This is known as the "Stoned Ape Theory" and was (to my knowledge) first popularized by Terrence McKenna. http://www.lycaeum.org/~sputnik/McKenna/Evolution/ ht

This is known as the "Stoned Ape Theory" and was (to my knowledge) first popularized by Terrence McKenna. http://www.lycaeum.org/~sputnik/McKenna/Evolution/ http://www.lycaeum.org/~sputnik/McKenna/Evolution/ From the link above: McKenna theorizes that as the North African jungles receded toward the end of the most recent ice age, giving way to grasslands, a branch of our tree-dwelling primate ancestors left the branches and took up a life out in the open -- following around herds of ungulates, nibbling what they could along the way. Among the new items in their diet were psilocybin-containing mushrooms growing in the dung of these ungulate herds. The changes caused by the introduction of this drug to the primate diet were many -- McKenna theorizes, for instance, that synesthesia (the blurring of boundaries between the senses) caused by psilocybin led to the development of spoken language: the ability to form pictures in another person's mind through the use of vocal sounds.