The Stoned Ape: Between Hypothesis and Myth

“The stoned ape hypothesis is neither proven nor falsified. It is something rarer: a genuinely interesting question that the available evidence neither confirms nor eliminates.”

The stoned ape hypothesis, in its strongest form, proposes that Homo sapiens' distinctive cognitive capacities, language, abstract thinking, religious consciousness, tool innovation, were catalyzed by the regular consumption of psilocybin-containing mushrooms during a critical phase of human evolution in East Africa, approximately 200,000 years ago.

Terence McKenna's version, articulated in Food of the Gods, is specific: as African grasslands expanded and the forests contracted following climatic changes, ancestral hominids followed large herbivores across open savannahs. Psilocybe cubensis, which grows in the dung of cattle and similar herbivores, would have been abundant in this environment. McKenna proposed three mechanisms by which psilocybin consumption at low, medium, and high doses could have conferred evolutionary advantages: enhanced visual acuity (useful for hunting), increased sexual arousal and group bonding, and at high doses, the dissolution of ego boundaries and expansion of social and symbolic consciousness.

The hypothesis has been criticized on multiple grounds. No archaeological evidence of psilocybin use by early hominids has been found, the time scale is too remote and the evidence too fragile. The proposed mechanism is speculative: it assumes that the selective advantages of psilocybin-enhanced cognition were sufficient to produce significant evolutionary change, and that early hominids were encountering mushrooms at the right frequency and in the right quantities to produce that change. Both assumptions are untestable with current methods.

Most importantly for the specific McKenna claim: Psilocybe cubensis is not native to East Africa and probably was not present during the critical period of human cognitive evolution. The mushroom's range has expanded with cattle domestication; its presence in East Africa as early hominid habitat is not documented.

What the hypothesis gets right, or at least what it points at correctly, is the broader question: what role did psychoactive plants play in human evolution and cognitive development? This is a real question, and the evidence that human cultures have consistently used psychoactive plants, that no known culture lacks plant medicine practices, is itself significant. The relationship between humans and these plants is ancient and universal enough to suggest it is not accidental.

A 2021 Neuron paper by Shao et al. at Yale provides the most relevant recent data: psilocybin induces rapid and persistent growth of dendritic spines in the prefrontal cortex of mice, suggesting that it promotes synaptic plasticity, the mechanism underlying learning and memory formation. The growth was detectable within 24 hours of a single dose and persisted for at least a month. This is a neuroplasticity mechanism that could, in principle, provide cognitive advantages, though the leap from mice to hominids to evolutionary selection is large.

Dennis McKenna, who has done rigorous neuropharmacological research on tryptamines for decades, has said that the general hypothesis, that psychoactive plants were part of the hominid ecological niche and may have had effects on cognition, is plausible. The specific mechanism Terence proposed is not something the evidence currently supports. Dennis is comfortable with this distinction. He has described the experience at La Chorrera as real, the mushroom monologue as real in some sense he cannot fully specify, and the stoned ape hypothesis as an interesting story that may contain truth without being literally true.

This is perhaps the most honest relationship available to the hypothesis: not proof, not dismissal, but residence in a category that McKenna himself inhabited, the genuinely interesting question that the available evidence neither confirms nor eliminates, that calls for more research without promising what that research will find.

What Food of the Gods contributes to this question, regardless of the hypothesis's truth value, is the framework: the idea that the human relationship with psychoactive plants is not a deviation from some drug-free baseline but a consistent and possibly constitutive feature of human culture. Every known traditional society has plant medicine practices. The current pharmacological environment, which excludes most traditional psychoactive plants from legal use, is the historical anomaly, not the norm.

Whether psilocybin shaped the hominid brain or merely reflects what that brain already was, the relationship between the two is real. McKenna's contribution was to take that relationship seriously as a subject of inquiry when taking it seriously was not academically respectable. Whether the specific hypothesis survives is less important than whether the question does.

Sources

• McKenna, Food of the Gods (1992)
• Shao et al., Psilocybin induces rapid and persistent growth of dendritic spines in frontal cortex in vivo, Neuron (2021)
• Wikipedia, Stoned Ape Theory
• Grokipedia, Terence McKenna
• D. McKenna, The Brotherhood of the Screaming Abyss (2012)