Can We Measure Plant Intelligence? Science Tackles a Question We Didn’t Know We Should Ask.

Humans are pretty biased when it comes to evaluating the intelligence of other species. We only recently admitted that our closest relatives use tools. Many people still struggle to understand that other species can feel many emotions and even have culture. The more different a species appears, the more we struggle with grasping its intelligence.

Then… there are plants. While they might be useful, we don’t think of plants as intelligent.

Tall and short, leavy and thorny, plants don’t seem to have a central nervous system. They certainly don’t have a head or opposable thumbs. Plants seem pretty dumb. They just take in nutrients and sunlight, make pretty flowers and tasty fruits, and produce oxygen… right?

The idea of plant intelligence might just be too much for many people - yet some scientists are plowing ahead. As humans we often treat plants as little more than inanimate objects, ignoring or even missing the fact that they’re actually living beings in their own right.  We assume that intelligence and depth of life are saved for those life forms with spines, with large brains, with hair and fast metabolisms.

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What would plant intelligence look like?

Intelligence is a tricky thing to measure, even in humans. The famed IQ test really only looks at one aspect of intelligence, and we all know a few people who seem to have great test scores but no common sense. Intelligence tests get even trickier when we look beyond the human realm because we lose the ability to communicate using language. It’s hard enough to test someone’s smarts when you can talk to them - imagine having to mime your way through a test!

Plants are a whole other matter. Most plants don’t move, and they don’t even seem to have any behavior. They don’t use tools or solve problems… but scientists keep finding little hints of something beyond what we expect.

In animals, intelligence generally involves social communication and problem-solving. Can plants communicate? Can they solve problems?

Let’s not get into exactly what constitutes intelligence here. It’s just too big of a topic. For now, let’s just examine some really unexpected results in plant research. Clearly, plants are capable of far more than simple photosynthesis. They can remove arsenic from water, so they’re already pretty impressive!

Recently, studies on plants have unveiled hints of plant intelligence:

 

Plants respond to classical conditioning.

As a professional dog behavior consultant, I know all about classical conditioning - it’s Pavlov. Give the dog a treat after ringing a bell enough times, and he’ll drool when he hears the bell. He’ll drool after the bell even if there’s no treat.

A recent series of studies by Dr. Monica Gagliano showed that plants might be able to learn a similar response. Since they don’t have brains, we have no idea how they “learn,” but let’s keep using that word for now.

Essentially, Dr. Gagliano “trained” her pea plants that a fan turning on meant life-giving light would appear from that direction. Plants will orient, bend, and grow towards sunlight. She repeated this association for a long time and then found that her plants would start to bend and lean towards the fan even if the light was not on yet. The plants were acting as if they were Pavlov’s dogs, expecting a sunny breakfast.

Later, Dr. Gagliano also showed that Mimosa plants will acclimate to a startling drop. These plants curl their leaves in when touched to protect themselves from being eaten. She dropped the plants a short distance using a machine, over and over. At first, the plants closed their leaves to keep themselves safe. Over time, the plants learned that the short drops from the machine were harmless and stopped responding. They also seemed to “remember” that this drop was safe for a long time after, and continued to not respond to the drops after a long time of living on stable ground.

So far, Dr. Gagliano has demonstrated that at least some plants can “learn” both to predict where food comes from and avoid wasting precious energy on unnecessary leaf-folding.

Learn more about Dr.Gagliano’s work at her website or by listening to the Radiolab episode, Smarty Plants.

 

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Plants can communicate danger.

You read that right. Not only can plants learn to find their food and avoid wasting energy, they can tell each other about the danger. Plants seem to be able to communicate using root networks.

It sounds a lot like Avatar, doesn’t it?

Truth can be stranger than fiction.

Studies on plant communication reveal that plants with extensive root connections seem to be able to “warn” each other of oncoming danger. When one plant in the network is damaged by a caterpillar, other plants that it is connected to start building up their chemical defenses. The caterpillars will avoid these plants if they have the option of selecting plants that were not “warned” of danger.

Oh, yeah. I did say that plants have chemical defenses. Essentially the clover plants in the study produce some chemicals that make their leaves harder to chew and less digestible. The caterpillars would rather eat fresh, naive leaves. This communication warns neighboring clover of danger, and when clover plants build their defenses, caterpillars will go elsewhere.

 

How can I find intelligent plants near me?

The amazing thing about all of these studies is that their subjects aren’t some faraway, exotic Amazonian species. Regular old pea plants learned to follow fans to find sunlight, and plain clover plants warned each other of danger. Scientists say that other plants can probably communicate and learn in a similar way.

Try using the PlantSnap app to identify plants around your home and you might just find the subject of a plant intelligence study!

plant learning lean towards sun behavior cognition intelligence