The Light Eaters…, Zoë Schlanger

These are notes on “The Light Eaters: How the Unseen World of Plant Intelligence Offers a New Understanding of Life on Earth“, by Zoë Schlanger. I’m reading this with Rachel.

Contents

Some nicely written turns of phrase

I savored these tears in the fabric of my day [16]
I watched the hard beaks of the purple crocuses crack the cold earth like hatched chicks. [16]
The birds … called wildly, like they were caffeinated. [52]
I had the dreamlike sense that it had just cunningly frozen in place,,, [53]
Nature, never a flat plane has always had more folds and faces still hidden from human view. The world is a prism, not a window. Wherever we look we find new refractions. [61]

Prologue

A beautifully written, lyrical introduction to how the author — a science journalist — became interested in plants. Initially an escape from burnout due to writing about the increasingly dire environmental situation being ushered in by global warming, it turned into a fascination with plants, and the discovery that botany seems on the edge of a revolution in its understanding of plants, particularly with respect to their behavioral/adaptive mechanisms.

Having read the Prologue and Chapter 1:
It looks to be a pleasant and fun read. I hope she will go deeply enough into the science to make it interesting to me.

C1: The Question of Plant Consciousness

Begins by describing the author’s urge to find something more optimistic to pursue than the increasingly dire findings of climate science. She began to follow papers in botany, and then, two weeks into this new pursuit, discovered that the first genome of a fern — a tiny one called Azoola Ficuloides — had been sequenced. This drew her attention to ferns…
Ferns alternate generations, with one generation being what we know of as a fern, and the other being a one-cell thick entity on the forest floor that produce motile sperm that can live for an hour. Some ferns are able to produce chemicals that slow the movement of competing species. Ferns are very ancient, and have up to 720 pairs of chromosomes, compared to the 23 humans have.
Comments on Oliver Sacks’ Oaxaca Journal, and his description of a numinous moment: “when there is a sense of intense reality, almost preternatural reality…” She begins to find descriptions of moments like this scattered throughout the literature on plants, from Dillard’s Pilgrim at Tinker Creek, to the biography of Alexander von Humboldt.
She became interested in plant behavior, and discovered that early research had been squelched by the debacle of The Secret Life of Plants, published in 1973, which caused scientific funding for research on plant behavior/adapatation to dry up until very recently.
Plants exhibit behaviors that seem similar to memory, recognition of genetic kin, the ability to sense the sound/vibrations of running water, and the ability to emit chemical compounds of the predators of pests that are attacking the plants
She talks a bit about her childhood, and her early fascination with plants.
Terminology and tensios. Discussion of the tensions around discussing whether plants can be said to have senses or intelligence or consciousness. Some scientists are wary of repeating the Secret Life, debacle; others argue that these terms are anthropomorphizing what is going on, and it is simply not helpful; others are less wary.

C2: How Science Changes Its Mind

A brief recap of the evolution of plants, beginning with the incorporation of cyanobacteria into at algal like cell 1.5 Ga. She refers to plants as chimera — I’m not sure if she means more than that their cells contain cyanobacteria…???
She ties the oxygenation of the atmosphere to the movement of plants onto land 500 Ma — is this correct? I am a little unsure of her timeline re cyanobacteria and oxygenation… below is what I get from ChatGPT, and so she is roughly correct (if we ignore the great oxygenation event and banded iron formations), although there is a lot more to the story…:
- 3 Ga: Cyanobacteria appear. Banded iron formations appear in geological record.
- 2.4 Ga: The great oxygenation event — Oxygen levels rose from almost zero to about 0.02%-0.04% (still very low compared to today).
- 800-540 Ma: Neoproterozoic Oxygenation event — Oxygen levels began to rise more substantially, reaching about 1-10% of present atmospheric levels (PAL), likely due to the evolution of more complex multicellular life.
- 540 Ma: Cambrian explosion: Oxygen to 10-20% PAL. O2 more prevalent in shallow oceans, facilitating development of more complex ecosystems.
  - 470 Ma: Plants — bryophytes and liverworts, begin colonizing land
  - 430 Ma: Vascular plants appear
  - 400 Ma Plants developed true leaves, roots, and woody tissues, leading to the rise of early tree-like plants such as Archaeopteris, which were among the first plants to form forests. (Flowering plants and seeds did not appear until 150 Ma)
- 360 Ma: Carboniferous: O2 reaches 1.5 PAL (35%) due to worldwide forests
- 300 Ma-present: O2 fluctuates but generally decreases and stabilizes at 21%

She goes on to describe photosynthesis and make the point about how all carbohydrates (and all organic compounds, for that matter) on earth were produced by plants.
She notes that plants are immobile, and that thus they have to develop a variety of strategies for dealing with predators, reproduction, and forming and maintaining communities.
She then shifts to Kauai, and biologists involved in trying to save species on the edge of extinction. She notes that it is estimated that 1 or 2 plant seeds made it to Kauai every 1,000 years, and thus it was fertile ground for adaptive radiation, and also that, in the absence of predators, plants lost their normal defense mechanisms (toxins, thorns, etc.) As a consequence, Kauai is losing plant species at a rate of 1-2/year, vs. a normal rate of 1-2/10,000 years.
Next she turns to human conceptions of plants — especially vis a vis sentience and awareness — and looks at the opinions of philosophers through the ages. Aristotle is the great villain in the demotion of plants of insensate organisms… With the exception of Theophrastus, Aristotle’s successor, who was ignored, plants were disregarded until Darwin began studying them after publication of TOofS, eventually writing four books on aspects of plant ‘behavior.’
Darwin was particularly taken with the “root cap” of plant roots, noting that it was exquisitely sensitive and could guide the growth of the root, and that it was the only part of a plant which, if removed, would grow back in exactly the same form.

reading break; next discussion Monday, 7 October 2024

C3: The Communicating Plant [Chemical Signaling]

There is a lot here I don’t agree with. The definition of communication seems very loose, and I suspect that simple signaling between plants will ‘inherit’, without any proof, characteristics of human-human communication. For example: “Communication implies a recognition of self.” — I don’t agree. And also “Communication is the formation of threads between individuals.” What does “threads” even mean? And what is meant by “individual?” Very fuzzy.

That is not to say that there are not some very interesting phenomena:

1977/1983: David Rhodes, Caterpillars and the Forest. In 1977, David Rhodes, studying the invasion of an experimental forest by a wave of caterpillars discovered that after a couple of years, the caterpillars suddenly began to dies as they fed on the trees because they had started producing toxins their leaves. Furthermore, trees that the caterpillars had not yet reached were also producing these toxins in their leaves. Conclusion: the trees were “communicating” ((or, at least, the affected trees were transmitting signals to unaffected trees that triggered toxin production)). However, although communication via roots had already been established, these trees were too far apart for this to be the explanation: Rhodes posited that communication was due to substances being released into the air.
Multicellular Organisms. At this point she zooms out and talks about the evolution of multicellular organisms, and what this means: “Each cell in an organism must know who it and what it does.” She goes on to talk of cells “communicating” with one another, and having “awareness.” I don’t care of the way this is expressed, but it does connect with points made in “The Master Builder.”
Definitions. She defines “communication” as when a signal is sent, received and causes a response. I think this can be simplified to “as signal is sent and causes a response.” I note that she does not require intentionality. So, with this definition, we can say a thermostat ‘communicates.’ OK, but this is such a broad definition that I’m not sure its useful, and I am wary that connotations of more complex forms of communications will be uncritically brought into play where they may not belong.
Rhodes as ‘ignored pioneer.’ Rhodes published on his research in 1983. Schlanger paints a picture of Rhodes being attacked (“bludgeoned”) by colleagues, though she does not provide references or describe in what ways or for what reasons he was attacked. She does mention, in passing, that he was unable to replicate his results — this is a huge problem, but she skates over it. Eventually, he stopped applying for grants, focused more on teaching, and then died. I suppose this is a nice bit of drama for the book…
1983: Baldwin and Schultz published a similar, lab-based finding in 1983, about 6 months after Rhodes. They were able to show, in an experiment with maple seedlings, that damaging the leaf of one seedling would cause other seedlings — whose roots were isolated from one another — to produce protective tannins in their leaves. Unlike Rhodes, Baldwin and Schultz’s careers prospered, even though, unlike Schultz, they used the word “communication” in their papers. To my eye, this discredits Schlanger’s narrative about Rhodes.
1`985: Wooten van Hoven observes in 1985 that kudu had suddenly begun dying on ranches in south africa. It appears to be due to (a) their feeding on acacia leaves triggering a build up of toxins in the leaves, and (b) the fact that they were confined on ranches and had no other food sources. Later, investigating why this was not a problem for giraffes, found that they did not graze on most acacias, but rather only on ones that were up-wind from already-damaged trees — and of course they were not confined and had plenty of options.
2019/2021: Rick Karban. Sagebrush releases chemicals that can be interpreted by nearby wild tobacco (which can release chemicals that attract predators that prey on caterpillars that are attacking them); also the chemicals released by sagebrush get a stronger response from sagebrush that are more genetically related.
Aino Kalske, et al. found that goldenrod that live in fairly benign environments release chemicals that can only be interpreted by kin; whereas goldenrod that live in more dangerous environments release chemicals that can be interpreted by goldenrod regardless of degree of kinship. The claim here is that this shows that the chemical communication is beneficial to the sender as well as the receiver… Later: oh, I think the claim is that the signaling benefits other plants rather than just the other parts of the sender. Still, I don’t see that that makes it “communication.” This is imagined as using public or private channels, and having ‘dialects’ and having a clear sense of who is who. — I find this pretty dubious.
Personalities — bundles of particular ways of acting or responding that differ between individuals. Researchers are looking at these in animals, and now in plants. Karban’s work seems to involve framing this as ‘tolerance for risk.’ Um. Certainly, it is easy to imagine that plants might find different balances between the speed and amount and type of signals they produce, and the expenses that those incur. It would make evolutionary sense for that to vary across a population, just as diversity in other characteristics varies — robustness is good.

C4: Alive to Feeling [Electricity]

How electricity works in organisms: calcium (etc.) channels and action potentials.
Anesthesia interfere’s with action potentials — venus flytraps and mimosa can be anesthetized. So can pea plants, which slowly wave their tendrils around over the course of 20 minutes.
Stoking plants can cause them to stop elongating and instead thicken their stems; other plants may grow more flexible. These responses can be seen as making the plant more resilient to winds and other forms of physical disturbance.
J.C. Bose (1920’s) showed that plants exhibited electrical responses to various stimuli.
Barbara Pickard (1993) discovered that plants have calcium channels that enable them to transmit electrical impulses.
Gilroy and Toyota (). Wound a plant, and a wave of electrical activity propagates across the whole plant. Possibly due to glutamate.
“Could the whole plant be a brain?” …I don’t think so.

reading break; next discussion 11/04/2024