New Science Revives Terence McKenna’s Stoned Ape Theory

When the Stoned Ape Theory was first proposed by philosopher and ethnobotanist Terence McKenna in the early 1990s, it was welcomed as an “exciting challenge to conventional thinking” by one reviewer, though it was widely dismissed and vilified by the scientific community. According to the hypothesis, the mysterious tripling of the human brain’s size over a relatively short span of evolution may be explained by the consumption of psilocybin mushrooms, more than 230 species of which grow worldwide. 

When pre-humans ate mushrooms, so the theory goes, they entered altered states of perception that could blur sensory boundaries and heighten pattern recognition. McKenna, who described language as a fundamentally synesthetic activity, speculated that such experiences may have encouraged new forms of communication, gradually contributing to the emergence of language, self-awareness, and human consciousness.

McKenna, who died in 2000 at age 53 from brain cancer, also speculated in his 1992 best-seller Food of the Gods: The Search for the Original Tree of Knowledge that the effects of tripping on mushrooms — such as enhanced visual acuity at low doses, reduced male dominance, and increased group cohesion — may have conferred evolutionary advantages. While McKenna speculated that such effects could have shaped early human social organization on the savannas of northern Africa — where it is claimed our Hominid ancestors must have eaten psilocybin mushrooms — these claims rest on the technically unproven premise that Paleolithic humans consumed psychedelic mushrooms.

“For sure the mushroom would have been sampled,” McKenna told the New York Times in 1993. “Then our proto-hominid forebears, like legions of hippies millennia hence, discovered that the usual activities comprising the whirl of their days — hunting and gathering, primarily — were out of the question.” This is because, at higher doses, “You are just simply nailed to the ground and you experience the bewildering phenomenon that we call the hallucinogenic experience … It laid the basis, I think, for religion and for language."

All of this had always been “plausible,” his younger brother and fellow ethnobotanist Dennis McKenna said in a recent keynote. But new circumstantial evidence, thanks to advancements in science, he claims, makes the far-out theory’s answer to the vexing evolutionary riddle “more than likely” to be true. “New data unknown to science in 1993 when the book was published, shifts the hypothesis from plausible to more than likely,” the younger McKenna told the Telluride Mushroom Festival back in August. 

When Food of the Gods was published, the adult brain was still widely believed to be relatively fixed — its basic architecture laid down early in life, its evolutionary trajectory governed largely by slow genetic mutation. But research over the past two decades has shown that the brain is far more malleable than previously thought, capable of reorganizing itself structurally and functionally in response to experiences, environments, and — crucially — psychedelics.

Despite some disagreement over the mechanism of action, psilocybin is understood to promote neuroplasticity through loosening entrenched neural pathways. It appears that it is one of a number of psychedelics which place the brain into a state of heightened flexibility — what some researchers describe as a temporary return to a more developmentally open mode of cognition that McKenna says could be central to explaining our ancestors’ relatively rapid cognitive change.

Alongside this, another field scarcely on the elder McKenna’s radar in the early 1990s has matured: epigenetics. We now know that environmental inputs — including diet, stress, and chemical exposure — can alter how genes are expressed and that some of these changes can be passed down across generations without any alteration to DNA itself. In other words, biology has a memory. If a compound like psilocybin reliably induces adaptive neural changes within individuals, epigenetic mechanisms offer a conceivable route by which those changes could affect developmental outcomes across generations. New research on horizontal gene transfer and “how mushrooms got their magic” has also added weight to the idea that psilocybin evolved in mushrooms to send insects crazy, Dennis McKenna says.

Taken together, these discoveries do not prove the Stoned Ape Theory, which mycologist Paul Stamets has also supported in recent years. But they do provide a potential mechanism and place it within a biologically coherent timeline, according to McKenna. What once seemed like mystical hand-waving — mushrooms “rewiring” the human mind — now overlaps with how neuroscientists describe psychedelic action. “When you look at us humans and how anomalous our brains are, it just makes a certain amount of sense,” Dennis McKenna tells DoubleBlind. “What else could have had this kind of influence on this rapid neural evolution?”

The remaining question is whether early humans would have encountered psilocybin mushrooms with sufficient regularity and over a long enough period to produce a significant effect. And here, too, the archaeological and ecological record has begun to strengthen the case, according to McKenna, though the possibility of pre-human mushroom consumption remains a hotly contested field of debate. 

In his talk at Telluride, McKenna cited new paleoclimatological data that suggests that large swathes of North and East Africa were significantly wetter two million years ago than they are today, supporting grasslands capable of sustaining large herds of cattle. Fossil and archaeological evidence places early species — ancestors of modern zebu, or domesticated cattle — alongside Acheulean tool-making hominins across this same terrain. Where there were cattle, there was dung; and where there was dung in warm, rainy conditions, there would likely have been mushrooms. 

In 2024, genomic and molecular technology was used to date psilocybin mushrooms back 65 million years, around the time an asteroid made dinosaurs extinct, long before early humans appeared around two million years ago, before evolving into modern homo sapiens 300,000 years ago. There is also emerging potential evidence of long-term psilocybin mushroom use in Africa, the cradle of humankind, while evidence has surfaced of limestone fossils containing non-psychedelic mushrooms dating back 115 million years. 

However, for many, the Stoned Ape Theory will remain nothing more than an elegant story in search of evidence — an idea that flatters contemporary psychedelic culture more than it explains the deep past. After all, there remains no direct archaeological proof that early humans even consumed psilocybin mushrooms, let alone with sufficient regularity to shape cognition across millennia. Unlike alcohol, opium, or cannabis, mushrooms leave no residues in pottery and no clear traces in bones, partly given their rate of degradation and the nature of the compound. 

“I don't think you're going to find a hominid with a psilocybin mushroom clenched in its jaw,” says McKenna. “These mushroom fossils are extremely rare due to the fact that soft tissues do not easily fossilize. But knowing what we know about the environment, it's quite reasonable to expect that these mushrooms would probably have been there.” People who insist there is no evidence, McKenna maintains, are being “deliberately obtuse” and “there’s enough circumstantial evidence that a jury of peers would convict.”

He is also at pains to explain how he differs from his brother on some important points. “Psilocybin mushrooms are not extraterrestrial, hence not alien — though the experiences they induce might seem very alien,” he said in the presentation. “We completely understand where psilocybin-containing species fit into the phylogeny of earthly life; their chemistry, genetics, and lineage are well understood and firmly established.

“Psilocybin containing species do not 'invade us' and turn us into 'zombies'; instead, they offer symbiotic partnership with our species, which we readily accept. Both the fungal species and our species benefit from this relationship. With our help, the fungi fulfill their 'agenda' to spread and to grow. And in turn, the fungi offer us a beautiful gift, psilocybin, which makes us better, more conscious humans and, again in Terence's words, ‘opens the vision screens to many worlds’ — but not necessarily extraterrestrial.”

Aside from speculation about alien influence, there are other explanations for the expansion of the human brain, which is known as encephalization. Meat consumption dramatically increased caloric intake, while cooking with fire reduced digestive costs — two factors widely regarded as central to encephalization. From this perspective, psychedelics risk becoming a solution in search of a problem, inserted where more parsimonious explanations already exist.

Archaeologist Elisa Guerra-Doce, an expert in prehistoric drug use, has been blunt in her assessment, calling the Stoned Ape Theory “too simplistic” and stressing that no single factor can account for the emergence of modern human cognition. Language, other leading scholars such as Stephen Pinker and Terrance Deacon have noted, likely evolved gradually through social pressures and vocal learning, not through chemically induced revelation. To attribute symbolic thought or religion to mushrooms alone could be to underestimate the slow grind of cultural evolution — and to mistake correlation for cause.

“From my point of view, McKenna’s hypothesis is too simplistic and lacks direct evidence to support it — that is, any evidence of consumption of hallucinogenic mushrooms by the earliest Homo sapiens,” Guerra-Doce told Inverse previously. “He points to the Algerian paintings of Tassili-n-Ajjer, which include some depictions of mushrooms, but we must bear in mind that these paintings date back to the [more recent] Neolithic [era].” 

David Luke, a professor of exceptional experience at the University of Greenwich, agrees that the theory is “too simplistic” but acknowledges that features of the hypothesis have been further supported by science since it was first proposed. “A recent preprint study of human gene expression in response to psychedelics indicates that ‘psychedelic-responsive genes are overrepresented among human accelerated genes’, suggesting a ‘potential link between psychedelic drug action, cortical circuits underlying higher cognition, and genes shaped by recent evolution’,” he says. The evolution of language remains an open question, Luke adds, with some theories positing synaesthetic origins, in which sensory overlaps could have led to corresponding visual or conceptual information being associated with auditory sensation, such that sounds convey new meaning. “Our research has shown that psychedelics quite reliably induce transient visual-auditory synaesthesia, which can occasionally be permanent, and this might have helped in the formation of concrete nouns,” he says.

“The oldest languages also have the greatest number of phonemes, which fits with McKenna’s idea that psilocybin-induced glossolalia could have also contributed to language evolution,” Luke continues. “Ultimately, though, there are far too many unanswered questions, but there are features of the Stoned Ape Theory that have been further supported by science since the 1990s.”

McKenna says that evolving hominids were obviously subject to multiple pressures that influenced the rapid evolution of neural structures and cognitive functions, and that he is not claiming mushrooms alone were responsible for this. “What I am asserting is that it was a significant influence,” he says. “So critics who claim that I'm pointing to this as the only catalytic mechanism are themselves being simplistic. Of course, meat eating, controlled use of fire, all of these things were important factors contributing to encephalization.”

Others point to natural selection’s conservatism. Psychedelics are powerful, unpredictable compounds. Even today, they can impair judgement, induce fear, or destabilise vulnerable individuals. It is far from obvious that a substance capable of disorienting perception would reliably enhance survival in dangerous environments filled with predators, rival groups, and scarce resources. Evolution, critics argue, favors robustness over revelation. 

McKenna, however, says that on low doses of mushrooms, “visual acuity, hand-eye coordination, and physical activity are actually enhanced” — thus conferring evolutionary and survivalist advantage. He acknowledges that under some conditions, high doses of psilocybin could destabilize and expose hominids to dangers. However, he adds, “We should not assume that being 'stoned' necessarily means being impaired, perceptually, cognitively,  or behaviorally. For this reason, I have come to regret, and reject, the pejorative subtext of the term 'stoned ape'. It's unfortunate that this has become a meme, and it's very hard to push against. A much better and more accurate term I think is 'awakened ape.’”

With such a flair for alliterative phrases, McKenna is perhaps most convincing when he distills the theory in more poetic terms. “For archaic humans,” he said in his Telluride conference, without evidence, “psychedelics functioned as neurocognitive programming tools, the software that activated our neural hardware and enabled it to create the hallucination in which we are all immersed; a consensual reality in which symbols, ideas, abstractions, expressed through language, as ‘real’ as the external world, in fact imbue it with meaning and significance.”

And so, if the “Awakened” Ape Theory remains unproven — although some psychonauts have claimed to receive confirmation during high-dose mushroom trips — it now occupies a different category than it did in 1993. Not as psychedelic fantasy, but an unresolved question sitting uncomfortably at the edges of mainstream science. Evolutionary history is rarely monocausal, and the growing picture of how brains actually change — chemically, developmentally, epigenetically — suggests that catalysts can matter as much as drivers. “Psilocybin,” says McKenna, “was a catalyst for the emergence of consciousness.” But any insights derived from psychedelic states, he adds, need to be thoroughly evaluated in the cold, hard light of sobriety.

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