A long piece by Amanda Gefter in Nautilus on the cognition of plants starts with her surprise at discovering that the rustling she was hearing in her room at night after bringing the plant home was coming from the plant:
Three jumpy nights passed before I realized what was happening: The plant was moving. During the day, its leaves would splay flat, sunbathing, but at night they’d clamber over one another to stand at attention, their stems steadily rising as the leaves turned vertical, like hands in prayer.
The piece is about the work of the Spanish researcher Paco Calvo, who studies plant behaviour at the splendidly named Minimal Intelligence Lab at the University of Murcia in Spain. He told her that she was suffering from ‘plant blindness’:
to be plant blind is to fail to see plants for what they really are: cognitive organisms endowed with memories, perceptions, and feelings, capable of learning from the past and anticipating the future, able to sense and experience the world.
No brains
Of course, to say this is immediately controversial. We know that plants don’t have brains, and human approaches to cognition are all about the brain. This is, to some extent, a legacy of Descartes. Calvo suggests that this is coming at the problem the wrong way round:
“When I open up a plant, where could intelligence reside?” Calvo says. “That’s framing the problem from the wrong perspective. Maybe that’s not how our intelligence works, either. Maybe it’s not in our heads. If the stuff that plants do deserves the label ‘cognitive,’ then so be it. Let’s rethink our whole theoretical framework.”
Calvo came into this line of work as a philosopher who started studying cognitive science at a time when the ‘computer’ model of the brain was gaining ascendancy. But that model was clearly wrong, as is widely agreed now:
Computers are good at logic, at carrying out long, precise calculations—not exactly humanity’s shining skill. Humans are good at something else: noticing patterns, intuiting, functioning in the face of ambiguity, error, and noise. While a computer’s reasoning is only as good as the data you feed it, a human can intuit a lot from just a few vague hints.
Neural networks
That took him into artificial neural networks, which are a bit better at deducing things from vaguer data, even if they are dependent on the language model they have been trained on.
Programmers train the neural networks, telling them when they’re right and when they’re wrong, whereas living systems figure things out for themselves, and with small amounts of data to boot. A computer has to see, say, a million pictures of cats before it can recognize one, and even then all it takes to trip up the algorithm is a shadow. Meanwhile, you show a 2-year-old human one cat, cast all the shadows you want, and the toddler will recognize that kitty.
So from artificial neural networks, Calvo moved on to trying to understanding how biological systems “perceive, think, imagine, and learn”. And that took him on to plants. (I liked the way that Gefter traced Calvo’s intellectual journey here, by the way.)
(Plants in captivity having a chat. Image: JHLA3350, via Wikimedia. CC BY-SA 3.0)
Seeing, responding, anticipating
It’s a long, long—and fascinating—article, and I’m not going to do much more here than nod at it.
So, first, plants can sense their surroundings:
Plants have photoreceptors that respond to different wavelengths of light, allowing them to differentiate not only brightness but color. Tiny grains of starch in organelles called amyloplasts shift around in response to gravity, so the plants know which way is up… Plants can sense humidity, nutrients, competition, predators, microorganisms, magnetic fields, salt, and temperature, and can track how all of those things are changing over time. They watch for meaningful trends—Is the soil depleting? Is the salt content rising?
And then, having sensed their surroundings, they respond to what they are sensing:
Their roots can avoid obstacles. They can distinguish self from non-self, stranger from kin. If a plant finds itself in a crowd, it will invest resources in vertical growth to remain in light; if nutrients are on the decline, it will opt for root expansion instead. Leaves munched on by insects send electrochemical signals to warn the rest of the foliage,2 and they’re quicker to react to threats if they’ve encountered them in the past. Plants chat among themselves and with other species.
They don’t just respond. They can also anticipate:
They can turn their leaves in the direction of the sun before it rises, and accurately trace its location in the sky even when they’re kept in the dark. They can predict, based on prior experience, when pollinators are most likely to show up and time their pollen production accordingly.
‘Consciousness’ controversies
Calvo also notes that while it is easy to dismiss these as reflexive behaviours, plants would not have been as successful as they have been, in evolutionary terms, if that is all they were doing. It’s fair to say that Calvo is out at the front here. His argument that plants are ‘conscious’ was critiqued by other biologists in a 2021 paper, as Gefter notes:
As Jon Mallatt, a biologist at the University of Washington, and colleagues put it in their 2021 critique of Calvo’s work, “ Debunking a Myth: Plant Consciousness,” to be conscious requires “experiencing a mental image or representation of the sensed world,” which brainless plants have no means of doing.
This takes us back to the start of the article. Maybe those definitions of ‘consciousness’ carry with them a whole set of assumptions that take us back to forms of human (or perhaps animal) exceptionalism. As Calvo suggests:
If the representational theory of the mind says that plants can’t perform intelligent, cognitive behaviors, and the evidence shows that plants do perform intelligent, cognitive behaviors, maybe it’s time to rethink the theory. “We have plants doing amazing things and they have no neurons,” he says. “So maybe we should question the very premise that neurons are needed for cognition at all.”
Beyond ‘machine’ models
If Calvo is out at the front, all the same, he’s not there on his own. Colleagues in the field also believe that the ‘machine metaphor’ of body and brain is getting in the way of understanding—even preventing us from seeing what’s in the data we see in front of us. Louise Barrett, for example, is a biologist at the University of Lethbridge in Canada:
“We need to get away from thinking of ourselves as machines,” Barrett says. “That metaphor is getting in the way of understanding living, wild cognition.”
Barrett and Calvo are among a group of biologists who suggest instead that ‘4E cognition’ is a better way to understand cognition—because there’s a group of relevant adjectives that in English all start with an E:
Embodied, embedded, extended, and enactive cognition—what they have in common (besides “E”s) is a rejection of cognition as a purely brainbound affair. Calvo is also inspired by a fifth “E”: ecological psychology, a kindred spirit to the canonical four. It’s a theory of how we perceive without using internal representations.
The world is its own model
The 4E group suggest that this is also a decent reflection of human cognition:
Humans don’t perceive the world by forming internal images either. Perception, for the E’s, is a form of sensorimotor coordination. We learn the sensory consequences of our movements, which in turn shapes how we move.
The article uses the example of how outfielders catch a ‘fly ball’ (I think this is about an American and Asian sport called baseball). They aren’t calculating the location of the ball, millisecond by millisecond, and sending messages to the legs. Instead, they just keep the ball steady in their field of vision, which will mean that “they and the ball will end up in the same spot.” This isn’t a new idea either. A 1991 paper by the robotocist Rodney Brooks said:
“Explicit representations and models of the world simply get in the way. It turns out to be better to use the world as its own model.”
Descartes was wrong?
And this is where this newer idea of consciousness diverges from the Descartes version. In his recent book, Calvo suggests,
Cognition is not something that plants—or indeed animals—can possibly have. It is rather something created by the interaction between an organism and its environment.
Clearly there’s something going on here, and my instinct is that this will become a dominant model of cognition, sooner or later. We’re just going through that Kuhnian phase where the advocates of the old model need to die off.
It also reminded me of that moment of insight I got when I first read about Maturana and Varela’s model of autopoesis, which goes back to the 1970s, and to which it has clear intellectual links. There’s also an evident connection to the movement towards ‘more than human’ thinking.
A review in the Guardian wasn’t quite convinced that Calvo made the case for plant cognition in his book. But the reviewer connected it to recent work by Peter Singer and Frans de Waal that challenged anthropocentric ideas about intelligence:
This is perhaps the most significant intellectual shift happening today, opening up the possibility that we can radically realign our relationship to the natural world. Instead of blithely thinking that we’re somehow superior to – and separate from – the animals and plants around us, we might start to appreciate that we’re deeply and irrevocably connected to these fragile ecosystems.
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A version of this article is also published on my Just Two Things Newsletter.
