Stoned Ape Theory: Psychedelics, Serotonin, and the Evolution of Humanity

Homo Erectus Skull
Photo by: Puwadol Jaturawutthichai/Shutterstock

Homo Erectus Skull
Photo by: Puwadol Jaturawutthichai/Shutterstock
In the early 1990s, ethnobotanist Terence McKenna released his ‘Stoned Ape Hypothesis’, also known as the ‘Stoned Ape Theory,’ in the book Food of the Gods. At the time, such a profound and likely unprovable hypothesis had been seen by the broad scientific community as the ramblings and poetic conjecture of a psychedelic fanatic.

This is not to say, however, that the book and the “stoned ape theory” failed to make their way into pockets of human society, or that McKenna’s findings were entirely shrugged off. As we will see, they were anything but.

What Is the Stoned Ape Theory?

Terence Mckenna developed and delivered the hypothesis known in popular culture as the “Stoned Ape Theory” as a means to explain the motor of humanity; that is, the innate human ability to convey broad and complex ideas with verbal or visual representations. Put more simply: the use of language and art in a socially developmental capacity.

McKenna hypothesized that the rapid growth of human brain size found after ancient humanoids (aka hominids) descended from the trees and adapted to life on the ground was a result of dramatic changes to the brain brought on by exposure to psilocybin mushrooms.

I know, I know… it seems like a crazy concept. As I’ve mentioned, the “Stoned Ape Theory” is likely unprovable. And yet, research in neuroscience and on psychedelic drugs in recent times has shown remarkable therapeutic potential for those with PTSD and other conditions.

Looking for Clues in Our Evolution

In the 25+ years since Food of the Gods was published by McKenna, a resurgence of interest is bolstering the somewhat cult, mystic, hippie-esque popularity maintained throughout his life.

The species homo erectus, thought to have lived 1.8 million to 200,000 years ago, moved from the trees to the savanna, the prairies, and the meadows of Africa as a result of changing climates, increased competition, and limited resources. New strategies for hunting and foraging were needed for survival in these different environments.

The spread of homo erectus to Asia and Europe, along with the fact they’re thought to have been fully bipedal (walking on two feet), communicates that many of these new strategies were adaptive enough to be quickly taken up (when compared to broad geologic time) between our ancestors. This aided our primitive ancestors at a period of technological innovation, allowing them to make more adept stone tools and learn to use fire.

During this period, the fossil record shows hominid cranial capacity (that is, brain size) increasing dramatically. Recall, according to the “Stoned Ape Theory,” rapid brain development was due (at least partly) to the ingestion of psilocybin mushrooms.

Increased brain size put pressure on early hominids, as the development of such large brains required a much larger investment of time before their offspring were developmentally ready for survival. As a result, having a child required a degree of security not required of previous generations.

The rapid development of brain capacity during the days of homo erectus could, therefore, signal the further development of human communities and tribes. As children now took years to develop enough to be on their own, the most readily available security to ensure child health and development surely became community.

Community could, after all, supply food. A community could provide security. A community could provide mates. And so, community grew into both culture and society.

Community, Kinship, and Cow Pies

The success of community, relationships, kinship, familial structure (pair-bonding), and numerous other strategies are just as much innovations of the human brain as they are functions of its size. Of course, there are other pair-bonded species, and yet, to this day, humans have been the only species to make such a drastic change to the environment in which we live.

The development of stone tools dates back to roughly two million years ago. We started using fire to cook foods between 1-2 million years ago, with the oldest evidence being a million-year-old site at the Wonderwerk Cave in South Africa. It is thought that ancient humans began domesticating animals, beginning with the dog, in the late Pleistocene, between roughly 126,000 and 11,100 years ago.

During this period, a reliance on community and meat sources meant cows, sheep, goats, and various other animals were domesticated. Living in rudimentary farms and on prairies, the animals would poop and, particularly in the cow dung, mushrooms would often sprout.

This is the heart of the “Stoned Ape Theory.”

The mushrooms would be harvested and eaten along with other meals. By this point, it would have been determined if the mushrooms were safe to consume, meaning it wouldn’t have been the first time they had been consumed. The “Stoned Ape Theory” suggests that the ingestion of these psilocybin mushrooms, over generations, contributed to the rewiring and growth of the human brain seen before genetically modern humans (aka homo sapiens) hit the scene.

How Serotonin Affects This Story

Psilocybin Mushrooms
Photo by: Kichigin/Shutterstock
By this point, I’m sure you are wondering what this is truly about. After all, this is a weed blog. The story I wish to tell is one of neurogenesis: the creation of new neurons at receptor sites throughout the brain and nervous systems.


The “Stoned Ape Theory” posits that psilocybin caused rapid brain changes at a time of rapid brain development over generations. Now referred to as serotonergic psychedelics, psilocybin, LSD, DMT, and others have been found to be structurally similar to serotonin and are able to, as a result, trick serotonin receptor sites in the brain or nervous system into thinking a burst of a neurotransmitter is on the way. The result is known as a hallucination.

It turns out, by tricking the serotonin receptors into expecting a wave of excited biochemical energy, the development and repair of healthy neuron connections or the surrounding myelin may be able to occur. For those with PTSD, it is speculated that this may make the emotional excitability from triggering events less overwhelming by simulating increased activity at serotonin receptors sites in the brain and nervous system.

Cannabis, as you may well know, has also been approved in a number of US states to treat PTSD. Using marijuana further activates the endocannabinoid system, which can have effects on the central and peripheral nervous systems, including serotonin receptor sites. It is thought that this may explain why cannabis may help depression, anxiety, and PTSD, among other mood disorders.

Are We on the Right Track?

The “Stoned Ape Theory” is based on the idea that eating psilocybin-containing mushrooms over centuries contributed to our growth in brain size. The growth in brain size reflects the compound effect of the neurological changes across millennia caused, in part, by the mushroom’s ability to simulate serotonin activity, which played a role in the health, wellbeing, and reproductive fitness of our ancestors.

Hominids came down from the trees. We began expanding, roaming the earth along a vastly diverse and changing environment. Our ancestors developed new social structures. We developed the ability to cook. We cultivated the knowledge of stone tools and passed on useful hints. After tens of thousands of years, the capacity for language (the ability to use sound to make pictures in another person’s mind) was finally accessible.

Psilocybin mushrooms, in low doses, brought about visual acuity and clarity, McKenna postulates, allowing hunters and gathers a competitive edge against predators and prey. In slightly higher doses, the undried mushrooms would have brought on an excitability in the central nervous system, leading to arousal and subsequently the spread of genetic material.

At even higher doses, the mushrooms could have led our primitive ancestors to the practice of glossolalia (speaking a language ritualistically), even if they had no idea what was being said or if it had meaning to begin with (like speaking in tongues).

While the “Stoned Ape Theory” may never be fully accepted into broader evolutionary understandings, the lack of supporting evidence has placed psilocybin and other psychedelics, including LSD, DMT, MDMA, and, in some capacity, cannabis, into a genuine place of intrigue.

Just as homo erectus may have eaten mushrooms, and those mushrooms attuned their primitive brain to better cope with their environment over generations, we as homo sapiens have only begun to grasp the concept that this could work for us too.

The scientific literature on psilocybin mushrooms has increasingly seemed to communicate that hallucinogens may indeed encourage neurogenesis between excited neurons and receptors. This places a great deal of potential therapies in the path of those willing to study them. And whether or not the “Stoned Ape Theory” may have been entirely accurate, it has provided us with a reference.

Could the idea lying at the foundation of the “Stoned Ape Theory” instead be a prelude to the next generation of novel treatments for PTSD, anxiety, or depression, among other social and mood ailments? Could it be that one of the reasons you can read this and I could write it is because hundreds of thousands of years ago our ancestors ate some fungus?

“The new vision of nature is not as matter or energy, but as information, and information is expressed in the DNA. It’s expressed epigenetically in culture. What’s happening is that information was running itself on a primate platform, but evolving according to its own agenda. In a sense we have a symbiotic relationship to a nonmaterial being which we call language. We think it’s ours, and we think we control it. This isn’t what’s happening. It’s running itself. It’s time-sharing a primate nervous system, and evolving toward its own conclusions.” -Terence McKenna, The Evolutionary Mind

Article by: Joey Wells