Animal advocates and wildlife enthusiasts like you and me are always excited when new research comes out demonstrating the intelligence of the “others” among us; for example, how crows solve problems or whales have complex cultures. But when we cross over into the area of plant intelligence, well, it often sounds a bit too New Agey for most of us.
A recent spate of studies, however, is proving that plants have volition, show altruism and understand kinship much like many animal species. Could this dramatically change how we view plants and, in turn, make us care about what happens to them in the way we’re concerned about threatened, charismatic wildlife?
Moving and mental ability
Four years ago, in 2011, I wrote an article about the intelligent behavior of trees. While those who commented on the blog had mostly positive things to say, social media posters had a field day with the piece. “Nonsense” wrote one and “Having a slow news day?” penned another.
In the years since, however, a number of new studies are continuing to show that plants are smarter than we think. It’s tempting to believe that since plants are rooted in place, they aren’t capable of the complex thought processes that an animal that can run from predators or make its way across town for a cup of coffee is competent enough to achieve. But in a recent article in National Wildlife, author Janet Marinelli cited several reports to the contrary, including one by Italian botanist Stefano Mancuso, a University of Florence professor and plant neurobiology pioneer, who states that just because plants can’t move or run in the way that we do doesn’t mean they aren’t smart.
In 2005, Mancuso and a group of international scientists established The Society for Plant Neurobiology to study sophisticated behavior in plants—much to the jeers of many of their colleagues. By 2010, Mancuso had enough data to give a TED (a nonprofit established to spread new ideas) talk on plant intelligence. In it, he notes that plants are much more sophisticated in sensing what’s around them than animals. Every plant root tip has a tiny region that functions as the locus of electrical signals—the same signals found in human neurons. In essence, every single root apex in a plant’s system can detect and monitor concurrently and continuously at least 15 different chemical and physical parameters. For a plant, a centralized neurological control center (such as a human brain) doesn’t make much sense because a predator—a grazing deer or lawn mower—could easily chop it off. So instead, this decentralized intelligence scattered throughout the roots works as a very effective survival strategy; a plant can persist when even 90 percent of its root tips are clipped.
As for movement, plants do move and they do so with intention. A plant flowers (activity that’s easy to see in time-lapse photography), orients its leaves to follow the light, goes into sleep mode and even “plays” (for visual proof, click on this TED talk link).
Doing the math
Not only do plants engage in neuron-like activity and movement, they make mathematical computations, see us and, like animals that act altruistically, show kindness toward their relatives. They are able to recognize themselves and communicate with animals and other plants via alluring airborne fragrances and a diverse repertoire of chemical compounds exuded through their roots.
In 2013, Antonio Scialdone and fellow scientists at the United Kingdom’s John Innes Centre who were studying Arabidopsis thaliana found that these small weeds in the mustard family are capable of doing some complex arithmetic to prevent starvation at night. Requiring starch to survive, the plants manufacture it by photosynthesizing sunlight. During the night, they measure the amount of starch left in their leaves, use an internal clock to estimate the amount of time until dawn, then divide their food reserve by the expected time to dawn so they have enough starch to last until the sun rises. They’re incredibly accurate: by the time they resume photosynthesis, about 95 percent of their starch has been consumed.
According to Marinelli, in 2012 Daniel Chamovitz, director of the Manna Center for Plant Biosciences at Tel Aviv University and author of What a Plant Knows, reported that plants “see” us via photoreceptors that perceive different wavelengths of light. They are aware of when we come near them and whether we’re wearing a blue or red shirt.
In yet another study, in 2007 plant ecologist Susan Dudley of McMaster University in Ontario, Canada, worked with sea rockets—members of the mustard family native to beaches throughout North America, including the Great Lakes—to investigate whether plants can recognize their relatives. Dudley and a graduate student found there was less root competition when closely related “siblings” shared the same pot than when groups of strangers grew in a common container. This demonstrated that the sea rockets not only recognized but acted altruistically toward their relatives, a behavior known as “kin recognition.”
Other studies have indicated that plants are capable of self-recognition. In 1991, researchers Bruce Mahall of the University of California–Santa Barbara and Ragan Callaway, now at the University of Montana, found that the roots of white bursage plants, residents of the Mojave and Sonoran Deserts, inhibited the growth of other plants with which they came into direct physical contact but did not impede the growth of their own roots, meaning that they could distinguish “self” from “other.”
According to the Center for Biological Diversity, of the more than 300,000 known species of plants, the International Union for Conservation of Nature (IUCN) has evaluated only 12,914, finding that about 68 percent of evaluated plant species are threatened with extinction. Will such new findings on the intelligence of plants cause us to treat them with more respect?
Perhaps your crazy aunt that sings to her plants and way-out-there blog writers who report news about talking trees are on to something after all.
Will a shift in thinking about plants as sentient beings help save them from extinction? Or is plant intelligence research too esoteric to translate into legislative actions?
Here’s to finding your true places and natural habitats,
That´s exacly why you all should stop eating meat, since 90% of forests are being cut down to make room for animal agriculture. If you really respect plants, stop eating animals and destroying the jungles and forests for the taste of meat. With all the grains industrial agriculture feed “livestock” we could feed 10 times over the whole world population. Stop justifying what cannot be justified. Leave the animals alone, none of them have done anything to any of us. Go vegan.
No plants are not sentient in the commonly understood, or really any actual definition of the word. A predetermined and fixed response to stimuli or sets of chemical reactions which is what is happening in each of these cases, does not make a plant sentient or intelligent. A computer character or a robot can be created to do the same things. Of course plants can sense blue or red colored shirts. They a genetically programmed (evolved) to respond differently to red light for reasons not worth getting into. Plants lack the ability to make choices. They can only follow a very complex, yet technically predictable formula through sets of chemical reactions.
How would you know, what if the reason they are tasty is simply because they are smart enough to know that humans will cultivate more of them. Is Pot smart, it is becoming one of the quickest spreading plants on earth because people get high on them, animals do to, but it doesnt help the plant spread.
“They can only follow a very complex, yet technically predictable formula through sets of chemical reactions.”
What are human emotions?
I very much enjoyed this piece. As a docent at Foster Botanical garden in Honolulu,I feel I’ve experienced some indication that the trees in particular exhibit some sort of “intelligence”.
Clear indications of reaction to stimuli are often noted. I believe there is a reluctance to anthropomorphize trees, as a person who believes in tree sentience, I think we limit ourselves by equating the innate intelligence of trees with that of humans. Perhaps, just perhaps, trees possess an as yet unidentified type of sentience and limiting that to the animal type is erroneous. After all, they’ve been here much longer, survived and adapted to many more changes and communicate in ways we don’t yet fully understand. They will likely also be here well beyond our span on the planet.
The Sikh Guru reveals that real peace can only be found when desire and greed are subdued and diminished. This will only happen when the individual realises that God is found in all the elements including water, earth and the woods and he stops damaging these elements purely to satisfy his material greed.
Air, water earth and sky are God’s home and temple – sacred places which need to be protected and looked after. The Sikh Gurus built many Gurdwaras surrounded by large pools which supported marine life, especially fish. This was clearly a sign to live in harmony with nature rather than in conflict with it.
Further, Gurbani refers to various species of trees, eulogising species, which are useful to the world and its various beings and creatures. The Gurus inferred that it is not the girth, size, or beautiful flowers that determine the significance of a tree but its usefulness that makes it important. The trees that have sanctity in Sikhism include Bohr (Ficus bengalensis), Pipli (Ficus religiosa), Jand (Prosopis spicigera), Garna (Capparis horrida), Karir (Capparis aaphylla), Phalahi (Acacia modeta), Reru (Mimasa leucophloea), Luhura (Cordia latifolia), Tahli (Shisham), Imli (Tamarind), Amb (Mangifera indica), Harian velan, Neem (margassa), Ritha (Sapindus mukorosa), Kalp (Mitragina parvifolia) and Ber (Zizyphus jujube). Perhaps no other religion has given importance to vegetation the way Sikhism has. Four of the most sacred trees associated with the Sikh shrines, namely beri of Dukh Bhanjani Beri of Sri Harmandir Sahib, Beri of Baba Budha (also of Sri Harmandir Sahib), Beri of Gurdwara Ber Sahib of Sultanpur Lodhi and Beri of Lachi Ber of Sri Harmandir Sahib highlight the role that trees have played in Sikh history. The world started talking about environment and ecological balance only during the past three to four decades while the Gurus realised their significance more than 500 years ago.
I loved this article! Especially since I am a science fiction author in the process of writing a story about a telepathic walking plant. I’m a physicist who could use some help from someone on the technical parts, like where the botanist in the story is studying his DNA. Any takers?
We can call anyone and anything “sentient”, sensitive”, “intelligent” and many other names as we please for many reasons. Just because someone desires to call plants “sentient” it doesn’t mean that we should feed our selves rocks, mud or rubber. I know this: Plants exist to keep the earth cool, filter the air and feed the species born herbivore and omnivore. Like: cows, horses, elephants, zebras, donkeys, goats, sheep, dogs, people,etc. It doesn’t mean that we should stop eating them at all. It only means that we must learn to respect, appreciate, protect and let them grow and thrive. The more plants – the better for everyone (human or not). Ripping off the roots of many plants is wrong and horrible thing to do. Just as is horrible to kill the entire cherry tree just to eat it’s fruits. I find that many kids and even adults have no idea what respect towards other species is. They are so brutal, arrogant, selfish and greedy that are ready and willing to destroy everything in their path for quick profits, leaving only devastation and death behind. Yet these days seem “normal” and even good thing to do. The arrogance, audacity and sense of entitlement some individuals have is appalling. Their moral compass completely out of whack and is scary. If we say nothing and do nothing – they will continue to thrive and destroy even more. The “human” race is without “humanity” … nothing to be proud off.
The way we have measured intelligence in other living beings has always depended on how we measure intelligence within our race. Thank you Candy for this wonderful article.
I’ve known this my whole life! The part of this docu that really stuck with me is at 42:21.
I’m so glad you posted that link. I’ve not seen that movie for 20+ years, but its always stayed w/me. Every time the topic of sentient plants I always think of “The Secret Life of Plants”. It actually had a great Stevie Wonder soundtrack as well!
I did always have an issue with the idea that it is immoral to kill animals but it’s OK to chomp your way through every plant that that isn’t immediately toxic… Perhaps the true moral issues lie in the way we farm ~ are we treating the animals and plants with respect while they live or being unnecessarily cruel?
Some acacias have worked with some ant species to my symbiotic relationships, with providing easy to grab and store bits of food for the ants, as well as openings in their thorns to they can live inside the trees, and the ant attack any animal or plant predators of their trees.
Many plant species have figured out how to entice, trap and eat small animals.
Some plants mimic animal scent amazingly (the largest flower in the world and other arums mimic dead mammal scent well enough to fool vultures, while other arums use other scent, like manure or yeast to attract preferred fly pollinators.
Plants are just slower than animals….
in the beginning God created the heavens and earth.
What does this have to do with plants being sentient?
It’s interesting to see how many people here are either totally opposed to this idea, or else they’re cynical and self-serving. As for ” “sentient” is not a synonym for “alive,” well, yeah, I think we’re all grownups here, and we all know that.
I have no real idea if plants are sentient or not, but I suspect that they might well be. Most people can’t see much beyond their own nose(s), and are all too often guilty of knee-jerk negative responses anytime something challenges their long held ideas. Personally I suspect that many, if not most, life forms are sentient, and that we simply can’t fathom what we don’t understand. There’s a great deal more about nature that we do not understand, than that which we do.
Thank you, Candice for this interesting and provocative post.
While I am impressed and awed by these findings, I am also not surprised. Sometimes I can sense sentience in a plant.
I”ll be with you when, with the first bite, my salad yells “OUCH”
Sea cucumbers are an animal, similar to a slug or worm, but they have no brain, heart, lungs or blood. Are they sentient? I love biting into them while they are still alive and hearing them yell “OUCH”.
Sea cucumber the animal, continental cucumber the plant, both where once living before you took that bite, who gave us the right to determine which life to take? Or if we just eat the cucumber and don’t kill the whole plant shall we just eat small portions of animals instead? Lizards tails grow back, so do crabs claws, earth worms can regenerate..
If your so compassionate about sentient beings do you investigate where your clothes and everyday items come from to ensure they haven’t been produced by slave labour or are blood diamonds etc?
Do you extract the vitamins and minerals in your fruit and veggies that came from fertilisers containing animal products?
Say a little prayer for all the insects that die as a result of insecticides?
Exploiting animals to pollinate the cotton plants for the clothes you wear when they could instead be pollinating any one of the tens of thousands of plant species that are in danger of becoming extinct? ouch..
Accepting this article at face value requires understanding the word “sentient” means “able to perceive or feel (i.e., respond to) the environment.” It does not mean *intelligent,* in the sense of having “will” or “agency,” or “volition.” And while I accept that languages are living, evolving systems much the way organisms are, I think in this case, the word is very poorly applied at best, deliberately misleading at worst.
Plants clearly sense their environments; this is not in dispute, I think.
Vis-a-vis Scialdone et al. (https://elifesciences.org/content/2/e00669), comparisons can be made to a Turing Test; passing the test doesn’t (necessarily) indicate intelligence, it indicates success at replicating a correct response–which is in no way “intelligence” or “sentience.” It’s just practice–and Natural Selection is really good at practicing.
Having studied with Mahall, I can confidently assert here Ms. Andrew’s interpretation of the 1991 (actually 1990) study on _Ambrosia_ and _Larrea_ is more about root-mediated plant-plant chemical interactions; some plants exude chemistries into the soil which negatively affect other plants. This doesn’t require a sense of self, only a naturally-selected capability to survive its own poisoning of a shared environment.
Some plant species also communicate with each other when they are browsed by game and then all the members of that species in a particular locality can change their biochemistry to become toxic to the animals. Game farmers who have kept kudu in confined spaces have lost animals due to this.
All this depends on your definition of “Smart”, “Intelligence”, “Sentience” etc.
But almost all of this can be programmed as auto responses. IF a stationary computer / robot in a specific factory can deal with all conceivable permutations and combinations of the manufacture process specific to its area of residence, does that mean that the system is sentient, or the chap/s that programmed it is/are sentient?? Even if we take artificial intelligence algorithms, does this make a robot/computer sentient??
Or are we confusing the word sentient with the word – alive?? Or do we have a natural compulsion to read the two words in conjunction, albeit subconsciously?
I think it is more valid to consider the matter from the slant of Mind. Is a plant mindful? And what is it to be Mindful??
This was inevitable.
Comment from a former colleague: “salad is what food eats”.
Anthropomorphism is a trap based on the notion that we actually understand what our brain is doing and can recognize it in other species and the erroneous notion that similitude is correlation.
Of course plants can do some curious things. My nasturtium seedlings can clock to the sun at an easily visible speed … don’t know if they’re PO’d when I flip their tray 180.
While studying phytochrome, one of those plant visual pigments, in grad school in the early 80s I took a med biochem class that studied human neurochemistry. I was struck by the similarities structurally between plant growth regulators and animal neurotransmitters. I came to the conclusion that plants did indeed have neurotransmission mechanisms; however, they did not evolve under the pressure of time response that animals did. Plants lack mobility for the most part, so they can react slowly.
Another interesting divergence is the size of most plant genomes. They tend to be much larger than animal genomes; they often have much more DNA and much more duplication. Under threat, they have mechanisms to induce higher rates of variance.
Taken together these define beings that have slower responses to their environment, but that nonetheless react and adapt, and they store more of this ability in their genomes: more ‘intelligent DNA’ in the sense that adaptation represents intelligence.
Thanks for a very interesting piece, Candy! And I appreciate the references to other work!! I’ll check some of it out…
I think it’s a bit of leap in faith to think plants have a state of consciousness. For example the example of the mustard plants calculating their starch reserves to last the night seems less a matter of intentional activity and more a evolved response to their environment.
I wonder what would happen if the plant is (in the middle of the night) transported to another time zone. Would the plant “calculate” the correct time or fail to do so?
Interesting Candice. But then, as living things, we expect them to have some expressions of life too.
What an interesting article! We share a huge proportion of our genetic heritage and biological systems with plant life so research such as this shouldn’t really come as much of a surprise should it. I’ve been reading a wealth of papers on Google scholar recently regarding this research area and it is increasingly relevant at a time when sadly it appears we are only just beginning to grasp the critical importance of complex ecological systems which our species is dependant upon. https://en.wikipedia.org/wiki/Life
Animals are sentient beings and yet we do eat them. The article does not says that we should stop eating plants but it talks about respect.
The fact that plants could be more “intelligent” than we presuppose is just another example that we should respect all things that are alive with all their differences.
But I am not optimistic: human beings are still killing each other because of cultural differences and racism is still rampant (even though there is only one single race: the human race). We are then far from having the cognitive and emotive ability for empathy towards other species when we can’t even have it for our own.
Thank you, Candice, for posting this. Plant intelligence is an intriguing topic.
I guess we should stop eating them?