In the realm of human evolution, few theories have captured the public imagination quite like the “Stoned Ape Hypothesis.” Originally proposed by ethnobotanist Terence McKenna in his 1992 book Food of the Gods, this provocative idea has recently resurged in popular discourse, thanks in large part to its discussion on Joe Rogan’s widely followed podcast. Rogan, a big fan of psychedelics, frequently calls it “the greatest theory of all time,” and if you hear the theory’s premise while stoned, you might just agree. According to the big idea, the evolution of our primitive ape ancestors into beings we consider truly “human” resulted from a revolutionary leap in cognition and consciousness brought about by the widespread use of psychedelic substances.
However, matching the enthusiasm for the theory is the skepticism that opposes it, and critics have branded it “pseudoscience,” successfully demoting it from a legitimate scientific hypothesis to fringe status. Since most academics approve of this characterization, I’ve long felt motivated to “steelman” McKenna’s theory, which I think will prove to be more right than wrong. This motivation has since evolved into an obligation, as I believe that scientific understanding of the evolutionary story, and the story of ourselves, will be stifled if the record isn’t corrected.
For this reason, I am proposing a “New Stoned Ape Theory” that revises McKenna’s hypothesis in light of decades of scientific advancement, while preserving its core insight that psychedelics catalyzed human evolution in significant ways. To understand McKenna’s theory, and why it wasn’t just a flight of fancy, it’s best to start with the great mystery it tried to solve.
The evolutionary mystery of the cognitive revolution
Between about 100,000 and 40,000 years ago, there was a period of rapid cognitive development in human evolution known as the “cognitive revolution,” or “Great Leap Forward.” During this period, which followed the transition from Homo erectus to Homo sapiens, there was a relatively sudden appearance of complex behaviors, such as abstract thinking, long-term planning, technological innovation, symbolic language, and artistic expression. It would not be an overstatement to say that this evolutionary transition represents the “birth of humanity.”
How these cognitive advances occurred so quickly has been a subject of debate and investigation in anthropology and evolutionary biology because our standard paradigms have struggled to account for them. After all, genetic change was traditionally understood to be a slow, incremental process, but the increase in brain size and computational power during this period was anything but gradual.
McKenna’s highly amusing and admittedly speculative answer to the puzzle was that psychedelic substances helped spark the rapid evolution in human cognition, consciousness, and culture. According to his story, our early hominid ancestors would have inevitably encountered psychedelic fungi while foraging for food in locations like the African savanna. The psilocybin in these mushrooms would have provided adaptive advantages to those who consumed them, including enhanced cognition, creativity, and elevated states of consciousness.
While empirical studies have demonstrated that psychedelics like psilocybin can produce these effects, it is another claim altogether that these changes occurring in a subset of individuals somehow became heritable genetic changes that spread throughout the entire species and drove its evolutionary development. For evolutionary theorists, this sounded too close to Lamarckism, the idea that acquired traits could be passed down to offspring, a theory that fell out of fashion with the emergence of Darwin’s theory of natural selection. Just as we don’t expect a naturally thin-framed man who bulks up through bodybuilding and dietary supplements to birth children who automatically inherit the brawny build, it doesn’t make sense to think that psychedelic-induced cognitive changes would be passed down to offspring. And certainly not to a degree that would change the fundamental nature of the entire species.
McKenna, though, had more than a few answers to these criticisms, which makes the theory difficult to judge as flat-out right or wrong, since some of his explanations could be more or less correct. One idea is that magic mushrooms, after being widely recognized as beneficial, became such a regular part of the diet for some groups that the adaptive effects could have influenced cognition and behavior enough to shape evolutionary change. Advocates of McKenna’s theory cite evolutionary mechanisms that had been overlooked or underappreciated by the neo-Darwinian paradigm known as the Modern Synthesis, such as epigenetic changes, and the Baldwin effect, which allow for Lamarckian-like evolution. However, critics argued that these effects are still likely too subtle to account for the significant evolutionary changes associated with the cognitive revolution.
One promising alternative explanation, which you could say represents the “status quo alternative” to McKenna’s theory, is that social and cultural factors played a unique role, such that increasing social complexity created a natural selection pressure that strongly favored intelligence over physical attributes. While this may solve some of the puzzle, the mystery remains, because this answer leads one to then ask what drove the emergence of society and culture, which would seem to bring us back to progressive developments in cognition and language in individuals. The main question then becomes: Is there more to the puzzle that McKenna’s theory could help explain, or is this “all we need” to account for the change, satisfying the sacred scientific principle known as Occam’s razor?
Given the evolutionary story emerging from our most cutting-edge paradigms, I do not believe the skeptic’s response captures the complete “causal picture” that we get if we add McKenna’s general idea to an explanation that involves cultural evolution.
The “New Stoned Ape Theory” — based on the “entropic brain hypothesis” proposed by psychedelics researcher Robin Carhart-Harris, in conjunction with the modern paradigms of neuroscience and complexity theory — offers a framework for understanding the potential impact of psychedelics on human evolution.
Unlike its predecessor, this new theory provides specific cognitive, cultural, and evolutionary mechanisms to support its claims — claims that would have been difficult to validate without certain key concepts that have emerged from the study of complex adaptive systems, which offers a lens that unifies our understanding of emergent phenomena, such as organisms, brains, and societies.
To be clear, the New Stoned Ape Theory does not support all the claims of the original theory. For example, it seems unlikely that a substance known to produce strong hallucinogenic effects — cognitive effects that can make many routine tasks challenging — became part of the typical human diet. And if psilocybin actually did for the reasons McKenna cites, why would psychedelics then mostly disappear from our diet, rather than being a regular part of our contemporary lives, the way a drug like caffeine is? While these objections keep me from accepting the original theory in its entirety, the New Stoned Ape Theory preserves the general premise of McKenna’s profound insight.
The cognitive revolution as a period of phase transitions
The most central concept in the New Stoned Ape Theory is the mechanism of transformation known as the phase transition — a sudden change in how a system is organized that leads to new functions and properties. We learn about basic phase transitions in school, such as the transformation of water into ice. Complex adaptive systems like brains and societies also undergo phase transitions, which produce a change in the system’s overall functional structure and control architecture. A phase transition may lead to an evolution of the current system, or it could produce an entirely new system — a metasystem that adds a new level of structure to the existing order, such that novel features come into existence. One such “metasystem transition” is the evolutionary leap from humans existing relatively independently to the formation of a cultured society, i.e., a civilization.
When considering the mystery of “the cognitive revolution” through a complexity theory lens, we understand that the “Great Leap Forward” was a period of phase transitions, both at the level of the individual, with the brain and mind, as well as the collective level: the level of society and civilization. The New Stoned Ape Theory proposes that the general premise of McKenna’s theory may be “more correct than not,” in that psychedelics likely did play a significant causal role in catalyzing a seismic leap in human evolution, and that this kind of process may be cyclical — in particular, recurring and nested — in a way that recursively drives not just evolution, but also emergence.
According to the New Stoned Ape Theory, psychedelics likely served as a “chemical catalyst” for a special kind of “cognitive-cultural phase transition,” characterized by a shift in perspective at the individual level that propagates through culture (“goes viral”) and restructures the worldview of society, bringing about a transition at the societal level. The theory also proposes that such transitions may have indeed played a causal role in some of the most significant emergences in human development, such as self-awareness, symbolic language, civilization, and religion.
The New Stoned Ape Theory is based on the Entropic Brain Hypothesis, which itself is rooted in a revolutionary paradigm in neuroscience known as the Bayesian Brain Hypothesis (also known as the Free Energy Principle, the Active Inference Paradigm, or the Predictive Coding framework). To fully grasp the New Stoned Ape Hypothesis, we must first understand the paradigm of the Bayesian brain.
The Bayesian Brain: You are a prediction machine
The Bayesian Brain theory is really a new evolutionary theory that explains what brains and minds are in a way that gets at the essence of life. According to this idea, life is all about prediction. Essentially, organisms stay alive in an unpredictable and chaotic world by encoding a model of its relevant rules and features. This model serves as a real-time map of the world that we use to anticipate future events well enough to maintain a stable state of existence against the forces of nature that threaten death and entropic decay.
This means that the “world model” your brain encodes is not just a map, but also an instruction manual for surviving and thriving. For a simple example: When you touch a hot stove for the first time, your brain learns that this action leads to pain, forming a model for what you might expect when touching a stove. This abstract manual encodes a cognitive-behavioral strategy — think of this as a computer program with a predetermined set of mental and bodily responses mapped onto a certain set of known sensory inputs that reflect various environmental states. The brain is described as “Bayesian” in this view because it’s constantly collecting and learning from new evidence in order to minimize the errors of its predictive models. (For example, you eventually learn that the stove is only hot sometimes: when the burner is turned on, or shortly after it’s been switched off.) In this way, the Bayesian brain mirrors the Bayesian statistical method used in AI and the process of science.
In this evolutionary picture, biological adaptation is a kind of learning, and human learning is a kind of adaptation. Although it is not widely recognized yet, this theory of brains is also highly relevant to understanding society and culture. Why? Because the “beliefs” of our predictive model encompass both low-level things, such as a hot stove, and also higher-level concepts, such as how your tribe is socially organized. Humans who are part of a cultured society have a particularly sophisticated type of world model that we call a “worldview.” A worldview can be structured according to a religion, a political ideology, or a scientific paradigm. For most people, it’s some combination of those things, along with more “instinctive” beliefs that stem from your genetic programming and unique lived experience. A worldview attempts to make sense of all these things; it is an uncertainty reducer, a cognitive dissonance-minimizer, and a sense-making lens.
Because our worldview represents a belief structure that shapes the logic of the predictive model that is keeping us alive, our belief systems, and their underlying neural networks, can be quite rigid. Somewhat ironically, evolution has made them rigid to a degree because the process has sculpted them to be “optimally” reliable, which means resilient to modification and collapse. As a result, they are often less flexible, and therefore less adaptable, than what is actually optimal or ideal, because evolution can apparently sometimes work against itself — a rather interesting paradox of life. In order to change one’s belief structure in a significant way, a certain amount of chaos or disorder must be injected into the system, which is where the Entropic Brain Hypothesis comes in.
The entropic brain hypothesis
The Entropic Brain Hypothesis, a Bayesian-Brain-based theory, emphasizes that the human brain operates on a spectrum between order and chaos. In our normal operating state, the mind is relatively ordered, because it is structured according to a particular worldview and belief structure.
The upside of this ordered cognitive structure is that it allows for consistent patterns of thought and behavior that are aligned with our established beliefs and expectations. The downside is that we are all trapped in one particular way of understanding the world, with a perspective that is inherently biased by our particular genes, life experiences, and the cultural beliefs of our “tribe.” So, although worldviews allow us to make predictions that help us navigate reality efficiently, they can also lock us into rigid, sometimes maladaptive, thought patterns and modes of behavior. And because neuroscience as a field has demonstrated a causal relationship between the brain and mind, we know that a rigid belief system corresponds to a relatively fixed pattern of neural connectivity.
However, psychedelics possess a unique ability to shake things up, and it is this property that necessitates a revisitation of McKenna’s Stoned Ape idea.
Psychedelics as “worldview shifters”
According to the Entropic Brain Hypothesis, psychedelics affect cognition by increasing the entropy (disorder) in brain activity. Think of turning up a knob that adjusts the “chaos level” of the computational system — temporarily disrupting the established patterns of neural connectivity that underlie our normal conscious experience. This increase in neural entropy can be clearly seen in brain imaging studies. For example, fMRI has shown that not only are the usual patterns of brain connectivity disrupted (such that strongly linked areas become less coupled), but also that regions that don’t typically communicate begin to interact. This neural shake-up helps explain the profound alterations in perception, cognition, and existential perspective that characterize psychedelic experiences. While these experiences are temporary, their effects can be long-lasting, and studies have shown that even a single psychedelic experience can lead to persistent changes in perspective and personality.
Once we understand this, it is easy to see how an entropy injection from a drug like psilocybin can temporarily dissolve a belief structure and catalyze a worldview shift. In the same sense that magic mushrooms can produce a visual hallucination (a type of prediction error), the psychedelic can also provide the “neural flexibility” for a more complex and sophisticated perspective to emerge and replace the older one.
Such a process is described by Carhart-Harris’ REBUS model, an extension of the Entropic Brain Hypothesis that stands for “relaxed beliefs under psychedelics.” As this 2019 paper states, “via their entropic effect on spontaneous cortical activity, psychedelics work to relax the precision of high-level priors or beliefs, thereby liberating bottom-up information flow.” The authors go on to explain how this model can account for a broad range of phenomena associated with the psychedelic experience.
The two claims of the New Stoned Ape Theory
Now, we’re ready to state the two claims of the New Stoned Ape Theory. The first is that psychedelics act as chemical catalysts for cognitive phase transitions, or sudden changes in cognitive architecture that precipitate radical new insights or shifts in worldview. By increasing neural entropy, psychedelics create a state of heightened plasticity where entrenched beliefs and cognitive patterns become more malleable. Like a kaleidoscope suddenly rearranging its fragments to reveal an entirely new pattern, the mind undergoes a rapid reorganization, coalescing around a novel perspective that fundamentally transforms one’s worldview and sense of self.
The second claim is that because these paradigm shifts produce insights that are useful or interesting, they don’t remain isolated within individuals. Instead, the new perspective or worldview spreads as a meme, a unit of cultural transmission that propagates through society, reshaping the cognitive systems they inhabit through a subtle but potentially powerful restructuring of neural connectivity patterns. If the psychedelic-inspired idea or worldview spreads sufficiently fast and far, it may become part of the zeitgeist and reshape the collective consciousness through cultural evolution.
To summarize the theory in a sentence: Psychedelics, as “worldview shifters,” can create a cognitive phase transition whose spread creates a social phase transition — a shift in culture. It’s that simple!
Using the same logic of the Entropic Brain Hypothesis at a higher scale of agent, the social organism, we can presume that social phase transitions are more likely to occur during times of chaos — only not in a neural sense but rather a social context, such as periods of civil unrest and war. This further suggests that psychedelics become cognitive tools for cultural movements that become revolutions — by producing worldview-shaping solutions in times of existential threat. This means that only a very small subset of any given population needs to directly experience chemically induced altered states to spark a social phase transition, because the psychedelic-inspired ideas spread to receptive minds without the need for drugs.
The psychedelic movement of the 1960s illustrates this phenomenon nicely; despite its relatively brief duration, it had a profound and lasting impact on culture, art, science, and social values. Many of the ideas about spirituality, environmental awareness, and the evils of war that were central to the psychedelic counterculture became mainstream. Even the way of dressing, the atmosphere of music, and the way people spoke changed essentially overnight. A whole new “cultural vibe” was birthed from the psychedelic era that is still very much with us today.
Overcoming previous criticisms
In this version of the Stoned Ape Theory, there is no longer the problem of explaining how drug-induced cognitive changes became heritable genetic changes, or how such changes spread across the entire human species. You no longer have: 1) the far-fetched-sounding story of mind-altering substances somehow becoming part of the typical human diet, and then for some reason largely dying out; and 2) you don’t need to rely too heavily on poorly understood evolutionary mechanisms, like epigenetics and the Baldwin effect. While those mechanisms are certainly still part of the evolutionary story, the shift to an explanation that emphasizes the causal role of cultural evolution bypasses much if not all of the earlier criticism.
In the context of our Bayesian Brain paradigm, it is easy to imagine how a new cultural worldview could create a top-down selection pressure that could shift the genetic makeup of an entire population, favoring genomes that encode predictive models that are consistent with a more accurate and adaptive paradigm. It would be no more mysterious than the question of how one bird that learned to open nuts created a viral strategy that then spread across the entire species, a classic example of the “Baldwin effect.” That first innovator saw a solution to a survival problem that was hidden in plain sight, one that everyone could utilize if they just had the right way to look at the world. But as obvious as this solution can look in hindsight, it initially required a “crazy” new way to look at the world, a way that might make the other birds think, “What kind of drug was Robin on when he figured that out?”
A more modest theory might try to attribute less grand human advances to psychedelics in an effort to come across as less extreme, and therefore more plausible to the careful-minded critic. But I think such an approach would be more of an attempt at diplomacy than truth. The drastic developmental advances that drive cognitive and cultural revolutions require a very special type of cognitive state to emerge, known as “criticality,” which is characterized by a “mental tipping point” or “neural avalanche.” The human critical state is triggered uniquely well by psychedelics, and any alternative explanation for a major human phase transition must propose a causal catalyst for such transformations in cognitive and societal structure.
While it is certainly true that similar critical brain states can also be achieved by meditative practices, deep contemplation, and the occasional fever dream, the historical use of psychedelics across cultures throughout time singles them out as a common worldview-shifting tool. From the ancient Greek Mystery Schools using kykeon (ergot), to the use of peyote by indigenous North American cultures, ayahuasca in Amazonian shamanic practices, iboga in African Bwiti spiritual ceremonies, and soma in ancient Vedic rituals — it is clear that these substances have served as spiritual “psychotechnologies” in cultural practices for eons. Given the historical evidence, I believe psychedelics should at the very least be considered as a causal factor for any major cognitive-cultural shifts that currently lack a sound and complete alternative explanation. If the human brain is forced into an otherwise-rare critical state every time a psychedelic substance is ingested, this would have been a not-too-infrequent experience for our foraging ancestors, and all the ancestral psychonauts who made “trippin’” an intentional revelatory practice.
Psychedelics reveal the nondual nature of reality
But psychedelic experiences don’t just create an arbitrary change in our worldview and perspective — we also seem to take on a mode of perception that recognizes the interconnected nature of our world, a lens that would have a unique adaptive advantage as a predictive model. This perception of interconnectedness can manifest at various scales: from recognizing that human civilization is one interdependent network (a “superorganism” or “global brain”), to perceiving the interdependence of all living things in the biosphere (the Gaia Hypothesis), or even sensing a special kind of personal relationship to the evolving cosmos as a whole.
Such a holistic perspective corresponds to what we now call a “systems thinking” lens, which is a kind of “meta-perspective” that brings about a whole new level of analysis that would have been a serious upgrade to a more primitive predictive model. Systems thinking frames real-world phenomena as part of larger, interconnected wholes rather than isolated parts. In this mode of meta-reasoning, individuals suddenly become aware of the complex web of relationships and feedback loops that constitute reality, which were previously hidden by a reductionist perspective that viewed the world as a collection of separate entities. This higher level of conscious awareness promotes practical insights and societal solutions that emerge from thinking about the challenges we face as an interconnected species. If psychedelics promote systems thinking, they would routinely inspire more adaptive and effective predictive models that would be favored by evolution, especially during times of division, which scream out for unifying perspectives.
From brain imaging studies with subjective reporting, we know that psychedelics illuminate nature’s interconnectedness via ego dissolution — a phenomenon affecting consciousness in which the boundaries between self and environment become blurred or disappear entirely. While meditative and contemplative states that could promote paradigm shifts may also dissolve the ego, nothing does it quite like a powerful psychedelic. The resulting meta-perspective that transcends ordinary, ego-bound consciousness is known as “nondual awareness” in Eastern philosophy, and scientists have even developed questionnaire measures to assess changes in nondual awareness after altered states of consciousness. Such a state of perception would be fundamentally “spiritual,” in the sense that it connects us to something larger than ourselves. This lends support to the idea that psychedelics could’ve sparked the birth of religion, and with that first sophisticated strategy for collective survival, the seeds of civilization.
What does it all mean?
As we come to the end of our story, it’s time to think about our story and our future. The New Stoned Ape Theory suggests psychedelic-inspired revolutions that advance human and cultural evolution occur in recurring cycles, and that we can spot them by looking for signs of heavier-than-usual psychedelic consumption during periods of social turbulence, which functions as an “entropy-injection” for social systems that mirrors the entropic effects of psychedelics. The Bayesian update of McKenna’s brilliant but half-baked hypothesis emerges as we appear to be entering a new period of psychedelic renaissance amidst a backdrop of civilizational chaos, and perhaps that is not a coincidence.
With the widespread decriminalization of psilocybin (magic mushrooms), DMT (the psychoactive ingredient in ayahuasca), and marijuana — which has subtle psychedelic properties — the New Stoned Ape Theory would predict that a global psychedelic era is coming, signaling a shift from a postmodern to “metamodern” worldview. This worldview, characterized by a shared meta-perspective and a systems-thinking style awareness, will unify cultures and align their interests while preserving their diversity, since a more complex and computationally powerful organization simultaneously requires greater diversity and greater integration, or human interconnectedness. This worldview may be an adaptive solution that is forced upon us by the threat of World War III, and the need to minimize conflict in order to solve all of our other existential crises, which are enough to keep us busy without us trying to kill each other. And it just might be a psychedelic substance that inspires the precise packaging of that worldview, as it must be designed to have synergy with the emerging psychedelic mindset that will drive its cultural transmission.
This leads me to a line of speculation that is perhaps more radical than McKenna’s theory, though it is maybe the same bigger picture he had in mind. If the biosphere is truly one interconnected organism, with human civilization forming something like “the brain of Gaia,” could psychedelics be what the global system feeds to its “brain” to make it self-aware? Could the next great leap in evolution be the emergence of a fully integrated “noosphere,” the mind of a planetary system that has “come to life” or “woken up” through a unified planetary-scale human cognition?
For fear of attracting the same kind of skepticism that has kept McKenna’s theory in the fringe and out of science, I’ll leave this speculation out of the formal New Stoned Ape Hypothesis, but something tells me that the apparent fact that the evolutionary process — a process of both planetary and human progress — has been driven by consciousness-elevating substances, is more than just a fortunate coincidence of our world. In light of our new perspective, it becomes a natural and sensible part of the story of a cosmos that is becoming increasingly conscious — a cosmic whole that, like a developing organism, is waking up. The most psychedelic part of this psychedelic story is that it seems to be doing so through us.
This article A new spin on the “Stoned Ape Hypothesis” is featured on Big Think.
