Bili Buzz - Popular Science, Nature, Medicine, Archeology, Future & Myths

Scientists gain new understanding of how plants’ self-defending toxins could become humans’ substances of choice

Our most popular and addictive drugs come from plant toxins; caffeine, tobacco, cannabis, cocaine, heroin, are all derived from what are supposed to be poisons. These toxins were developed by plants to ward off herbivores who would otherwise eat them. So why is it that we not only tolerate them, but have found ourselves in a position of craving them, sometimes desperately? It is a paradox at which researchers are taking a fresh look.

Scientists have long assumed that the toxins in these plants, when introduced to the human brain, rewire its natural pathways and fool it into thinking it’s getting a fitness benefit when it is in fact being poisoned. That thinking, however, is based on an assumption that humans and toxic plants evolved in mutually exclusive environments wherein the human brain was never given the chance to adopt a protective response.

What is more likely, according to a new analysis, is that humans evolved detoxification enzymes around the same time that plants evolved to produce toxins. For example, human populations in and around Turkey have quite a lot of the enzyme which metabolizes opiates, in response to the poppy being native to the region. The developments likely co-evolved in response to each other. It seems, too, that the ability to produce the enzymes is an inherited genetic trait and is tied in humans to the plants in their region.

Carnivorous plants generally stick to a diet of bugs that they ensnare. On rare occasions, though, tropical pitcher plants—which drown and break down prey in vase-shaped traps that can be smaller than a little finger or larger than a football—have been found holding the skeletal remains of frogs, geckos and even small rodents. But what about human flesh?

Chowing down on a vertebrate is incredibly dangerous for the plant, says Barry Rice, conservation director for the International Carnivorous Plant Society and author of Growing Carnivorous Plants. It takes a long time to digest meat, so the meal could rot prematurely, killing the trap.

That’s not to say that a giant meat-eating plant wouldn’t have a taste for humans. While recovering from a case of athlete’s foot, Rice fed infected skin to Venus flytraps to see if they would eat it. A week later, he was astonished (and a bit appalled) to find barely a trace of his skin remaining in the traps. Healthy skin and internal organs would probably meet the same end, Rice predicts. “I’m still fond of my fingers, though,” he says, “so I’m not taking the experiment to the next level.”