Looking beyond simply “medicinal” properties, there are examples of plants that have evolved their chemical composition in response to animals. Hot peppers, for example. The capsaicin only affects mammals, not birds. Birds can eat the fruit and more widely disperse their seeds than mammals would. It’s advantageous to the plants that birds eat the fruit instead of mammals.

So it’s not unreasonable that other plants may have also developed specific chemicals in response to some pressure from animals.

Though in a twist it turns out that one specific mammal has spread hot peppers far more than any birds ever before.

> So it’s not unreasonable that other plants may have also developed specific chemicals in response to some pressure from animals.

Wouldn't it make most sense for plants to develop chemicals that kill us, rather than cure us from a disease?

I don’t mean that medicinal plants developed those properties to benefit us, but rather it may have evolved as a response to some animal for some purpose, and it happens to be beneficial to us in some way.

Take caffeine for example, likely it evolved as a defense against pests.

Caffeine at low levels in flowers can stimulate insect activity and even potentially memory, increasing pollination activity.

At higher concentrations yeah it’s an insecticide.

Cool, I didn’t know that. But all the same, the same principle applies.

Possibly too costly. From what I've read, every chemical defense has a metabolic cost. This is why antibiotic resistant bacteria will lose their resistance over many generations if not constantly challenged by the antibiotic.

On the other hand, some plants do kill us.

Peppers evolved to produce capsaicin because mammals chew on vegetation in a molar fashion which destroys seeds (birds do not). In fact, the majority of capsaicin in a pepper exists in the pith, where the seeds attach.

It has nothing to do with us. It’s evolutionary warfare against microbes.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC88925/

Sounds plausible, but I suppose that not every disease cured with plants has a microbial origin.

Fig leaves are proving to demonstrate strong anti-cancer properties for roughly half of cancer patients, though more testing is required because those anti-cancer properties could become toxic in excess quantities. That is evidence of plants curing diseases without a microbial origin.

But how can you explain that from an evolutionary perspective then?

Plants are continuously evolving a variety of chemicals to ward off pests. Most stimulants like caffeine and nicotine, for example, are actually potent insecticides.

Among the most interesting of plant responses is plant latex. Latex is found in lettuce, thistles, rubber, fig, and variety of other plants. Latex is thick with a variety of anti-microbial chemicals to ward off fungus, viruses, bacteria, insects, and more. These chemicals provide a wide distribution of medicinal value. Opium is a plant latex.

Have you considered why Australia has the most poisonous animals on the planet? Many venoms found there can easily kill humans many times over. It is supremely excessive, for humans, but not for the other animals living there. It is a constant state of evolving bio-chemical warfare because the intended victims evolve resistances to the strong venoms until they no longer become strong, so the predators and insects continually develop more targeted venoms to keep up.

Cannabis suggests we evolved with it, see Endocannabinoid system or whatever it is called. However, I do believe it is random. Magic mushrooms have been around for longer than we have, so it's probably just chance that they make us trip (which enabled lots of mental healing power).

Isn't it much more likely that cannabinoids are poisonous to insect larvae?

Interesting because nicotine in tobacco evolved to ward off insects as well and that's why there's so many pesticides made from related chemicals: neonicotinoids.

I'm sorry but that sounds like "wet pavements cause rain" to me. The naming need not be causative in that direction. I'm not disagreeing with that we did indeed evolve with them.. Grug smoke plant. Plant make strong, heal. Grug stomp stupid weeds and make more space for plant. etc

Mushrooms have been around longer than we have, but that doesn't mean they've been making psilocybin that long.

Just because we have receptors that have affinity for molecules that we call cannabinoids doesn't mean much in terms of evolution related to plants. There is a wide range of molecules that have a shape that bind to the wide range of receptors that are a part of what we call the endocannabinoid system.