This, he suggests, is where we need to look for a “phytonervous” system. It transmits electrical signals, like a “green cable that carries news throughout the plant”. Their vascular system consists of tubes arranged in layers, like the mammalian cortex, that run from root to shoot. In the absence of nerves, plants use networked cells to regulate themselves. But although they lack our grey matter, Calvo believes they have a unique “green matter”. But he guides us patiently through the latest research and builds a compelling case that, unlikely as it may seem, deserves to be taken seriously.Ĭlearly plants don’t have brains in any familiar sense of the word. Of course, these are revolutionary ideas and, as Calvo admits, contested by many scientists who study the physiology of plants. The conclusion must be that they constantly collect information, processing and retaining it in order to “make predictions, learn, and even plan ahead”. They store this knowledge – an internal model of what the sun is going to do – for several days, even when kept in total darkness. Other studies show that some plants retain a memory of where the sun will rise, in order to turn their leaves towards the first rays. If plants can be put to sleep, does that imply they also have a waking state? Calvo thinks it does, for he argues that plants are not just “photosynthetic machines” and that it’s quite possible that they have an individual experience of the world: “They may be aware.” He also notes that the process of germination in seeds can be halted under anaesthetic. It is effectively asleep, just as a cat would be. Tests show the plant’s electrical activity has stopped. After an hour the plant no longer responds to touch by closing its traps. In lectures, he places a Venus flytrap under a glass bell jar with a cotton pad soaked in anaesthetic. He also shows how, like animals, they can be anaesthetised. In the course of his book, Calvo describes many experiments that reveal plants’ remarkable range, including the way they communicate with others nearby using “chemical talk”, a language encoded in about 1,700 volatile organic compounds. In plants, it reveals a range of faculties “from learning and memory to competitive, risk-sensitive behaviours, and even numerical abilities”.
And observing behaviour is the route to understanding intelligence. Darwin realised before anyone else that these movements were in fact “behaviour”, comparable to that of animals. As he convalesced, he was forced to live slowly – “to become more plant-like”, Calvo writes – and this stillness opened his mind to the wonder of his vegetable companions: “It allowed him to see them more on their terms, to experience plant life at plant pace.”ĭarwin has clearly been a guiding presence in Calvo’s attempt to open up a new frontier in science: “He learned to think differently and clearly outside the frameworks in which most of his contemporaries happily confined themselves.” The result of his confinement with the cucumbers was a 118-page monograph on The Movements and Habits of Climbing Plants. Confined to his sickbed for weeks, the author of On the Origin of Species occupied himself by studying the movements of cucumber plants on his windowsill. “I am getting very much amused by my tendrils,” Darwin wrote to a friend in 1863. He argues that it’s time to accept that other organisms, even drastically different ones, may be capable of it. We humans have a tendency to believe that the world revolves around us, but Calvo writes that intelligence is “not quite as special as we like to think”. Although he presents detailed scientific evidence to support his case, he also draws on philosophical arguments about the nature of consciousness. Calvo is a professor of the philosophy of science in the Minimal Intelligence Laboratory at the University of Murcia, Spain.
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