Stoned Ape Theory: Magic Mushrooms and Human Evolution

"For a while I had the idea to write a book that would have been called 'Hallucinogens and Evolution,' but never got around to it," Dennis says via email. "While Terence's approach is different from what I would have written, there are complementarities. Terence's ideas were certainly fertilized by those conversations."

Neither Terence nor Dennis referred to this hypothesis by the name "stoned ape," which Dennis believes misrepresents the idea and dumbs down the concept. In essence, the hypothesis suggests we owe the emergence of language, self-reflection and other unique functions of the human brain to ancient ancestors who ate psilocybin mushrooms.

The exact timeline for the emergence of consciousness varies, but Dennis believes the process may have begun as far back as 2 million years ago.

"We know the brain tripled in size about 2 million years ago, and probably the ecosystems which put hominids, cattle and mushrooms together were around that old," Dennis says, referring to the dung from which psilocybin mushrooms emerge.

According to Dr. Thomas Falk, a professor of Philosophy and Education at the University of Dayton, the hypothesis also provides an explanation for the so-called "creative explosion" that occurred 40,000 years ago in homo sapiens, prior to their migration from Africa to Europe.

It is here that we see an apparent leap in cognitive ability for early humans.

"For the first time ever, these humans lived in worlds of their own creation, materially and symbolically," Falk says via email. "Like you and I, these humans were capable of creating worlds in their heads and then re-creating those worlds in the external physical and social environments. Although other homo species may have efficiently exploited nature, they remained its passive subjects. The key to this major distinction between homo sapiens sapiens and all other hominids appears to be language."

Falk, whose areas of study include phenomenology and anthropology, says that while we have no shortage of good evidence and theory regarding the course of human evolution, the leap to self-consciousness remains a mystery.

"The stoned ape hypothesis offers a possible keystone that appears to fit together with much of the existing scientific evidence and theory," he says, though he stresses that this is only one possible answer.

In "Food of the Gods," Terence McKenna made his argument based on noted qualities of the psychedelic experience (such as augmented empathy and sensory perception), shamanistic traditions in ancient cultures, and the known and hypothetical range of psychedelic plants and fungi in ancient times.

The journey takes us back to the Pleistocene epoch, stretching between 2.6 million and 11,700 years ago, which saw major changes in climate. The changes would have put our ancestors on the move through new, challenging and bountiful environments.

"This would likely have entailed major experimentation," Falk explains, "much of which would have been harmful, and some of which would have been mutagenic, leading to epigenetic changes. This does not mean that new foods would have altered the hominid genome, but rather that they would have affected the expression of genes that were already present, thus changing our ancestors physiologically, neurochemically and culturally."

Thus, Terence presented an interpretation in which our ancestors would have followed herds of cows and other herbivores, depending on them for food and clothing, but also harvesting fungus from their dung (where psilocybin mushrooms commonly grow).

The regular consumption of these psychedelic mushrooms could have proven advantageous as early humans spread out into new territory.

"Psychedelic mushrooms appear advantageous for adaptation to new circumstances because they de-pattern the mind/brain, alter modes of perception and induce synaesthesia," Falk says. "Terence McKenna and mycologist Paul Stamets argue that these mushrooms may have allowed our ancestors to forge connections between sounds, symbols and meanings, which is the essence of 'the creative explosion': human language, symbol manipulation and communication."

Terence also argued that psilocybin would have increased visual acuity at low doses, increased sex drive and enhanced cooperation — all factors that could have proven adaptive to our ancestors.

Stamets, a vocal supporter of the theory, has also pointed out the leadership qualities that would have resulted from the mix of bravery and empathy brought on by these substances.

Written during what is sometimes described as the dark age of psychedelic research, "Food of the Gods" argued that the criminalization of psychedelic substances and lack of research into their powers paradoxically cut human beings off from an important aspect of their ascendency.

Terence was no stranger to wild personal anecdotes of psychedelic experience, and even wilder contemplations on the nature of reality. Yet while the book is full of the author's signature wit and vision, it is also, in the words of science writer John Horgan, a serious work that presents a rigorous argument.

"Rereading it after nearly 30 years, I remain impressed by how thoughtful it is," Dennis says, who wrote a new foreword for the book. "It's not heavily referenced but the key references are there. I think it was a credible piece of scholarship. The very idea invites derision and ridicule, and there was plenty of that by reviewers and others. But I think much of it betrays that many who criticized it never actually read it, or read it only superficially. Thirty years later, the idea has more support than ever based on what has been learned since."

In his 2018 book "How to Change Your Mind," Michael Pollan called Terence McKenna's 1992 book "the epitome of all mycocentric speculation," stressing that its very premise is not susceptible to proof or disproof.

The stoned ape theory is simply not the sort of hypothesis that can be taken up by a scientific study. It involves the emergence and nature of consciousness, as well as the true potential of psychedelic compounds — all subjects rife with their own mysteries.

However, it's not the only possible explanation on the table.

"Human intelligence/consciousness appears to have been an emergent phenomenon," Falk says. "That is, there were many evolutionary factors, likely unrelated, that nevertheless entered into random combination and in so doing created a whole that was greater than the sum of its parts."

Changes in environment forced societal changes to ensure survival, and these societal changes demanded upgrades in mental capacity. Fire mastery and the emergence of cooking technology improved nutrition and made room for greater cultural and societal advancement.

Dennis, however, stresses that the stoned ape hypothesis is not meant to stand as the lone factor in human evolution.

"Obviously there were multiple factors involved," he says. "It's simplistic just to postulate that people ate mushrooms, so they were better equipped. There were many factors that influenced evolution."

The stoned ape theory gained little traction in academic circles, but it became a staple of psychedelic culture. Among its most notable advocates is mycologist Paul Stamets, who along with Dennis, points to scientific advancements in fields such as epigenetic inheritance and neuroplasticity that may further explain the mechanisms involved in psychedelics-assisted cognitive advancement.

The stoned ape theory is not likely to leap to the level of scientific theory in the foreseeable future, but the sort of modern psychedelic reconnection that Terence McKenna and others advocated might well come to pass — especially as more studies examine potential therapeutic uses. Dennis says:

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.