Admittedly, it is unhelpful and inaccurate to say that any plant “wants” something or has any kind of cognitive desire; however, we can speak of the genetic benefit for many domesticated plants due to their intimate and mutualistic relationship with humans. A good friend of mine emailed me a link to Michael Pollan’s lecture and panel commentary from “Cannabis, Forgetting and the Botany of Desire” as presented at UC Berkeley. What follows is a synopsis and sparse analysis of his talk.
It is easy enough to guess why humans (and other animals) ingest plants that affect our consciousnesses. Andrew Weil described humans’ desire to change their consciousness as the fourth human drive after water, food and sex.  For many centuries and through almost all cultures, different plants have been consistently chosen to aid in the process of consciousness altering. In addition to their mind-altering effects, we’ve also learned that many “drugs plants” act as energy stimulants, pain relievers, and antidepressants for existential pain and boredom.
Pollan poses an important question: “What’s the use of these drug plants in evolutionary terms?” Drawing from Steven Pinker, a brain scientist, he proposes that our large brains may have combined two important adaptive traits: 1) the release of chemicals (e.g., endorphins) when we have done something “heroic or useful” and 2) the ability to solve complex problems. In this manner, our brains have problem solved how to easily obtain the satisfaction of conscious-altering chemicals by ingesting everything from the gentle (for some of us) stimulant of caffeine  to the potent spiritual sublimation of, say, DMT.
Pollan places his attention on Cannabis. “Why did this plant make THC in the first place?” he asks. His answer is that the plant does not want you to get hight but evolved THC for some other, unknown, reason. Possibly, it evolved to deter insects, block UV radiation, or, he muses, to interrupt the memory of predators that consume it so that they can’t find their way back to the plant afterwards. (A long shot theory? Yup, and Pollan recognizes the lack of science behind his somewhat flippant theory.)
First domesticated around 15,000 years ago in China, Cannabis was one of the earliest plants domesticated. Initially used for its fiber as hemp, the medicinal and cognitive effects were also discovered early. The plant then began it’s two fold co-evolutionary path with humans, one strain used for its fiber, the other for medicine. Regardless of why THC was first developed by the Cannabis plant, genetically speaking, the plant took advantage of how this chemical affected the human brain. We changed the plant by selecting for better fibers and a more potent drug, but it changed us, both individually and culturally, by providing pain relief or an altered mind-state.
At this point in his talk, Pollan side-tracks to indulge in some more abstract musing on the interplay between weed and homo sapiens. “Besides being mental tools, plant drugs work on us at this higher level, at a cultural level.” With several pop-culture references and a nod to David Lenson’s On Drugs, Pollan suggests that THC is to be thanked for the mid-20th century explosion of improvisational music in the US. He flirts with the idea that much of modern art and music would not have been produced were it not for the “naturalistic imagination” provided by THC. Pollan claims, however, that the true marvel of THC has come in “studying, not smoking it.” He cites Raphael Mechoulam‘s discovery of anandamide (an endogenous cannabinoid named from Sanskrit for “inner bliss”)  and Allyn Howlett’s discovery of the cannabinoid receptors on the brain and elsewhere.  He briefly touches on the now commonly known phenomenon of chocolate extending the effects of anandamide.
This leads one to wonder why we even have a system of cannabinoid receptors. Pollan asks the experts mentioned above. Howlett says that these brain drugs are ideal for medicating the human condition of childbirth and physical toil. Mechoulam posits that the chemicals are involved in producing emotional experience. We now know that cannabinoids such as anandamide work similar to THC affecting short-term memory, pain, emotion and appetite, but the ones that our bodies produce are short-acting neurotransmiters.  They provide us quick drips of relief often in the form of forgetting. Pollan’s lecture, although meandering, finally focuses on this potent ability of THC and similar naturally-occurring chemicals in our brain to strip our consciousness to its most immediate and present surroundings, forgetting not just past memories and future anxieties but distant affairs and overwhelmingly close stimulus.
Why would our brains evolve a drug that promotes short-term memory loss? Isn’t that maladaptive? Not necessarily. Forgetting can be as important a mental operation as remembering when your mind has too much information to process or can not cope with a traumatic experience. He suggests that the difficulty we have with remembering the experience of pain may be due to these drugs.
In trying to answer this questions, Pollan admits that the literature is scarce on forgetting while brimming with memory. Two texts that he does reference are publications by psychologist. The Mind of the Mnemonist, written by A.R. Luria, a Russian psychologist, explores the life and subsequent trauma of a man who could remember via visualization an indefinite string of words or symbols. With time, his lack of forgetting became debilitating as he could not forget what was not important in order to follow a story or argument, nor could he lose images in his head be them disturbing or pleasing. This implies to Pollan that abstracting or distilling information depends upon forgetting.
Friedrich Nietzsche also wrote on forgetting. Pollan quotes Nietzsche that those who can act are those who “forget most things, so as to do one thing.” In order for us to focus our mental faculties we must ignore and, in this neuro-chemical sense, forget the vast majority of what surrounds us. I would be remiss not to quote this pivotal part of Pollan’s lecture:
I mean, forgetting is not just about the past, it’s an important thing to remember. To be here now depends on forgetting a great deal of sensory information in the near present, and even forgetting the future, too— worries, anticipations, intentions, all these things can be forgotten also. So what I’m suggesting is that anandamide is crucial to this operation, to editing out all of the near-term memories, so that you can attend to what is before you.
Andrew Weil in The Natural Mind also discussed this “disturbance of immediate memory” that “seems to be a common feature of all altered states of consciousness in which attention is focused on the present.” Examples abound in various schools of philosophy and religion where, Pollan states, “this experience of the present becomes our door onto eternity.”
Like always, after reading Pollan, I was struck by the cultural and historical breadth of his argument and, although some of his ideas are far fetched, I find myself wanting to believe them even if only to keep this omnivore optimistic.
 Pollan argues that animals often gave early humans clues as to what plants might act as short cuts to providing the much desired chemical release. Coffee was discovered by Abyssinian herders observing the feeding behavior of their goats.
 One of Mechoulam’s students discovered 2AG another endocannabinoid like anandamide. These chemicals act like short-acting THC.
 The uterus to name just one other organ.
 There is now research showing that THC can act as an anti-inflammatory and neuro-protectant in addition to its well known side effect of increasing one’s appetite.