So fiction is an important part of this narrative, and while I think epigenetic heritable gene modification is a powerful mechanism we are just starting to understand, (Lamarck rolls his eyes i his grave) it’s probably naive to discount the forces of natural selection and vanilla evolutionary forces on our current iteration. It’s possible that a series of brushes with hallucinogenic fungi crossed with epigenetic heritability led to the shared fiction phenomenon, not seen anywhere else in the animal kingdom, and the rest is history.