I have a piece in the NYT Mag on CBD, or cannabidiol, the molecule from cannabis (AKA marijuana, weed) that has recently become so trendy (CBD enema anyone?). I could see the piece being controversial for any number of reasons — or perhaps not, given the accelerating acceptance of cannabis — but for the moment, my mind keeps returning to a riff in the story that’s probably not controversial at all: the part where I discuss theories on why the cannabis plant produces the cannabinoids (THC, CBD as well as more than 100 others) that we so prize for their ability to tweak our own bodies and minds.
Obviously, no one really knows why cannabis produces cannabinoids. These are just theories. One theory is that they’re actually a kind of sunblock. The rationale: the molecules structurally resemble melanin, the coloring and natural sunblock in human skin, and could thus absorb UV radiation.
But it may also be that, as I point out in the piece, they’re part of the plant’s defense system against microbes and insects. Still-very-inconclusive studies suggest they have antifungal and antibacterial properties. They may also fend off insects — a possibility that was explored in an old but fascinating study (explained here) in which a scientist fed caterpillars cannabis bud, saw the caterpillars get sick, but also observed that the caterpillars nonetheless preferred the cannabis because, as they accumulated the apparently toxic cannabinoids in their own bodies, they became less palatable to predators. In other words, eat a little poison and maybe you’ll get a little sick. But at least whatever eats you will get really sick — and learn not to eat you.
Of course, not all phytochemicals that plants make really are biopesticides — i.e. meant to drive away would-be grazers. Some might actually be trying attract or otherwise favorably manipulate beneficial insects. Such is the case with the coffee bush which, some scientists argue, offers caffeine to pollinators so that they better remember the location of the bush. And not all noxious stimuli are noxious to everyone. That’s the lesson of the hot stuff in chili peppers — capsaicin — which apparently doesn’t register on the pain receptors of birds, only mammals. They eat chilis and spread the seeds far and wide, aiding reproduction. Mammals learn not to eat it. (Unless you’re a person in which case you learn to enjoy the pain.) It’s interesting to speculate how these scenarios might apply to cannabis.
And then there’s this: whatever the the original, evolved purpose of the cannabinoids in cannabis, once humans domesticated the plant, it really had entered a symbiosis in which we (people) took care of various aspects of growth and reproduction, eliminating competition and selecting for plants that produced more and more THC. At that point — which was thousands of years ago probably somewhere in Asia — the plant wasn’t producing cannabinoids just to fend off insects, but also to manipulate human chemistry. Michael Pollan makes a version of this argument in his book The Botany of Desire. And I think he’s right. After we entered this mutually beneficial symbiosis called “domestication,” the plant was arguably targeting the human endocannabinoid system, and got TLC in return.
Also, here’s an only marginally related tidbit. I’ve written before about the scientists who argue that we evolved for so long with intestinal parasites present that our bodies actually expect them to be there, and when they’re absent, our immune systems become unstable. Well, turns out that parasitic worms secrete endocannabinoids, probably to manipulate their host’s immune system. Parasite endocannabinoids are probably part of the mechanism by which parasites control the host immune system and tamp down on the inflammatory response, preventing your body from expelling them. Or as the headlines read when the news hit, “Worms get you high.”
Finally, as a resource, the CBD Project, run by the journalist Martin Lee, is a good clearinghouse of CBD-related science and goings-on.
