|Various plants in an outdoor planting table / Photo by OhSurat via Shutterstock|
The sentience and consciousness of plants have been up for debate for a couple centuries now, and scientists are still raging back and forth over it. Plant consciousness has been a documented topic of passionate discussion in the scientific community since at least the 1880s when Charles Darwin first took note of how plants can get stressed and become unable to rest. As such, the debate is at least as old as the theory of evolution for all intents and purposes. Biologists consider the complexities of plant life to be further obfuscated by the way that certain plants like fungi communicate with not only each other but also with animals through the release of chemicals in their leaves, branches, and roots. In order to make any modicum of sense to it, though, the conversation always has to be steered at some point toward defining consciousness.
A Cambridge fellow, neuroscientist, and author at Magdalene College, Hannah Critchlow, says she sees so many neuroscientists — possibly over-represented — in Cambridge, and she notes that they all seem to jog regularly. The physical fitness that comes with this activity is obviously one explanation for the commonality of the routine, but she adds that they’re all really more focused on ramping up their neurogenesis, which is the birth of new nerve cells in the brain. “People used to think that once you were born, that was it, that was all the nerve cells you have throughout life,” Critchlow explains.
“Then, 20 years ago, Rusty Gage [a Salk Institute professor in California] discovered that you get neurogenesis in adults, in a region of the brain called the hippocampus, which is involved in learning and memory. It turns out that jogging is really good at increasing neurogenesis in the brain.” She, herself, is a runner, and she happens to have just written a book on the topic of consciousness in its broadest sense. “Our brain contains around 86bn nerve cells,” the book reads. “To scale it down to something more palatable, if we took a dot of brain tissue the size of a sugar grain, it would contain roughly 10,000 nerve cells.” She adds therein that each neuron is connected to another 10,000 neurons on top of that, so it’s an incomprehensibly dense and intricate circuit board in our brains.
Neuroscience boils living organisms down to incalculable combinations of chemical and electrical reactions, and each species is like a unique combination pattern, let alone the distinctions among individuals within said species. It’s definitively been established and accepted by the scientific community that animals, even in adulthood, form whole new connections all the time, and the human brain is no exception. Perhaps one of the most pertinent things she says about consciousness despite not specifically alluding to plants is that it’s possible to “see consciousness happen, new connections forming.” She even references “gorgeous videos” of this occurring in the brain.
Critchlow’s book addresses plant consciousness in this vein, speaking of plants relying on electrical signals to convey information to living organisms in their environment. Her example is that of a caterpillar eating a leaf. “The plant will start to produce a chemical to repel the insect. Even if the plant is simply played an audio file of a munching caterpillar, it will respond, indicating that plants can hear.” That’s just as significant as the increasingly popular results of a study published earlier this year in which a Venus flytrap — many people’s first example of plant sentience if not consciousness — is sedated. It appears to lose consciousness, which immediately begs the question of whether or not it was conscious in the first place.
The Venus flytrap study was published in Annals of Botany by a team of German researchers among whom was Frantisek Baluska, a plant cell biologist from the University of Bonn. “Plants are not just robotic, stimulus-response devices,” Baluska says. “They’re living organisms which have their own problems, maybe something like with humans feeling pain or joy. In order to navigate this complex life, they must have some compass.” The study is one of many in recent years to illustrate that plants can be stressed, but it also showed that they experience competition, too. Plants consume information from their respective ecosystems and create their own anesthetics — chief examples being ethanol, menthol, and even cocaine. Human beings similarly produce their own biological chemicals to numb pain in traumatic experiences for that matter; that’s epinephrine’s purpose. The thing is that our anesthetics work on plants, too, which is what Baluska’s team discovered.
|Plant growing in arid areas like oasis / Photo by Stor24 via Shutterstock|
Plants have been shown to have preferences, too. Their roots reposition themselves to be closer to water sources based on hearing the water move nearby in, on or through the ground. Many have defense mechanisms as well, and research has demonstrated that plants have recall much like we do. It’s an increasingly common misnomer to say that they have memories when really, like animals, they don’t store experiences so much as recreate them for what amounts to posterity. A 2014 study had researchers dropping potted plants known as Mimosa pudicas short distances, and doing so initially caused the plants to curl their leaves defensively. There came a point in the study, though, when the plants stopped doing so because they realized no harm would come to them on the basis that being dropped previous times never harmed them either. That requires recall, and recall implies consciousness.
Implying consciousness and constituting consciousness, though, are two separate things, and thus far, there’s no definitive answer to quash the debate regarding whether or not plants are, in fact, what we call “conscious.”