The origins of behavioral modernity and what exactly makes us human are topics which have fascinated people for hundreds of years. There is a plethora of theories as to which archaic human ancestor first displayed traits that set them aside from other apes, and the reasons that this behavior may have evolved.

One question that people have tried to find an explanation for is how humans evolved from our Homo erectus forebears, doubling our brain size within a span of about 200,000 years – which in evolutionary terms is the blink of an eye.

Terence McKenna – a renowned mystic and psychonaut – broke the traditional mold when he presented his theory of how humans advanced so quickly in such a short space of time. The theory, which is known as the ‘stoned ape’ theory looks at the question from outside the box. But is it really as ridiculous as some people believe, or is it possible McKenna was on to something?

Terence McKenna during a panel discussion at the 1999 AllChemical Arts Conference, held at Kona, Hawaii. (Jon Hanna/ CC BY SA 3.0 )

What is the Stoned Ape Theory?

The Stoned Ape Theory presented by McKenna proposes that the evolutionary leap between Homo erectus and Homo sapiens was a result of a surprising addition to the human diet Psilocybe cubensis (magic mushrooms).

It sounds outlandish at first – how could eating mushrooms possibly make such a huge difference that Homo erectus doubled its brain size? McKenna based the theory on research conducted in the 1960s by Roland Fischer, a scientist who conducted a lot of research on the effects of psychedelic drugs .

He believed that Homo erectus were forced to turn to new food sources, including magic mushrooms, as the climate in Africa changed. The effects of the mushrooms meant that the thought processes of Homo erectus rapidly reorganized.

Psilocybe Cubensis. (Rohan523/ CC BY SA 3.0 )

Stoned Apes

The Stoned Ape theory argues that the effects of magic mushrooms played a pivotal role in the evolution of the species. Increased clarity of vision would make hunting easier. Increased sexual desire would mean they were more prolific.

McKenna also notes the effects of magic mushrooms on modern humans – stimulating the language portion of the brain and inducing religious experiences would have opened the path towards behavioral modernity and if Homo erectus had similar experiences he calls them an “evolutionary catalyst”.

A reconstruction of a Homo erectus, exhibit at the Westfälisches Landesmuseum, Herne, Germany. ( CC BY SA 2.5 )

Sceptics of the Stoned Ape Theory

With a theory as outlandish as the Stoned Ape theory, it is unsurprising that there has been a lot of skepticism. One of the issues raised against the theory is a purely practical one – magic mushrooms don’t grow in Africa. People who believe strongly in the theory could argue that we don’t have evidence they did not grow in Africa thousands of years ago, but it seems like when the known climate , flora, and fauna are considered our ancestors probably did not encounter magic mushrooms at that time.

Secondly, McKenna either misquoted or misinterpreted Fischer’s research. A pivotal part of the Stoned Ape theory centers on the effects the mushrooms have on clarity of vision, but the research only pointed to improved vision within very specific parameters – and it would not have been in a way that helped improve the odds of a successful hunt. There is also no scientific evidence that magic mushrooms have an effect on sexual desire.

Psilocybe cubensis from Coyopolan, Veracruz, Mexico. (Alan Rockefeller/ CC BY SA 3.0 )

There are a number of inaccuracies in McKenna’s research into human evolution – some of the dates he gives for migration are wrong by more than 100,000 years. This makes it unlikely that his picture of human ancestors being forced to source new foods in changing climates is accurate.

Finally, the effects of magic mushrooms are temporary. Any major breakthroughs in behavior or thought process would not have lasted longer than any other effects of the mushrooms.

The theory certainly captures the imagination and its proponents believe staunchly in the Stoned Ape hypothesis, but the data and further research in this case points to the theory being invalid. But whether they agree with the hypothesis or not, one thing that most of the discussions about the hypothesis does agree on is that McKenna seems to have had much fun conducting the research.

Top Image: The Stoned Ape theory proposes magic mushrooms helped the Homo erectus evolve quickly. Source: INVERSE

By Sarah P Young