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Posted by jbotz 5 hours ago

Why is the liver so weirdly regenerative?(dynomight.substack.com)
154 points | 111 comments
senfiaj 45 minutes ago|
Most of the body doesn't regenerate because there was not enough evolutionary pressure. Even with regeneration you could still easily die from some severe injury, blood loss or disease. While salamander regeneration is impressive, it has its limitations. For example, no known adult salamander can regenerate an entirely removed eye. Also if you chop a salamander, it will not regenerate like a Planarian worm, it will just die. And a fun fact, Axolotls can regrow a limb yet cannot regenerate an adult eye lens.

Also, although the article is mostly true, there are some inaccuracies:

>> Neurons and cardiac muscle cells don't reproduce after childhood

There is some evidence showing a slow cell turnover in cardiac muscle, estimated around ~1% per year in young adults, falling toward ~0.5% in older people. Most neurons don't regenerate, but there an evidence that some parts of the adult brain (such as hippocampus) still produce new neurons, although the number is very low.

Liver regeneration is not perfect either: https://www.youtube.com/watch?v=rOv7Sr3X-eo .

asdfman123 18 minutes ago|
Actually I would argue that the evolutionary pressures run against it: if one generation dominates then the species can't evolve.
senfiaj 1 minute ago||
Regeneration is unlikely to warrant eternal life. In the wild, most animals die before even showing serious signs of aging. Even if regeneration increased lifespan, poorly adapted individuals would still die.
cityofdelusion 1 hour ago||
The author suggests humans are overturned to repairing skin and blood, but I strongly disagree. People with problems with wound healing can face significant disability and mortality. Wound healing allows us to have surgery and close up with simple sutures. A lot of complications post-surgery in humans and other animals are specifically from impaired wound healing capability. It’s a good trade-off: nearly everyone will eventually get cut open by accident or on purpose. The skins ability to heal is so amazing that many types of wounds require nothing other than some cleaning, the body will fully clot, bridge, build, and scar back to most retained function. Wound healing allows us to heal large burns and even simply leave many wounds open to air.

Complications with healing are pretty brutal. Necrosis, amputation, infection are all common without the built-in cascade we have.

seethishat 50 minutes ago||
Many problems with would healing are due to nutrient deficiencies. For example, people who are sulfur deficient will heal and recover much slower than those who are not.

That's why so many professional athletes take MSM (Methylsulfonylmethane). Their bodies would not be able to recover as quickly without the extra sulfur.

shiandow 3 minutes ago||
Huh, another reason to eat more spinach I suppose.
WhiteOwlLion 1 hour ago||
Your liver makes platelets so if your liver function is not optimal, wound healing is harder.

Some people also have rare diseases where they don’t have clotting factors so require a transfusion of clotting factors before surgery for optimal wound healing.

BigTTYGothGF 1 hour ago||
> Your liver makes platelets

Megakaryocytes are primarily bone marrow cells.

leereeves 2 minutes ago||
Indeed, but your liver does make clotting factors and also thrombopoietin, which stimulates platelet production.
Noe2097 1 hour ago||
> And even after taking [immunosuppressants], there’s a 30% chance the kidney will be rejected within 10 years. This is not helpful.

To the author: thank you, you made my day. It had been a very, very long time since I last read an article on the Internet that felt written by a human being - with humor, some poetry, and science.

WhiteOwlLion 1 hour ago||
Immunosuppressants like tacrolimus given at too high of a level for many years can wear down your kidneys faster requiring a transplant potentially after ten years.
buildsjets 38 minutes ago||
I asked ChatGPT if it is OK to an explain a joke without being asked to do so, and She said no.
varispeed 15 minutes ago||
Why nature did this? So that 3rd parties don't engage in organ swaps?

Almost like Apple with component serialisation.

epcoa 2 hours ago||
"Some day, your immune system may decide to attack your pancreas."

Immune attack of the pancreas is usually a disease of youth. Type 2 diabetes which is overwhelmingly the diabetes associated with aging is not an autoimmune disease.

joshmarinacci 1 hour ago|
Adult onset Type 1 has become a lot more common in recent decades. Ask me how I know.
patagurbon 38 minutes ago|||
I don’t know how adult 22 is considered but yeah. A younger sibling got it when they were ~13.

When we noticed the signs and went into the ER a few of the (younger) doctors thought it was Type 2, while the attending knew it was just late onset Type 1.

mschuster91 1 hour ago|||
Just like a ton of other autoimmune diseases.
ramijames 46 minutes ago||
Psoriasis sufferer checking in. Brutal.
vconnor 3 hours ago||
The punishment for Prometheus stealing fire from the Gods and gifting it to humanity, was to be chained to a rock and having an eagle feed on his liver which would regrow the next day.
bheadmaster 3 hours ago|
For what it's worth, Prometheus was a Titan, and Titan was immortal, so his liver regrowing the next day wasn't really that special. If eagle fed on his heart, or lungs, they would've regrown too.

The Greeks chose liver because it symbolized the defiance Prometheus had against gods.

pazimzadeh 2 hours ago|||
I don't know about the Greeks but I know a lot of ancient cultures thought the liver was the most important organ (probably because it's full of blood).

For example in Persian poetry the word liver is found pretty much everywhere you would expect to see the word heart.

"You are my liver" is a nice/romantic thing to say to this day.

The_Blade 1 hour ago||
i mean it's called the liver not the dier
bryanrasmussen 2 hours ago||||
There's really no knowing why the Greeks chose liver, or some specific Greek chose liver.

It could have been because the liver was regenerative and they were using the titan with the regenerating liver as another reference to humanity, or it could have been as someone pointed out because predators like to eat the liver first, or it could have been that you can take damage to the liver and live for hours afterwards in agony whereas the same amount of damage to the heart or lungs is apt to cause death to come much quicker.

Perhaps there are undiscovered variants out there were the eagle or a serpent or some other animal attacks his genitals, or his eyes.

But at any rate the Eagle ate his liver, it means nothing in particular, and at the same time it means every particular interpretation we can place on it.

bheadmaster 2 hours ago||
Whatever the actual reason for choosing the liver was, we can be certain it wasn't its regenerative property, since such proprerty was unknown to the Greeks at the time.
bryanrasmussen 2 hours ago|||
Probably not, I don't think I ever read Galen mentioning it, but then again people would get injured in the liver and recuperate better than other injuries I suppose, which makes me think it is surprising if he didn't.

Just went and checked, evidently he never said anything about it.

old American translation of Galen and Hippocrates for anyone interested, as it can be difficult to find otherwise

https://oll.libertyfund.org/titles/coxe-the-writings-of-hipp...

rightnutwingjob 1 hour ago|||
[flagged]
mwigdahl 2 hours ago||||
I thought they chose it because it tastes great with some fava beans and a nice Chianti.
seizethecheese 3 hours ago||||
Why would liver signal defiance?
bheadmaster 2 hours ago|||
I phrased it awkwardly. Simply put, in Ancient Greece, liver was something like heart in modern society. It was the seat of human emotions.

So by destroying Prometheus' liver, Zeus attempted to destroy his human emotions, including his pride and defiance against gods.

seizethecheese 2 hours ago||
I don’t think it was phrased awkwardly, I was just curious.
Sleaker 2 hours ago||||
It was the believed area of emotion, passion and 'soul'. I think western/modern religion has morphed from the liver to the heart essentially.
pinkmuffinere 2 hours ago||
This is still the normal in the middle east (and likely elsewhere)! In Turkey you call somebody dear to you "my liver" as a pet name.
jephs 2 hours ago||||
There are a bunch of Japanese words (including a several loanwords from Chinese) that use the liver / gallbladder metaphorically for courage. Both derive from associations between the humours and personality / behavior. I have no idea, however, why both Eastern and Western naive psychology associate gall with, well, gall.
BobaFloutist 1 hour ago|||
>I have no idea, however, why both Eastern and Western naive psychology associate gall with, well, gall.

Possibly because it's filled with strong acid.

vconnor 2 hours ago||||
In Italian, to have 'liver' (fegato) means to be courageous.
card_zero 1 hour ago|||
The Greeks did get to India. https://en.wikipedia.org/wiki/Greco-Buddhist_art
Bluestein 2 hours ago|||
Humors perhaps. Not my area, so I do not recall the correspondence ...
bell-cot 2 hours ago|||
I'm thinking the Greeks chose liver because it is the first thing that many predators will eat from a kill - large, more nutrient-dense than almost any other tissue, and relatively quick to access.
joshmarinacci 1 hour ago||
Many if not most of these oddities about humans come down to either they don’t affect reproduction, or because humans are social animals. Menopause makes sense because a grandmother will have more successful descendants if she stops having babies and helps her daughters with the grandkids. I would guess the few other species that exhibit menopause are also social animals.
amluto 4 hours ago||
The lack of heart cancer might be more complex than the OP imagines:

https://www.science.org/content/blog-post/no-heart-cancer-th...

jaggederest 3 hours ago|
Other animals do get heart cancer, which is fascinating. It's still very uncommon compared to other cancers, but not virtually absent as it is in people.
schnuri 4 hours ago||
I am in awe about how wonderfully engineered by evolution the body is. E.g., what we are able to do with it and how it heals itself when we have an injury. Sure, many people would not live long without external intervention, but many others would. I still want to see the robot that can survive 80 active years without maintenance.
dgunay 3 hours ago||
Well, we do at least have to eat enough food and sleep ~1/3rd of our lives. That's kinda maintenance
vconnor 2 hours ago|||
Compared to most animals that spend their entire day foraging for food, it's not too bad. Adapting to eating dense and very nutritious animal flesh is a great time-saver, and as we didn't evolve long fangs, we had to learn to use tools instead, and the rest is history. (mixing cause and effect here for dramatic purposes)
nerdralph 1 hour ago||
I think learning to cook food was likely a greater benefit. It's like we externally expanded our means of digestion.

I watched a Ted talk where the speaker suggested our large brains with their high energy consumption would not have been possible were it not for cooking.

NetMageSCW 34 minutes ago||
Which came first, steak or intelligence?
yhjc2692 2 hours ago||||
quite the delightful maintenance too
micromacrofoot 3 hours ago|||
that's absolutely maintenance, without it you have a total system failure in a week
ericmay 3 hours ago|||
When you watch those sci-fi shows and folks have nanobots implanted in them that heal wounds really fast or do other cool things I can't help but think in many ways we already have that technology we just need it to do more, faster as our brains and ability to create things have outpaced the rate of evolutionary change.
onlypassingthru 1 hour ago|||
The human machine doesn't just survive without external intervention, it actually gets better at being a machine. Speed, endurance, power, coordination... all improve with usage.
fhn 1 hour ago||
until you get old and goes the opposite direction
RobotToaster 3 hours ago|||
Humans don't last long without topping up their fluids and consumables.
markyc 3 hours ago|||
no you don't
arcanemachiner 3 hours ago||
Well, so much for that discussion.
chistev 3 hours ago||
The human body can't survive 80 active years without maintainance. They take drugs, they see the doctor, etc.
CookieCrisp 3 hours ago||
What did people do 500 years ago?
EduardoBautista 3 hours ago||
Die as a child at alarming rates
lukan 3 hours ago||
But those who did not, got quite old without ever seeing a doctor.

(If we are talking about hunter gatherers, not poor exploited peasants)

steve_adams_86 2 hours ago|||
Humans have assisted each other medically, supported injured and disabled tribe members, and sought out medicinal herbs since long before history was written. I'm not sure how you'd delineate between modern health care and when humans never had some notion of health care and/or support when bodies enter failure modes. We don't survive well without a lot of assistance and care, and living long lives required plenty of bodily maintenance regardless of how fortunate and healthy we were.
b112 1 hour ago||
I think, if you add clarity, such as how aspirin alone is a wonder, how iodine to clean wounds is a life saver, how soap is a miracle, and all the parasites we don't have, yet all this we take for granted.

We are certainly much healthier, with the little trinkets we keep in our houses.

lukan 19 minutes ago||
Willow bark was used like aspirin. Soap is a old concept (ash is desinfectant as is vinegar ). Alcohol for cleaning wounds is a very old concept alike. As was jumping into clean water every day (also in winter).
fhn 58 minutes ago||||
quite old as in 50 because the avg lifespan back then is certainly lower than it is now.
1attice 3 hours ago|||
Citation required
Fezzik 2 hours ago||
Gurven, Michael & Hillard Kaplan (2007). “Longevity Among Hunter-Gatherers: A Cross-Cultural Examination.” Population and Development Review, 33(2), 321–365

If you made it past age 5 as a hunter-gatherer you’d likely live to 50-60 years of age.

1attice 2 hours ago||
Interesting. Yet as someone approaching the first of those two last numbers, I would say that that isn't very old at all
Fezzik 2 hours ago|||
It’s also worth noting that, while this is (I think) likely the most cited paper on the topic, all the observed societies are from the 20th century. So we can’t necessarily extrapolate from that that hunter-gatherers 300,000 years ago fared the same.
exe34 2 hours ago|||
Old people are at least 20-30 years older than I am.
warumdarum 2 hours ago||
Because alcoholism forces hunter gatherer cultures into settlements, which are the next stage of civilization and reward those doing that choice?
asdfman123 13 minutes ago||
Actually it may be the opposite. Alcohol is needed for people within settlements to bond.
danecek099 1 hour ago|||
I love this theory
The_Blade 51 minutes ago||
wouldn't it be our ancestors just liked booze too much and the liver said alright genes, hold my beer
warumdarum 46 minutes ago||
But if you want to avoid withdrawls.. you better harvest and store that honey. And that wheat- all that beer, all that mead. Just to stop shivering.. the addiction of civilization.. and all you need is earthen kegs and a cellar.
daitangio 54 minutes ago|
Very nice, well written and interesting! Amazing!
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