Inside the Minds of Plants

Last June when Koko the gorilla was found dead in her sleep at the age of 46, the Gorilla Foundation in California, where she lived, released a statement saying that the western lowland gorilla would be “deeply missed.” For those who didn’t know who she was, they explained: “Koko touched the lives of millions as an ambassador for all gorillas and an icon for interspecies communication and empathy.”

Koko and her kitten. Credit: Creative Commons

It was a loving tribute, but it no doubt upset those who have long been troubled by the humanizing of Koko. Born on the fourth of July in 1971 at the San Francisco Zoo, the infant gorilla soon became the subject of a controversial language research project being conducted by psychologist Francine “Penny” Patterson. Over the years, Patterson taught Koko to use over 1,000 words of modified American Sign Language and the gorilla became famous for, among other things, her emotional expressiveness, love of cats and ability to enchant just about everyone, including celebrities like Robin Williams and Mr. Rogers.

But was Koko really capable of communicating in the way Patterson and others claimed she was? Some skeptical scientists have long said no, arguing that apes simply don’t possess the emotional and mental capacity to communicate on such a complex level. To them, Koko’s perceived abilities were nothing more than a textbook case of anthropomorphism. And if there is one thing scientists of that sort disdain, it is people going about attributing human traits to non-human lifeforms.

Holed up in places that clearly must not allow any pets for them to observe and interact with, these scientists are undaunted in their quests to prove human superiority despite decades of research demonstrating the intelligence and emotions of many living creatures—octopuses, chimps, dolphins, elephants and crows to name a few.

Fortunately, there are also scientists out there who get that humans are great and all, but other living things, including plants, can also do amazing things. Monica Gagliano is one of those scientists. An evolutionary ecologist at the University of Western Australia in Perth, she studies plants as few other do by exploring questions about their behavior, learning and memory. I heard about Gagliano’s work while listening to an episode of Radiolab’s podcast called Smarty Plants.

Sensitive plants close their leaves, like butterflies fold their wings together, when touched. Credit: iStock

Co-hosts Robert Krulwich and Jad Abumrad were jostling with the question: Do you really need a brain to sense the world around you? To remember? Or even learn? Krulwich thought not, but Abumrad disagreed and the episode unpacked the idea, primarily zeroing in on Gagliano’s work with sensitive plants, Mimosa pudica, which she chose because they can be counted on to respond to stimuli by dramatically closing up their leaves.

Run out and buy Monica Gagliano’s book Thus Spoke the Plant.

For her first tests, examining plants’ ability to learn, Gagliano constructed what amounted to a tiny carnival ride that hoisted the sensitive plants up a short ways before dropping them onto a soft, cushy surface. Over and over, dozens and dozens of times, the plants were dropped and each time they closed their leaves until finally, they stopped. Because “the plants realized that was not necessary,” she says, explaining that the plants had learned something.(Watch her interview with TheScientist here.)

Krulwich was amazed, but Abumrad wondered aloud whether the plants had simply run out of energy to close up. Gagliano had thought of that too, and she’d tested the theory by shaking the plants that were no longer closing up their leaves from side to side rather than dropping them. The plants responded by quickly closing up, so it was not exhaustion they were exhibiting.

Three days later Gagliano returned to the lab and started dropping the plants again. This time, they stopped closing their leaves almost immediately, indicating that they hadn’t just learned something, they had also remembered it. Gagliano waited a few more days, and the plants still remembered. A few more days: same thing. At last, she waited 28 days before dropping them again. The result? Galiano believes those mimosa plants somehow remembered what had happened and did not close up on the way down.

At the very least, her research makes clear that plants, like animals, are capable of much more than we give them credit for. It makes you think, right? What do plants feel or sense or know when our shovels bite into the soil around them? I shudder to think about what might be going on with them when they somehow sense that pruners, or worse—an electric trimmer is nearby. Gagliano may not yet understand how plants are learning and remembering, but she is showing the world that they are doing those things. It’s thrilling to imagine what else may be discovered.

A version of this essay appeared in a 2018 issue of Northern Gardener.