Updated: Jul 28, 2020
We humans have a silly habit of thinking we are the only species capable of complex communication, but science is proving that idea will be left in the dust. Today we have learned that all animals we have studied have rich communication methods, complex thoughts and emotions, strong intentions, and a capacity for joy. But what about plants? Do they communicate? Do plants have moods? Do we have more in common with plants than we realize? Do they respond to music styles and have preferences? Do they like being talked to in loving ways as you might have read in The Secret Life of Plants? Although the science has gone beyond this 1970's book, the results are no less fascinating.
It is clear that Nature communicates. Humans, animals, plants, and all of nature – the question is can we begin to understand how this communication occurs. For example, an Acacia tree under “attack” from giraffes and antelopes or other animals who stop to chomp their leaves, will emit a bitter tannin to the leaves to discourage the animals. But according to zoologist Wouter Van Hoven from Pretoria, these trees also communicate. They warn their neighboring trees, by emitting a chemical, ethylene, into the air which can travel up to 50 yards. The ethylene warns other trees of the impending danger, which then step up their own production of toxic leaf tannin within just five to ten minutes.
Carl Safina explores some of the ways that plants communicate in his book "Beyond Words - What Animals Think and Feel," he says "With no apparent nervous system, plants make the same chemicals, such as serotonin, dopamine, and glutamate -- that serve as neurotransmitters and help create mood in animals, including humans." And plants have signaling systems that allow them to communicate with other plants, such as to alert them to the dangers of predators. As Michael Pollan says, "plants speak in a chemical vocabulary, we can't directly perceive or comprehend."
We know that plants' leaves will turn and track to the sun. A new study shows them responding to the recorded sound of a munching caterpillar by producing defensive chemicals. Safina continues, "Plants attacked by insects and herbivores emit "distress" chemicals, causing adjacent leaves and neighboring plants to mount chemical defenses, and alerting insect-killing wasps to move in, blunting the attack."
It may be hard to conceive that motionless plants have what we might call mental sophistication. But we are just at the dawn of understanding the complex communication of plants. As Charles Darwin observed in his book "The Power of Movement in Plants," "It is hardly an exaggeration to say that the tip of the (root)...acts like the brain of one of the lower animals... receiving impressions from the sense organs and directing the several movements."
Elizabeth Pennisi writes in ScienceMag:
"Plants may lack brains, but they have a nervous system, of sorts. And now, plant biologists have discovered that when a leaf gets eaten, it warns other leaves by using some of the same signals as animals. The new work is starting to unravel a long-standing mystery about how different parts of a plant communicate with one another.
Animal nerve cells talk to each other with the aid of an amino acid called Glutamate, which—after being released by an excited nerve cell—helps set off a wave of calcium ions in adjacent cells. The wave travels down the next nerve cell, which relays a signal to the next one in line, enabling long-distance communication."
Ira Flatow interviewed Michael Pollan on his show "Science Friday" and asks the question of whether or not plants can be said to be intelligent. Pollan explains that plants have memory -- and thus can adapt and possibly learn from experience.
Below is an excerpt from this interview, to hear the full fascinating interview, go to:
This new research, Pollan says, is in a field called Plant Neurobiology — which is something of a misnomer, because even scientists in the field don't argue that plants have neurons or brains. "They have analogous structures," Pollan explains. "They have ways of taking all the sensory data they gather in their everyday lives ... integrate it and then behave in an appropriate way in response. And they do this without brains, which, in a way, is what's incredible about it, because we automatically assume you need a brain to process information."
We humans tend to view intelligence from our own perspective. Thus we assume you need ears to hear. But researchers says Pollan, have played a recording of a caterpillar munching on a leaf to plants — and the plants react. They begin to secrete defensive chemicals — even though the plant isn't really threatened, Pollan says. "It is somehow hearing what is, to it, a terrifying sound (to a plant) of a caterpillar munching on its leaves."
Pollan says plants have all the same five senses as humans, and then some. In addition to hearing, taste, touch, for example, they can sense gravity, the presence of water, or even feel that an obstruction is in the way of its roots, before coming into contact with it. Plant roots will shift direction, he says, to avoid obstacles or find water.
We are just beginning to learn how plants sense and react to stimuli. "They don't have nerve cells like humans, but they do have a system for sending electrical signals and even produce neurotransmitters, like dopamine, serotonin and other chemicals the human brain uses to send signals."
Pollan describes an experiment done by animal biologist Monica Gagliano. She presented research that suggests the Mimosa Pudica plant can learn from experience. And, Pollan says, merely suggesting a plant could learn was so controversial that her paper was rejected by ten scientific journals before it was finally published -- simply because she used the word "learn."
Mimosa is a plant, which looks something like a fern, that collapses its leaves temporarily when it is disturbed. So Gagliano set up a contraption that would drop the mimosa plant, without hurting it. When the plant dropped a few feet, as expected, its leaves collapsed. She kept dropping the plants every five to six seconds.
"After five or six drops, the plants would stop responding, as if they'd learned to tune out the stimulus as irrelevant," Pollan says. "This is a very important part of learning — to learn what you can safely ignore in your environment."
Pollan says this concept of plant learning threatens some people — "that the line between plants and animals might be a little softer than we traditionally think of it as."
As exciting as understanding plant-communication systems are, the idea that plants can LEARN from experience is revolutionary. In the above mentioned study, if something appears to be dangerous, such as being dropped a few feet, and then it turns out not to be dangerous, the mimosa plant will initially respond to the danger -- and learn over time that it is not dangerous, thereby not wasting precious energy in reacting to a false danger. Some plants can also produce their own natural anesthetic when they experience pain. If only humans had these levels of intelligence and ability to flexibly and resiliently respond -- we could cure PTSD!
We have a long way to go before we will ever fully understand the inner lives of plants, but as the late botanist, Tim Plowman commented on how sophisticated their world is, "They can eat light. Isn't that enough?"
On the last day of the world I would want to plant a tree. - W.S. Merwin -
Genie Joseph, PhD
Director: The Human-Animal Connection