I always wondered if certain fungi reached earth via an asteroid that hit earth and was from a fertile exoplanet, and somehow reached here. I like the idea of panspermia[0]. I always imagined psilocybin-containing mushrooms as somewhat alien and almost designed to alter consciousness, as if from another planet. McKenna's 'stoned ape' theory, if true, would explain much of the 'missing link' problem.
[0] https://en.wikipedia.org/wiki/Panspermia