I think plant consciousness is one of the most interesting subjects of scientific research out there. Of course there are other ways to investigate the matter but the National Science Foundation won’t give you a grant to go drink ayahuasca in the Amazon, more’s the pity. Here are some recent studies (the titles are links to the articles):
Researchers at the University of Missouri have found that Arabidopsis (rockcress) plants react to the sound vibrations made by caterpillars chewingadjacent leaves. When recorded munching sounds are played back, the plants react by producing more mustard oil, which deters predators. The plants can tell the difference between the munching vibrations and vibrations produced by wind or other insects. One researcher notes,
“This research also opens the window of plant behavior a little wider, showing that plants have many of the same responses that animals do, even though the responses look different.”
I wonder if the herbs we use for medicine–so many of which belong to the mint family–produce more of these oils in response to our plucking leaves? The aromatic oils that are medicinal for us are the same ones the plants use to ward off insects, but I don’t know if they have other compounds for warding off other kinds of herbivore predators.
In fact, another study using Arabidopsis also drew a parallel to animal consciousness:
“In both plants and animals, electrical signals function in an analogous manner. They transmit information from one location to another. If someone wounded your hand, an electrical signal travels through neurons from your skin, up your arm, to your brain, to let you know you have been wounded, and to draw your hand away. Similarly, when a herbivore wounds a plant, an electrical signal is generated which, instead of travelling to a centralised brain, travels through the phloem to other parts of the plant, informing them that wounding has occurred.”
What I thought was really ingenious about this study is that the researchers actually used live aphids as the electrodes measuring electrical conduction in the phloem, which they could do because the aphids actually insert their mouth parts into the phloem to suck the sap. As long as their aren’t too many aphids, it doesn’t seriously harm the plant. This way, the scientists didn’t have to wound the plants with measuring equipment which would have made it impossible to determine what the plant was responding to.
In this study, researchers found that plants have receptors for the same molecule–adenosine triphosphate, or ATP–that drives all life processes in animals. In plants, ATP seems to be involved in how the plant senses dangers or changes in the environment, and how it sends the signals that enable it to respond. It’s believed that when a plant is injured, it releases ATP into the wound, which then turns on the genes that make the proteins necessary for repair.
So far all the studies I’ve mentioned look at consciousness within a single plant, but plants also communicate with insects. Of course we know that plants use color and scent to attract pollinators. But they have other methods: When butterflies lay eggs on a plant (the plants studied were black mustard, which like Arabidopsis is in the brassica family), the plant “cries”–that is it makes chemical and structural changes to its body that both repel butterflies and attract wasps that eat the butterfly eggs and caterpillars. But this is only in response to the eggs of one butterfly species; other species’ eggs don’t produce such changes. So we see that plants are able to distinguish among different species of predator and to communicate symbiotically with insects which are predators of the plant’s predators. Unfortunately this study found that some predators are actually attracted by plants’ distress signals. That’s an example of the “Red Queen Effect” in evolution–a hypothesis that states we’re all evolving as fast as we can just to stay in place. That is, as our predators evolve better and better weapons, we must evolve better and better defenses.
Plants also communicate with one another. Tomatoes infested with cutworms release chemicals that signal neighboring plants to defend themselves. Specifically, the forwarned plants produce a pesticidal chemical called HexVic ((Z)-3-hexenyl-vicianoside). Interestingly, the chemical secreted by the infested plant is (Z)-3-hexenol, a precursor of HexVic. The researchers found that the chemical produced by the infested plant is actually used by the neighbor plant to make its pesticide, even though it has its own (Z)-3-hexenol. Is this a case of the plants not only warning, but actually physically assisting, each other? It seems that way.
This study found that plants are able to mainpulate their scent profiles in response to their environment. They can make themselves more attractive to pollinators–focussing on reproduction–or they can make themselves more attractive to the wasps that kill their predators.
If you are interested in this subject, I recommend the PBS Nature documentary “What Plants Talk About.”
I have always been a big animal lover, but even as a kid I had issues with some justifications of vegetarianism and veganism. Specifically I refer to the argument that consumption of animals or their secondary products causes them suffering and is therefore immoral, but plants can’t suffer so killing them is ok. I don’t dispute the truth of the statement that animals suffer in becoming our food, and I have long believed that our “civilization” should prioritize more humane and sustainable ways to acquire food. The part of the premise that didn’t sit well with me was I couldn’t figure out how we could ever know whether the plants suffer too.
There is ample evidence that plants do have some kind of consciousness and do experience forms of distress, and while some scientists maintain that this distress does not amount to pain or fear, I question where and how one draws that line. Part of what makes the findings on plant consciousness totally fascinating to me is the thought that we may finally be overcoming our bigotry toward the non-mammalian and non-animal worlds.
Of course this does further complicate the issue of what to eat. It seems that the moral dilemma surrounding food isn’t whether its acquisition/production causes death and suffering but, having acknowledged that (1) all animals* must kill to live, and (2) everything is trying to avoid getting killed and may** experience some measure of suffering upon realizing that its life is coming to a premature end, how does one then kill/eat ethically? Once upon a time, acquiring food could result in our death too, and that does still happen sometimes–although nowadays it’s E. coli or malaria*** that get us and not an angry mammoth.
I think about it a lot because I wonder how much suffering I cause a plant when I harvest some leaves to make a tincture, or take the entire plant in order to use the root. Plant consciousness and communication is still alien enough that I will probably never know.
Some people say that they ask the plant’s permission before taking any part of it. I think that’s a nice idea and probably good practice just in case intentions really count for something in the end or the plants can somehow read our minds. But I have rarely felt a plant say no. Is this because plants are just inherently generous and self-sacrificing, or because I can’t hear them? Some people seem to believe that whatever their heart tells them in these situations is right, but my heart, though well-intentioned, makes no claim to being an expert plant communicator. We have taught our children for about 10,000 years to believe that plants exist for our pleasure. And hearts try too hard to please. So I don’t think anyone’s heart produces very reliable information unless subjected to rigorous questioning. My point is, there is so much more for us to learn on this topic, and what we learn will probably blow our minds.
*So far as I know.
***Malaria doesn’t reach us through food of course, but the spread of irrigation, especially wet rice agriculture, and humans living together in dense groups have led to its spread. (And that of a lot of other diseases and parasites.)