Highly controversial (and definitely strange) theory about early human brains comes from Terence McKenna, an American philosopher, ecologist, and drug advocate. In the early 1990s, McKenna developed a theory popularly referred to as the “Stoned Ape” theory.

According to McKenna, early man, upon leaving the jungle and moving into the grasslands of north Africa, saw mushrooms growing on cow dung (something they hadn’t seen in the jungle) and decided to give them a try. He points out that modern apes will frequently eat dung beetles, so it’s not completely unheard of for primates to eat things typically found on or around excrement.

McKenna believes that those mushrooms, ancestors of today's “magic” mushrooms, probably increased visual ability at low doses (much like modern mushrooms), making them biologically useful. Further, at moderate doses, those same mushrooms are sexual stimulants, also handy for a burgeoning species. Lastly, large doses would promote conscious thinking and possibly assist brain growth. Thus, it was evolutionarily beneficial for humans to consume these mushrooms.

Don’t get too excited, though. McKenna’s theory has never been taken seriously by scientists or heavily studied, so there’s currently no real evidence to support it.