Science Friday - The Unseen World Of Plant Intelligence

Episode Date: June 4, 2024

Are plants intelligent? Until recently, botanists were hesitant to ask that question, at least publicly. But that’s changing.In recent years researchers have learned more about how plants communicate with each other, respond to touch, store memories, and deceive animals for their own benefit: All bits of evidence that suggest plants possess a unique form of intelligence that humans have been overlooking.Guest host Arielle-Duhaime Ross talks with science journalist Zoë Schlanger about her new book, The Light Eaters: How The Unseen World Of Plant Intelligence Offers A New Understanding Of Life On Earth. Schlanger is currently a staff writer at the Atlantic covering climate change. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

Is it time to rethink what plants are capable of? I think we're all kind of culturally coming around to this idea that intelligence might exist in things that are brainless. It's Tuesday, June 4th, and you're listening to Science Friday. I'm sci-fi producer Shoshana Bucksbaum. Are plants intelligent? Maybe that's not a question you ever thought to ask. And until recently, even botanists were hesitant to ask the question, publicly that is. But that's changing.

In recent years, scientists have identified how plants communicate with each other, respond to touch, store memories, and deceive animals for their own benefit. All bits of evidence that suggests that plants possess a unique form of intelligence that we've so far been overlooking. Here's guest host Ariel Doom Ross with more. Joining me now is Zoe Schlanger, author of the new book The Light Eaters, how the unseen world of plant intelligence offers a new understanding of life on earth. She's also a climate reporter for the Atlantic based in Brooklyn, New York. Zoe, I loved your book. Welcome to Science Friday.

I'm so glad to hear that. So great to be here. Yeah, thanks for being here. So it's not often that I read a popular science book and I am genuinely having my mind blown throughout. How did this book happen? What compelled you to write this? Yeah, I was compelled to write this because of how mind-blowing these findings were to me as well. I'm a climate reporter and I've been covering climate change for something like seven years and I was starting to get really burnt out. I'm sure you could relate to this. Climate news is a drag. And I was feeling really numb to the material, just sort of disconnected from all of the real impacts of climate. And I was looking around for something else I could cover to kind of very. re-enliven myself. And I sort of switched my lens from climate journals to botany journals.

And to my immense surprise, botanists were fighting over whether or not plants could be considered intelligent or even conscious. And I realized right away, if scientists were talking about this in public, in journals, that there must be a whole world of evidence and findings that were forcing this to bubble up to the surface. And so I started calling botanists and they were also the most delightful people I've ever spoken to for work, as you might imagine. Yes. Plant people are great. As I was reading your book, I was consistently surprised by the cleverness of plants, for lack of a better word, when it comes to their ability to protect themselves against harm. What's your favorite example of a plant's devious behavior to get insects to leave them alone? Oh, yes. Okay. So,

I love thinking about tomato plants because they're everywhere. We all grow them in our gardens. What scientists didn't realize until like the late 90s was that tomato plants would sample the regurgitant and saliva from whatever caterpillars were eating them. So caterpillars are their predators in this situation. And from that information, they would synthesize chemical compounds in their bodies and then exude them through their pores that would summon the exact parasitic wasp that would want to come inject their eggs into the caterpillar bodies. And then these wasp eggs would hatch. And the larva eats the caterpillar from the inside out.

And then glues its little tick-tac-shaped cocoons to the outside of the caterpillar body. And, you know, that's how the plant tries to save itself. It's just an extremely metal approach to self-preservation. And also, like, playing the long game, right? Because this process doesn't exactly happen super quickly. It takes a while. Yeah, we see that a lot. There's this interesting dance between all kind of predators and prey in nature, including the one between insects and plants. Because if you think about it, in a lot of cases, the caterpillar stage of the insect is the one that's eating the plant. And they don't want to be destroyed. The plant doesn't want to be completely destroyed. But yet in the later phase of its life, the winged insect that might come after the caterpillar phase might be its pollinator. So everybody's sort of coming within this hair's width of death in a way or this funny struggle to ultimately all survive. The plant wants the caterpillar to make it to the butterfly stage, but it doesn't want to get completely eaten so much so that it can't benefit from that stage.

Exactly. And by the way, I just want to be clear. When I say that a plant wants something, I'm sure Zoe, you've had to do this the whole time that you've been talking about your book, We're using these words that aren't typically used for plants, and I understand if for some listeners this might be a stretch, but that's something that you address in your book. Totally. You can't see me, but I'm using big air quotes every time I'm using these words. And I think that's really important to emphasize because I'm not suggesting plants are kind of little humanoid or like little animal creatures just in a different form. They are this branch of life that's so entirely their own. And they're so alien to us in so many ways. I mean, they've diver. from us evolutionarily so long ago that all of their strategies are really, really so other, very fundamentally other from us. So it's useful to use these words that makes sense to our human brains like wanting or, you know, communicating or thwarting predators, things like that. But you

just have to hold in your mind at the same time that whatever's going on here looks a lot different than it would to you or I. Right. It might be worth diving into this a little bit more because I studied zoology for my undergrad and it was there that I really understood how important it is not to project our own human values, desires or compulsions onto other animals because you might miss something if you don't put yourself fully in their shoes, so to speak. And as I was reading your book, I found myself really loving how some of these researchers

were talking about plants. So I got to ask, what's the right way to talk about plants? And how should we think about using human terms for plants? I love this question. I love that you have this zoology background because it's so interesting. What's happening now is that there are a lot of principles and methodologies from animal behavior being applied to plants that actually seem to pan out when you really take the plant's point of view and adjust the methodology to make sense to something that evolved the way plants evolved. So it's complicated, right? On the one hand, these are not animals.

We have to hold that in mind. On the other, there are parallel processes going on. And so the bridge between those two things, I think, is mostly metaphor, at least when it's two, like, lay people talking to each other as opposed to two scientists. I do think we have to use these metaphors, which are kind of near at hand to our own understanding, to understand plants. But I like to think of it as, like, a plant decision, not a kind of normal decision, but a plant decision.

I like that. Prefix before the word. So your brain has a chance to be like, okay, wait, I'm going to hold back from completely anthropomorphizing. Love that. Okay, so let's get back to some plant facts for a little bit here.

I got to ask you, keeping everything that we just said in mind, do plants have personalities or are we able to say that yet? So this is an interesting one. It is a field that's just starting to poke through. There's only been a, one serious assessment paper on this. But there's a school of thought that plants could be seen

to have personalities because of the way they consistently respond or the way that some of them consistently respond in similar ways throughout their lifetime. Animal personality is measured on this shyness to boldness continuum. That's the most basic way we assess animal personality. Right. Risk averse versus risk taking, right? Precisely, exactly. So we know that plants, many plants emit volatile chemicals when they're being attacked that then can be absorbed into the bodies of neighboring plants. And those neighboring plants can act on that information. They can boost their immune systems, start producing defensive compounds before the pests even reach them. So this is what we're talking about mostly when we're talking about communication and plants.

Some plants will signal wildly at like the slightest disturbance. Right. So the risk averse ones. Exactly. And then there's this interesting kind of boy who cried wolf phenomenon where other plants in the area might not boost their immune systems in response to the calls from those individuals. But then other plants have a much bolder propensity, so to speak, in that they will only signal when the threat is really severe. And other plants appear to actually respond to those calls much more sensitively. Wow. Okay.

this again, this is just, the stuff in your book is just so interesting. You also write about the daughter vine. What does its behavior tell us about what plants are capable of? Oh, I love the daughter vine. And because this has been brought up before, it's daughter, D-O-D-E-R, not daughter as in your offspring. Right. Before I explain the very metal things this plant can do. So daughter vine is parasitic, and it comes out of the ground as a baby vine. It looks like a little orange, worm because it doesn't have any need for chlorophyll because it doesn't photosynthesize. It gets everything it needs from other plants' bodies. So this little daughter vine emerges and it has about a day to find a host to parasitize.

So it starts circling the air and you can see this on time lapse and presumably it's sampling chemical compounds nearby. And researchers have found that it can assess from afar which plant nearby would be optimal to climb on. So researchers have put it between a tomato and a wheat, and wheat is a grass. It's very hard to climb. And before even making contact, the daughter will swerve and go towards the tomato. And when researchers tried to figure out how it was doing this, they found it was actually because of the quality of the light passing through the bodies of other plants, that it was able to sense the forms of plants near it. Then researchers have also found that it can sense the

nutritional quality of the plant it's climbing. When researchers grew it between plants that had been grown in like a nutrient scarce environment or with nutrient supplements, it would almost always decide to climb onto and hook its fangs into the plant that was grown with nutrient supplements. So then it grows these little vampiric spikes all along its edge. It's very vampire plant. And the amount of coils it makes represents how much energy it thinks, quote unquote, it will need to parasitize it. And then it keeps these plants like hobbling along. It doesn't want to

kill its host. It's a good parasite. It just sucks out enough sugar that it makes it very hard for these plants to grow fruit. So Daughter's actually this like extremely nasty agricultural pest in like 55 countries. Wow. Okay. I want to go back to something you said though. You mentioned the plant sensing light, which, you know, instantly my mind went to to, to suck. right? Does this mean that some plants can quote unquote see? You are touching on this very hot issue in botany at this very moment. There's a vine I went to go see in Chile in the southern cold rainforests of Chile called Bochila trifoliolata. And it is a super common vine in this forest, but just like 10 years ago, a researcher realized that this vine was transforming its body to look pretty much exactly like.

whatever is growing beside, which is unheard of for plants. I mean, we have some plants that mimic other plants, but it's like a one-to-one relationship. O'Kila can mimic apparently spontaneously. Whatever is growing beside, it will attempt to transform its leaf color, leaf shape, texture, even the vein pattern of these leaves will change to match what it's growing next to. And I saw that when I went down there. It was absolutely unbelievable to. watch a plant that's transforming in real time. That's incredible. I know, right? This has provoked

some speculation from one camp of botanists that this is evidence plants can see. They're kind of like plants have so many photoreceptors on their bodies. They have more types of photoreceptors than we have in our eyes. And we already know they're very sensitive to light. They're constantly sensing, you know, whether they're being shaded by a cloud or by another plant. They can in some cases tell whether that plant is their genetic kin or not and behave accordingly. So there's the plant vision hypothesis, but there's also a huge camp of botanists who are going, uh-uh, that's too far. Plants can't see. There's no brain. There's nowhere to translate that information. Right. So one of my favorite scenes in the book is this trip that you make to a lab where you describe really vividly

being asked to pinch a plant really hard. You write about this beautifully. It's actually quite funny because I believe the first time you don't pinch quite hard enough. And you have to be like sort of egged on to finally do it the right way. But I would love it if you could explain, you know, what you were doing. Why were you asked to pinch a plant? And what did that help you and the scientists in the lab see that day? This was at the lab of Simon Gilroy, who is at the University of Wisconsin-Madison. and he studies plant responses to touch. And in his lab, he has all these plants that have been grown to have these green fluorescent proteins from jellyfish imbued throughout them.

So in every cell, there's this green fluorescent protein expressing itself. And that protein is bound to calcium, which is thought of as a potential proxy for electricity. So when the plant is glowing, that means there's electricity moving through the cell, which means maybe there's an action potential. There might be electricity happening here. So I was, as you said, I was like in this dark microscope room, and I was given this pair of tweezers, and they were like, okay, pinch. And I, having just spent the last several years studying plant receptivity

and how sense of there and everything felt a little reluctant to pinch very hard, as silly as that sounds. And so I pinched it the first time, and the plant lit up a little bit. But then they were like, you have to really go. at it. So I pinch quite hard, and I pinched across the midrib of the leaf, this like the main vein that you can imagine all the leaf. All of a sudden, there was this green glow emanating from the place I had pinched this leaf that I then watched over the next two minutes travel down the vein system and spread through the veins to the entire rest of this plant. And this was a tiny little

Arabopsis plant, which is kind of the lab rat plant of the botany world. And I was literally watching it become, you know, aware of my touch, so to speak. This is entirely new information to botany, this idea that there may be an electrical signal moving through the plant body from the place it's touched. And that could be one way it's understanding its world, that it has this ability to respond very quickly to being wounded. Yeah, I mean, I feel like there are two immediate questions that come to mind for me. The first one being, is this a pain signal? And the second one, which comes right out of that, which is, does this mean that, you know, if the plant has an ability to transmit this information via something like a pain signal, does that mean that plants have

a nervous system? So your first question about pain, I would say definitively, no, not at the moment. We have no reason to believe plants are experiencing pain. They don't have a brain. which is one of these things that we think of as quite necessary for any experience of pain. Okay, got it. But there's something very nervous system-like about how all this all works. And those aren't my words. Those are the words of other researchers that have, like, looked at what Gilroy is doing and gone, huh, does this mean plants should be considered to have a type of nervous system, in a sense?

And it sparked this conversation around whether or not nervous systems could be considered the product of co-vergent evolution where like a system arises across different types of forms of life separately multiple times like flight evolved separately and bats and bees and birds right and to very similar effect could this be another case of that and what's also very interesting is that we are now understanding plants use neurotransmitters including glutamate so that the tweezers that I was pinching this plant with were dipped in glutamate, which is an important neurotransmitter in our own bodies and appears to also be important to signaling in plant bodies. We have to take a quick break. And when we come back, I'll continue

my conversation with science journalist Zoe Schlanger about her book, The Light Eaters. We'll tackle the big questions. Are plants conscious or are they intelligent? Stay with us. This is Science Friday from WNYC Studios. Okay, so we've talked about chemical seeing. We've talked about photoreceptor maybe seeing of some sort. We've talked about summoning animals to kill a predator in some ways. We've talked about a nervous system. All of these findings, does that point to plant consciousness?

This is the big, sticky question. I think one has to back up and remember that we still. know the mechanical basis for consciousness even in ourselves. That's still, you know, what is consciousness is an open question for humans? And we also are just starting to ascribe consciousness to other beings. I'm sure you saw this news a couple weeks ago where consciousness has now been conferred to fish and insects and crustaceans. So we are constantly widening this circle of what we think contains consciousness. And there's also a school of thought that suggests there's consciousness all the way down.

You know, there's some prominent consciousness researchers who suggest that even something as basic as a cell contains some modicum of consciousness to function. I think about consciousness as a sort of awareness of self and then intelligence, which is maybe even higher than consciousness in some ways, is the ability to make good decisions based on information that you acquire from your environment and then kind of sift through that and assess it and then produce a response that is matching that information. Which is a little bit what you've described in some of these findings, right? Exactly. This is my very long and smushy way of saying, we do not know, but it really depends

on how we choose to think about intelligence and consciousness. We may never come to a moment where we're like, this is definitively what consciousness is and plants have it. But I think there's a lot of evidence to suggest these are good questions to ask. I do have to ask. We've mentioned multiple times that plants don't have brains. I guess the next logical question is, you know, can a plant be intelligent without a brain? I think we're all kind of culturally coming around to this idea that intelligence might exist in things that are brainless. I know that probably a lot of listeners, have thought about fungi and the new findings about these mats of mycelium under the ground that are able to communicate across their entire body, but are very disparate and have no centralized

kind of command center. And I'm thinking we're starting to get more comfortable imagining intelligence as a network phenomenon, that there's forms of intelligence that are sort of system wide rather than centralized. And I like to think about the fact that we evolved with brains for very good reason. I mean, we have to run around, we have to flee from threats, we have to go find our food. So it made sense we have this very portable command center, but plants evolved rooted in place. So there's something to be said for the fact that evolution wouldn't have produced a compact command center. Plants are modular. They can lose a limb at any time and be pretty much fine. They also have to sense their environment from this one spot. So they have to be able to sort of spread out both above and below

ground and then have a way to kind of coordinate their findings, so to speak, about what's going on around them. Would that necessarily require a brain? It's not clear. That's an excellent question. To me, what this points to is the fact that your book is sort of a snapshot in time of a field that is changing. And we're going to find out more over the years, which is really exciting. At the same time, I can't help but think back to a previous book. That also had a huge impact on the world of plants. And your book, The Lighteaters, is basically in dialogue with it sort of throughout, right? I'm talking about a book that was largely incorrect, published in 1973,

called The Secret Life of Plants. Tell me about that book and its relationship to yours. Absolutely. So I was sort of haunted by this book the entire time reporting out this. the light eaters because botanists were telling me that when that book came out, it was such a phenomenal popular success that it was incredibly embarrassing for the field when it turned out that about half that book or maybe more was just pseudoscience. I mean, there was stuff in there about plants reading people's minds. There's this whole scene with a CIA agent who hooked up a

polygraph test to his houseplants and then thought about setting them on fire and said that the Test went wild, which was suggesting they were reading his malevolent thoughts. And then also, if you ever hear people talk about how their plants enjoy Mozart more than rock and roll, that's all from this book. And the effect of all of that was that the very conservative funding bodies of science kind of stopped funding studies that had any whiff of plant behavior or kind of veered into this what was then beginning to be seen as a kind of woo-woo new age concept. And it's taken 30, 40 years for that taboo to finally wear off. I think we're there now, and that combined with all of this incredible new technology we have for sensing gases and all the

chemical compounds plants make and, you know, the genomic revolution has all made it possible to ask these questions again with much more rigor. And I'm not talking about the mind reading questions, but plant behavior questions that are genuinely rigorous. So in some ways this book is an answer to that. We saw that kind of hit the field really hard in a negative way. And I'm hoping this will do the opposite. It certainly seems likely. I want to ask, though, from your perspective, in writing this book, The Light Eaters, how have you shifted your understanding of the role of plants in the world? How has this affected your relationship with your houseplants? Oh, my houseplants. Oh, my goodness. Yes. I definitely walk through the world with a different

awareness that all the plants around me are engaging these very complex plant dramas all the time. Like, I know that they are potentially fighting underground or communicating underground or, you know, rearranging their leaves to either shade their neighbors or not shade their neighbors or, you know, summoning insects and, like, forming collaborations with insects. And that has totally re-enchanted my life. I mean, it's such a delight now to just look around and see a climbing vine on like a chain link fence and kind of internally commend it for its total resourcefulness now that I know so much more about vines and what it takes for them to like seek good structures and clamber over obstacles. So I love that about it. And it's also couched in this general awareness

now that plants are totally the primary beings out here. I mean, they're they're photosynthesizing. They're eating light. That's still the coolest thing they can do. And that means they have made, every single molecule of sugar through that process that we have ever consumed. And our whole bodies run on plant sugar. I mean, glucose. You can't do without it. You will shut down very quickly without glucose. And we get it from nowhere else.

I mean, any other form of sugar we eat was recycled from sugar plants first made. And holding that kind of the preeminence of plants in mind really kind of unsettles this very human notion that we are on some top of some. evolutionary heap. You know, it kind of settles, settles us back into the mess of biology rather than some thing on some perceived hierarchy. I love when new findings or a set of new findings have this humbling effect on me. And your book certainly did that for me and also introduced so much wonder into my life. So I really, really appreciate the book itself and also appreciate you taking the time to talk to us about it today. Thank you so much.

I'm so glad. I'm so glad it had that effect. It's great talking with you. Zoe Schlanger is the author of The Light Eaters, how the unseen world of plant intelligence offers a new understanding of life on Earth. She's also a climate change reporter for the Atlantic, based in Brooklyn, New York. If you want to read an excerpt of the book, go to ScienceFriiday.com slash light eaters. That's ScienceFriiday.com slash light eaters. That's all the time we have for today. Lots of folks help make the show happen, including Felissa Mayors.

Danielle Johnson. Beth Rami. Emma Gomez. Tomorrow, inside the movement of indigenous nations, working to take control of the data collected from their communities. I'm sci-fire producer Shishana Bucksbaum. Thanks for listening. Catch you next time.