First proposed by 20th century ethnobotanist and psychedelic advocate Terence Kemp McKenna (who died in 2000) in his 1992 book Food of the Gods, the stoned ape theory (or hypothesis) is based on the concept that the consumption of psychedelic fungi—in other words, magic mushrooms—may have played a crucial role in the development of human mind and culture. The theory, which has since been advocated for by psilocybin mycologist Paul Stamets is now going through a revival thanks to a trending video on TikTok.

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♬ An Incredible Pearl (feat. Terence McKenna) - We Plants Are Happy Plants

In his book, McKenna proposed that the transformation from humans’ early ancestors Homo erectus to the species Homo sapiens mainly had to do with the addition of the mushroom Psilocybe cubensis in their diet. An event that (according to his theory) took place in about 100,000 BCE, which is when he believed that the species first diverged from the genus Homo.

McKenna based his theory on the main effects, or alleged effects, produced by the mushroom while citing studies by the likes of Roland L. Fischer from the late 1960s to early 1970s. The ethnobotanist believed that, due to the desertification of the African continent at that time, human forerunners were forced from the increasingly shrinking tropical canopy into search of new food sources. They would have been following large herds of wild cattle whose dung—yep, poo poo—harboured the insects that were undoubtedly part of their new diet, and would have spotted and started eating Psilocybe cubensis, a dung-loving mushroom often found growing out of cowpats.

Okay, so let’s assume our ancestors found some magic mushrooms hidden in cow shit, then what? According to McKenna, low doses of psilocybin—a psychedelic prodrug compound produced by more than 200 species of fungi, including Psilocybe cubensis—improve visual acuity and particularly edge detection. This means that the presence of psilocybin in the diet of early pack hunting primates could have caused the individuals who were consuming those mushrooms to be better hunters than those who were not, resulting in an increased food supply and in turn, a higher rate of reproductive success.

Then at slightly higher doses, McKenna said that the mushroom acts to sexually arouse, leading to a higher level of attention, more energy in the organism, and potential erection in the males thus rendering it even more “evolutionarily beneficial,” as it would result in more offspring. At even higher doses, McKenna proposed that the mushroom would have acted to “dissolve boundaries,” promoting community bonding and group sexual activities. In all fairness, that doesn’t sound too different from the last mushroom party I attended.

As a result, all thanks to this magic fungi, there would have been a mixing of genes, greater genetic diversity, and a communal sense of responsibility for the group offspring. McKenna went as far as to argue that psilocybin could have also triggered activity in the “language-forming region of the brain,” manifesting as music and visions, thus leading to the emergence of language in early hominids. He also pointed out that psilocybin would dissolve the ego and “religious concerns would be at the forefront of the tribe’s consciousness, simply because of the power and strangeness of the experience itself.” Sounds pretty familiar too.

Long story short, the psychedelic advocate was sure our newly-founded access to and ingestion of mushrooms was an evolutionary advantage to humans’ omnivorous hunter-gatherer ancestors while also providing humanity’s first religious impulse. For him, psilocybin mushrooms were the “evolutionary catalyst” from which language, projective imagination, the arts, religion, philosophy, science, and all of human culture sprang. Big theory there, McKenna. But that was all in 1992.

After making such claims, McKenna did not receive much attention from the scientific community, apart from some criticising his theory’s lack of citation to any of the paleoanthropological evidence that informs our understanding of human origins so far. Many deduced that he had misinterpreted previous findings.

It wasn’t until 2017 that McKenna’s theory was supported by someone else from the scientific community; Paul Stamets.

At Psychedelic Science 2017, Stamets presented his theory through a talk titled ‘Psilocybin Mushrooms and the Mycology of Consciousness’. In it, he sought to rehabilitate McKenna’s hypothesis as a totally plausible answer to a longstanding evolutionary riddle. “What is really important for you to understand is that there was a sudden doubling of the human brain 200,000 years ago. From an evolutionary point of view, that’s an extraordinary expansion. And there is no explanation for this sudden increase in the human brain,” he said.

Stamets portrayed a group of early humans making their way through the savannah and coming across “the largest psilocybin mushroom in the world growing bodaciously out of dung of the animals.” It didn’t need to have been unusually large to have its effect, of course. In his talk, Stamets invited the crowd to suspend their disbelief and admit that McKenna’s idea constitutes a “very, very plausible hypothesis for the sudden evolution of Homo sapiens from our primate relatives,” even if it’s an unprovable one.

Although it should be noted that the people attending his talk were initially here for a conference on psychedelic science, and thus predisposed towards such theories, at the time, the audience’s response was reportedly enthusiastic.

That being said, other researchers who have also studied early humanity’s use of drug plants remain sceptical of the stoned ape theory. Elisa Guerra-Doce, an expert in the field, considers the idea too simplistic, potentially a reduction of a complex evolutionary process into a single ‘eureka!’ moment. According to Big Think, she’s also troubled by the lack of evidence of such a pivotal moment, or of drug use at all, so early in the archaeological record.

On the other hand, Amanda Feilding of the psychedelic think tank Beckley Foundation says that “the imagery that comes with the psychedelic experience is a theme that runs through ancient art, so I’m sure that psychedelic experience and other techniques, like dancing and music, were used by our early ancestors to enhance consciousness, which then facilitated spirituality, art, and medicine.”

It’s clear that our relationship with psychedelics began centuries ago. Sadly, we’re still not sure exactly when and the kind of impact it had on human evolution as a whole. As for the lucky ones who got to discuss the stoned ape theory with McKenna and are still around today, I’m just not sure the memory of these renowned psychedelic enthusiasts will be that reliable. The downside of a good high, I guess.