Last evening, an episode of Nature on PBS purported to demonstrate that plants, like animals, exhibit behavior. A range of examples included chemical communication between plants, chemical signaling between plants and their pollinators, chemical defenses used by plants, competition between plants for nutrients, sunlight and space, the symbiotic relationship between fungi and plants and the sharing of nutrients between various plants within an ecosystem.
For students of biology, the show was interesting but none of the data was surprising or game-changing. Whether plants manifest behavior depends on how we define that trait. In many ways, plants communicate and compete at a level that compares with lower forms of animal life; though immobile, plants manage to locate food, defend themselves from predators, communicate stress and cooperate with other plants. In neither case (plant or lower animal) are these forms of "behavior" conscious; rather, they demonstrate reflexive chemical mechanisms (including chemical driven growth patterns) that have evolved over the eons. Since plants, unlike animals, do not possess a nervous system, it is not fully understood how "plant behavior" is coordinated; on the other hand, there is a great deal of chemical signaling in animals (including humans) that does not involve the nervous system (hormones, for example, are delivered through the bloodstream).
In reality, all life forms, from bacteria to plants to humans, are the product of their genes, which determine the structure and functional capabilities of that organism. In that sense, plants are no different from animals and one might choose to view many of their chemical-induced physiologic functions as behaviors. Indeed, were it not for our own neuroanatomy and chemical messengers, we could neither contemplate nor debate this issue.
