Plant Neurobiology?

In reference to my July 25 post on "plant intelligence," coincidentally the September/October 2024 issue of SKEPTICAL INQUIRER contains an article by Massimo Pigliucci titled "Are Plants Conscious?" In his view, a science labeled "plant neurobiology," based on the idea that plants could have intelligence or consciousness, constitutes a "category mistake." Neuroscience studies "brains and their associated nervous systems," physical features of animals but not plants. He concedes that plants in a sense process information. As for responding to "environmental cues," he points out that all living creatures do that. He objects to conflating those general terms with the specific types of behavior we call "cognition" and "intelligence" in animals. Moreover, the claim that plants feel pain is extremely unlikely because, as far as anyone knows, pain and awareness of any other physical sensation require a nervous system. He proposes, "Plants are fascinating in part precisely because they are so different from animals."

If plants feel pain, by the way, consider the ethical implications of eating them. I'm reminded of the satirical song "Carrot Juice Is Murder," by the Arrogant Worms. "I've heard the screams of the vegetables, watching their skins being peeled. . . ."

Carrot Juice Is Murder

The PBS network features a miniseries about the vegetable kingdom called GREEN PLANET, hosted by Sir David Attenborough:

Green Planet

Stop-motion photography produces sped-up films of plant growth to illustrate that these organisms are far from inert and passive. Attenborough's narration talks about phenomena such as seedlings and saplings competing with their neighbors for light and air, or fungus in the nests of leaf-cutter ants telling the ants what type of leaves it wants. That kind of language and the accompanying dynamic videos make it temptingly easy to view plants in anthropomorphic or at least theriomorphic terms.

Noticing how English ivy climbs our window screens seemingly overnight after heavy rains, regardless of how often it's trimmed back, I could easily imagine the vines have "conscious" intentions and preferences.

Margaret L. Carter

Please explore love amonng the monsters at Carter's Crypt.

A Plant-Animal Hybrid?

Here's a Wikipedia entry about the emerald green sea slug, a mollusc living in marshes, pools, and shallow creeks, which feeds on algae and incorporates their chloroplasts into its own body. It thereby not only turns green but gains the ability to nourish itself with sunlight:

Elysia Chlorotica

The slug can "capture energy directly from light, as most plants do, through the process of photosynthesis." Once it has established a stable population of chloroplasts, this creature has "been known to be able to use photosynthesis for up to a year after only a few feedings." Some research suggests that a slug may "possess photosynthesis-supporting genes within its own nuclear genome."

An article discussing its biology in less technical language:

The Green Sea Slug Steals Photosynthesizing Power from Algae

The caption on that page declares the emerald green sea slug a true "plant-animal hybrid."

Could a human being -- maybe a superhero mutant -- live on light by photosynthesis, like a tree? I've read this wouldn't be physiologically feasible because that lifestyle requires a mainly stationary existence of standing around exposing a large amount of surface area to the sun for many hours per day. Elysia Chlorotica, however, seems to live like an animal and yet derive nourishment from the sun. Suppose a larger creature with intelligence comparable to ours could do that? Wouldn't that make a cool alien species?

Margaret L. Carter

Please explore love among the monsters at Carter's Crypt.

Plant Intelligence

A new nonfiction book, THE LIGHT EATERS, by Zoe Schlanger, delves deeply into the potential of plant intelligence. According to the blurb, she explores the abilities of plants "to communicate, recognize their kin and behave socially, hear sounds, morph their bodies to blend into their surroundings, store useful memories that inform their life cycle, and trick animals into behaving to their benefit, to name just a few remarkable talents." Here are two articles about THE LIGHT EATERS and the amazing ways plants interact with their environment:

Being Green

The New Science of Plant Intelligence

This topic raises the question of what "intelligence" means. I've always thought of it as a product of consciousness. Yet most people accept that advanced computer programs are in some sense intelligent without being conscious. If plants have intelligence, that quality must not necessarily require consciousness. And what does "memory" mean when applied to a creature without a brain? Do plants engage in "behavior," or should that word be restricted to animals? Botanical research has come a long way since THE SECRET LIFE OF PLANTS (1973) popularized the claim that they enjoy music and benefit from being talked to.

The second article linked above meditates on these questions and related philosophical issues. We human beings have an innate compulsion to "order the universe into comprehensible categories" and a tendency to "rank ourselves at the top." About plant communication, the author of this essay advances the astonishing proposition, "It also changes the notion of what a mind is. We have taken it to be the product of a brain attached to a nervous system, but perhaps a mind is a complex, self-organizing system networked across the entire organism. Perhaps the whole plant is a mind."

Schlanger defines intelligence as "the ability to learn from one’s surroundings and make decisions that best support one’s life,” a criterion plants fulfill. However, the temptation to anthropomorphize them should be resisted. For one thing, as many SF authors have highlighted, they must surely "think" on a different time scale from us. Rather than trying to see plants as human-like, we should appreciate their very alienness.

Margaret L. Carter

Please explore love among the monsters at Carter's Crypt.

Do Plants Think?

A relatively recent (2021) article on plant intelligence, which includes an interview with Monica Gagliano, a professor in Evolutionary Ecology at Southern Cross University in Australia:

Plant Intelligence

It's known that plants can communicate with each other to "warn" their neighbors about potential attacks. Some plants also use animals to defend against pests, such as by releasing chemicals to attract wasps that prey on caterpillars. Researchers have discovered evidence that plants may have "memory" of a sort. In the interview, Gagliano defines intelligence as decision-making in reaction to one's environment. She insists that "you do not need a nervous system or a brain to embody this kind of behaviour and decisions." She goes so far as to declare, "Of course plants are intelligent, as much as bacteria and amoebas, and fish and birds and humans."

Bacteria? That wide-ranging application of the concept may come as a shock to many people's mental categories, as it does to mine. We typically think of intelligence as requiring brains and involving sapience or at least consciousness. I'm reminded of a vintage horror story that begins with a conversation about the nature of mind, in which one character rhetorically asks, "With what does a plant think, in the absence of a brain?" The other character scoffs, while the first maintains that intelligence exists everywhere in many shapes. When or if we eventually travel to extrasolar planets, we might plausibly discover plants or a vegetative group mind possessing a capacity for thought we'd recognize as similar to our own. However, mutual communication might be hard because organisms the size of trees or larger might think on a slower time scale than we do—like Tolkien's Ents, only much more so.

Another article on plant intelligence I came across queried whether, if plants can think in some sense, we would be obligated to stop eating them. If so, we'd be stuck with rather narrow diets, composed entirely of foods we could harvest without killing any complex organism (dairy products, unfertilized eggs, fruits, nuts, honey, the leaves of green vegetables that regenerate throughout the growing season—that's about it). Fortunately, the writer of that essay reassured us we wouldn't, since animals regularly consume plants as part of the cycle of life. Besides, many plants have parts (e.g., fruit) especially meant to be eaten by animals for the purpose of spreading seeds.

Remember the Shmoos in the old "Li'l Abner" comic strip, delicious animals that rejoiced in sacrificing themselves as food?

Shmoo

Maybe on a world shared by intelligent plants and humanoids, some vegetative life forms would partake in a symbiotic partnership whereby they produced renewable offshoots to feed sapient animals in exchange for helpful services such as fertilizing and pest control.

Margaret L. Carter

Carter's Crypt

Slime Mold Intelligence

Slime molds, a type of gelatinous amoebae, despite having no brains, have the capacity to form memories:

Slime Molds Redefine Intelligence

One species "can solve mazes, mimic the layout of man-made transportation networks and choose the healthiest food from a diverse menu." When chopped into multiple pieces and scattered through a labyrinth, a specimen not only reunited its separated bits but modified its behavior to find the most efficient routes. As well as mapping their surroundings and retaining memories of areas they have explored, they apparently "navigate time as well as space, using a rudimentary internal clock to anticipate and prepare for future changes in their environments." The article describes some of the intriguing experiments that revealed slime molds' abilities. Lacking brains or nervous systems, nevertheless they "choose conditions most amenable to their survival" and "remember, anticipate and decide."

I once read a story in which two characters argue about the potential intelligence of some nonliving entity. One man asks, "With what would it think, in the absence of a brain?" The other one counters, "With what does a plant think, in the absence of a brain?" Do slime molds and plants "think"? If we equate intelligence with abstract thought, probably not; if we define it as the ability solve problems through adaptation, intelligence could be attributed to almost any kind of organism. If a centuries-old redwood has thought processes, they might operate on a time scale so different from ours that it couldn't communicate with us. If we visited a world dominated by sapient slime molds, would we recognize their intelligence and vice versa?

Margaret L. Carter

Carter's Crypt

The Internet of Trees

An old song laments, "I talk to the trees, but they don't listen to me." Apparently, however, trees listen to each other. Some of them communicate among themselves by means of a symbiotic fungus connected to their roots:

Plants Talk to Each Other

Mycelia—thin threads that make up the underground portion of mushrooms, far more extensive than the part we see aboveground—"act as a kind of underground internet, linking the roots of different plants." In a symbiotic relationship, mycelia that colonize the roots of plants "help the plants suck up water, and provide nutrients like phosphorus and nitrogen," while the host plant supplies the fungus with nourishment in the form of carbohydrates. The fungus also enhances the host's immune system. In addition, through their mycelial connections some plants "help out their neighbours by sharing nutrients and information – or sabotage unwelcome plants by spreading toxic chemicals through the network." By transferring nutrients such as carbon, phosphorus, and nitrogen, large trees have been found to "help out small, younger ones using the fungal internet."

The article compares this network to the global communication among trees in the 2009 movie AVATAR. The fungal internet also brings to mind Clifford D. Simak's 1965 novel ALL FLESH IS GRASS, which portrays an invasion by a "planetwide biological computer that works through photosynthesis," manifesting in the form of purple flowers, as discussed on this website:

Intelligent Plants in Science Fiction

Do plants in fact have some form of intelligence? A few scientists think they might, according to this article about plant neurobiology:

New Research on Plant Intelligence

Of course, plants don't have neurons. They do, however, display reactions analogous to memory, learning, and response to stress. Their roots shift direction to avoid obstacles without coming into physical contact with the obstruction. Experiments have shown plants producing defensive chemicals when they "hear" a recording of a caterpillar eating a leaf. So it all depends on what we mean by "intelligence."

If we visited a planet dominated by a global hive-mind composed of sentient trees, would we be able to communicate with it? Or would the time scales on which our thought processes operate be too different for mutual comprehension?

Margaret L. Carter

Carter's Crypt