By Jenna Ahart
Since sentience research began in the late 19th century, its definition has expanded to include previously unanticipated species—from insects to invertebrates. Still, research on non-human sentience largely neglects one of Earth’s most pervasive kingdoms: plants.
In their recently published research article, Miguel Segundo-Ortin and Paco Calvo call for increased efforts investigating the potential for sentience in plants. The pair currently works at the Minimal Intelligence Laboratory at the University of Murcia, where they study patterns in plant behavior through time-lapse footage. In addition to acting as the lab’s director, Calvo has written “Planta Sapiens,” an upcoming book on plant intelligence.
Segundo-Ortin and Calvo’s article emphasizes plant behaviors that warrant further investigation. Plants can communicate with one another via airborne compounds, recognize fellow species members through root systems, and decide where to best forage for light and nutrients.
Frank Stearns, who taught a Plants and Society course at George Washington University, has encountered similar anecdotal evidence from a friend who studied music.
“He did an experiment that showed that if you play the sound of plants being eaten, that they would respond by increasing their defenses,” Stearns said. “There weren’t even any insects around that would attack them. It was just the sound of an insect plant being eaten was enough to increase their defenses—it’s kind of like they can hear.”
In her book “Lessons from Plants,” Beronda L. Montgomery even discusses the concept of memory in plants. Plants familiar with more nutrient-rich environments wager their energy by expanding root systems. Meanwhile, plants that have experienced nutrient scarcity tend to conserve energy for survival.
“Altogether, these types of responses suggest that plants are able to learn and remember, if we understand learning as a change in behavior based on active recall,” Montgomery wrote.
Despite these accumulating suggestions of plant sentience, though, many researchers still have reservations against experimentation. For Segundo-Ortin and Calvo, biases against plant sentience are likely cast through an anthropomorphic lens. Researchers can reason by analogy when testing for animal sentience by looking for more immediate, human-like reactions to stimuli—like wincing at pain. In plants, however, reasoning must slow down to match a more gradual timescale.
“Animals are locomotives and need to respond fast—run, hunt, and hide,” Calvo said. “Plants don’t require such a fast medium of communication.”
While an animal can face the sun in milliseconds, plants like Lavatera cretica spend an entire night reorienting their leaf blades toward the sunrise during a three-stage process. Comparatively, plants’ environmental reactions become less obvious.
Montgomery discusses how theories of plant sentience are also cast aside because of the “long-standing belief that behavior is only possible in organisms with a central nervous system, which plants lack.”
Anthropomorphic biases afflict even the vocabulary describing plants, according to Calvo. While precisely the same melatonin hormone appears in both plants and animals, a distinguishing prefix carefully separates the two in the term Phytomelatonin. And although plants contain neurotransmitters, many scientists argue that the same term used to describe animals’ neural networks couldn’t possibly apply to plants.
“We tend to have a stronger affinity to things that we’re more closely related to—mammals over lizards and birds, vertebrates over invertebrates, and animals over plants,” Stearns said, explaining a common hesitancy toward plant sentience.
For Segundo-Ortin and Calvo, proper research can begin only once this human-centric lens is shattered. Broadened definitions of sentience have already cleared room for invertebrates, honey bees, and termites—organisms once never thought to have sentience without a neocortex. In the same way, opening the pool of sentience candidates up to plants would require looking past another preconceived requirement: the central nervous system.
Segundo-Ortin and Calvo hypothesize that plants can be better understood through MRI and PET scans. Just as neuroimaging has connected animals’ abilities to store information and enjoy sentience, it may well shine new light on plant behaviors.
But rather than scanning a neural network, these experiments would analyze plants’ vascular systems—a network of tissue transporting water and nutrients from the roots to the leaves and back. By tracing plants’ electrical signatures, researchers could map out their paths of information processing to determine whether increased integrated information indicates stronger levels of sentience for plants, too.
This experimental approach chips away at sentience qualifications once set in stone. According to Segundo-Ortin, though, research could become harder to navigate without a sturdy sentience definition. After all, scientific research largely depends on abiding by pre-constructed theories—like a required central nervous system. As those grounding assumptions grow shakier, experimental procedures often begin to rattle, too.
“Just because you need to start from a theory to do science, doesn't mean you need to commit 100% of this theory. You could explore the different hypotheses that different theories will give you, and then see if you can apply them to plants,” Segundo-Ostin said.
With an open approach to experimentation, he and Calvo are hopeful that plants will begin to decode larger sentience debates. Some researchers hypothesize that sentience developed as a product of evolution—at the tissue, cellular, subcellular, or even the quantum level. Better understanding the form sentience takes in plants may be the next step to exploring its evolutionary origins.
But before any of those larger impacts can flourish, researchers must first dig into the roots of their reservations against plant sentience. As Calvo put it, “You need to train your eye to appreciate plants’ behavior and not simply put them in an animal or human mold. Put yourself in the species’ shoes. Don’t simply project your preconceptions that humans are the gold standard.”
Jenna Ahart is a senior studying journalism and astrophysics. This summer, she interned at NASA's Goddard Space Flight Center, where she wrote news and web features about gamma-ray astronomy research. She plans to continue studying science writing upon graduation.
Commentaires