Psychedelics and Other Clues
Psychedelics like ayahuasca seem to be a powerful means of re-accessing these lost perceptual abilities (any wonder our left brained society has made these things illegal?). Its been said that shamans for example who work with it enough can eventually bring in an altered state of consciousness willingly, without even drinking the brew. The beta-carbolines in ayahuasca alone are powerful MAO inhibitors with psychoactive properties by themselves (along with many other beneficial effects). Were chronically deficient in not only a complex cocktail of plant MAO inhibitors but also the ones that our pineal glands would have produced in much higher amounts as well, given that flavonoids stimulate this gland. Pinoline is just one example.