[arp242]

> Meanwhile, evolving resistance also comes at a cost. We don’t know that directly, but we can infer it pretty well. If resistance to tetrodotoxin were cheap and easy, everything would evolve it. [..] We don’t know, but we’re pretty sure there must be something. We know that garter snakes outside of the Pacific Northwest are much less resistant to tetrodotoxin. They’ll drop dead from doses that their Oregon cousins simply ignore. So evolving the resistance must have some cost or drawback.

I'm not so sure that's really the case; it's more that for many animals there simply isn't any pressure to evolve (or retain) this trait.

It's not like the natural selection process has a feature list it can tick off. It operates with zero foresight and an incredibly dumb principle: whatever helps procreation.

Cows are not dying due to tetrodotoxin poisoning in significant numbers, as far as I know, so there is no reason for them to evolve resistance to it. The same applies to most animals, including the snakes outside that area.

Your dog can synthesise their own vitamin C and will never develop scurvy. Most animals can do this – humans and some other primates are the exception. An ancestor lost the trait for vitamin C synthesis by chance, and because these primates were living in trees eating lots of fruit with vitamin C, evolution simply didn't notice. There is no disadvantage to being able to synthesise vitamin C, and no advantage in dropping the trait. It didn't affect procreation (at the time). Now we're all stuck with it.

Now, maybe all of this does have a cost for the snakes. But it's far from a given that there is one.

[mekoka]

I think it might be more useful to look at the author's claim from the other side of the lense. We do carry around barely useful traits, like resistance to toxins that we seldom come in contact with. We can assume that carrying such traits is cheap. If resistance to tetrodotoxin was one such cheap trait, it might have been more prevalent, but it's not so, it could be inferred that it's expensive. Or at least, not cheap.

[xenadu02]

This is another case of a huge fallacy humans seem endlessly afflicted with: The Root Cause Fallacy.

You are assuming there is but one cause for development and/or loss of resistance.

There may not be much pressure to develop resistance to tetrodotoxin for most species. Simultaneously there might be a higher metabolic cost to retaining it for some species but not for others. It is also possible that resistance with low cost is very rarely lost which is why we carry resistance to toxins we don't often see but population bottlenecks in ancestral lines can cause loss of a trait to propagate - even by accident. And much like Vitamin C loss if it doesn't matter the loss sticks. We should not forget that there are multiple resistance mechanisms as well: an immune system generally primed to fight certain common causes of mortality can, entirely by accident, also be primed to recognize and destroy certain proteins conferring resistance to some toxins and not others.

I have barely scratched the surface above. The random walk of evolution and its constant hoarding tendencies should make everyone skeptical simplistic mechanisms of action as well as "just so" explanations of evolutionary history.

FWIW most things are multi-causal. I previously made the same argument about house prices. People who claim it is caused by foreign money, low interest rates, restrictive zoning, etc all want their pet theory to be The One True Reason. In reality the market is complex and many of the proposed causes are merely contributing factors.

[mekoka]

> You are assuming...

I made no assumptions. As I pointed out to another commenter, you might be in too much of a haste to play at being a contrarian. It might be more useful to pay closer attention to what you're objecting to.

Evolutionary game theory demonstrates that evolution is a matter of fitness payoffs. If cost of a trait increases, fitness is reduced. The prevalence of a trait in a fit population is indicative that, at best, the trait increases fitness, at worst, it doesn't hinder it. In both cases, the genes tend to be passed on and the game is allowed to continue. When carrying the trait becomes costly, there's pressure to get rid of it (through the usual evolutionary means).

The above model encompasses all the unnecessary specificity you tried to bring into the matter. If you object to it, address your concerns to the scientists that are leading us all astray.

For now, let's circle right back to the author's original argument. Absence of an actually useful trait to increase fitness (i.e. protecting ones from certain food sources and others from predators) might be indicative of a hefty tax to pay for carrying it.

[kylebenzle]

As a biologist, reading your comments is deeply distressing :(

[zxexz]

Isn’t evolutionary game theory a behavioural model from the 1970s? Not that it’s not interesting; I don’t see the relevance here. Maybe it’s just your condescending tone.

(No offense, I hope you don’t realize how you are coming across, or that if you do this comment will trigger some introspection)

[mbonnet]

You need to accept that you don't know what you're talking about.

[jkman]

Jesus man, your hubris is astounding. 'I made no assumptions'? Ridiculous lol

Behave yourself

[pegasus]

That resistance to toxins we don't encounter often enough to constitute selective pressure, we carry around only if it's the accidental byproduct of another selected-for trait. Otherwise entropy would take care of it, sooner or later. Parent is right, evolution doesn't pay an annual subscription fee for some service which was useful in the past and might come in handy in the future.

[mekoka]

You may just be trying to disagree with the author for sport.

> we carry around only...

Not true. We can carry resistance to some ancestral pressure which isn't part of the current environment.

> sooner or later...

Yes, sooner when it's costly, later when it's less so, through normal evolutionary pressure (entropy and all).

The point is, most species at time T do carry traits that aren't that useful to them anymore. The costlier ones yield enough negative fitness points in evolutionary game theory to rid the gene pool of them quicker. It brings us right back to the author's original argument.

[catlifeonmars]

It would be interesting to see how toxic these newts would remain if the garter snakes were eradicated. If this was indeed a costly trait, we should see a drop in toxicity over a long period of time (possibly evolutionary time). To rule out coincidence, you could follow multiple lineages as they speciated.

In fact, looking at related newts whose ancestors were toxic (assuming the trait is not novel in these ones) would give us some idea as well.

[pegasus]

In the context of TFA, are you sure it's not GP who's arguing for sport? Maybe this clarifies the issue: one way to reword the root (critical) comment is "of course there is a cost, since entropy is always exacting a price". There's constant upkeep necessary for any trait if it is to be preserved. It points out a glaring blind-spot in the article.

[zxexz]

(I agree with you)

It’s funny how often this sort of thing comes up. I’ve always felt that “biology” as a field was unique in the way that it is often taught. Bio 101, etc. - most of undergraduate biology - is often taught with this sort of sweeping worship of the process of evolution in a way that leads to it transcending rational thought. Natural selection is very real, and it’s also such a sorry excuse for an evolutionary algorithm :D

It’s been a long time since my first bio classes so I can’t remember the way I was first taught it, but I do remember all more advanced bio literally being told to unlearn what we had already been taught.

[kylebenzle]

You really seem to lack any understanding of how evolution or biology work :(

[Retric]

It’s not some binary thing but degrees of adaptation.

People can handle significantly more of a wide range of plant toxins like theobromine and caffeine (both found in chocolate) which harm more pure predators like dogs in very low doses, but where rare for out imitate ancestors.

Cattle, deer etc however can handle many of those at much higher doses.

[nkrisc]

> like resistance to toxins that we seldom come in contact with.

Is that because resistance to those toxins was strongly selected for in humans, or because the source of those toxins did not strongly select for effectiveness in humans?

[kylebenzle]

You wildly misunderstood the topic being discussed and user above you is correct.

[pokpokpok]

Not wrong, but one could frame that as a "cost" that you pay in the space of genealogical problem solving. Having one less constraint makes it easier to adapt to other evolutionary pressures

[y-curious]

Agreed, it's just shorthand/abstraction. Just like my for-loop in python doesn't actually mean my computer speaks Python

[arp242]

I omitted some bits from the quote for brevity and HN's faux-quoting sucks, but that's not really the type of "cost" the article is talking about: "maybe they’re suffering from much more subtle neurological effects, like being prone to insomnia or hallucinations or sexual dysfunction. Or maybe they’re just a bit dim."

[odyssey7]

That claim jumped out to me as well. Evolution is supply and demand, cost and benefit, capacity and constraints, none of it balanced by anything apart from luck.

[mattigames]

This is categorically false, we know evolving bigger brains required us to reduce our muscle mass compared to other primates, for the energy budget required to create such brains.

[pegasus]

And those adorable koalas made the opposite bet, shrinking brain size in order to conserve energy so as to be able to carve a niche no other mammal cared for: https://youtu.be/dXUp_JMQjvg

[mr_toad]

Do we know that? I thought that the evidence suggested that early hominids lost muscle mass, especially in our arms, as they came down from the trees. We also switched from stronger muscle fibres to high endurance muscles.

You’re right that there was an energy trade-off, but it was being able to run faster and longer that was more important than strength for our ancestors, who still had quite small brains (the brain of an Australopithecus is only 35% the size of a human).

Brain size developed later, probably in a feedback loop with our diet - as we began to eat more meat our brains got bigger, which made us better hunters. And hominids actually got bigger and stronger as their brains grew.

[mattigames]

The diminished muscles in our jaws are one of the direct causes we have bigger brains, source: https://www.newscientist.com/article/dn4817-early-humans-swa...

Humans evolved Wesker muscles to gain brain mass, source: https://www.nationalgeographic.com/culture/article/140527-br...

[catlifeonmars]

From the first article:

> Humans owe their big brains and sophisticated culture to a single genetic mutation that weakened our jaw muscles about 2.4 million years ago, a new study suggests.

_A new study suggests_

I don’t think you can treat these claims as categorically true. It’s plausible and probably warrants further study, like most things in biology.

Edit: I could not read the second article you linked as it was behind a paywall, but I found the full text of the original paper[1]. The paper appears to make a much weaker claim: that a weakening of jaw muscles in humans coincided with acceleration in brain size. This is certainly intriguing, but correlation does not imply causation.

[1]: https://pmc.ncbi.nlm.nih.gov/articles/PMC4035273/

[mattigames]

So we are to believe evolutionary paths are free? A stronger homosapiens could have done much more in their lifetime than an equal specimen with the same brain matter but less muscles, even with all the niceties of common era I very frequently find myself in scenarios where being stronger would have helped, I had to move to a building without an elevator and had to carry the freezer, the washing machine and other stuff to the fifth floor, having more muscles certainly would have helped, more recently I found a screw I couldn't unscrew just because I lacked enough force (not because it was a stripped screw), just imagine the amount of scenarios I would find myself if we didn't had all this technology and kitchen appliances that we have this days? You think our manual farming ancestors didn't need all the extra help they could get? To me it's almost preposterous to suggest we gave up our muscles just because we didn't use them because we lacked reasons to use them.

[odyssey7]

That cost and benefit trade-off emerged as an opportunity only through luck and it survived only through luck, even if the odds were in its favor.

[mattigames]

That's a very broad definition of the word luck, like saying I landed a job by having luck that some company was offering that role, therefore everything is luck, and communication wise would make the word almost useless.

[odyssey7]

You’re comparing the intelligent design of your job search to evolution.

[mattigames]

Luck is defined as something happening that was unlikely to happen, so having that in mind that evolution kept happening that is no luck, happens on every living organism (last specimens before extension being the exceptions), that the smarter apes got to reproduce is not luck, it is predictable, that they had to use less muscles if they are smarter is also predictable, that muscles are something primates can give up easier than e.g. liver function it is fairly predictable, that you would prefer to take better care of your smarter offspring is also fairly predictable (not saying it's morally justifiable), and so there are so many aligned factors and feedback loops at play that calling it luck would be a disservice, yes evolution has a slight "brute-force" approach to it that arguably involves "luck" but that it's just a small part of it

[fc417fc802]

Biased random walk and luck are related but not the same thing. It is not necessarily correct to term the outcome of a stochastic process as luck.

[bsder]

> An ancestor lost the trait for vitamin C synthesis by chance, and because these primates were living in trees eating lots of fruit with vitamin C, evolution simply didn't notice. There is no disadvantage to being able to synthesise vitamin C, and no advantage in dropping the trait.

The fact that guinea pigs, fruit bats, and passerines (almost half of all bird species!) also have a mutated GULO gene suggests that there is in fact some pressure to get rid of it as soon as it is bioavailable from diet.

[wbl]

Eh, enzyme mutations leading to inactivity aren't uncommon. It could just be drift when enough vitamin C is available.

[lurquer]

> There is no disadvantage to being able to synthesise vitamin C, and no advantage in dropping the trait.

So why did the trait of that mutant primate spread throughout the entire population? There should instead be a mixture of those who can and those who can’t synthesize vitamin C.

(Indeed, one should perhaps not so blithely assume that there was sufficient fruit for everyone and so C didn’t matter… for it is precisely the ability to survive in times of drought and scarcity that drive evolution, and there id no reason to suspect a population that could synthesize their own vitamin C was less fit than a population that couldn’t. The issue of vitamin C is far from simple…)

[arp242]

There is no reason for it to spread, but also no reason for it not to. Presumably there was another (completely unrelated) trait, and it happened to spread because of that.

> There should instead be a mixture of those who can and those who can’t synthesize vitamin C.

Probably was for a long time. All of this happened about 60 millions years ago. It's been a while.

[shellfishgene]

It's more likely that a mutation in the gene/pathway arose multiple times independently, instead of one spreading through the population.

[pfdietz]

> There is no disadvantage to being able to synthesise vitamin C,

Synthesizing vitamin C takes energy, energy that could be used for other biological processes. It's also possible excess vitamin C has some minor deleterious effect. For example, it's an antioxidant, and these render immune cells somewhat less effective against certain threats (which they use oxidizing chemicals to destroy). It's been found larger doses of the ACE vitamins causes increased growth of lung cancer, probably due to reduced immune attack.

Some have argued against this idea, though, although I'm not convinced by the argument (see if you can spot the problem.)

https://pmc.ncbi.nlm.nih.gov/articles/PMC3145266/

[mattigames]

Survivorship bias, you perceive it doesn't come with a cost, but perhaps some species that were exposed to it died from it because they failed to adapt because it does come with a cost they couldn't pay, so they went extinct, like it's wildly common.

[ashoeafoot]

Reptilian Predation squeezed mamalian reproduction into the fast and the furious . Meanwhile birds and turtles reproduce hapoy at methusalem ages. No creator, no design, just merciless pressure that stupidly rewards successful maiming to adapt.

[aqme28]

But a nonzero number of animals and people die of tetrodoxin poisoning, so there is some pressure. Therefore if it were cheap and easy enough, it’s likely we all would have evolved it. That cheapness threshold might just be incredibly high.

[amanaplanacanal]

If it is rare enough it probably doesn't exert much selection pressure.

Has anybody modeled what percent of a population has to die from something for the protective gene to become widespread?

[gptacek]

If you're willing to abstract a bit from populations of animals to populations of bacteria, there is the minimum selective concentration (MSC), which is the smallest amount of antibiotic you can add to the growth medium and detect antibiotic resistant bacteria competing out non-antibiotic-resistant bacteria:

https://revive.gardp.org/resource/minimal-selective-concentr...

[thaumasiotes]

> Has anybody modeled what percent of a population has to die from something for the protective gene to become widespread?

The question is incoherent. The gene spreads if the organisms carrying it average more children. It unspreads if they average less. All of them could be dying of the same thing, and it wouldn't matter.

The rate of spread is given by the https://en.wikipedia.org/wiki/Selection_coefficient , but cause of death isn't relevant.

[skipants]

Yes! Thank you! I’m barely knowledgable when it comes to biology and I still get annoyed when evolution is framed as cause-and-effect.

[bsder]

Well, there is some "cause-and-effect" in evolution.

Whenever a species winds up isolated in a cave, it loses eyesight really quickly in evolutionary terms because making and maintaining an eye is so metabolically expensive. So, while the mutations are random, any of them that can save the energy of developing vision get selected for very quickly.

So, even though the mutations are random, it really looks like "cause-and-effect" from the outside: get isolated in cave->lose vision; get exposed to outside light again->regain vision.

By the same token, changes that aren't very expensive metabolically will have very weak "cause-and-effect" because there is no particular pressure to carry the mutations forward or clean them up.

[pegasus]

No need to be annoyed. I think if you look deeper, you might find that, in fact, all occurrences of what we call cause and effect are of a similar nature.