Plants furnish humans with all the calories we need either directly or indirectly. We also harvest chemicals from plants to harm others, inebriate us, or keep us awake. An excellent example is the poison ouabain from the Acokanthera shrub. African hunters have long added iit to arrow tips. The poison induces cardiac arrest in the unfortunate victim. We use chemicals extracted from chrysanthemums to kill insects and many of us knock back plenty of the extract from coffee berries (the ones in the picture kept behind barbed wire) and tea leaves to help keep us awake. The ephedra bush is the source of ephedrine, a potent stimulant. It’s sometimes called Mormon tea because Mormons aren’t allowed to drink caffeine, but could drink ephedra tea.
The natural world overflows with toxins whether in the liver of the pufferfish, the skin of certain newts or the leaves of the tobacco plant. It’s always made me wonder why “all natural” is such a positive claim. Lead is all natural, but I don’t want it in my breakfast.
Some of these toxins relieve pain and cause suffering at the same time. One of these is opium. Humans have cultivated poppies and harvested the latex from their seed pods since before recorded history. And that’s before the poppy-seed bagel was invented.
Opium is an unusually perfect drug. Our bodies use opioid compounds for signalling; we make opioids ourselves. Endorphins, the source of “runner’s high” was the first “endogenous morphine” to be discovered. Subsequently more have been identified and all look, at least chemically, very much like the various opioids extracted from poppies.
It’s not just us either. It turns out that one of the most primitive animals that has a dorsal nerve (not even a backbone) has opioid receptors: hagfish (Dreborg et al PNAS, 2008). Pretty name, yes? Don’t worry they’re much uglier and grosser than they sound. But they could get high off opium if you injected them. I’m not sure if they’d behave oddly because all they do is eat and secrete slime.
Why do plants make molecules that we use for signalling? One might think the plants use them for signaling, but they don’t. The opium is meant to discourage herbivores. Humans do a lot of stupid things (look at Texas’ voting record). If another animal ate a plant that made it fall asleep in the middle of a field, it probably wouldn’t be around long enough to make babies. Pretty effective deterrent. Humans, on the other hand, think: “hmm, let me have another try at that, maybe this time I’ll see something weird.”
A simple enough explanation, but it’s staggering to think about the evolutionary complexity. A plant has developed a toxin that perfectly mimics a molecule in animals. We love it so much people grow it on huge tracts of land and kill to protect it. That’s a pretty adaptive trait.