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The last decade saw the rise of the field of "plant neurobiology (神经生物学)". That debatable field is based on the idea that plants--which do not possess brains --handle information in ways similar to complicated animal nervous systems. This thinking implies that plants could feel happiness or sorrow or pain, make intentional decisions and even possess consciousness. But the chances of that are "effectively zero," Lincoln Taiz and colleagues write in an opinion piece in Trends in Plant Science. "There's nothing in the plant remotely comparable to the complexity of the animal brain," says Taiz, from the University of California, Santa Cruz.

Some plants are capable of complicated behavior. Wounded leaves can send warning signals to other parts of the plant, and harmful chemicals can warn animals that eat them. Some plants may even have a version of short-term memory: Tiny sensing hairs can count the number of touches that come from a clumsy insect. But plants perform these with equipment that's very different from the nervous systems of animals, no brain required, Taiz argues.

He and colleagues point out methodological (方法的) faults in some of the studies that claim plants have brain-like command centers, animal-like nerve cells and changing patterns of electricity that are similar to activity found in animal brains. But beyond the debate over how these studies are conducted, Taiz's team argues that plant consciousness doesn't even make sense from an evolutionary (进化的) point of view.

Complicated animal brains advanced in part to help a living being catch a meal and avoid becoming one, Taiz says. But plants are rooted to the ground and rely on sunlight for energy, an inactive lifestyle that doesn't require quick thinking or outsmarting a predator (捕食者)--or the energetically expensive nervous systems that enable those behaviors.

"What use would consciousness be to a plant?" Taiz asks. The energy required to power awareness would be too costly, and the benefit from such awareness too small. If a plant worried and suffered when faced with a threat, it would be wasting so much energy that it wouldn't have any left to do anything about that threat, Taiz says.

Imagine a forest fire. "It's unbearable to even consider the idea that plants would be conscious beings aware of the fact that they're being burned to ashes, watching the young trees die in front of them," Taiz says. The frightening scene illustrates "what it would actually cost a plant to have consciousness."

Furthermore, plants have plenty to do without having to be conscious, too. With sunlight, carbon dioxide and water, plants create the compounds (化合物) that sustain much of the rest of life on Earth, Taiz points out. "Isn't that enough?"