No doubt that Terrence McKenna is one of my favourite authors/speakers, he is up there with Alan Watts, Rudolf Steiner, Eckhart Tolle, Carl Jung among others. "The mitochondria, which power the animal cell, were originally free swimming bacteria that got into a symbiotic free swimming bacteria that got into a symbiotic relationship with a membrane-like matrix & before they knew it had been incorporated as a sub-cellular organelles of a larger system. Mind that this doesn’t happen to you" is one of my favourite quotes by him, and it's a great caution that should be listened to.