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Comment by lqet | Hacker News Reader

I chopped off around 3-4mm off the tip of my left index finger as a kid with a lawn trimmer. 20 years later, I punched a nice groove around 3mm deep into the tip of another finger tip while trying to get tea out of a tea tube [0] (don't buy these things).

It took weeks, but both times, the tips grew back perfectly round and smooth, even the fingerprints are back. The regrown tips felt a bit numb for 1-2 months, but then everything was back to normal. The second time I asked a friend, who is a medical doctor, how the body "knew" the form of the fingertip and the fingerprints. Where was this information stored? His answer was basically: we have no idea, just be grateful it works.

[0] https://www.hochland-kaffee.de/media/catalog/product/cache/1...

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Regarding how the body "knows" how to form missing pieces, might be worth checking out Michael Levin's research regarding bio-electricity. Most interesting finding to me is that once modified, the animal bodies continue to produce different parts as if there is some electrical "memory" in the cells.

Here is an overview video: https://www.youtube.com/watch?v=XheAMrS8Q1c, though there are much longer lectures and papers which I would recommend if you are interested.

even more crazy : https://phys.org/news/2013-07-flat-worms-retain-memories-dec...

Another related article:

https://knowablemagazine.org/article/living-world/2020/how-d...

I caught my finges in the chain of a swing as a child and tore about half the pad of my pinkies away to a similar depth, one narrow strip was still attached so I held it on with bandaids after washing it. It grew back together but now there is an offset or fault line in my print.

At first I thought you meant to write fingers, then I realized your must have been referring to the truncated fingers, that is “finges”.

Did you just do that on your own without telling an adult? I totally did similar things.

I cut my thumb to the bone when I was 10 by whittling a stick towards myself, and I also have a fault line there now.

Any idea if your fingerprints are the same as before?

Good point, is identical only an assumption?

It seems somewhat plausible. Identical twins often have broadly similar, although still distinct, fingerprints: https://pubmed.ncbi.nlm.nih.gov/22558204/

Maybe everyone should get their prints on record as a way of verifying in the future.

Nice try.

Aren't we already doing this (see smartphones).

> I punched a nice groove around 3mm deep into the tip of another finger tip while trying to get tea out of a tea tube

Out of curiosity, how did this happen? Is the opening sharp?

Its not that sharp, its a tube of brushed aluminium around, around 2cm in diameter, the walls ca. 1 mm thick. It's tapered at the top (which can be seen in the image). I put tea in there and coudldn't get it out after it had swollen in the hot water. I opened the bottom, put the handle of a wooden cooking spoon in, hold the cooking spoon with both hands and pushed the tea tube against a wall. The tea suddenly gave loose, and the tea tube shot down the cooking spoon to where my hand was holding it. It only hurt after the shock of seeing a groove in my fingertip was over, and it seemed like and eternity until there was blood (but then lots of it).

Some time ago there was a post on HN about one scientist who made a simple organism to grow two heads by messing with the intercellular magnetic fields. No DNA changes, just magnetic fields.

There's a way to check this hypothesis without cutting fingers. Salamanders can regrow tails. So get a salamander, cut its tail, use some magnetic field generator to mess with the regrowth process and see what happens.

The scientist is Michael Levin and his work, while absolutely legit, is so far from current mainstream that I am a bit afraid it might not be adapted for medical use in our lifetimes. Or possibly only after a major upheaval, much like mRNA deployment was accelerated by Covid. (mRNA co-pioneer Dr. Katalin Karikó ran into similar problems - the concept of mRNA was too revolutionary to be fully grasped by the PennU administration.)

https://wyss.harvard.edu/news/mike-levin-on-electrifying-ins...

https://www.newyorker.com/magazine/2021/05/10/persuading-the...

My finger tip got pinched under a lid and a small chunk was torn off but somehow it all healed with matching fingerprints that blends in.

Pure wild speculation: I suspect that an awful log of our biological form is fractals formed from chemical gradients, with our DNA controlling the amounts of each chemical, both how fast they're produced and consumed. Included in this are some wild "Programs" were Chemical A causes Chemical B to be produced, Chemical B produces Chemical C and chemical C shuts off chemical A - In wild patterns that eventually form the beauty of our bodies. On a mass scale, with dozens of signaling chemicals and switches flipped - Organelle A produces chemical B and C and they osmose. B spreads far and wide, and an organ grows wherever B is concentrated. C doesn't spread, and eventually it grows concentrated enough to shut itself off. Thus, the physical limits of a body are formed.

Fingerprints would then be where this all happens on a micro scale - Running the game of life in 3d on the cells of your body, until they reach an "end state" of a stable limit of your skin.

You might be interested in reading up on homeobox genes.

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

There are several parts embryo development that does operate on chemical gradients especially the initial stages. But like most of biology it gets really complex and isn’t limited to any one approach.

For example as you gain fat tissue you need to increase the number of capillaries feeding that tissue, which in tern needs to link up to arterioles and arteries on one side and veins on the other. https://www.ncbi.nlm.nih.gov/books/NBK53238/ This happens well into adulthood.

Turing’s diffusion/reaction algorithm involved this. As you intuited, it is a good system for making fractal-like designs and patterns. Cheetah spots, zebra stripes, maybe even 3D structures like capillaries...

But, such a system can’t make discrete forms—like a nose.

There’s something else going on.

For instance... deer grow antlers every season (antlers are not horns; rather, they are complex structures with tissue, bone, skin, nerves, etc) Anyway, if a growing antler is nicked, scar tissue will form... no big deal, right? But, this is where it gets weird... When the antlers fall off and then grow the following year, the scar will be present on the new antlers. Let that sink in.

Not that such a thing is impossible with epigenetics, but do you have a source for that?

It may be a way for deer especially with high status to recognize each other. Also marks of trauma or injury often persist in human nailbeds.

One of my finger nail was wrecked last year and it looked horrible. I thought it would never grow back. Now I can’t even tell which one had been wrecked.

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