Instant Genius - Why your plants are more intelligent than you think

Episode Date: August 18, 2024

Right now, in labs and lecture halls all around the world, there’s a war raging. Not a physical war of fists and gunfire, but a war of ideas, and of research and of fact. The battle ground is this: Could it be that we animals are not alone in our ability to make decisions, to feel the world around us, to listen and communicate, maybe even be conscious. In short, could it be that plants are intelligent too? Today’s guest is Zoë Schlanger, a staff writer at The Atlantic covering the environment, and the author of The Light Eaters, a book exploring the fascinating science of plant intelligence and behaviour. She argues that plants are more than just a green blob in the ecosystem, but an active part of it; one with the agency to decide its own destiny, and, fundamentally, one which we humans should show respect and reverence towards. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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Music just as the artist intended. Visit name audio.com to learn more. Hello and welcome to Instant Genius, the bite-sized masterclass in podcast form. Each week, you'll hear from world-leading scientists and experts talking about the most fascinating ideas in science and technology today. I'm Tom Howarth, trends editor of BBC Science Focus. Right now, in labs and lecture halls all around the world,

there's a fierce debate raging among plant scientists. The battleground is this. Could it be that we animals are not alone in our ability to make decisions, to feel the world around us, to listen and communicate, and maybe even to be conscious? In short, could it be that plants are intelligent too? Today's guest is Zoe Schenger,

a staff writer at the Atlantic covering the environment, an author of The Lightheaters, a book exploring the fascinating science of plant intelligence and behavior. She argues that plants are more than just, just a green blob in the ecosystem, but an active part of it, one with the agency to decide its own destiny, and fundamentally, one which we humans should show respect and reverence towards. So, plants, it's fair to say they're a bit of an obsession of yours, maybe? Yeah, absolutely.

Could you start by telling me where this kind of love affair began, because you were a journalist and now you've produced this book, The Light Eaters, which is all about plant intelligence? Yeah, absolutely. I had been covering climate change in a newsroom for a number of years. And as you probably can relate to, covering climate change is a pretty depressing topic. And I was starting to feel very numb to the material. And I realized I really needed to find something out there to cover that would make me feel enlivened rather than sort of doled by tragedy. And I started looking at botany journals. I had always been interested in plants. I, you know, grew up in a family that had a general appreciation for plants. No one was a scientist or a florist or anything very truly adjacent. But, you know, I grew up in the woods. I grew up also mostly, you know, my other sibling is very much younger than me. So I feel like only children have a sort of special relationship to sitting outside and turning all of the outside world into like your friend in a way. But so flash forward to being a journalist and starting to look at

these botany journals and realizing that scientists were fighting out in the open in opinion papers in these journals about whether or not plants might be intelligent or conscious. And I knew as a science reporter that if scientists were saying these things out loud in the public arena, there was clearly a lot of science going on in the background that justified this debate even existing. And sure enough, there had been a number of fascinating papers, just finding incredible things about how plants can communicate and have memory and count and recognize kin. And very quickly, it started to look like the best story of my career. So I pivoted completely. One of the kind of debates, before we get onto the debate over intelligence that's

going on, you say in the book that no one quite knows what a plant really is. What exactly is it that stumping scientists in landing on a definition of this really ubiquitous form of life? I think it's the same thing that stumps sort of all of taxonomy, which is that it's actually very hard to parse where an organism begins and ends in a way. I mean, particularly when you think about plants, they are so infused by other forms of life, microbes. Fungi are entwined in all of their roots, and sometimes these third-party organisms are constituting aspects of their life that we would think of as very plant-like, much like how we are learning about our microbiomes and the ways that microorganisms impact and substantiate or contribute to our own selfhood,

but also because some of these findings around plant behavior are upending the classical view of plants as quite passive. Of course, most plant scientists would never think of a plant is passive, they know better, they've seen what plants can do. But we still have this cultural impression, I'd say, that plants are maybe closer to rocks than to animals, for example. And some of these findings are really shaking up all impressions, prior impressions of what plant life really is. So I'm going to ask you a question which might be quite hard next, but for the audience, it will be useful before we really delve into this. What is intelligence? What do you mean when you're trying to argue if plants are intelligent or not, what is it that we're arguing that they have?

So intelligence has no scientific definition. Neither does consciousness. These are slippery terms. They are mushy. They are much more the realm of philosophy and ethics than hard science in a way. So they're really hard to debate about and can kind of morph in whatever you want them to be. But I like to think about intelligence in sort of the most stripped down version, which the word comes from interlegerre, the Latin root is interlegeret, and that means to choose between. So the capacity to make decisions that are advantageous for your life is something I think of as intelligence, and especially when those decisions are spontaneous and plastic in the sense that they can change when circumstances change, that one is alert and alive to the

the fluctuating world that is impacting you and able to navigate it with some alacrity and some forethought and planning. And certainly plants do you do this. So you mentioned that there's a war going on over this plant intelligence debate. And one of the things that you talk about in the book kind of kicking all of this off was a book called The Secret Life of Plants that was published in 1973. And you said that it nearly killed the whole debate for good because it was quite outrageous. What was it that the book laid out that was so damaging for the genuine scientific investigation of plant intelligence? This book, I mean, maybe many of your listeners have even encountered it. It was phenomenally popular. It was published in 1973, so sort of at the

height of the New Age movement. And the public was really primed to read a book about plant intelligence and swallow whole, whatever it had to say. And unfortunately, probably about half of the contents of this book were effectively pseudoscience. They were forms of citizen science or kind of quite mystical approaches to science that couldn't be replicated later. So for example, one chapter involves a former CIA agent who was actually the one to give rise to the polygraph test. I believe he invented the polygraph test. And he decided to apply that test to his houseplants. And so he strapped a polygraph up to a house plant and then thought about setting the plant on fire and said that the polygraph went wild, which suggested that the

plant was reading his malevolent thoughts. And this is also a book that included the notion that plants enjoy classical music more than rock and roll. And that is also something I know. It was very sticky. People still feel this way. So for plant science, this was a big problem. None of these things could be replicated. And it was quite embarrassing. I mean, scientists are a conservative bunch. They don't talk about things until they're sure of them. And they stick to peer-reviewed science when talking about what their study subjects can do. And this wasn't that. So the funding systems in the US for funding science, the NSF, became very reluctant, according to researchers, I spoke to to issue grants to study. The financing basically dried up for plant behavior research.

The field didn't want to risk another embarrassment like this. So for about 30, 35, 40 years, the field went a bit underground. There was lots of amazing plant science being done, but very little of it was looking at these kind of spontaneous and plastic and perhaps intelligent behaviors of plants. and until the past 10 to 15 years when the taboo has mostly worn off and also technology has advanced enough to give us the capacity to verify things we couldn't verify before and make a rigorous science out of something that could have had a lot of holes poked in it before. You know, you mentioned technology is allowing us to finally test a lot of things. Was there a point where this field kind of switched back on, a catalyst point where it became more

fashionable and funding suddenly came back? I don't know if it was a catalyst point, but I think it was a sort of trickle that started to grow. I also think that the next generation, the younger generation of plant scientists, were open to some of these ideas, which is not to say certainly some of the researchers, many of the researchers in this book were actually figures in the earlier plant behavior movement who had stuck it out. So certainly very eminent and tenured professors are also involved in this work. But no, I think it was a slow wearing off the taboo, really. But, you know, things like the genomics revolution really, really elevated this science. My understanding is gas spectrometry has advanced enough now that we can decipher chemical signals that plants emit

to do things like communicate or defend themselves or Lauren pollinators. Our capacity to see how complex those are has advanced. So we can ask much more sophisticated questions of plants and get really rigorous answers now. So the book kind of takes us on this fascinating journey to all corners of the world, meeting lots of interesting characters, and takes us through a lot of experiments and examples of ways in which plants can be perceived as potentially intelligent. Could you give some examples, some of your favorite ones that really sort of capture this argument of the ways that plants behave that really people might think that plants couldn't behave like that? Absolutely. I love to think about the ways that plants can manipulate animals because this is a real inversion of how we normally think of the order of operations between organisms.

Plants are constantly using animals, mostly insects, to meet their needs. In some ways, it's a bit like I see lots of videos of crows using tools, for example, on the internet. And it's a bit like that. The plants are using these insects as their tools. So, for example, I love to think about how corn plants and tomato plants, when they're being eaten by caterpillars, have the capacity to sample the saliva and regurgitant that the caterpillars are leaving on their leaves. And from that, understand what species of wasp they need to come parasitize it. So presumably, they're sorting out what type of caterpillar is chewing on them, and then sorting out what predator they need to summon to come deal. with the caterpillars. And then they produce this chemical compound in their bodies. They synthesize

the correct compound and emit it through some pores called stomata. The pores kind of look like fish lips under a microscope. And this gas floats on the air and is picked up by parasitic wasps. And these parasitic wasps then know where to come to find the perfect host for their eggs. So the parasitic wasp arrives to the tomato plant, sees these caterpillars, uses this kind of syringe-like appendage to inject their eggs into the caterpillars. The caterpillars hatch and the larva eat the caterpillar from the inside out and then glue their cocoons to the outside of this caterpillar husk. And in this way, the plant is attempting to save itself. It's a sort of a slow motion saving. But I've heard from many gardeners that they've seen this.

They've come out to their garden and looked at their tomato plants, and there's these strange zombie forms bristling with kind of silky, tick-tac-shaped cocoons. And that is a brilliant form of plant defense that is in action there. It's a pretty gruesome example. But plants and wasps seemingly work very well together. I think there's another example. Perhaps you could explain about orchids and wasps.

Maybe if you could just explain that, that really surprised me. There's a whole category of orchids, many of them in Australia, that are known as sexually deceptive orchids. These orchids grow parts of their flowers to mimic female wasps. So one in particular grows this very slender sepull strand, this augmented pedal that has a bulb at the end of it that is sort of dark in color and is roughly the shape and size of a female wasp. And for most of time, it was believed that that was kind of how they were tricking male wasps into attempting to copulate with the flower and then gaining pollination through that process. But recently it was discovered that it's really not just this visual trick. The orchids are actually producing a nearly exact replica of the female wasp pheromone in their bodies. So really, this all comes back to these chemical compounds.

plants possess this capacity for chemical synthesis that constitutes an entirely other sense of which we have basically none ourselves. And these orchids make this compound again through their pores and along come male wasps. And the male wasps mate by picking up flightless female wasps and flying through the air, having sex in midair and then dropping them back off on another flower. So the wasp comes along and grasps the appendage on the pedal and bounces around wildly and eventually smacks into the middle of the orchid where the orchid is ready to sort of glue a packet of pollen to its back. And eventually, presumably the orchid realizes what's going on or doesn't and sort of disengages and goes around looking for another female wasp and is inevitably lured in by another sexually

deceptive orchid. and thus pollination is achieved. One of the themes, I mean, both of the examples already, is this sort of chemical language which is floating through the air all the time that we can't perceive. How do plants use that to communicate with each other? That's one of the kind of fundamental parts of this debate. Absolutely, yeah. Researchers since the 80s have realized that plants,

when they're under attack by pests, will produce these warning signals. these distress calls in a way that are able to be interpreted by nearby plants and sometimes far away plants. Again, we're dealing with a gas that can float through the air. And those plants will use it as information. They will use that gas to understand that there is some sort of predator situation in the area and that it's time to boost their defenses. Often this means amping up their immune system or doing things like making their leaves filled with tannins so they're less palatable or making them less nutritious so that they sort of start.

their enemy to death. So they can do a host of things with that information, but fundamentally it starts with this form of communication. Researchers are also finding that that communication can depend on things like kin structures that plants will sometimes communicate differently with their genetic kin than they would with stranger plants, even of the same species. There's also fabulous couple of papers looking at golden rod and sagebrush, and finding in both of them that, that they're able to have sort of regional dialects, these regional differences in these chemical languages, kind of variations on the more dominant generic chemical language of these plants.

So plants in an isolated geographic area, much like with us, will develop variations on that chemical language. So it's all really incredibly sophisticated and complex and exciting, and we're realizing that social dynamics among plants actually really impact the way they communicate. There's a sort of plant culture evolving out of these places. Ambition comes in all shapes and sizes. At First Citizens Bank, we roll with your goals because we're built for what you're building.

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Today, in partnership with French acoustic specialist focal, name audio creates systems that deliver exceptional sound and unforgettable listening experiences at home. Try it for yourself at a focal powered by name boutique. Visit focal powered by name.com for more information. So we've got plants communicating with animals, plants communicating with each other, even having different dialects, cultures, as you say.

one of the other ways that we can consider as part of their intelligence is how they feel. Could you maybe explain what scientists have found out about the ways that plants can feel the world around them? Absolutely. And just to be super clear, we're not talking about emotions, not how they feel happy or sad, but how they physically experience touch or wounding. They are capable of sensing being touched, which has changed my relationship, to the plants in my own home, again, touches information. So evolution has granted them the capacity to use it for information. And there is some research finding now that when a plant is wounded, the signal of that wounding can travel throughout the entire plant body and alert the entire plant very quickly, actually, to what it would consider as an assault. I was able to go to

a lab in Wisconsin where they're studying plant touch receptivity. And we went into this dark microscope room and I was handed a pair of tweezers. And below the microscope was a plant that had these fluorescent green proteins imbued in it, these proteins from jellyfish. And those proteins were bound to something that is something like a proxy for electricity moving through a cell. And so, of course, in us, our capacity to sense touch is a very much electrical phenomenon and appears maybe it might as well be for plants. And so with these tweezers, they told me to pinch a plant leaf very hard and sort of crushed the midrib of a leaf, you know, the vein running down the middle. And I did that and I could see this green eminent sort of moving out from the place

where I had crushed that little vein and traveling down the vein system. And within about two minutes, the entire plant's vein system was glowing green, which means likely the electrical signal of that touch had traveled through the entire plant. And then, of course, the plant can use that to start to begin to defend themselves. So it is changing our understanding of how plants sense the physical world. Of course, there's been actually papers about this since the 70s. There's a whole series of papers in the 70s where researchers would stroke the stems of plants repeatedly. And then measure how their growth changed, and it did invariably change. Often, the plants would become stiffer or more stocky or sort of stop upward growth and harden themselves, literally. And

this makes total sense. It's if you are being pestered by an impolite animal, you better make yourself more resistant to being trampled on or broken by a passing animal or harsh winds. So these things absolutely affect plants and they respond very quickly to them. I mean, this idea of electrical signals traveling all through the plant, you're very careful not to liken it to our own nervous systems and like we need to be clear that that's not the case because we have so evolutionarily different to plants. But there's parallels there, right? There is. And this is something that other scientists have suggested. It's not my invention. Thinking about what I saw in that lab in Wisconsin, there is this.

branching pattern of the vein system along which it does seem that electrical signals can be carried. And some researchers are suggesting perhaps we could consider that a form of a nervous system. There are no nerves in plants. We have not found any nerves. We found no pain receptors, nothing to suggest they're feeling pain. But we do see a system of conduction, of communication through electrical signals. And this brings up the idea of convergent evolution. which is very useful for thinking of how this could be considered something like a nervous system. And this is when very similar biological effects arise in different organisms through separate evolutionary channels. So plants, of course, diverged from animals a very long time ago,

but perhaps in a similar way that, let's say, wings are a product of convergent evolution. insects and bats and birds each developed wings completely separately, but to very similar effect. So perhaps a nervous system is a more general biological phenomena that arises again and again, and we should just acknowledge that this could be a form of nervous system. Of course, plant nervous system, I find it very useful to sort of add that to the beginning of when we use words like this that may conjure different things in our brains than they should, you know, maybe we just use that language and augment it slightly to recognize the otherness of plants, but yet also their parallels. Yeah, or I suppose almost like the way that an octopus is intelligent,

but its brain is sort of spread all around its body. So it's a different form of intelligence. Right, exactly. I'm more diffuse sort of network intelligence. Yeah. And do we know what they're using those signals for yet, or is that an area for future research? It is an area of ongoing research. We do know in certain species what those electrical signals are used for. In the Venus flytrap, for example, we know that those electrical signals are used for both counting and for triggering the trap to close and to trigger digestion. So a Venus flytrap, of course, is this carnivorous plant that can digest animals that fall into its mall.

But it has these little trigger hairs inside of its. augmented leaf, the thing that functions as a trap. And those trigger hairs need to be flicked a certain number of times to trigger first the trap to close and then another couple times to trigger digestion to begin so that the Venus fly trap doesn't risk expending all this energy on like a fallen bit of twig. They want something that's wriggling. So these hairs have to be flicked a certain number of times over a certain period of time. So there's counting actually going on in the Venus flytrap.

and those hairs are producing action potentials when they're flicked. So these are bursts of electricity, and researchers have found that they can simply zap the plant with electricity and produce the same effect. So we know there, it's a rare case where we know exactly what the electricity is being used for. It's quite remarkable, though, because, of course, plants have no brains. When there's electrical activity in our own bodies that triggers something to happen with us, Very often this is routed through the brain, not always, but it is remarkable to think about

where a plant is integrating all this information for lack of a brain without that centralized processing. It's taking these signals and counting somehow, but we don't know where that counting is exactly taking place yet. Exactly. One of the other behaviors, which I found really interesting, was this idea, because, you know, okay, so plants can pick up chemical signals in the air as a form of communication, but they can also actually hear things. I think there was an experiment where there was water and the root

was trying to grow to the water that it could hear. Do you maybe explain a little bit more what that was in this idea that plants can also hear? Yes, the field of phytoacoustics is very exciting and developing right now. Plants can hear, but we have to use sort of air quotes around that word here, because for plants, sound is pure vibration. It's a physical stimulus. And this makes sense, right? Vibration can move the plant body very, very subtly, you know, the sound of a caterpillar chewing on a leaf, for example, moves a leaf up and down something like one 10,000th of an inch. And they can use that also as information and respond to it. So you're talking about a paper that came out several years ago now that found that plant roots can grow even towards just the sound of running water.

So plant roots are capable of sensing moisture gradients, very, very, very, very, very subtly and finely, they can seek water through the soil just by being aware of subtle moisture changes. We knew that already. But if presented with water running through a sealed pipe or just the audio playing of water, roots are also able to head towards that, which probably explains why there's so much root intrusion in city infrastructure. It's a major problem. Tree roots just burst through water mains on a semi-regular basis, and this is likely how they're doing it. But other examples of sound, I mean, evening primrose, which is also a flower, I think a lot of people are familiar with, it's sort of pale yellow and shaped like a little bowl the flower. Researchers have found that when

it's played the audio of a bee buzzing, it will sweeten its nectar three times. So it's using that world of sound to its benefit in that case to increase the chance of pollination. So all of this is hugely interesting. I think there's a million and one more examples we could talk about all day, probably. But I want to talk about sort of what this revelation means for our relationship with plants. Most of us kind of see them as a green blob. You know, we eat them. They're pretty in our homes. What do you think that this ongoing research means for our relationship with plants? I think beginning to see plants as active and alert and sensing beings that have sort of their own motivations and lifestyles is a radical change from exactly what you described. And it brings them closer to us in a way.

But it also just introduces a space of awe. I mean, I found myself absolutely an awe of everything plants could do and everything I hadn't understood plants were at the outset of this research. But awe is a very powerful emotion. I think it leads away from exploitation, for example. One has a different orientation towards something one feels awe about. It introduces a big amount of respect, and it sort of brings plants into our moral conversations a bit more. Now, I'm not suggesting suddenly there should be a movement to not eat plants.

We all are animals who need to eat plants. Continue eating plants, please. But there's a lot of ways in which we really. guard plants as purely just sort of instruments for our own human activities and in ways that can be sort of destructive to the point that they don't need to be. So I'm thinking a lot about how we will like raise a mangrove for us to build a hotel or, you know, use a 300-year-old tree to build a deck when there's other options. I'm not sure of what the exact implications ought to be, but it should at least introduce this consideration of the fact that plants are as complex as any other biological organism and should be treated as such.

Yeah, it's almost like developing a respect for them that we perhaps haven't had for a long time. And new orientation, I think, also towards the fact that we are so completely dependent on their continuation. You know, every single molecule of sugar you've ever consumed was literally spun out of thin air by a plant through photosynthesis. And of course, the oxygen we breathe. I mean, we wouldn't be here. And one final thing is it's a debate about plant intelligence. What for you would settle the debate, or is your mind already kind of made up? You know, I think that the idea of plant intelligence will be less of a scientific decision that we just come to make. and more of a social one.

Science is producing these rigorous, exciting results, and whether or not that denotes plant intelligence is more of a kind of cultural choice than anything else because intelligence is not an inherently scientific concept. I think we can look to the history of animal behavior research as a kind of guide for how this may go, which is so interesting, right? We've only just begun understanding some animals

as having consciousness. The idea of animal intelligence is a very recent concept. In just the last 150 years, we went from assuming animals had no capacity to feel to the point where we were doing live dissections on them without anesthesia,

to now bestowing consciousness on things like mammals and birds and cephalopods. So really it's all a choice of what we decide to believe plants are are using the best available research and holding their difference in mind at the same time. I don't want to flatten plants or reduce them into sort of little humanoid forms in our minds that would do them a great disservice.

They are, in fact, utter aliens, again, diverged from our own branch of life so long ago. And yet they're no less examples of biological evolutionary creativity than we are. So I do, I think it'll ultimately be a cultural choice. And in many ways, it's important to remember that it doesn't matter whether or not we decide plants are intelligent. That doesn't change anything about them. They will go on being plants being stupendously creative on their own. In fact, I actually sometimes like to think about the word agency more than intelligence. Intelligence is loaded with a lot of human concepts.

I do think we can expand it to fit other species. I think that would be a wonderful project. But before that, you can just talk. about plant agency. An agency is sort of this ability to have a say in the future of one's life, that you have a personal stake in your own development and survival, which certainly plants have, that you are alert enough to the world to sort of make good choices for your future. So plants are agentive organisms, and maybe that's all they really need to be for us to begin to see them for what they are. So that was Zoe Schlanger, a staff writer at the Atlantic, an author of The Lighty

how the unseen world of planet intelligence offers a new understanding of life on earth. Give it a read to discover more about the topics we've covered today. Thanks for listening to this episode of Instant Genius, brought to you by the team behind BBC Science Focus magazine, which you can find on sale now in supermarkets and newsagents up and down the country. If you've enjoyed this episode, make sure to give it a subscribe via your preferred app, and why not write as a review? You can, of course, also find us at ScienceFocus.com. This podcast is sponsored by Name, Audio and Focal.

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