But the potted cacti, yucca, and swiss cheese plants we’ve welcomed into our homes are entirely passive houseguests. Aren’t they?
Research suggests that at least one type of plant – the french bean – may be more sentient than we give it credit for: namely, it may possess intent.
The issue of whether or not plants choose their actions and possess feelings or even consciousness is a thorny one for many botanists, with the more traditional-minded strongly disputing any notion of sentient vegetation. Although plants clearly sense and react to their environments, this doesn’t mean they possess complex mental faculties, they argue.
Others, like Paco Calvo at the University of Murcia’s minimal intelligence lab in Spain, are more open-minded. Intrigued by the ability of climbing beans to sense structures such as garden canes and grow up them, he devised an experiment to investigate whether they deliberately aim for the cane, or simply bump into such structures as they grow, and then turn them to their advantage. “The question is, are they showing goal-directed behaviours consistent with anticipation and fine-scaled tweaking of their movements, as they approach?” Calvo said.
Together with Vicente Raja at the Rotman Institute of Philosophy in London, Canada, they used time-lapse photography to document the behaviour of 20 potted bean plants, grown either in the vicinity of a support pole or without one, until the tip of the shoot made contact with the pole. Using this footage, they analysed the dynamics of the shoots’ growth, finding that their approach was more controlled and predictable when a pole was present. The difference was analogous to sending a blindfolded person into a room containing an obstacle, and either telling them about it or letting them stumble into it.
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“We see these signatures of complex behaviour, the one and only difference being is that it’s not neural-based, as it is in humans,” Calvo said. “This isn’t just adaptive behaviour, it’s anticipatory, goal-directed, flexible behaviour.”
The research was published in Scientific Reports. “Although the research seems sound, it is not clear that it teaches us much new about plant sentience or intelligence,” said Rick Karban, who studies plant communication at the University of California, Davis. “For more than a century, scientists have been aware that plants sense aspects of their environments and respond, and understanding how plants [do this] is an active area of current research. Whether you choose to consider these processes sentience or intelligence depends entirely on how to choose to define these terms.”
Calvo acknowledges that this experiment alone doesn’t prove intent, much less consciousness. However, if plants really do possess intent, it would make sense. All biological organisms require the means to cope with uncertainty and adapt their behaviour to pass on their genes, but the timescale on which they operate makes this particularly imperative for plants: “They do things so slowly, that they can’t afford to try again if they miss,” Calvo said.
One possibility is that this “consciousness” arises out of the connections between plants’ vascular systems and their meristems – regions of undifferentiated dividing cells in their root and shoot tips, and at the base of leaves.
In a separate paper, Calvo and his colleagues set out a theory of plant consciousness based on integrated information theory (IIT) – a leading theory of consciousness – which posits that we can identify a person’s (or any system’s) level of consciousness from the complexity of the interactions between its individual parts.
Others rebut such claims. IIT is based on an assumption that everything material has an element of consciousness, even nonliving complex systems: “It cannot have any special significance for plants,” said Jon Mallatt at the University of Washington, US. He believes claims about sentient plants are misleading, and risk misdirecting scientific funding and government policy decisions.
Calvo said he was happy to be disproved, but experimentally, rather than on theoretical grounds. In another paper scheduled to appear in the Journal of Consciousness Studies, he proposes a set of experiments which may settle the matter once and for all. “If successful, these experiments could position plants as the next frontier in consciousness science, and urge us to rethink our perspectives on consciousness, how to measure it, and its prevalence amongst living beings,” he said. The gardening gloves are off.
