Are plants intelligent?

In A Fire Upon the Deep, the 1992 science-fiction novel from Vernor Vinge, the action takes place in a vast galaxy populated by a variety of interesting alien species. On one planet, there’s a race of canines that operate with hive minds. Elsewhere, there’s a race of trees that can speak with fronds and which move about on mechanical platforms. (The 1999 prequel A Deepness in the Sky features another interesting race, one resembling spiders.)

Before that, J.R.R. Tolkien’s The Lord of the Rings featured the Ents, a hyper-intelligent (and powerful) race of tree-like beings that existed in a world that largely ignored (or was unaware of) them. The Ents moved and talked s-l-o-w-l-y, but because their lives were long, they had amazing memories and tons of wisdom.

In our real world, few people give credence to the idea that plants might possess intelligence. The notion seems absurd. Yet a recent article in the The New Yorker by Michael Pollan has raised the question: How smart are plants?

Pollan discusses past research into this question, including the best-selling (but flawed) 1973 book The Secret Life of Plants. But he spends most of his time discussing current research into the subject of plant intelligence. He interviews a number of scientists, including Daniel Chamovitz, author of What a Plant Knows.

Proponents of plant intelligence argue that:

The sophisticated behaviors observed in plants cannot at present be completely explained by familiar genetic and biochemical mechanisms. Plants are able to sense and optimally respond to so many environmental variables—light, water, gravity, temperature, soil structure, nutrients, toxins, microbes, herbivores, chemical signals from other plants—that there may exist some brainlike information-processing system to integrate the data and coördinate a plant’s behavioral response.

Those who believe that plants are intelligent say that “it is only human arrogance, and the fact that the lives of plants unfold in what amounts to a much slower dimension of time, that keep us from appreciating their intelligence and consequent success.”

Detractors argue that those who believe plants are intelligent are anthropomorphizing (a charge still leveled at many folks who believe animals are intelligent). Too, there’s debate over the definition of “intelligence” — and the definitions of other words that describe how organisms interact with their environment. According to Pollan, the debate isn’t over what plants do, but over how these actions should be labelled and classified.

In many ways, plants are like an alien species. Though they account for 99% of the biomass on this planet, their lives are strange to us:

• They’re sessile. That is, they’re permanently rooted to one spot.
• They’re modular. Humans (and most other animals) don’t have redundant parts. And if we lose certain organs, we die. But a plant can lose up to 90% of its body without being killed.
• They have no central nervous system. They have no brain. We have a single organ dedicated to mental processes. Plants seem to derive what intelligence they may have from the tips of their roots.
• When plants communicate, they do so with chemicals rather than motion or sound.
• As noted earlier, plants exist on a different time scale than we do. They move so slowly that their actions seem imperceptible to us.
• Plants “eat” light.

In his article, Pollan describes research into plant behaviors that resemble what we might call “learning” or “decision-making”. He discusses whether or not plants feel pain. He also talks about communication and cooperation and, amazingly enough, simple plant “economies” in which different species trade with each other.

Here’s a video clip that demonstrates some plant behavior that resembles intelligence:

What do you think? Is it possible that plants are intelligent? If so, what are the implications?

I first explored the idea of plant intelligence at this site more than six years ago. If you’d like more on this subject, Pollan did a follow-up interview on NPR’s “Science Friday”.