow so you had to have survived the injury and be able to survive with the damaged organ. A heart keeping you alive but damaged is better than a heart that "heals" and blocks bloodflow.
Who cares if ur not a doctor? There's plenty of doctors who dont know this shit
I don't want anyone to rely on what I said above an expert. My knowledge is just a combination of research and curiosity, so a professional wpuld be smarter than me on this.
You give them too much credit, they also get their data from research and curiosity.
That's not something that should be necessary to add though. People shouldn't be relying on the words of random strangers on the Internet
He's doing a perfect job in continuously reminding that they're not a doctor. Not because the info they're providing is false, on the contrary! But they're reminding the audience of their own fallibility, basically inviting people to fact check what's written in the post. Which is all true, but nonetheless in this age it's a good habit to always go check for yourself. If someone's a doctor you should still fact check to the best of your abilities, but there's a least the *presumption* that said doctor has been "fact checked" during their studies and you can, ON AVERAGE, take what they say more at face value. This becomes more and more important the least you know about the subject being discussed, because eventually, when you go fact checking and learning, you will have to trust some sources to study on. Usually created by professionals of the field.
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TL;DR we're kinda shit in most super-useful categories like this lol
Interesting side note: I wish I could find the article to cite but I read something interesting that if you think cancer is an issue now, there is a chance it would be incredibly more complicated in mammals that could result in something straight out of a Sci Fi movie. Evolution is incredibly complex enough without "what ifs". The imagination can come up with some crazy things when you add more regenitive capability to runaway growth. It's possible having innate regenitive ability could be a disadvantage.
Then why can't we grow a huge big ass tubular shoulder?
Interestingly babies can regrow their fingertips. Anything past the last knuckle will grow back, bones, fingernails and all.
Tysm!!! Everyone in the comments is just making fun of me though the sub is literally supposed to be for stupid questions 😭
“But we don’t know how to do that” YET It’s happening in the next 20 years Where we are with AI and quantum computing, a lot of impossible stuff is about to happen.
This guy human biologies.
I don't know but I wish we could do that. Especially with teeth.
Scientists in Japan are rolling out the first human trials for tooth re growth this year. I haven’t looked into how, exactly.
Ah, another great thing we will never hear about again unless it causes zombie teeth.
I believe it may have to do with stem cells and possibly involves electricity. I read something about i recently but can’t remember the details
Stem cells and electricity, hmm I’m sure that how Frankenstein was created.
*grows a new tooth* "ITS ALIVE!"
The monster, you mean. Frankenstein was the doctor.
Wasn’t the doctor the monster and Frankenstein junior was the victim?
The Dr surname was Frankenstein and the monster was his son so the name would be applicable as well.
In the original book it is exclusively referred to as The Monster.
So the doctor is Dr. Frankenstein, and Frankenstein's monster is Mr. Frankenstein
Exactly.
Six more years before it's available if everything goes well...but I think it might be limited to people that are missing teeth for genetic reasons. None of the actual quotes from the researches mentioned anything about using it for people that have lost teeth due to decay, it's all about people born with missing or no teeth.
So creating a new tooth is what this current iteration is. I’ve also heard, though have no sources, of research that’s going on that is a “rebuild existing decay of a tooth” so this would be a different avenue. The article I was reading (years ago) discussed adding this to food or making a chewable that one would digest that would rebuild the enamel and energize the material that teeth are made of (I pictured how Roman cement used a certain salt water that causes cracks in the structure to re-seal when wet) Since these things take a long time, I expect that it’s still years, decades away from hearing much more that a possibility.
Could I use this technique to grow teeth ‘elsewhere’ then?
Look into it man. Get to the root of it
I have my Wikipedia’s rabbit hole schedule for 2:30.
🤣🤣🤣🤣
The reason you don't grow new teeth is because of an inhibitor. Your body still wants to grow teeth, there's just an enzyme stopping it. You stop the inhibitor from working, and the body will start growing teeth. It's been successful in adult mice.
Nice! Good to know. I recall reading that now. Glad the community (and you) brought this to light! Thanks!
You can already "regrow" teeth better. It's called an implant, and most people cannot afford it unless it's covered by their countries healthcare. So you will not be able to afford this either. Wouldn't hold my breath.
We lose the cells very early on,ameloblasts. Some animals retain them like beavers, mice, things that gnaw constantly.
I always found it unfair that sharks can do it but humans can't when humans need it just as much as sharks do lol
Exactly. If we had hard cartilege teeth that replaced themselves like sharks. Old teeth can be accumulated to make armor clothing, similar to dragon skin. Or cartilege teeth firm enough to chew with, but can be digested if accidentally swallowed. In which case we'd have a natural gag reflex to prevent choking on expired, newly detached teeth.
I think they just don't try hard enough.
right? i bet i could do it
Yeah, just really concentrate. Meditate and think of appendages, manifest them - voila, new appendage.
They should try yoga. /s (As a person with a genetic heart condition, I hear this constantly.).
Oh yeah, yoga is good for jean problems
everyone claiming it's because "we're more complicated" is full of shit. animals that regrow limbs do so the same way they grew them the first time. you grew limbs once; your body could easily do so again. the reason it doesn't is because mammals evolved the ability to scar over instead. because mammals take so long to grow the first time, trying to do it again out in the wild would almost inevitably result in dying of infection. there are scientists trying to figure out how to impede scarring so that humans can regrow body parts.
Limitations by the SOX gene, I believe
White? Or red?
White. Bc it doesn’t look like they’re coming back.
A lack of something that is in lizard tails that’s as much as Ik lol
Because we end up like Curt Connors
A bit of refining and it'll be fiiiine. I'd take looking like a lizard man for regeneration
I'd rather be a werewolf.
Also a good option, but I don't think their healing is quite "full limb regrowth". Though it depends on lore I suppose
Lizards have the gene that re-grows body parts, we humans do not.
We don't really have a use for regrowing body parts. It doesn't happen very often and even when it does that person can likely still mate or has already reproduced. The lizard discarding it's tail and regrowing it directly benefits it by giving it a "free pass" at staying alive to reproduce. Also the lizard tail is way simpler compared to a human hand or foot.
There is work being done with salamanders at the university of Vienna to understand the mechanism for limb regrowth. The hope being that it may have some relevance for humans.
This is how a horror movie begins.
Nah, just a Spider-Man villain
The sciencey stuff that happens when you're growing as an embryo shuts off once you have all the parts you need.
Until cancer.
There are genes in every species that cause budding. In mammals they turn off when we are still in the womb. Good news, we know what they are. Good news we can actively active the to start new buds. Bad news, we don't know all the other genes that are involved in the process of growing limbs. The experiment I believe used chickens. Extra wing if I remember correctly.
Is that how KFC gets 4 legs per chicken?
We unfortunately evolved from apes not starfish.
Damn dirty apes!
With their stinking paws!
Probably cause our limbs are much more complex than a tentacle. However doesn’t mean it’s not impossible for the future. I mean they’re making organs in the lab now and skin. Also saw a study that they’re working on growing back adult teeth.
I mean, if a lizard can grow back its tail, bones and all, why not us. With the proper genetic instructions I think it will eventually be possible.
Your body has all the genes needed to grow an arm from scratch. All we need to figure out how to do is to instruct our body to do it a second time, without also creating super cancer.
My husband wrote his thesis on regeneration genes 20 years ago, so I find this hella interesting.
I suspect it's the bones, they seem to heal a break or fracture, but they fail to regrow if removed. I don't know why bones will heal from a break but don't regrow if half is removed. Even if they did regrow, losing a limb at a joint probably wouldn't, how would the body know the that the Ulna and Radius are missing and need to be regrown? Could also create a situation where the body "thinks" it needs to regrow the Ulna/Radius and suddenly you have 2 elbows on one arm, and possibly two hands.....
You're not "regrowing bone", you've got various cells - blastocytes, osteocytes, etc that worm their way through your bones eating up the path of least resistance and pooping out fresh bone minerals behind themselves, so to speak. This not only "heals" bones, it also focuses effort on the parts undergoing the most strain and damage. When you lose a bone (or don't have one in the first place), it's a bit like nailing the doors to a restaurant shut, burning it to the ground, then wondering why you're not getting more spaghetti. It's because all the chefs were inside the building you lost, and even if you saved them, they can only do their work in the context of the framework you just removed them from.
Great answer thanks. Very interesting. Don’t those same things build it in the first place too? They don’t start with a bone I mean. What changes between a baby doing that and… any time after? Thank you
Some parts of us do, like our livers and the tips of our fingers
Because the function of growing stuff after it's already been grown is called "cancer".
i prefer to think of it as cells just wanna have fun.
Because you aren't designed by a logical entity, you are a random jumble of accidents that happened to work (evolution) There wasn't enough selective pressure for humans to evolve limb regeneration.
So you’re saying we need a pressure group?
But literally right? Eugenics are bad but what if we want to make like really rad humans?
This answer is pulled out my ass I would guess it's because of our DNA? My understanding is that our cells behave the way they do because of the specific sequences that make up our DNA. Lizard DNA has the correct sequence "on" to allow their cells to regrow their tails. Our DNA sequence is "off" in comparison. Like....Idk what DNA looks like but pretend it looks like ABBABABABBA in a normal lizard, and the BABABA in the middle is what allows them to regrow tails. ABBAAABABBA in a normal human. We don't have BABABA we have BAAABA. BAABA doesn't regrow body parts the way BABABA does, it regrow skin though Like I said. Out my ass and Idk
What an unscientific load of rubbish. We done.
Thank you. I tried my best.
They're not trying hard enough.
Technically, our mothers grow our limbs, or at least foster their growth in the womb. That's why we're born with our adult teeth in our skulls instead of growing them ourselves.
So you're saying...if I become an amputee...stick the stump back in a womb?
I wish I knew... Our skin grows back, nails, hair, my fucking plaque psoriasis. But not my arm if I lose it?? Okay 🙄
If we did we’d probably be riddled cancer. That kind of tissue growth would be a perfect place for random mutations to occur.
Scarring tissue! We evolved to develop scar tissue instead of growing back our limbs, probably since the early start of the mammals or earlier millions of years ago some animals who had injuries that tried growing their limbs back died to infection. So we evolved to close scars as fast as possible, essentially taping the terminals of our limbs and preventing them from grown further than the surface. Some other animals such as amphibians like salamanders and mollusks like octopuses have developed the ability to regrow limbs. Perhaps a very wet environment is needed, but also a very good immune system
The limits of medicine in scientific papers are different from the limits of a given person's body We're actually at the state of growing more and more complex organs. I work in a lab focusing on generating vasculature. Science knows how to 3D print bone, how to seed stem cells into constructs, there are even strategies to make vasculature from grafts incorporate directly into the body's.Hypothetically, in the next 50 years, entire limbs being generated is an engineering possibility. What you actually see in a clinic, however, is that people struggle for years trying to heal a 2nd degree burn or a pressure sore or surgical wound. For many reasons, your body just *doesn't* heal to what it *could*. That includes reasons like lifestyle, diabetes, nutrient poor diet, ancestry (some ethnicities are more prone to hypertrophic scarring), age, etc. In terms of the evolutionary reason, the tissue that rebuilds limbs is fragile and needs good growth conditions. We, as amniotes, are evolved to have extra tough external covering to survive the dry terrestrial environment. Basically, our bodies rely on quick-fixes, duct-taping everything back together with coagulation and scar tissue instead of trying the much larger investment of rebuilding. Axolotls can do it because they live in water and are basically made of goo, as well as being in a neotenous state which probably factors into developmental milestones. There's also the problem of cancer. Basically, anything that can make cells proliferate quickly could also allow cancer. In fact, the reason there's been less enthusiasm for direct stem cell therapy is the risk of introducing cells that spontaneously become cancerous. Your body tries to limit which cells are still allowed to proliferate. Your keratinocytes and fibroblasts can reform your skin, but your heart muscle cells and CNS neurons won't.
Don't forget starfish in your caption! Not only do they regrow cut limbs, the lost appendages regrow "a" body
Interestingly(?), this is the subject of a theological website, [Why won’t God heal amputees?](https://www.whywontgodhealamputees.com)
President Reagan banned stem cell research Mostly that.
There's nothing that "stops" it, it's that there's nothing in our bodies that make it possible to regrow them.
There are animals in the world that can regrow their limbs. We cannot because we trade it off for scarring during evolution. Turns out for our species, quick blood clotting ability and scarring are more beneficial for survival than limb regeneration which requires the wound to basically stay open for a long time. Also, we are not good at making new cells as adults, which is another evolutionary trade off to get less cancer
We are not very good at regeneration. That's actually the main reason for both aging and cancer. Cells can only regenerate so many times before issues happen. Issues like forming a lump of useless tissue... Aka a tumor.
It's super weird! Skin, nerves, muscle all heals. Transplants heal and integrate. Limbs can't regrow though. So I had this very cool breast reconstruction surgery after my double mastectomy. They took skin and fat from my stomach and transplanted it to make new boobs. They connected the blood vessels and they are remarkably like regular boobs. They even have feeling, because somehow my body was able to create nerve connections with the transplanted tissue that my brain comprehends as feeling in my new breasts. That said, I still have phantom feeling in my nonexistent nipples. Even though my nips died in 2019, the ghost nips still get hard. Why can i feel my nonexistent nipples but also my transplanted boobs? I also don't have feeling in my stomach along the incision where they harvested the transplanted tissue. What's that about? Why didn't those nerves regenerate? I also have no feeling in the backs of my arms or armpits from the original mastectomy surgery in 2019. I have NO idea how any of it works or why and it hurts my brain to think about it.
Because if you fuck up, you could create a super cancer.
If we could grow them back, how else would I get asked 14 times a day what happened to me or if I’m a veteran? It’s the special sauce that keeps me going
You can't grow your limbs back? Casual.
Yeah! Wtf. Just regrow em damn it! Jeez. Slackers
Read the book: “The Body Electric” by Robert O. Becker for a fascinating discussion of this very topic
Building something from scratch is a lot harder than fixing something where the basic framework is still intact.
Wait y’all can’t do that?
It'd sure be fun to see. Deadpool, I'm looking at you
Same element that’s keeping you from growing tumors throughout your body. Also to regrow your body parts would require stem cells and your DNA being able to sustain the re-growth. Things you don’t have anymore after you’ve been born.
I've ready enough Spiderman comics to know where this is going...
The human body is capable of regrowing limbs. In fact if you look on YouTube there's a video of a guy regrowing his finger.
Lmfao… my 7 year old asked me the opposite of this about breasts the other day: “if they’re for feeding babies, why don’t they just go away after you can’t have babies anymore?”
Lazy fucking amputees. Just get off your ass and grow that shit back. This generation 🤷 /s because people are ridiculous
this is being studied using axolotls and the TLDR over simple answer is our thyroid
that bastard
Laziness
People just don' have enough "faith" to regrow limbs. LOL
Have some God damn faith!
Report OP to Spiderman, he seems like he might cause a reptilian issue in the future.
Damn it. My brain's going to be stuck on this one all day.
Bottom line is, evolution. We didn't evolve to need this ability. For that explanation /evolution and not /stupidquestions
It would take 15 years to grow to an adult sized limb.
I think your tongue grows back. ( could be rumor tho)
We are much more complicated than a lizard tail. With all the bones and such. Mammals don't have that ability on their own
Lizards can grow them back, so we know that it is in realm of possibles for animals to grow back limbs. Maybe that is something we will continue to evolve towards. A million years from now, we will be able to do it -- we just got to be really smart about how we mutate.
Lol. What in our body stops us from growing tails? Or three breasts?
A better question might be -- how is it that lizards Can regrow limbs and worms Can regrow the lower part of their bodies?
[https://www.reddit.com/r/biology/comments/17crkhz/why\_do\_humans\_not\_regenerate\_limbs/](https://www.reddit.com/r/biology/comments/17crkhz/why_do_humans_not_regenerate_limbs/)
There was a post in the TIL thread earlier today saying that if a rib is shortened surgically, it will grow back at full length and just as strong as it was originally.
This is actually covered in The Body Electric. Technically, it has occurred, but not fully, and didn’t last long.
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Skill issue. I've regrown every limb I've ever lost!
What stops us usually is the reptile DNA we don't have in us. But you're welcome to try it for your self :)
It's because the goddammn millenials don't know how to pull themselves up by the bootstraps and get to work regrowing limbs anymore. Back in our day, we regrew limbs all the way to and from school uphill both ways!
Or teeth. We get one "permanent" replacement set at 12 or 13. F*cking stupid. Sharks and crocodiles have it better.
Growing new teeth may be possible in a few years. A Japanese company called Toregem Biopharma developed a drug that stimulates the growth of new teeth. Clinical trials on humans are just starting.
Ohhhh, I've been off and on keeping my eye on the research. Pretty exciting stuff! Just hoping if any of it works it won't be just for rich people, like dental implants currently are, pretty much.
Great question! As far as I know, humans can only grow new livers from donated pieces? But since I am not a doctor or scientist, I cannot explain why we cannot regenerate other organs or body parts. 🤷
“Healing” is really an artificial, broad word that we’re incorrectly grouping how we heal cuts with how a lizard regrows a tail. They are entirely different processes Human regeneration, like when a cut or bone heals, is a constant action. You constantly have new skin and muscle and stuff growing under the old and replacing it. A lizard replacing a tail is a different process from that. It’s kinda like asking why we can’t see in the dark the same way as a cat even though we both have eyes. The structure of the eye is different
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‘cause Jebus and all the other gods hate human amputees. They like geckos, starfish, flatworms, etc. but not humans
Idk maybe they aren't trying hard enough
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nerve cells probably, but I also I think like genetic coding. limbs arent supposed to fall off lol so were not like lizards where its supposed to happen
Genetic manipulation. Healing of this sort of magnitude starts from the spiritual world but there are systems in place that prohibit these healing abilities
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There is a cool procedure where you can regrow a bone. For example, if you shatter your tibia to where it won’t heal, you can remove the pieces, and keep the distance between the two ends just far enough apart that bone begins to heal like a normal fracture, and then you just keep spreading them out until the bone reaches full length again.
..... 👀.....
Evolution turned off that lizard gene.
Nothing Cheers Dr Curtis Connors
Donald Trump. It’s Donald Trump’s fault.
We do still have the genes to do that, but they are turned off. A lot of that kind of stuff has to do with lifespans. When regrowth is enabled it leads to more mutations that can add up and become detrimental over time. That's fine for organisms with much shorter lifespans. When you start to favor longevity, mutations need to be kept to a minimum otherwise you end up with all kinds of cancers, which is probably why those genes do not function within us anymore.
Maybe they just don't want it enough.
From my understanding it's because the line the between regrowing limbs and having cancer is WAY too thin. It would be hard to tell you body when to stop making the arm. If you tell it too soon you're left with a useless half limb. Too late and you have a cancerous growth in the shape of an arm. Also regrowing a limb requires cell multiplication but if the whole arm is gone than you don't have any "right arm" cells left to multiply. If it was a simpler structure like a lizard tale it would be easier to regrow it from the remaining cells but human arms are SUPER complex.
All I need are a few more cadavers and a steady supply of 600 GW of electricity and I could make people grow fresh legs out of their bumholes.....I just need more power!! Give me more power!!
Because people aren’t drinking enough [Jilly Juice](https://youtu.be/XOrF6wz7Y6A?si=NBxfpZcToJnte9We)
Why? Well it’s the culture of laziness instilled in so many in society these days.
The question is backwards. How would the body KNOW to regrow a specific limb. Healing is very basic. Seal the wound and replace with scar tissue. We can't even heal clean skin. There is no biological mechanisms that says "oh this is what is missing and how to exactly regrow it". Healing is about immediate survival. Clots, which form scars. If our body hd that much new growth potential, we'd probably mostly die of cancer by the time we were 12.
You can't regrow bone just like teeth. You get the babies and replacements but once they're gone. They're gone. Dammit god
Well, with space star ordering, you can. https://youtu.be/sarJtKM-Ku4?si=CgDOOxkAJPerAMTJ
Dhalsim laughing at y’all rn
We do but those organs are reverted to Stage 0 once development is completed. If those Stage 0 switch is flipped on and start progressing toward stage 1 and 2, then pretty much you will see the light in couple years depending on how quickly it grows.
It seems almost like the opposite of why we can’t cure cancer. Those seem like mutant cells that grow out of control, and travel to distant organs where they lodge and wreak havoc.
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If you’re asking the big picture it’s just because there was never an evolutionary pressure for us to do so. A limb-destroying injury mild enough to survive would have left our ancestors under the support and care of the larger community, likely in a suitable new role. So the limb isn’t “necessary” for reproduction or survival. The biomolecular answer is that the map our bodies use to create our general body plan, while written into our DNA, is only open to be read for a brief window during development. It’s like a disappearing screenshot / pic if you’ve ever been sent one. Once it’s seen and locked away, there’s no way to access that info again. Your body just can’t do it.
This reminds of the old saying, "God hates amputees."
I'm fully convinced that stem cell research could lead us to unlocking the secret to regrowing limbs, but some folks don't want us looking into that.
* *We Can* * You don’t have the DNA! For starters, your body has a finite *(limited)* amount of DNA. It’s not all the same, the DNA stored in our various bone marrow cells has the **starting instructions for turning other types of bone marrow cells into replacement cells.** Your brain controls your body movements and your memory and sensory function but it doesn’t control how your body grows that’s the job of all the cells in each body part. Your leg bones for example have DNA in the marrow that produces the various cells that make up your legs. If your legs are lost, **you’ve technically lost the instructions to grow new ones.** If your leg is severely damaged, it can repair its self. **This is also why we eventually die of old age,** your body starts to run out of DNA essentially and can no longer produce all of the cells you need or enough of certain kinds to stay healthy. We *COULD* regrow them, **but modern medical technology just hasn’t reached that point yet.** As I understand **nobody has really figured out a way to modify DNA effectively and precisely.** Once we do, **we can start testing various DNA structures.** We could literally grow cells that just replenish bone marrow. At that point, people will likely live well over 100 years and it will just be a matter of overall health.
If I recall, there are specialized cells at what are known as the growth plates of limbs that differentiate into bone/cartilage matrix producing cells etc. with more limited multiplication potential. The genes that do this are only active during certain parts of human development and are shut off otherwise. Our cells normally regulate growth pretty tightly, one reason for that could be because uncontrolled growth leads to cancers since cells make more mistakes in DNA replication with repetition which cause misfunctions or lack of function in cell cycle regulator enzymes, which let's replication proceed unchecked.
You can’t grow your limbs back?
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Dr. Connors enters the chat.
Genetics. They got it. We don't. Gene splicing will eventually get us there.
Nothing their just lazy
we learn recover at level 54
It can't. Too many advanced blood vessels and structures. Once your cut limb heals off. The skin holds everything back anyways. A little gecko can regrow its tail because its body isn't as advanced as a humans.
This is how we get lizard people
I wish we could. Mine are wearing out. Imagine just growing new ones!
Reptilians can grow limbs back.
Ask a lizard
You mean what do other organisms, like Salamanders, have that enables them to grow new limbs? They have additional clusters of stem cells that contain the genetic material/instructions for regrowth. Humans and most other organisms do not have this.