“Planted evidence” (Plant sentience)

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A sentient plant is usually considered to be in the realm of science fiction. Think Audrey II from The Little Shop of Horrors. But some researchers are open to the idea that plants are capable of emotions and the ability to feel, perceive, or experience stimuli objectively. These Proponents compare electrical signaling in plants to nervous systems in animals.

Those on the other side of the debate consider this analogy superficial and think it fails to consider the brain’s functions and complexity. The model of consciousness developed by neurobiologist Todd Feinberg and medical professor Jon Mallatt ascribes to brains a certain level of structure and ability that enable the bodies that house them to have subjective experiences. The electrical signaling system in plants lacks these distinctions, they say.

Feinberg and Mallatt compared simple and complex animal brains, and in an interview with the Genetic Literacy Project, retired biology professor Lincoln Taiz said the duo “concluded that only vertebrates, arthropods, and cephalopods possess the threshold brain structure for consciousness. Plants, which don’t even have neurons, let alone brains, don’t have” this structure. Instead, he continued, “What we’ve seen is that plants and animals evolved very different life strategies. The brain is very expensive organ, and there’s absolutely no advantage to the plant to have a highly developed nervous system.”

As to electrical signals, plants use them like a distribution center to send charged molecules to membranes, and also to deliver internal messages. When the former happens it might cause a plant’s leaves to curl since ionic movement may force water to leave the cells, changing their shape. In the latter, when an insect chomps on one leaf, this might initiate a defensive mechanism in the rest of the appendages. These types of actions can make it seem like the plant is choosing its responses, but Taiz stresses the reactions are the result of genetic coding and fine-tuning via natural selection.

Plants might curl their leaves when touched or grow more rapidly near competitors. They can even seduce and trap  insects, with the Venus Flytrap being the best-known example. But Taiz, Feinberg, and Mallatt argue there is no sound evidence that indicates plants choose their actions, gain knowledge, or suffer pain.

One study cited by plant sentience proponents involves possible conditioning of the perennial flower mimosa pudica. In experiments, its leaves defensively curl when the plant is dropped. After many iterations of this without damage occurring, the leaves cease to curl. But when the plant is shaken, the leaves again curl, which seems to rule out fatigue as the reason that response stopped.

But this is a misinterpretation, Taiz cautions: “The shaking was actually quite violent. Because the shaking stimulus was stronger than the dropping stimulus, it doesn’t definitively rule out sensory adaptation, which doesn’t involve learning.”

So it seems that thinking, acting plants are still in the domain of movies and tabloids. That’s fine by me. I don’t much care for such notions as a killer cactus or poison oak having the ability to spew its sap.

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