Did cannabis consumption contribute to rapid brain evolution?
Evolution is responsible for modern humans (whether that is a good or bad thing I’ll leave for personal debate). There is a 95% overlap of genetic material with us humans and chimpanzees—but that 5% makes a big difference. While obvious features like lack of full-body hair and other structural differences certainly creates a dividing line, the biggest difference lies of course in our brains. 
Humans are the most intelligent species and the only ones to have complex, verbal language. I could list our many other achievements, but I will forgo that exercise in exchange for a different discussion. While much of the evolutionary process is well understood, there are a few questions that remain unanswered. One example revolves around the issue of the human brain—how did it get so big, change shape, and become capable of incredible feats in a short period of time? 
According to ethnobotanist Terence McKenna, it’s because the species we evolved from consumed a lot of mushrooms—of the psychedelic kind.
In McKenna’s book, Food of the Gods, he posits that consuming mind-altering psychedelics found in nature—psilocybin from “magic” mushrooms—was the catalyst that led to rapid brain evolution and brainpower. In it, he writes:
“Even as the nineteenth century had to come to terms with the notion of human descent from apes, we must now come to terms with the fact that those apes were stoned apes. Being stoned seems to have been our unique characteristic.” 
While many are quite critical of McKenna, as there is no evidence to support his theory, the renewed interest in psychedelics as medicine has also rekindled interest in his work. Especially when it comes to the effect of psilocybin on the “default network.” 
The default network has been described by neuroscientists as the baseline state of the brain. Ever end up at work on a Saturday because you forgot it was the weekend and drove there mindlessly? That’s your default network at play, also known as “autopilot.” 
Psychedelics have been found to alter the default network. In fact, it is believed that psilocybin exerts its anti-depressant effects through this mechanism.  By breaking free of this network, patients may un-do patterns of negative thoughts that have been reinforced over the years. In fact, a very small trial found preliminary support for its safety and efficacy in people with treatment-resistant depression. 
Sounds pretty cool, right? But what does this have to do with cannabis?
Well, there is debate over whether cannabis can be classified as “psychedelic,” despite many anecdotal tales about experiences that are similar to those of other substances known to be psychedelic. However, there is some data showing that cannabis consumption can also disrupt the default network.
A small study of 20 healthy volunteers found that administration of 6 mg of THC followed by three doses of 1 mg of THC reduced deactivation of the default network, suggesting an important role of the endocannabinoid system in this brain state. 
Anecdotally, many people report feeling more creative and able to tackle problems in a different way thanks to their cannabis use. In fact, one study showed that cannabis users are more open to experience, which affects their creativity.  But could cannabis, as well as other psychedelic substances in nature, really have led to rapid brain evolution?
While we may never know the answer to that question, with greater access to cannabis for research purposes, neuroscientists can continue to look at how cannabis affects widespread connections in the brain. Disrupting some of these connections could explain some of its beneficial effects on creativity, cognition, and certain neurological conditions.
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