Food of the Gods: The Search for the Original Tree of Knowledge : A Radical History of Plants, Drugs, and Human Evolution

Terence McKenna hypothesizes that as the North African jungles receded, giving way to savannas and grasslands near the end of the most recent ice age, a branch of our arboreal primate ancestors left the forest canopy and began living in the open areas beyond.

There they experimented with new varieties of foods as they adapted, physically and mentally, to the environment.

Among the new foods found in this environment were psilocybin-containing mushrooms growing near dung of ungulate herds occupying the savannas and grasslands.