In sci-fi movies, aliens are often modelled after insects or other invertebrate animals, which seems to be a reflection of a common view of how alien insects are. I would argue that although insects are very different from humans, plants, despite their prevalence, are quite a bit more alien.
As humans we often treat plants as little more than inanimate objects, ignoring or even missing the fact that they’re actually living beings in their own right. We assume that intelligence and depth of life are saved for those life forms with spines, with large brains, with hair and fast metabolisms. How can we possibly judge just by first impressions a life so incredibly different from our own as the life of a plant? Plant life is subtle, and their fascinating details are easy to miss.
People have the habit of using the term “co-evolution” when it comes to two other species and using words like “domestication” when it involves humans and another species. For instance, we feel we’ve domesticated crops like corn, but the history of how corn became a part of human life is not so clear cut. Hidden in the dark passages of prehistory, corn and humans have both benefited from their partnership. Corn has provided us nutrition, changed from human selection, and in turn, has received enormous help in reproduction. Corn in its own way has used humans to spread across the globe, to destroy competitors, to be watered and fertilized all by human hands.
Corn is just one example of a model that applies to virtually all plants humans cultivate. If another animal, like ants, are adapted to live in one plant that they protect vigorously, we think of it as an unthinking partnership. I see no reason to think an ant-plant relationship is unthinking evolution benefiting both parties while human plant interactions are thoughtful and benefit humans chiefly. Plants on their own have severe limitations for how far they can spread and use fruits, nectar and other enticements to get birds, butterflies, bats to pollinate. Plants also get hosts of frugivorous animals of all types and nut storing squirrels to spread their seeds. Humans are just one other herbivore utilized by plants providing delicious nutrition to receive reproduction and broader distribution of their offspring.
You may have heard about experiments showing plant reacting to the sound of classical music. Many green thumbed enthusiasts feel that talking to their plants encourages better growth and greater plant success. Less common is knowledge of experiments mirroring Pavlov’s experiments with dogs. Pavlov showed that dogs, like humans, can learn to associate a ringing bell with being fed. Recently, research has taken pea plants in a dark room and conducted a similar experiment. Pea plants were put in a room with a small light next to a small fan. Unsurprisingly the plants grew towards the light. What is surprising is that after the light has been removed, plants will grow towards the fan by itself, suggesting that the pea plants have associated the fan with light, which they need for life.
Of course everyone knows about Venus Fly Trap plants, those strange plants that I so desired as a child. I was fascinated at a plant with eerily gaping leaf mouths into which I could put a bit of ground beef to be eaten. The plant is one of a few carnivorous plants, mainly plants which have adapted to poor soils by consuming insects. Other examples are pitcher plants which lure creatures into their trap with smells of rotting meat. Once a hungry fly has made its way into the depths of the plant looking for dead flesh, they’re trapped and digested in a vat of digestion fluid. There are the more obscure sundew plants that curl prickly leaves around their prey.
Mimosa Pudica is a plant adapted to react to herbivory in a strange way. When an animal such as a deer bumps the plant, trying to get a bite, all the leaves immediately fold up. The plant gains the appearance of unappetizing sticks, instead of a lush, leafy snack. An experiment has been done to see if these odd plants can learn when there is actually no threat to stop reacting in this way. An experimenter dropped these plants over and over, in a safe, controlled environment and she discovered what seems to be learning. After several drops, the plants stop reacting to being dropped but will react to being touched in their normal way. After waiting almost a month between droppings, the plants ‘learn’ to stop reacting to drops even faster.
Recently, plants have been sedated, even though sedation seems to require a nervous system, which plants lack. In an experiment, plants were exposed to a range of anesthetics, including those used on humans during medical procedures. The anesthetics stopped the plants normal sun following behavior. It seems plants can be drugged unconscious. The real question is what does it mean for a plant to be conscious in the first place?
Carnivorous plants and moving mimosa plants seem odd things, exceptions to the rules we implicitly expect plants to follow but the closer we look the more we find odd abilities of our green neighbors. What is intelligence besides a thoughtful reaction to the surrounding environment? It’s easy to see that plants react and interact with their environment. What’s less obvious is whether there is anything that could be considered thought in a plant. We usually assume that something with no brain is not thinking in anyway whatsoever. It’s hard to explain especially complex interactions with an environment without thought though. What does it mean for a plant to interact with its environment in a sophisticated way without a brain? Perhaps it should make us reconsider our ideas of intelligence and thought.