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Comment by progne | Hacker News Reader

This technology doesn't seem to be limited to existing limbs and organs. After replacing a missing arm you could add a third arm. A man could grow a uterus since he has the X chromosomes and with a transplant that includes Y chromosomes, a woman could grow testes. Parthenogenesis could become a choice. Another head seems possible. The limits are more likely to come from regulation than a reluctance of people to transform themselves.

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So, in other words, if this technology pans out, this could be possible https://mortalkombat.fandom.com/wiki/Goro

This implies that your brain could handle 4 arms. Chances are they would just be dead limbs.

Obviously we can grow an extra brain that will operate the extra limbs.

Conjoined twins Abby and Brittany Hensel look fairly normal apart from the two heads, but are really one-armed amputees each (but they were born with four arms and two heads): https://www.youtube.com/watch?v=VJN2sauvEb0

Not really. You would need some training but as long as the limbs nerves are connected you can manipulate them.

I think that's wildly over-optimistic: We have plenty of problems with existing limbs when it comes to fixing nerve-damage and then re-training everything. That's also with the advantage of decades of active prior use and in places/amounts that are supported by ten millions years of evolved physiological prep.

Babies do it.

Male monkeys of some species are born colorblind. Researchers used viral gene therapy to add the other rhodopsin shapes for the other colors and they learned to process the new info in less than two weeks. Brains are amazingly plastic, but they are finite, something else would maybe have to go.

I don’t think that’s necessarily true. We have mirrored nerve bundles dedicated to limbs with specific junctioning in the CNS. I don’t think it’s just brain plasticity at play, it’s fundamental wiring structure from limb to brain as well.

The problem isn't (just) the brain power, the shoulder joint is also a necessary component of the full range of motion and degrees of freedom your arm has. You can't just slot a ball and socket somewhere into the side of your ribs (and all the supporting musculature) and have it work the same way.

So I wonder how much brain power (if any significant) is being taken up by the uterus during pregnancy.

Well, I don’t know if it’s the brain power or the gray matter pruning that goes on, but my wife was an absolute space cadet for a while during pregnancy and quite a while after. She’d forget almost everything.

I've read literature that the hormone fluctuations resulting from pregnancy, and from parenting regardless of sex actually trigger the destruction of particular parts of the brain in humans.

This is a long shot, but I've always wondered if it might be genetically related to the part of the brain responsible for "abandon one of the babies to escape predator" type reasoning that you see in animals with litters. Something that would have been selected out of human evolution fairly quickly.

I once spend a ( drunken ) evening discussing with a neurosurgeon about the possibility to add a prosthetic tail to the human body.

The base structures to control a tail are present in our brain, sure we lost it a few million years ago but still a tail is much more realistic than e.g a second pair of arms.

no more need for poles when tightrope walking!

Almost certainly wouldn't be an issue. There's a huge amount of plasticity in embodiment. Think about how easily we can control videogame avatars of many physical forms, or adapt ourselves to a musical instrument, or even learn 'pilot' an artificial limb.

Plus all your shirts would need to be tailored.

Biological systems have an incredible plasticity. That same Michael Levin once used his discoveries to make a tadpole with an eye somewhere near the gut. The eye formed correctly and grew a nerve that connected to the spinal cord. The tadpole was able to see out of that eye. It's definitely a non-stock configuration yet it worked. I'm sure it's much more complicated than having 4 arms.

The just in time for Halloween scenario is they grow back but with Alien Hand Syndrome.

So they're constantly giving you wedgies, making rude gestures to loved ones, writing bad checks, and trying to choke you out.

Our brains can learn to handle new limbs - experiments with sensors that detect nerve impulses and control robotic arms have proven that.

Our brains can learn to handle new senses - experiments with sonar or infrared being sent to panels of pins that push on someone's arm have proven that.

Start with something simple and wonderful like growing a new set of teeth.

Indeed. I've been hearing about teeth being grown in vitro or regrown in vivo in various different trials for about 23 years now. Most recent is still saying "perhaps in ten years…"

Let's hope they don't come through the way the current set does.

Something simple like elongated heads

Pair that with a caries vaccine and now we're talking.

Getting a new pair of chompers in middle age would be super great, especially if they won't decay the same way.

That is in progress: https://www.japantimes.co.jp/news/2023/09/24/japan/science-h...

To be honest I would prefer something non-trivil like fixing broken spinal-column disks ;-)

> After replacing a missing arm you could add a third arm.

But it would cost you an arm and a leg. At least initially.

Plus a costs of custom tailoring.

"Accepting the limitations of birthform betrays a lack of imagination."

- Civilization: Beyond Earth

If only they would make a sequel! I don't understand why that game was poorly received.

I think it was partly that you have to be quite well-read in sci-fi to know where the names for the tech, buildings, victory conditions etc. come from, so most people don't get an easy anchor to remember what benefits they're likely to get from their choices.

Probably also didn't help that the first version had a very anti-climactic victory sequence; they improved it, but I do remember it being jarringly sudden the first time I played.

I'm a massive Science Fiction buff and bought the game, played it for a few hours and decided it was not for me. I think it's because I couldn't relate to the factions, if that makes sense.

I don't quite remember the factions, but I do remember that like most Civilization games, it was significantly better with the expansions

highly dumbed down compared to the base game

I imagine for an extra arm you'd need to also figure out how to grow the right neurons to control it.

Plus extensive musculature at the new shoulder joint and reinforced bones for the new muscle attachments. I won't be first in line.

I get the sense that if it's connected, your brain will figure out how to make it work.

The curious thing about Michael Levin's work is that they figured out "top level abstractions" in bioelectricity that tell the body to figure out everything, including the proper wiring. The have grown eyes in the wrong places that figure out how to connect to the brain, and even two heads.

These guys are decoding the actual bioelectrical code that governs morphogenesis, in a way that you don't need to micromanage anything, you just say "grow an eye" and the cells figure out the rest.

It doesn't work like that at all. Your brain's already plastic enough to be able to (quickly) accept new sensory input if you were given a new sense via prosthetic. Being able to twiddle your third thumb after it grows would be automatic.

One sex could decide it no longer wants to deal with anyone not of their sex and wipe them out. Humanity could go on with the artificially created sex organs. Lots of possibilities, not all of them the fun, wild and crazy anything goes utopia some are looking for.

This technology can also be used to turn cancerous cells into healthy cell Michael Levin https://www.youtube.com/watch?v=g798Mck7dPk

Now there's a future society you don't see written about: a standard part of a marriage is the partners exchange immune-compatibilized gonads with their genetic material, so if one partner dies the other still retains the ability to grow viable off-spring from the pairing.

"Ma'am, I'm here to enforce the terms of the divorce agreement. I need you to take his gonads out of your purse and hand them over."

I mean I imagined it would be like, having them surgically implanted somewhere near the kidney's (large blood supply organ).

Which would make this scenario far more cyberpunk.

Nuts!

Now I'm thinking about that song about the man with a detachable penis who looses it.

https://youtu.be/byDiILrNbM4?si=oiR7pKrCkjXOnUqJ

Isn't this already possible by freezing eggs or sperms?

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