The Stoned Ape Theory

by Brian Dunning
June 30, 2020

Come back with us now to One Million Years BC as an early hominin treads across the dry cracked mud, spear in hand. Finally he spots the object of his quarry, a dry disk of manure. He bends down and turns it over to expose its moist and pungent underside, and there is what he seeks: a pair of stringy mushrooms which he quickly peels off and gobbles down. An hour later we find him again, stretched out in the grass, watching the sun and the clouds dance overhead. And then at the faintest sound of a small rodent, strangely amplified, he springs to his feet and lets fly the spear. Our young hunter has just demonstrated his ability, unique among all predators, to turn the power of hallucinogens to his advantage. His tribe and his fathers before him have been advancing rapidly for millennia, thanks to what some of today's believers call the Stoned Ape Theory.

Did early protohumans indeed turn to natural psychedelic compounds to power some of their greatest societal and physical adaptations? There are those who believe that this is not just a part of the human experience, but perhaps the single most important part. We'll get into an analysis of the validity of the Stoned Ape Theory, but first it's appropriate to view it in its proper historical context. Stoned Ape Theory is not an idea that came out of the worlds of cultural anthropology or archaeology; in fact, you won't even find any mention of it in their textbooks. The concept is really only discussed and supported within the psychedelics community, and even then only since the early 1990s. It's not a formalized theory — strictly speaking, it's really only just a loose idea, not really even a hypothesis let alone a theory. The idea came from the 1992 book Food of the Gods by psychedelics guru Terence McKenna.

Although McKenna is usually described as an ethnobotanist, he had no formal education or credentials in the field. He began studying art history at UC Berkeley but soon dropped out to travel the world in search of psychedelics, a journey that took him to Indonesia, the Amazon, and even a stint as a hashish smuggler in Tibet. It was on these journeys that he developed his intense lifelong interest in hallucinogens, daily marijuana, and shamanism. Most of his professional career consisted of illegally growing and selling shrooms in Hawaii. By 1990 his reputation as a psychedelics guru and public speaker — he's often referred to as the "Altered Statesman" — was such that he was able to write and publish decently-selling books.

Food of the Gods is where he posited that the use of psilocybin, found by fortune on the savannah, is what drove Early Man to think abstractly, to develop complex skills and ideas including language and religion, and to succeed biologically by becoming especially prone to sexual passion and to be able to focus intently on life-sustaining activities such as hunting:

The boundary-dissolving qualities of shamanic ecstasy predispose hallucinogen-using tribal groups to community bonding and to group sexual activities, which promote gene mixing, higher birth rates, and a communal sense of responsibility for the group offspring. At whatever dose the mushroom was used, it possessed the magical property of conferring adaptive advantages upon its archaic users and their group. Increased visual acuity, sexual arousal, and access to the transcendent Other led to success in obtaining food, sexual prowess and stamina, abundance of offspring, and access to realms of supernatural power.

McKenna illustrated his Stoned Ape notion with a fanciful tale of a primitive boy on the savannah, his senses heightened by drugs, striking and killing a mighty lioness, and thus filling the bellies of his whole clan:

This example makes clear the way in which a beneficial plant, in this case a powerful stimulant, once discovered, can be included in the diet and thus confer an adaptive advantage. A plant can confer strength and alertness and so insure hunting success and steady food supplies. The person or group is much less threatened by certain environmental factors, which may have previously limited individuals' life spans and hence the growth of the population as a whole... Even as the nineteenth century had to come to terms with the notion of human descent from apes, we must now come to terms with the fact that those apes were stoned apes. Being stoned seems to have been our unique characteristic.

One of McKenna's most important assumptions was that over a span of three million years, the brain size of protohumans tripled; a growth spurt which he claimed "Scientists were unable to explain." But he was. He wrote:

The action of hallucinogens present in many common plants enhanced our information processing activity, or environmental sensitivity, and thus contributed to the sudden expansion of the human brain size. At a later stage in this same process, hallucinogens acted as catalysts in the development of imagination, fueling the creation of internal stratagems and hopes that may well have synergized the emergence of language and religion.

McKenna's tripling of brain size in three million years is roughly correct within the normal variation of fossil skulls and the amount of time various species survived; Australopithecines had brains in the 400-500cc range and those of modern humans average 1350cc. Most people who retell McKenna's theory don't seem to have read his book; they always say the brain size doubled in two million years, but he actually wrote:

At the end of these truly remarkable three million years in the evolution of the human species, human brain size had tripled!

And that's actually correct. As far as his assertion that scientists are unable to explain it, though, that didn't quite ring true; the cooking of food to make it more nutritious, the appearance of the opposable thumb, and other factors, have long been considered the driving influence. And about the time McKenna was writing his book, anthropologists were cementing these ideas with what's known as the expensive tissue hypothesis, which provides a metabolic and biochemical explanation for how protohumans were able to afford the greater energy requirements of a larger brain on the same basic energy budget, by reducing the relative size of the gut — which became possible once food was being cooked to make its nutrients much more bioavailable.

Animal models have confirmed this. The brain and the gut are the two most expensive systems in the body, in terms of the energy needed to make them function. In nearly every species studied, we find a negative correlation between brain size and gut size — that is, as one shrinks the other grows, and vice versa. How big the gut needs to be depends on the quality of the diet. A high quality diet means you can get away with a small gut, therefore there's energy left over to power a larger brain; a low quality diet requires a larger gut to process, leaving less energy capable of powering only a small brain. Think of a cow; all it eats is grass, a terrible diet virtually devoid of nutrition. So it needs four enormous stomachs and a great long digestive system, all energetically expensive tissue, leaving it with a tiny brain. Humans eat a far more energy dense diet, allowing our digestive systems to be tiny and fuel efficient, leaving plenty of energy to feed our great big brains. Even rats, which are very smart; it's no accident that they forage for much more energy-rich foods than does a rabbit.

And so McKenna's Stoned Ape Theory turns out to have been completely unnecessary to explain the growth in brain size, and all the attendant advances which led to Homo sapiens. McKenna's idea was answering a question that already had a better answer, just one that was unknown to him because he lacked the relevant expertise. Something that should really jump out to long-time Skeptoid listeners about the Stoned Ape Theory is its similarities to ideas discussed in least two other episodes. The first and most obvious is the Aquatic Ape Theory, another theory of human evolution proposed by people without relevant expertise and which also provided answers to questions that didn't need any. First proposed by an expert on marine ecosystems and later popularized by a screenwriter, Aquatic Ape Theory wondered why humans have no fur and can consciously control our breathing, and concluded that the most probable explanation must be that we used to be aquatic, like dolphins or seals. This idea gained traction because TED let the screenwriter give a TED talk promoting it, in which she spouted all the usual conspiratorial complaints about why science doesn't take it seriously — enough that it compelled Animal Planet to base its fake documentary Mermaids: The Body Found on it. Probably, we need only start our stopwatches before the TV pseudoscience channels make a show promoting the Stoned Ape Theory. They're both examples of concepts developed outside of the relevant expertise, and are thus as wrong as logic would predict them to be; and yet, both publicized by media to seduce a general public hungry for sensationalism.

The second Skeptoid episode that the Stoned Ape Theory recalls is the one about the conspiracy theory that a cabal of industrialists including William Randolph Hearst was responsible for the destruction of the US hemp industry, thus costing us a wonder product that is the best possible raw material for virtually any manufacturing need. The parallel here is that we have two similar groups of activists who each favor a certain recreational drug, so much that they're willing to make up miracle claims for it that aren't true, but that they hope will sway others to their cause. The marijuana enthusiasts claimed that hemp makes the world's best fabrics, papers, ropes, and oils, therefore we should encourage its cultivation; and the psychedelic people claimed that magic mushrooms catalyzed an important step in human evolution by sharpening our senses and expanding our minds, therefore we should encourage their popularization and use.

However, stacking on the false claims actually hurts both causes. Marijuana is a very popular recreational drug with none of the harmful effects of alcohol or other alternatives, and it provides welcome temporary relief to some sufferers of conditions like chronic pain and depression. These are valid and defensible arguments. But when you add invalid and indefensible arguments — like it cures disease and makes better rope — your overall argument is the weaker. The same goes with psychedelics. Their general safety and perceived enhancements to creativity and insight are not disputed and can stand on their own as arguments in favor of the drug's use; but attempts to augment that case with nonsense like they are the root cause of everything that separates humans from animals just makes the whole argument childish and silly.

To McKenna's credit, he did not claim his Stoned Ape Theory was necessarily valid; after the book came out, he always said he was just throwing it out there as food for thought. And it's certainly an intriguing thought experiment. But it's also a good reminder for those of us who have ideas that seem to be quite clever to us, that we should run them by people who know a lot more than we do in the relevant field. Chances are there is something to learn. It's when we only talk and fail to listen that we tread on dangerous ground; and the Stoned Ape Theory is an idea that arose from just such an environment. We should learn from the observation that it is not part of anthropology. McKenna himself did not have much opportunity to get this feedback, as he died much too young from brain cancer only a few years after he published Food of the Gods (no, it was not related to his drug use). His most important contributions were to psychedelic culture, where he rightly holds a venerable seat. And it's in that seat where we should probably let him remain, and not necessarily in the annals of anthropology.

By Brian Dunning
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