Intelligent Plants

What is consciousness? I’ve been thinking about this a lot lately. To be conscious is, according to the dictionary, “to be aware of and responsive to one’s environment.”

A large contingent of scientists and atheists insist that consciousness is strictly a product of the brain, and by that they mean neuronal activity. For example, in Daniel Dennett’s Consciousness Explained, which I read recently, he suggests there is no such thing as consciousness in the way most people think of it. There is no witness, no I. Dennett postulates that our sense of self is just a narrative that we use as a survival tool, similar to the shell a hermit crab inhabits. The narrative creates mental models of the world around us, as well as a mental model of our self.

Each normal individual of this species [humans] makes a self. Out of its brain it spins a web of words and deeds, and, like the other creatures, it doesn’t have to know what it’s doing; it just does it. This web protects it, just like the snail’s shell, and provides it a livelihood, just like the spider’s web, and advances its prospects for sex, just like the bowerbird’s bower.

Dennett’s conclusion is that consciousness is analogous to software running on the hardware of the brain. Neurons fire in patterns and this produces activity that we call the mind.

But what if organisms without brains and neurons possess consciousness? What would this mean about consciousness in general? Would it mean that consciousness is not a function of brains and neurons?

We don’t have to leave our own bodies to question the proposition that consciousness/intelligence is in the brain. We have a “gut reaction,” a “sinking feeling in our stomach,” or a “heart throb” that often is more accurate a response to our situation than the thoughts in our minds.

Michael Pollan has a fascinating article in The New Yorker about intelligent plants. In it I learned of a controversial new field: “plant neurobiology.” The authors of a 2006 Trends in Plant Science article presented evidence that plants have extremely sophisticated behaviors that (in Pollan’s words)

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.

Plants have evolved between fifteen and twenty distinct senses, including analogues of our five: smell and taste (they sense and respond to chemicals in the air or on their bodies); sight (they react differently to various wavelengths of light as well as to shadow); touch (a vine or a root “knows” when it encounters a solid object); and, it has been discovered, sound. 

Scientists have since found that the tips of plant roots, in addition to sensing gravity, moisture, light, pressure, and hardness, can also sense volume, nitrogen, phosphorus, salt, various toxins, microbes, and chemical signals from neighboring plants. Roots about to encounter an impenetrable obstacle or a toxic substance change course before they make contact with it. Roots can tell whether nearby roots are self or other and, if other, kin or stranger.

One of the main researchers in plant neurobiology, Stefano Mancuso, showed Pollan time-lapse video of bean plants growing towards a pole. Watching it, it’s easy to interpret the movements as purposeful and intelligent: the plant seemed to know where the pole was. I always thought the shoot of a climbing plant moved in every direction until by chance it ran into a support. Instead, the video shows the plant “throwing itself over and over like a fly rod” right at the pole until it made contact. Pollan narrates a version of that video here. 

In the video the bean plants definitely appear “to be aware of and responsive to their environment.” If plants are conscious, intelligent organisms, what could the mechanism be?

Pollan quotes Mancuso: “Intelligence is the ability to solve problems.” In place of a brain, “what I am looking for is a distributed sort of intelligence, as we see in the swarming of birds.”

What the plant neurobiologists are proposing is that consciousness and intelligence are emergent properties of networks. Our brains are networks of neurons, and this research suggests that what’s important is not the neurons but the network.

In a TED talk, Mancuso shows an animation of the action-potential signals in a plant’s root tips that are just like the action-potential signals of neurons in our brain. A single rye plant has 11 million root tips, and another diagram compares the network those roots form to the Internet. (The talk starts with an amusing look at how plants have been considered less than animals for thousands of years, but just as a warning, Mancuso’s English is heavily accented.) He suggests robot developers consider using plants as a basis for their designs; here’s a sketch of a “plantoid”:

It’s only recently that researchers have discovered the incredible underground networks that connect trees in forests via mycorrhizal fungi. The network connects the trees’ roots and allows the exchange of information about such things as insect attacks, and resources such as water. Suzanne Simard, a forest ecologist at the University of British Columbia,

injected fir trees with radioactive carbon isotopes, then followed the spread of the isotopes through the forest community using a variety of sensing methods, including a Geiger counter. Within a few days, stores of radioactive carbon had been routed from tree to tree. Every tree in a plot thirty metres square was connected to the network; the oldest trees functioned as hubs, some with as many as forty-seven connections. The diagram of the forest network resembled an airline route map. 

The pattern of nutrient traffic showed how “mother trees” were using the network to nourish shaded seedlings, including their offspring—which the trees can apparently recognize as kin—until they’re tall enough to reach the light. And, in a striking example of interspecies coöperation, Simard found that fir trees were using the fungal web to trade nutrients with paper-bark birch trees over the course of the season. The evergreen species will tide over the deciduous one when it has sugars to spare, and then call in the debt later in the season. For the forest community, the value of this coöperative underground economy appears to be better over-all health, more total photosynthesis, and greater resilience in the face of disturbance.

An individual tree has consciousness through the network of cells in its “body.” The forest has consciousness through the mycorrhizal fungi-root network. A human has consciousness through a network of neurons. The network linking humans, known as the Internet, is creating a global consciousness—Peter Russell wrote about this in the mid-1990s in his book The Global Brain.

An amoeba in a petri dish, Robert Pirsig wrote in Zen and the Art of Motorcycle Maintenance, will respond to a drop of sulfuric acid by moving away. That is clearly a sign of being “aware of and responsive to their environment.” As usual, humans have assumed that consciousness is something special reserved just for us. Instead, it’s a fundamental aspect of being, and the more complex the structure of the being, the more fully the underlying consciousness can be expressed.

I believe the underlying nature of the universe is consciousness, and as organisms get more complex, they develop mechanisms to tune into the underlying consciousness, like a radio tuning in to invisible radio waves.