Zoë Schlanger's new book The Light Eaters offers uncanny examples of plant intelligence.Heather Sten/Supplied
The idea that plants might be intelligent, and endowed with human abilities such as seeing, feeling, hearing and decision-making, has, until now, mostly been the stuff of science fiction or the purview of hippies who play guitar to their spider plants. But real, hard science is now proving that plants may do all these things, and even more. In her engrossing new book The Light Eaters, Zoë Schlanger, a science writer for The Atlantic who splits her time between Brooklyn and Montreal, offers uncanny examples of plant intelligence while exploring the possible ramifications of this for humans (and plants themselves). Schlanger recently spoke to The Globe via Zoom.
At the beginning of your book you pose a question: What is a plant? Why is that a question that needs asking?
We know what a plant is, in a way. But I pose that question more to highlight how biology is rewriting itself in terms of understanding how dynamic and sensing and alert to the world plants actually are. For most of recent scientific history, plants were considered fairly passive. But what they’re finding now is that they’re able to do things like make decisions, be considered to have actual behaviour. So their status as an organism is slipping into a new, active realm.
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Some of the scientists in this book were reluctant to talk about their research for fear of blowback. Why is the idea that plants might be intelligent so threatening?
Words like intelligence and consciousness are things we don’t have specific scientific definitions for – they have more to do with social ideas – so scientists don’t like to use them. They’re concerned with accuracy and having airtight arguments. Not answering ethical questions like “What is consciousness and who has it?”
One fairly small camp of botanists is pushing to expand our vision of the words intelligence and consciousness to include what plants are doing. The other camp says we don’t need to drape human notions of intelligence and consciousness onto them. They can just be their own thing. Intelligence is used to divide humans into groups, so why should we put that onto a plant?
I understand their hesitation, but I am at this point more on the side of expanding our notions to imagine plants as intelligent beings, because intelligence, at the core of it, is making good decisions for the future; making choices, choosing between options. Plants are absolutely doing that.
A popular book from the seventies, The Secret Life of Plants, has had, until now, a dampening effect on the study of plant intelligence. Tell me about that.
Some of it was legitimate scientific history, but probably more than half of it was pseudoscientific, let’s say, “citizen science.” There was a chapter in which a former CIA agent hooked a polygraph test up to his houseplant and then imagined setting the plant on fire. The polygraph went wild, implying that the plant was somehow reading his malevolent thoughts about it.
There were other things in there about how plants prefer classical music to rock. Such things really stuck to the public imagination. But almost none of these findings were able to be reproduced by scientists.
It was the first time a book had become so popular about botany, so this was hugely embarrassing for the field. Funding agencies shut their doors to things like plant behaviour, anything that sounded adjacent to what was at that point seen as a disgraced field. They didn’t want the same thing to happen again.
Fifty years later, the taboo is starting to erode. It has a similar arc to the psychedelic research movement. A lot of legitimate research was happening with psychedelic compounds in the sixties and seventies. It went underground for decades and is re-emerging now as well.
You talk in the book about the idea of giving plants legal rights, that this could revolutionize the legal and ethical system. How so?
Legal scholars are already contemplating whether non-human subjects could be considered legal persons. There’s plenty of precedent for this. Ships and corporations have legal personhood. There have been cases in other countries where a forest gets to represent itself in court, or a river or dolphin. So the law is creeping in this direction. In the U.S., the White Earth Band of Ojibwe brought a case against Minnesota on behalf of wild rice, because a pipeline was going to go through the rice habitat and the White Earth Band had recognized the rights of the rice to thrive and evolve. The case was ultimately thrown out for lack of legal precedent.
It’s going to be a long road for something like this to change legal structures, but it is creeping up through casework and the culture.
Of the many astonishing plants and plant feats you cover in the book, the most amazing to me was this South American vine, the boquila, that can mimic the shape of other plants.
Yes! The normal form of this vine – which is ubiquitous in Chile – is utterly boring. It’s a little three-leaf kind of bean plant. But you’ll see it disappear into a bush and take on the leaf shape, colour, vein pattern, texture of whatever it’s growing beside. It was discovered in 2014, and since then, there’s really only one guy who’s doing work on it down there, Ernesto Gianoli.
I found the first instance of this plant perfectly mimicking a maidenhair fern. Maidenhair ferns have black stems, and it wasn’t able to change the colour of its stem, but it did everything else. It made these feathery little wispy leaves, whereas the typical form of this plant is nothing like that.
We’ve never seen a plant have this chameleonic quality. There’s a plant in this forest that was only introduced 10 years ago, and the boquila is already beginning to mimic it.
There’s a group of botanists who are pushing the idea that this means plants have some kind of vision, which brings up a lot of problematic questions because plants don’t have brains.
And then there’s Gianoli, who believes it suggests something even weirder, which is that perhaps a plant’s form is determined by micro-organisms like viruses or bacteria. Perhaps the boquila is more receptive to the micro-organismal clouds of plants beside it than other plants are. It’s a totally wild conception of life: the idea that all plants are actually composite organisms.
Both these arguments – plants seeing or being controlled by even smaller creatures – are mind-bending and speak to how much we still don’t know about the most basic thing that dominates the planet, which is plants.
I found myself tiptoeing a bit around my houseplants after reading your book. Has your research changed your personal relationship with plants?
I have a tough time pruning my plants because of what I know, even though pruning a plant is good for it in the long run.
I went to this lab in Wisconsin, where I was able to see the reaction or a plant sending a signal of me pinching it throughout its whole body, and it made me aware in this very tangible way of how sensitive plants are to touch. How if you touch them enough times they’ll treat it like an assault and activate their immune systems and perhaps produce defensive compounds, perhaps alert other plants to some kind of an attack. I do think about that now.