So, about one mushroom species in five is poisonous. Why is the ratio so low, why are there lots of edible ones? Without hard-shelled seeds to spread, why be eaten? And the poisonous ones apparently don't use color as a warning signal, and don't smell all that bad, and some of the poisons have really mild effects, like "gives only some people diarrhea" or "makes a hangover worse". Meanwhile three of the deadliest species seemed to need their toxin (amanitin) so much that they picked it up through horizontal gene transfer. Why did just those ones need to be deadly? In addition to which we have these species that don't even make you sick, just make you trip out, a function which looks to have evolved three times over in different ways. What kind of half-assed evolutionary strategies are these? What do mushrooms want?

It's really fucking suspicious that mushrooms evolved mechanisms to produce serotonin.

But it helps when you remember that a mushroom is the fruit of a (usually) much larger organism. Then you can start applying normal fruit rules. Some want to be eaten, or picked up and moved around. Some want to keep insects from infesting the fruit. Others don't give a damn and release spores into the wind or water.

Also remember that nicotine is an insecticide. Insects that nibble on tobacco die, which prevents infestation at scale. (Un?)fortunately it's also neuroactive in apes, so we farm incredible quantities of tobacco to extract its poisons.

There is no logic in evolution at large scales. Things happen, sometimes there's fourth order effects like some oddball internal hormone causing wild hallucinations in apes. It's all random optimization for small scale problems that ripple out to unintended large scale consequences.

Two things:

0) Humans (and even our recent ancestors) eating you are a very recent thing to be concerned about, numbers-wise. By the time our numbers were enough to provide evolutionary pressure, we started farming what we wanted, which kinda breaks the process. Also. most poisons don't effect everything equally, so what might prevent a horse from eating you might taste delicious to us (like the nightshade family) or even be sought after for other reasons, like capsaicin.

1) You're succumbing to the usual evolution fallacy. Evolution doesn't want anything more than 1 and 1 want to be 2. It's just a process, and sometimes (hell maybe even often) it doesn't work in a linear fashion. Lots of "X steps back, Y steps forward", and oftentimes each of those steps can take anything from decades to centuries or more to make, and by the time it happens what was pressuring that change is gone.

So many people, even when they obviously know better, like to think of evolution as intelligent. It's obviously not. But every time someone says stuff like this, it reinforces the fallacy and then we get people saying things like "if evolution is real, why come $insane_argument_against_evolution?"

Many good answers, but I'll add another angle I don't see any replies covering, which is that being poisonous/toxic is expensive. We humans lead charmed lives by the standards of the biosphere, where we get obese, and even before we got obese, many of us had unbelievable access to nutrients and energy. The steady state of the ecosystem is a war where every calorie must be spent carefully. This is particularly clear in the bacterial world but it progresses up to macroscopic plant life as well. Producing poisons is energy you could be using to grow or reproduce. Some poisons require additional care because they're still poisonous to the producer, it's just that the producer spends additional resources on containing the poison so it doesn't affect them.

There is a constant, low-level evolutionary impetus to stop spending any calorie that doesn't need to be spent, which would generally include the production of poisons of any kind. This low-level impetus is clearly something that can be overcome in many situations, but it is nevertheless always there, always the "temptation" to stop spending so much on poisons and redirect it to growth or reproduction. Over time it's a winning play quite often.

Its the same evolutionary patterns that plants went through.

Most mushrooms are edible because their spores can pass through the digestive system of most animals, thus allowing them to spread.

Other mushrooms developed toxins to protect their fruiting bodies - often the biggest threat isn't larger animals, but insects. Toxins that are neurotoxic to insect nervous systems, happen to cause mostly "harmless" psychedelic trips to our brains. Other toxin mechanisms happen to be deadly to both insects and humans.

As proof of this evolutionary arms race, there are fruit flies that have developed resistance to amatoxins.

"one mushroom species in five is poisonous"? 20% ??? That seems like a crazy high estimate to me, at least if you mean deadly poisonous to humans. In the USA there are only a few species of amanita, galerina, a few of the hundreds of species of cortinarius, maybe some gyromitra and a handful of others I can think of that will kill you. Among the many thousands of mushroom species in the USA, there are only a few dozen known deadly poisonous ones. It's a really tiny percentage. Of course that doesn't mean that the others are edible, just not gonna kill you...

Fruit bodies are reproductive organs, spores can survive digestion, and there are plenty of species that use animal waste as a substrate.

The same logic of hard seeds applies to spores.

A mushroom doesn't produce seeds, it produces spores.

If you pick a mushroom the spores use you, your clothes, your pets, your horses as vectors for spreading.

> And the poisonous ones apparently don't use color as a warning signal, and don't smell all that bad, and some of the poisons have really mild effects, like "gives only some people diarrhea" or "makes a hangover worse".

Some of the poisonous ones even taste really good, and don't start making you sick for a day or two (and then you die horribly). You hear about it from time to time, where people have the best dinner of their life and then are dead.

Natural selection cuts both ways.

Sure, many things evolved to be less edible. But humans themselves are hunter-gatherer omnivores - who evolved to be very good at eating a lot of very different things. There are adaptations in play on both ends.

There are, in fact, many countermeasures that would deter other animals, but fail to deter humans. In part due to some liver adaptations, in part due to sheer body mass, and in part due to human-specific tricks like using heat to cook food.

If your countermeasures just so happen to get denaturated by being heated to 75C, good luck getting humans with them. It's why a lot of grains or legumes are edible once cooked but inedible raw. The same is true for many "mildly poisonous" mushrooms - they lose their toxicity if cooked properly.

Those countermeasures don't have to be lethal to deter consumption! If something causes pain, diarrhea or indigestion, or some weirder effects, or just can't be spotted or reached easily, that can work well enough. So the evolutionary pressure to always go for highly lethal defenses isn't there. It's just one pathway to take, out of many, and evolution will roll with whatever happens to work best at the moment.

Human takeover of the biosphere is a recent event too, and humans are still an out-of-distribution threat to a lot of things. So you get all of those weird situations - where sometimes, humans just blast through natural defenses without even realizing they're there, and sometimes, the defenses work but don't work very well because they evolved to counter something that's not a human, and sometimes, the defenses don't exist at all because the plant's environment never pressured it to deter consumption by large mammals at all.

And with the level of control humans attained over nature now? The ongoing selection pressure is often shaped less like "how to deter humans" and more like "how to attract humans", because humans will go out of their way to preserve and spread things they happen to like.

Amanita Muscaria seems like it does use colour as a warning signal - it's bright red.

I dig your style, you sound like my inner monologue :D

That’s also my thought. The seem to be inside some type of evolutionary gray area or dead-end, where mutations in the edibility axis do not seem to matter much for the survival of the specifies. So we end up getting species of all extremes: extremely poisonous, highly valuable for coursing, trippy, non-trippy, mildly poisonous, etc.

I appreciate your thirst for knowledge

Some are saying: "Don't come anywhere near me". Others are are saying: "Take a little, I'll show you a good time. Take too much... I will make you end your own life."

They want the same thing as every other organism wants - maximal exploitation of a niche by a lineage. Each adaptation that survives overwhelmingly tends toward advantage in the exploitation of a niche - fending off predation, establishing control over resources, symbiotic support, parasitic drain, and a myriad other capabilities that are highly environment dependent.

Just look at antelope in north america - they evolved incredible speed and agility in order to outrun and evade megafauna predators, but there's nothing left nearly fast enough to be a threat to them. Environments can change, and leave an organism with features that are no longer necessary or even beneficial in terms of overall quality of life and energy efficiency. The slightest noise can disturb a herd of antelope into bolting as if there were prairie lions or sabertooth tigers on the prowl. They don't need to be hypervigilant in the same way, and it burns a lot of calories to move the way they do, so whitetail deer and other slower species that aren't quite as reactive or fast are better at exploiting the ecosystem as it is.

With mushrooms that have mysterious chemistry, there will be a lot of those sorts of vestigial features. Extinct species of insects and animals and plants will have been the target of specific features, or they might end up in novel environments where other features are particularly suitable, but some become completely counterproductive in practice.

As far as psilocybe mushrooms go, in lower quantities, they actually provide a cognitive advantage sufficient to make a symbiotic relationship plausible between mammals and the mushrooms, albeit indirect. Animals under low levels of psilocybin influence have better spatial perception, can better spot movement in low light conditions, and there's a slight reduction in the neural influence of trauma inspired networks. Large quantities can be beneficial in a number of abstract ways. Any animal that sought those mushrooms out could thereby gain adaptive advantage over competitors that didn't partake.

Having an extremely toxic substance might be useful for killing large organisms and their decomposition either feeding the fungi directly, or feeding the organisms beneficial to the fungi. This can be plants, other fungi, or the feces of scavengers. Horizontal transfer might occur if there's an initial beneficial relationship, animals like the smell and taste of a thing, and then the fungi picks up the killing poison, and the consequences are sufficiently beneficial to outbreed the safe ones.

If too many become deadly, animals get killed off, and the non-deadly ones tend to gain the upper ground, since they aren't spending any resources on producing any poisons. Where there's a balance of intermittent similar but poisonous mushrooms, they take down enough animals to optimize their niche.

There are dozens of such indirect webs of influences and consequences that spread from seemingly simple adaptations, and it's amazing that things seem so balanced and stable as they do. It's a constant arms race of attacks and temptations and strategies.