There are a lot of competing theories out there for how or why humans have consciousness. Not just that we think, but why we even started thinking at all. Out of all the theories that exist, the one that may be considered the most controversy would be the Stoned Ape Theory.
The basic idea is that ancient humans—humans that did not yet have higher consciousness—sparked that higher level of thought into existence after consuming psilocybin mushrooms (often called magic mushrooms). The idea was theorized by Terence McKenna. Let’s walk through the theory.
Overview of The Stoned Ape Theory by Terence McKenna
First theorized in Terence McKenna’s 1992 book, Food of the Gods, what separates us, Homo Sapiens, from our predecessors, Homo Erectus, other than our minor physical differences, is our higher consciousness. This change happened because Homo Erectus started incorporating ‘Psilocybe cubensis‘ — a psychedelic mushroom into their diet.

Psilocybin mushrooms are commonly found growing out of cow dung. Ancient humans needed to go where the food was, which meant they needed to track herds of wild cattle. Now, this is where this gets just a little bit gross.
For those who don’t know what psilocybin mushrooms are, they are a unique class of drugs known as psychedelics. Psilocybin mushrooms aren’t quite a stimulant and not quite a depressant, and they come bundled with all sorts of visual and mental effects. At least, that’s how they are perceived currently, now that we already have consciousness. So, when Homo Erectus eats psilocybin mushrooms, we call it the Stoned Ape Theory.
Did Psilocybin Mushrooms Sparked Human Consciousness

The idea was that the small-dose effects of psilocybin mushrooms—things like enhanced visual acuity and greater auditory awareness—made early humans better hunters. Which, in turn, allowed for more significant food stockpiles for the stoned apes. This meant prosperity, higher rates of reproduction, more downtime, etc.
When you increase the dose of psilocybin mushrooms because you’re now hanging around doing nothing, you achieve slightly more intense effects, things like better focus, increased energy, and sexual arousal. Yada, yada, yada, now you have more food AND more babies. Then comes the final step, the one that launched our ancient brethren into higher consciousness.
Higher Doses of Psilocybin Mushrooms
That happened when our stoned apes started taking larger doses (after all, remember, there wasn’t much else to do). At higher doses, psychedelics get a little wonky. It goes beyond higher energy and visual awareness, things start to get kinda weird.

Because of the higher doses of psilocybin mushrooms, our ancient humans began to have thoughts about the world beyond themselves. The effect started ideas about the boundaries between life and the environment. If there’s a boundary there at all, could it be connected to relationships in their lives?
Remember, we’re talking about ancient humanity here, pre-language and all. We’re talking grunts and hand signals. But the idea is that these consciousness-expanding experiences catapulted human ingenuity and spurred the creation of language, art, and philosophy. Religious experiences or rituals may even predate proper communication.
Evolution of Consciousness
One thinks of the famous opening scene to 2001: A Space Odyssey, and it isn’t hard to imagine us as the apes worshipping the obelisk. Spiritual exercises, communal rituals, combined with continued use of psilocybin mushrooms, mean greater interconnectedness, communication, and even the development of language itself. When you get your stoned apes talking to each other, that’s when you’ve achieved higher consciousness.

Basically, the Stoned Ape Theory is the idea that when people take psilocybin mushrooms or any psychedelic, they are achieving a higher level of interconnected mental awareness, “man.” Maybe they don’t just have a drug experience, perhaps they really are having that heightened level of consciousness. That’s exactly what our ancient ancestors were tapping into as well.
Conclusion
I mean, for what it’s worth, there really aren’t any better ideas out there for how we achieved higher consciousness. Right now, the best idea science has is, “Our brain’s just got so good that we became conscious.” I’m simplifying, but it isn’t far off from that. Higher consciousness is such a crazy thing in the first place that perhaps an equally crazy theory, such as psilocybin mushrooms, is a valid one to explain it.