I'm Bill Hicks and I'm dead now.: Have you heard Mckenna's hypothesis about psilocybin mushrooms and human evolution?

billhicks:

Basically, a long time ago, we were tree-dwelling primates. As Africa began to dry up, we were forced down from the canopy and into the savanna. In the savanna were lots of ungulate (cow-like) droppings. Under these droppings are often larvae and grubs, so we quickly learnt to look under them…

Source: skaterboytae