Disclaimer: Keep out of reach of children. For use only by adults 21 years of age and older.
Outside of human civilization, nature operates on the principle that those best suited to their environment will be most likely to survive and reproduce. A huge part of survival is the ability to work together and protect one another from predators. Animals have evolved complex ways of communicating with one another that help ensure the safety and survival of the herd, even if notifying the herd of a predator means that an individual has to sacrifice itself in the process.
These communal warning cries are common across many different animal species. But what about other types of organisms? Are animals the only living things capable of this type of collaboration?
It turns out they’re not.
It’s commonly thought that animals are the only living things that can communicate or experience pain, which makes sense given that animals are the only creatures we know of with a complex nervous system. While plants may not have a true neural system in the same way that, say, a mammal does, biologists believe they’ve found other ways that plants can relay information. What’s striking is how similar those communication methods are to our own neural pathways.
Any time a plant comes under attack—for example, when a horde of hungry insects starts to feed on its leaves—it cannot physically move or fight off its attackers. Instead, it releases volatile organic compounds (VOCs), a blend of organic alcohols, aldehydes, esters, and ketones that effectively work as an emergency air raid siren for plants.
VOCs can have a number of effects. Some plants have the ability to communicate between leaves on the same stalk; when one leaf is cut off by humans or chewed on by insects, it sends distress signals to other leaves by pumping calcium throughout the plant. The whole process takes mere minutes, making it a highly effective warning system. Some plants are then able to produce higher concentrations of chemicals that would deter an herbivore, saving the rest of the plant despite losing the first leaves that have been cut or eaten.
Not only can plants communicate internally with other parts of the same plant, they can also communicate externally with other plants to warn them of an impending attack. It’s not quite pain or fear that plants are experiencing and communicating, but it’s clearly an awareness of danger.
When one plant releases VOCs, other plants in close proximity will begin to release their own VOCs as well. This has the potential to save the larger population of plants in a number of ways. Plants that are capable of producing insect-repelling chemicals rapidly begin to store those chemicals in greater concentrations. Other plants release chemicals that attract pollinators like wasps, which in turn feed on the insects that were attacking the initial plant.
It’s easy to anthropomorphize plant behavior to make it seem human, as though this were an act of higher intelligence. Scientists are quick to warn that it isn’t exactly akin to human experiences or mammalian biological mechanisms. Plants do not have a true nervous system, so they’re not capable of experiencing pain the way that humans experience and communicate it. However, plants clearly have the ability and the awareness to recognize when they’re in danger. They also have a hardwired evolutionary aversion to being cut down or eaten, and they use their signaling capabilities to save themselves as well as other plants.
These chemical signals aren’t just for species preservation either; researchers believe that a plant’s chemical communications can actually take place between entirely different plant species. In one study, sagebrush plants were “attacked,” and as a result, a group of tomato plants growing nearby began to store higher concentrations of chemicals that deter insects from eating them. Scientists involved in that study concluded that plant communication allows other plants to limit the ensuing damage that’s done to them by herbivorous insects, a sort of interspecies plant defense strategy.
One year after that study, another team of researchers found that caterpillars eating a plant elicited a different type of response: an electrical signal rather than a chemical one. That research team also found that glutamate, a key neurotransmitter in the central nervous system of humans and other animals, is also present in plants and plays a crucial role in plants’ response to stress and stimuli.
Many questions remain about how plants use neurotransmitters and communication pathways despite lacking a true nervous system. Plants may not be able to register a disturbance as pain the way that our brains do, but they are capable of sensing damage caused by insects as well as by humans. They also seem capable of recognizing that this damage poses a threat to each plant’s stability, or homeostasis, and they communicate that information to other plants, ostensibly for the good of the community (to put it in slightly more human terms).
The next time you visit a greenhouse or harvest vegetables, try not to think about the fact that the carrot in your hand was silently “screaming” to other plants… and try not to think about what your cannabis has gone through either.