When I was a boy in Sri Lanka, I was fascinated by a small plant that grew close to the ground. It had tiny leaves that looked like miniature versions of coconut palm fronds. When you gently touched even a single leaf, the entire set of fronds would immediately curl themselves in, as if to escape from me. It was extraordinary. I used to go through the plant bed, touching each one until they all were curled up. After being left alone for some time, they would unfurl themselves.
Did the plant have intelligence? Was it seeing me as a threat to withdraw from and re-emerge only after I left? It never occurred to me then to wonder. To even pose such a question is to invite controversy, if not outright ridicule. We tend to think of an intelligent organism as having a mind, which presupposes the existence of a material brain and a nervous system, and also having a body which enables the organism to have agency and move around freely in response to external conditions. Plants were long thought to lack pretty much all those features, although they have limited movement in response to light and water and other features of the environment. Some can also trap and devour insects. But we tend to stop short of using the term intelligence to describe those actions.
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