When I was a kid, my best friend’s mother had a habit of singing arias to her houseplants. I did not know this at the time, but she was likely under the influence of The Secret Life of Plants, a 1973 best seller that claimed, among many other things, that plants enjoy classical music more than rock and practice a form of telepathy. Thanks to these nonsense claims, mainstream botany mostly avoided the debate of whether plants can, in any way, be considered intelligent. But recently, some scientists have begun to devise experiments that break down elements of this big, broad question: Can plants be said to hear? Sense touch? Communicate? Make decisions? Recognize kin?
In this episode of Radio Atlantic, we talk to staff writer Zoë Schlanger, author of the upcoming The Light Eaters: How the Unseen World of Plant Intelligence Offers a New Understanding of Life on Earth. How could a thing without a brain be considered intelligent? Should we expand our definition of intelligence to include such an alien variety of it? And if we do, how will that change us? Schlanger has spoken with dozens of botanists, from the most renegade to the most cautious, and she reports back on the state of the revolution in thinking.
Listen to the conversation here:
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The following is a transcript of the episode:
Hanna Rosin: Okay, so, you have a glowing petunia?
Zoë Schlanger: It was very thrilling to me because I got the first full-size petunia ever. I beat the influencers. I got it like three weeks early, organized a little exclusive on the petunia.
And the scientist who crafted the technology that made this possible hand delivered it to our offices in New York.
And so I just met him on the sidewalk, and I rushed up to our office, to the darkest part of our office, with this plant, which is the podcast recording studio, and turned out all the lights and waited, and then slowly my eyes adjusted.
It does take a minute for your eyes to, you know—our eyes are like cameras. The aperture has to sort of open to take in that low level of light. But once it did, you know—stunning experience to suddenly see your first glowing plant outside of a lab.
[Music]
Rosin: This is staff writer Zoë Schlanger. And what she’s describing is a real plant, the first commercially available houseplant that glows in the dark.
Schlanger: It glows in this very subdued, sort of matte way. There’s no other way to describe it. It’s a bit like moonlight. It’s very contained. You really have the sense that it’s glowing from within.
Rosin: Which, technically, it is. Scientists, including the one who delivered that plant to Zoë, borrowed a cluster of five genes—some from a bioluminescent fungus—and these genes somehow reroute the plant’s metabolism through a process that emits light.
The company that developed the plants sold out of their first run of 50,000 petunias. Probably, many of those will show up on your favorite Instagram feeds any minute. But Zoë wasn’t doing it for the ’Gram. She’s interested because she believes that the glowing petunias offer the first chance at breaking through a deep human bias.
Schlanger: I’m really interested in the ways that we, culturally, don’t really perceive plants as having as much vitality, let’s say, as animals.
To suddenly have this product available, where if people are clued into the fact that they’re looking at the plant’s metabolism activating when they see that glow, it kind of brings them into this realm of livingness in our minds.
You’re really seeing the plant being alive. It’s very much its livingness.
[Music]
Rosin: I’m Hanna Rosin. This is Radio Atlantic. And I’m here today to tell you that your houseplant is not just alive but thinking—maybe. In her new book, The Light Eaters, Zoë Schlanger documents a revolution in the world of botany. Scientists—and these are respectable, academic scientists—are starting to ask themselves questions like: Can plants hear? Do they talk to each other? Are they intelligent?
Now, The Atlantic does not have a full-time plant reporter. Zoë’s actual beat for years has been climate change. But she was getting tired of the doom and gloom.
[Music]
Schlanger: As anyone who reads climate change news knows, it’s harrowing, and as a reporter, I was just sort of getting numb to this material.
Rosin: So Zoë went out looking for something that gave her the opposite of that feeling. And she found her thrill in—
Schlanger: Botany journals.
Rosin: Botany journals, which were, at this moment in history, so alive with a radical question.
Schlanger: Plant scientists were debating openly in journals about whether or not plants could be considered intelligent.
Rosin: Like, they were using the word intelligent?
Schlanger: Yes. There had been a few kind of rabble-rousing scientists who had formed an alliance to try and push this idea into the fore of their field. And because of that, there was a discussion of whether or not neurobiology could be altered as a field to apply to plants.
Rosin: Whoa. Okay. I have a loose sense that in the ’60s, there was a mushy idea that you could play music to your plants or that somehow you could communicate with your plants, and then there was some spirituality. But it wasn’t serious.
Schlanger: Totally. You are talking about an era in which a book called The Secret Life of Plants came out. That was more like ’73, but it was sort of bubbling up through the culture up until that point. And this book was full of that sort of a thing. It is one of the reasons people started talking to their plants, and it contained the claim that plants enjoy classical music more than rock and roll.
Rosin: Of course. Of course. Like babies. Like, everybody loves Beethoven.
Schlanger: Exactly. Makes them smarter. And it included a CIA agent who strapped a lie-detector test to his houseplant and then thought about burning it. And he says that his thoughts made the plant’s lie-detector test kind of go wild, suggesting it was reading his mind.
Rosin: Ooh. Okay.
Schlanger: This book was so popular. For the first time, botany had a pop-science book that captivated people—perfect for the new-age moment. But the problem was a lot of it was just not true.
Rosin: So it probably discredited the whole field of: Are plants intelligent?
Schlanger: It did. It made all of the institutions that fund this kind of science kind of clam up and get nervous and stop funding it.
Rosin: Uh-huh.
Schlanger: But, for sure, in the last 15 years, technology has come up so far that they are able to confirm things they had never previously been able to in the Secret Life of Plants era.
Rosin: And what are the kinds of things that are being debated?
Schlanger: The main debate is: Are plants behaving intentionally? Are plants behaving at all? Can they be said to behave when something doesn’t have a mind? You get into all these murky discussions of what intelligence really means.
If intelligence means responding in a way that has a good future outcome, then there’s probably a good argument for that.
But does intelligence mean a sort of more academic awareness of events and this more mushy quality of consciousness? Then you get into stranger territory.
And, science is a very conservative institution. Scientists don’t want to be using words that they can’t precisely define.
So this caused a lot of fights and is still causing fights. Nobody can quite decide how to refer to plants.
Rosin: So now, basically, plants are in this large, maybe post-Biblical-era debate about what else besides us could be said to be intelligent—like primates, dolphins, whales, pigs—that we’re used to. And maybe plants has now entered the legitimate realm of those discussions, rather than the far-out-there realm.
Schlanger: Yeah, plants have entered the consciousness chat, for sure.
Rosin: Oh my God, the consciousness chat.
[Music]
Schlanger: It’s very hard to make some of these plant-science findings tangible. The idea that, let’s say, a plant makes decisions or is communicating with airborne chemicals—you can’t see any of that.
Rosin: So what’s the first, say, surprising thing that your eyes were opened to once you started to look into it? Like, an ability or a skill or a thing that a plant could do that you didn’t know about before?
Schlanger: One of the biggest things was, I didn’t realize that plants could feel me touching them.
That was a big one. I, you know, pet my houseplants all the time.
Rosin: You do?
Schlanger: Yeah, you know, fresh leaves that have just come out—they’re really soft. It’s lovely. But now I think about that twice because I realize that there are sensors.
No one’s quite sure of the mechanics of this, but the plant has an ability to sense that touch and treat it like an assault. It might amp up its immune system to respond to that. It might change its growth pattern.
Rosin: Uh-huh.
Schlanger: From what we now know, many plants will ramp up their defenses when they’re touched too many times. That ultimately might mean a tougher exterior, a more flexible stem, or just an invisible cascade of chemicals to prevent infection.
[Music]
Rosin: So plants can sense touch, which isn’t intelligence in the same way that, say, writing a great book about plants is intelligence, but it is an element of intelligence—something like using one of your senses to make a decision. So let’s try another sense-related intelligence question: Do plants hear?
[Music]
Rosin: All right. So let’s get into one of the experiments. We’re going to listen to a sound here. I’m sorry, podcast people. This is a sound that people listening to shows hate, but here we go.
[Caterpillar audio]
Rosin: I actually think it’s kind of beautiful.
Schlanger: Mm-hmm.
Rosin: All right. What is that? What are we listening to?
Schlanger: You are listening to the delicious noises of a cabbage white caterpillar chewing on a leaf. This recording was taken by these two researchers named Rex Cocroft and Heidi Appel, and they study the world of phytoacoustics, or the way that plants respond to sound.
Rosin: Now, mind you, this isn’t an actual caterpillar chewing on an actual leaf. It’s a recording being played back to the plant.
Schlanger: So they recorded these caterpillars chewing and clipped little guitar pickups to the same plants. And these pickups vibrate the leaf at the same frequency, amplitude that the caterpillar’s mouth chewing the leaf would. And what they wanted to know was, would a plant respond to just the noise of their predator eating them, even if they weren’t really being eaten?
Rosin: Right. So not the smell or not the sensation of the caterpillar there, but just purely the sound.
Schlanger: Exactly. Because we already know other plants will detect the saliva of a caterpillar and respond. But they just really want to know, what is the role of sound in a plant’s life?
To their shock, honestly, the plants reacted by priming their chemical-defense systems. So when the researchers brought in real caterpillars, they were ready for them. They produced all these pesticides. They made their leaves unappetizing.
Rosin: Okay. I want to elaborate on how wild that is, because what do you mean the plant is listening to an acoustic recreation, amplification of a caterpillar? Like, how?
Schlanger: It’s astonishing to me too. The “how” of this is that sound is vibration.
Rosin: Ah.
Schlanger: So vibration is a physical stimulus. It’s a physical thing that the plant is encountering, which is kind of like how the hairs in our ears work. You know, they get hit by sound waves, and the hairs in our ears vibrate. And then that sends a message to our brain, and we perceive that as a sound.
Rosin: I can see the philosophical problem now. Because as you first started talking, the plant is vibrating—I’m thinking, Okay, it’s just reflex. Like, once you say that, it seems like no big deal. But then once you explain how we hear, then it doesn’t seem vastly different, except I guess you don’t have the brain to transmit the signal through. So that is different.
Schlanger: And that’s the boiling-hot core of the entire plant-science debate: How does the plant respond when there’s no centralized place for all these signals to go? How do you do this without a brain?
Rosin: I see. That then leads to the question of: Can you have intelligence, consciousness, decision-making without a brain?
Schlanger: Exactly. That gets into questions like: Is network intelligence possible? Do you need the signals to go to a centralized place, or can we accept a sort of more diffuse, whole-body awareness in the way that we think about a computer network?
Rosin: Okay. After the break, now that we’ve gotten to the core of it, I make Zoë go through a lightning round of questions.
Rosin: Do plants communicate with each other?
Do plants recognize their relatives?
This one is crazy: Do plants have personalities?
Rosin: And then we figure out: What are we supposed to do with all this expanding knowledge about plants? Never walk in a grassy field again? That’s coming up.
[Music]
Rosin: Okay, this is a lightning round of questions, but I want you to answer at the speed of plants—not necessarily quickly, because they’re big and interesting questions.
Do plants communicate with each other?
Schlanger: Plants do have ways of communicating with each other. They’re able to synthesize all these incredibly specific chemicals in their bodies to match different conditions. And then they project them out via their pores. And then other plants take them up via these little pores. They have these pores on the backs of their leaves that look like little fish lips. It’s very funny under a microscope. And that contains some information.
So if a plant is being eaten by caterpillars, it will synthesize a chemical that then alerts other plants to sort of up their defenses before the caterpillar or pest or whatever even reaches them.
And there’s some really interesting research coming out now around regional “dialects” in plants, which blows my mind. These researchers have found that fields of isolated plants can have what they’re calling regional dialects that are specific to that single field that’s a more specific version of the general, more universal language of that species.
Rosin: And when you say “dialects,” you mean they’re communicating with slight variations of a chemical, right? It’s not like, you know, they have different French accents or something.
Schlanger: Right. It’s a regional variation of how they use chemicals to send signals, although the term dialect is actually how the researchers themselves describe it.
Rosin: Okay, another wild question: Do plants recognize their relatives?
Schlanger: So kin recognition in plants is a fascinating field. It’s a very muddy field. We have parsed very little of this so far.
But we do know that sunflowers, for example—the traditional thinking with sunflowers is that you have to plant them quite far apart because otherwise they compete for resources so much that they try and shade each other out, so you end up with fewer sunflower seeds, which is not what sunflower farmers want. But certain research has found that when you place sunflowers with their genetic siblings, you can actually pack them so tightly because they will angle their stems to avoid shading each other.
Rosin: (Gasps.) You mean they don’t steal resources from their relatives? They, like, protect their own?
Schlanger: Exactly.
Rosin: That’s crazy.
Schlanger: And there’s clear evolutionary theory around this for higher animals, but we had not yet considered that for plants.
Rosin: So that’s, like, widely accepted?
Schlanger: Well, I wouldn’t say widely. (Laughs.) The caveats in this whole field are just unbelievable. But it’s also only been something that people have been considering for about 10 years, so it’s probably going to take another 20 before everyone’s like, Here’s how this works exactly.
Rosin: Okay, this one is crazy: Do plants have personalities?
Schlanger: So there’s some limited research emerging about variations in plant behavior and whether those variations do amount to a kind of personality.
We’re used to scientists studying what you might call personality in animals, where an individual animal is more quote-unquote “shy” or more quote-unquote “bold” than other members of their species. But one researcher has applied that framing to plants and found what he believes are similar variations there.
There’s some evidence to say that some plants are something like The Boy who Cried Wolf. They’ll kind of signal wildly at the slightest disturbance. And other plants are more reticent to do that. They’ll kind of wait for the disturbance to be really bad—for the pests to be really bothering them—before they let out their kind of distress call that alerts other plants to there being some kind of pest invasion.
Rosin: You know, the way you’re talking about plants—it really sounds like how we talk about people, like how people make decisions. Is it fair to call how some plants interact with the world decision-making?
Schlanger: So this is where I’d remind everyone that this is still a very new and very hotly debated area of science, especially when it comes to the language we use. And it’s easy to get into trouble when the language might make it sound like plants are people or plants have minds. They aren’t, and they don’t.
But what I will say is that after spending all this time with the research, there’s a lot of plant behavior that looks a lot like decision-making. Often these are very, very simple decisions, like, input: There’s water over there. Output: Let’s grow towards it. But it also shows how much we don’t know. For instance, we know some plants are capable of storing information and then acting based on that information later.
Or, you know, in some instances, plants can count and then choose to do an action based on a certain number of things. There’s a classic example that people call the memory of winter—that a plant needs to have a certain number of days of cold for it to then bloom in the spring.
Rosin: But why isn’t it just responding to sensations? Like, if we’re talking about the difference between reflex and intention, which is how I’m thinking about it, is it just a reflex? There’s heat, you know. It’s stored a certain amount of sunlight. I’m not sure what the reflex would be in response to, as opposed to the word you used, which was counting.
Schlanger: It comes down to a question of how far you need to distance what a plant is doing from what ourselves might be doing. There’s another example of counting plants in a Venus flytrap: They have all of these little hairs in their maw, in the leaves that snap closed, and it’s not enough for a little pebble to fall into that trap. It won’t close on a pebble. It needs multiple of those little hairs, those little trigger hairs touched. So it has to be a squirming animal that falls in there for the plant to bother closing. So it counts to at least five in that case.
[Watch ticking sound]
Schlanger: And then it counts time elapsed. If 30 seconds pass, and it doesn’t feel more movement, it’ll reset. But if the animal in there keeps moving, then they’re sure that they have a little fly or something, and digestion begins.
Rosin: Right.
Schlanger: And it tracks all this movement by counting how many hairs are triggered and over what amount of time. So that’s kind of math at another level that requires storage and addition in some ways.
Rosin: Okay, so I’m asking you this now straightforwardly: Are plants intelligent?
Schlanger: I, at this point, would say that they are, with the caveat that I came to this with a lot of skepticism of that perspective.
Rosin: Mm-hmm.
Schlanger: I’ve seen enough to feel like all of the hedging that people do around this is maybe a bit overblown. And the most important thing is that they’re not intelligent in the way we expect ourselves to be intelligent.
We’re dealing with an alien life form in a lot of ways. You wouldn’t expect aliens to have developed intelligence through the same routes as we did. But if we can expand our brains to sort of eliminate this human, academic version of intelligence, there’s no doubt they’re making choices for themselves.
And they’re doing that despite everything coming at them. They’re dealing with a very complicated, continually changing environment, and they’re spontaneously reacting to rise to the occasion.
Rosin: But, okay, so what does it matter? Like, we’re having a mini debate here about intelligence and maybe consciousness and decision-making and reflex. Like, it could be just semantics, so we’re arguing over definitions, but if we decide it’s reflexive, then what? And if we decide it’s a decision, then what?
Schlanger: If we decide this is all reflexive, then we all continue how the culture has always continued. That just regards plants as quasi-living, not particularly sentient, capable of interesting things, but ultimately closer to a rock an animal—closer to a rock than, like, a whale or something.
Rosin: Mm-hmm.
Schlanger: But if we decide that there’s some element of subjectivity in a plant, that starts to put them in a different category. I mean, it all is about how human culture responds to them.
So, we draw these kind of lines in the sand between animals and plants. And then within animals, we draw lines in the sand between intelligent animals and dumb animals. And, you know, it seems like every year we start admitting new animals into this category of creatures we consider intelligent or conscious—I mean, dogs and dolphins. And, you know, it’s been only a decade or so since we’ve accepted those things as conscious.
But in the last couple of years, we’re understanding that bees can, you know, have elaborate communication styles. They have this waggle dance that tells their hive mates where there’s good food sources, or they can actually detect different styles of art if they’re shown enough of the same pictures.
So how much farther down that ladder do you look in a way? What’s, like, past insects?
Rosin: Mm-hmm.
Schlanger: What happens if we include plants in those categories? That opens up a lot of moral considerations. And then you have the potential for something like what we’ve seen with animal-rights movements.
It brings up the question of what happens if we have a plant-rights movement, which is actually something that legal experts are writing and thinking about right now. It introduces this interesting idea: What do we do about the fact that we’re animals that need to eat plants? There’s just no way around that.
Rosin: This seems like it really upends a lot of things that we just do routinely without thinking about it. Like, I was going to ask you: Do you still stroke your plants? I imagine you think twice about it now. That’s a small question.
Then there’s the slightly bigger question of: When you put a plant in a pot in your house, is that the equivalent, or does that have some resonance with keeping an animal in a cage?
And then I guess there’s the much bigger questions of, you know, broadly thinking about protecting plants on Earth.
Schlanger: Yeah, it’s interesting you bring up the potted houseplant example. I have come to some amount of consternation around this because after I did a lot of research around plant communication and how plants interact with other organisms below ground, how their roots are hooked in with fungi and other microbes, and how there’s all this information being transferred below ground. And then I look over to my many houseplants sitting in their discrete pots.
But I am soothed a bit because I’m looking at all these plants in my Brooklyn apartment, and they are all tropical varieties that have been raised in nurseries for probably generations.
And when you raise a plant in optimal conditions for several generations, it loses its hardiness. These plants are not going to survive without us at this point, the ones in our houses.
Rosin: (Laughs.) This seems like a dubious argument. This is like, this is a pet chinchilla that you bought that was raised in a, you know, from a family in a series of pet stores, and so—
Schlanger: I mean, you know, it’s a bit like our dogs and cats. We’ve created these domesticated species, and now they need us. And that’s the situation.
So that makes me feel better.
Rosin: Okay, that’s good. I can bear it more with dogs and cats. Like, they do have a—well, dogs anyway—they do have a centuries-old mutual dependence.
[Music]
Rosin: Do you walk around now and see nature just vibrating? Like, how do you see the world differently than you did before you started this?
Schlanger: I do walk into the park by my house very differently. I do have this new awareness that there’s all of this drama going on around me.
Rosin: I feel like I’m going to have a hard time stepping on grass now.
Schlanger: Yeah, they know you’re doing that, and they hate it. (Laughs.)
Rosin: No, stop!
Schlanger: But, I mean, caveat to the being worried about harming plants thing: We layer all of our human feelings onto this situation and all this new awareness we have about plants. The truth is plants are modular. They’re designed to lose a limb and be fine.
You know, you cut grass; it grows right back. That’s not killing the organism. You can’t cut our arm off and it not have any consequences. But plants are designed to have this kind of diffuse, modular capacity to just grow a new arm.
Rosin: Mm-hmm.
Schlanger: But it does introduce this kind of sense of wonder, that plants are no longer a background decoration in my life. They’re no longer this kind of general wash of green. I’m really aware that there’s all these individuals. There’s all of these distinct species. There’s all of this biological creativity, all this kind of evolutionary nuance that is playing out all around me.
You know, it has the effect of unseating us a little bit from this assumption that we’re sitting sort of on the top of the evolutionary heap.
Rosin: Mm-hmm.
Schlanger: Once you start to realize the incredible evolutionary fine-tuning that goes into plants, it kind shifts the ground beneath humanity to settle us a little more among other species, and it’s a humbling realization that I think our species could use a lot more of.
[Music]
Rosin: This episode was produced by Kevin Townsend and edited by Claudine Ebeid. It was engineered by Rob Smierciak and fact-checked by Ena Alvarado. Claudine Ebeid is the executive producer of Atlantic audio, and Andrea Valdez is our managing editor. I’m Hanna Rosin. Thank you for listening.