I'm reading Michael Pollan's book 'How to Change Your Mind', which is largely about psychedelic mushrooms. In discussing the biology of the mushrooms, he writes:
'Even if psilocybin in mushrooms began as 'an accident of a metabolic pathway', the fact that it wasn't discarded during the course of the species' evolution suggests it must have offered some benefit.'
I'm wondering if this is actually true. In general, I'm wondering if it is true that traits that do not confer advantage will eventually be weeded out.
Being ignorant of the finer points of evolution/natural selection, I can make arguments both ways. On the one hand, it seems that the intense competition would make investing any resources at all in a trait that was not beneficial a totally losing proposition. Therefore no traits that weren't positively adaptive would survive. On the other hand, there seem to be all kinds of traits that are 'neutral' in fitness terms but which survive anyway. E.g. coccyx, male nipples, appendix, whale legs, etc.
I am not talking about information encoded in the genome, which can be present but not expressed. I am talking about phenotypes, i.e. traits that get expressed in interactions with the environment, such as the psilocybin chemicals in these mushrooms. (Though I suppose unexpressed genetic info could never be selected for or against by natural selection by definition.)
So to put a very fine point on my question: Is it possible/likely that psilocybin mushrooms produce a chemical that happens to engender hallucinations, not because doing so is adaptive, but just incidentally? So that this property would be something like the redness of blood, i.e. not adaptive in itself but just a matter of happenstance?