In his book, Food of the Gods (1992), Terence McKenna describes one of his many controversial ideas. This idea, known as the 'Stoned Ape Theory', is about how our ancestors evolved from an upright walking ape into an upright walking ape who could produce language and create art. The theory basically says that magic mushrooms sped up the evolution of our ancestors and that, ultimately, the psychedelic experience is responsible for the origin of culture.
Between 2 million and 700,000 years ago the brain size of our ancestor, Homo erectus, doubled. The cause of this rapid expansion in brain size is still debated within the scientific community. Humans may have needed a larger brain in order to handle the complex motor skills that are necessary for making and using tools. We may have needed a larger brain for purposes of living in a complex society, for developing a greater capacity in memory, or in order to develop language. It could be a combination of all these factors working together. One hypothesis that is not considered in the scientific community, however, is McKenna's. It has long been said that psychedelics “expand your consciousness”, but McKenna actually thought they literally expanded our ancestors' brains.
Is McKenna's theory ignored for a good reason, namely because it is unscientific and lacks evidence to support it? To answer this question, it will be useful to look at the assumptions that McKenna makes. In support of his theory McKenna refers to a study conducted by R. Fischer and R.M. Hill, claiming that they found that psilocybin in low doses increases something called visual acuity. Visual acuity is clearness of vision or how clearly you can see things. McKenna asserts that if our ancestors ate a low dose of magic mushrooms, then they would have an increase in visual acuity or edge detection ability, and therefore be more successful at hunting.
The problem with this line of argument is that it relies on a series of assumptions which, while possible, are not backed up by convincing evidence. Perhaps magic mushrooms in low doses could increase visual acuity, but McKenna goes on to assume that magic mushrooms grew where our ancestors lived, that our ancestors ate these mushrooms, that they hunted under their effect, that they hunted more successfully, and so on. The argument basically consists of: “If this is possible, then so is this, and this, and this, etc.” McKenna's theory is undoubtedly imaginative, creative and compelling, but each of his assumptions beg the question: how can we know if this is true?
It also appears that McKenna misrepresented the findings of Fischer and Hill. In their study, what they actually discovered was that psilocybin changes perception, not visual acuity or edge detection – the drug changes how things look, not how clearly they are defined. In fact, in a paper by these two scientists they state that the change in perception caused by a low dose of psilocybin “may not be conducive to the survival of the organism." This conclusion is completely at odds with McKenna's interpretation of their findings. It seems he may have skewed their conclusion in order to support his own ideas about human evolution. Furthermore, Fischer and Hill didn't even study psilocybin at low doses, but at medium doses.
McKenna, and others who support his Stoned Ape Theory, might be inclined to believe his argument relating to visual acuity because, under the influence of psilocybin, it may feel like you can see objects more clearly. But there is no evidence to suggest that this actually takes place while under its influence. Some experiment – such as asking a tripping and non-tripping person to do some task or take some visual test – would be required to substantiate this argument.
Another strange thing that McKenna argues is that in higher doses magic mushrooms increase sexual arousal. From this he claims that if our ancestors consumed high doses of the hallucinogen they would be more likely to reproduce, and therefore pass on their genes. For McKenna this shows that the consumption of magic mushrooms would be adaptive and advantageous. Again, however, McKenna cites no evidence to support his claim. There is nothing in the scientific literature which points to the “fact” that magic mushrooms increase sexual arousal.
McKenna also argues that an even higher dose of magic mushrooms would lead to ecstatic, visionary experiences and that these experiences would serve as the foundation of religion. This is an interesting idea, no doubt, but it has not been verified by the facts. The first signs of “religion”, if it can even be called that, would be found in the cave art of Europe, dating back to 40,000 years ago. This is far more recent compared to when our brain size doubled 700,000 years ago. There is just no evidence of religion existing at this time, so it is pure speculation to say that our ancestors were tripping at this time and that this initiated the origin of religion.
In addition, it may seem obvious that an increase in sexual arousal will lead to more sex, but this is not necessarily true. If our male ancestors had to compete for mates, then being a bit more 'horny' than other males is not likely to carry an advantage – other characteristics are more useful in mate competition. On the other hand, if the hominids that McKenna refers to are the Homo erectus species (which would fit his timeline), then an increase in sexual arousal may lead to more sex, since the hunter-gatherer society of Homo erectus could have been quite egalitarian or even orgiastic. Evolutionary scientist Richard Leakey has said that Homo erectus was probably socially very similar to us modern Homo sapiens. However, sexual dimorphism (differences between the male and female) is greater for Homo erectus than for Homo sapiens. The male was 25% larger than the female, which is suggestive of male competition for sexual mates.
My own view is that McKenna's Stoned Ape Theory is entertaining as a narrative or story, but, in the end, it is not supported by reliable evidence. This is not to rule out the possibility that McKenna's theory could one day be vindicated – after all, his theory is still within the realm of possibility and is even plausible.
A positive feature of Terence’s theory is that it does appreciate the behavioural side to the evolutionary process. It has been well documented that adaptive behaviours (those that are conducive to survival and reproduction) are crucial in natural selection. These adaptive behaviours can be heritable, meaning that they are passed on by genes – either through a mutation in the genetic sequence itself or through phenotypes (how genes are expressed), which depend on environmental cues. A heritable adaptive behaviour can also involve genes which give an individual a tendency to respond to environmental cues better than others (say, by eating a certain quantity of magic mushrooms, for example). An adaptive behaviour can also be non-heritable, meaning that the behaviour is not passed on genetically, but is passed on as a taught behaviour.
Some say that eating magic mushrooms could have been part of an epigenetic process. An epigenetic process is when an environmental stimulus changes how genes are expressed, as opposed to changes being made in the gene sequence itself. Despite this counter-argument, it is still difficult to show how tripping on mushrooms would have had an adaptive value. Other proponents of the theory may claim that eating magic mushrooms could be a culturally inherited behaviour. But once again, there is no clear evidence that this behaviour has an adaptive value.
To try and add some more plausibility to Terence's theory, Dennis McKenna (Terence's brother) has proposed that psilocybin could have caused synesthesia in our ancestors. Synesthesia refers to a condition in which one sensory modality is translated into another. An example of a synesthetic experience would be “seeing sounds” or “hearing colours”. Dennis argues that meaning, symbol and metaphor (all central to language) depend on this cross-wiring of different sensory systems. Language is inherently synesthetic because it involves attributing meaning to mouth noises. He maintains that the synesthetic experience of a magic mushroom trip could have made the synesthetic experience of language possible and that, once the benefits of language were experienced, language would be naturally selected for from then on.
It seems like the McKennas were such huge enthusiasts of magic mushrooms that they attributed to them an influence in our evolutionary past which they might not have had. Perhaps they were so blown away by the effect that magic mushrooms had on their consciousness that they thought it could have radically changed our ancestors' consciousness as well. Terence also remarked in an interview that the Stoned Ape Theory proposed in Food of the Gods was “consciously propaganda”, as a way to persuade people that “drugs are natural, ancient and responsible for human nature” and not “…alien, invasive and distorting to human nature.” In other words, it was in a sense fabricated to promote his own agenda (which is not to say that his agenda was bad).