Learning and Feeling

Re: the  NOVA/PBS video on slime mold. 

Slime molds are certainly interesting, both as the origin of multicellular life and the origin of cellular communication and learning. (When I lived at the Oppenheims’ on Princeton Avenue in the 1970’s they often invited John Tyler Bonner to their luncheons, but I don’t remember any substantive discussion of his work during those luncheons.)

The NOVA video was interesting, despite the OOH-AAH style of presentation (and especially the narrators’ prosody and intonation, which to me was really irritating and intrusive), but the content was interesting – once it was de-weaseled from its empty buzzwords, like “intelligence,” which means nothing (really nothing) other than the capacity (which is shared by biological organisms and artificial devices as well as running computational algorithms) to learn.

The trouble with weasel-words like “intelligence,” is that they are vessels inviting the projection of a sentient “mind” where there isn’t, or need not be, a mind. The capacity to learn is a necessary but certainly not a sufficient condition for sentience, which is the capacity to feel (which is what it means to have a “mind”). 

Sensing and responding are not sentience either; they are just mechanical or biomechanical causality: Transduction is just converting one form of energy into another. Both nonliving (mostly human synthesized) devices and living organisms can learn. Learning (usually) requires sensors, transducers, and effectors; it can also be simulated computationally (i.e., symbolically, algorithmically). But “sensors,” whether synthetic or biological, do not require or imply sentience (the capacity to feel). They only require the capacity to detect and do.

And what sensors and effectors can (among other things) do, is to learn, which is to change in what they do, and can do. “Doing” is already a bit weaselly, implying some kind of “agency” or agenthood, which again invites projecting a “mind” onto it (“doing it because you feel like doing it”). But having a mind (another weasel-word, really) and having (or rather being able to be in) “mental states” really just means being able to feel (to have felt states, sentience).

And being able to learn, as slime molds can, definitely does not require or entail being able to feel. It doesn’t even require being a biological organism. Learning can (or will eventually be shown to be able to) be done by artificial devices, and to be simulable computationally, by algorithms. Doing can be simulated purely computationally (symbolically, algorithmically) but feeling cannot be, or, otherwise put, simulated feeling is not really feeling any more than simulated moving or simulated wetness is really moving or wet (even if it’s piped into a Virtual Reality device to fool our senses). It’s just code that is interpretable as feeling, or moving or wet. 

But I digress. The point is that learning capacity, artificial or biological, does not require or entail feeling capacity. And what is at issue in the question of whether an organism is sentient is not (just) whether it can learn, but whether it can feel. 

Slime mold — amoebas that can transition between two states, single cells and multicellular  — is extremely interesting and informative about the evolutionary transition to multicellular organisms, cellular communication, and learning capacity. But there is no basis for concluding, from what they can do, that slime molds can feel, no matter how easy it is to interpret the learning as mind-like (“smart”). They, and their synthetic counterparts, have (or are) an organ for growing, moving, and learning, but not for feeling. The function of feeling is hard enough to explain in sentient organisms with brains, from worms and insects upward, but it becomes arbitrary when we project feeling onto every system that can learn, including root tips and amoebas (or amoeba aggregations).

I try not to eat any organism that we (think we) know can feel — but not any organism (or device) that can learn.


Yes, plants can produce sounds when they are stressed by heat or drought or damage.

They can also produce sounds when they are swayed by the wind, and when their fruit drops to the ground.

They can also produce sights when their leaves unfurl, and when they flower.

And they can produce scents too.

And, yes, animals can detect those sounds and sights and scents, and can use them, for their own advantage (if they eat the plant), or for mutual advantage (e.g., if they are pollinators).

Plants can also produce chemical signals, for signalling within the plant, as well as for signalling between plants.

Animals (including humans) can produce internal signals, from one part of their immune system to another, or from a part of their brain to another part, or to their muscles or their immune system.

Seismic shifts (earth tremors) can be detected by animals, and by machines.

Pheromones can be produced by human secretions and detected and reacted to (but not smelled) by other humans.

The universe is full “signals,” most of them neither detected nor produced by living organisms, plant or animal.

Both living organisms and nonliving machines can “detect” and react to signals, both internal and external signals; but only sentient organisms can feel them. 

To feel signals, it is not enough to be alive and to detect and react to them; an organ of feeling is needed: a nervous system.

Nor are most of the signals produced by living organisms intentional; for a signal to be intentional, the producer has to be able to feel that it is producing it; that too requires an organ of feeling.

Stress is an internal state that signals damage in a living organism; but in an insentient organism, stress is not a felt state.

Butterflies have an organ of feeling; they are sentient. 

Some species of butterfly have evolved a coloration that mimics the coloration of another, poisonous species, a signal that deters predators who have learned that it is often poisonous. 

The predators feel that signal; the butterflies that produce it do not.

Evolution does not feel either; it is just an insentient mechanism by which genes that code for traits that help an organism to survive and reproduce get passed on to its progeny.

Butterflies, though sentient, do not signal their deterrent color to their predators intentionally.

Nor do plants that signal by sound, sight or scent, to themselves or others, do so intentionally.

All living organisms except plants must eat other living organisms to survive. The only exceptions are plants, who can photosynthesize with just light, CO2 and minerals.

But not all living organisms are sentient.

There is no evidence that plants are sentient, even though they are alive, and produce, detect, and react to signals. 

They lack an organ of feeling, a nervous system.

Vegans need to eat to live.

But they do not need to eat organisms that feel.

Khait, I., Lewin-Epstein, O., Sharon, R., Saban, K., Perelman, R., Boonman, A., … & Hadany, L. (2019). Plants emit informative airborne sounds under stress. bioRxiv 507590.

Wilkinson, S., & Davies, W. J. (2002). ABA‐based chemical signalling: the co‐ordination of responses to stress in plantsPlant, cell & environment25(2), 195-210.


Oui, les plantes peuvent produire des sons lorsqu’elles sont stressées par la chaleur, la sécheresse ou les dommages.

Elles peuvent également produire des sons lorsqu’elles sont agitées par le vent et lorsque leurs fruits tombent au sol.

Elles peuvent également produire des vues lorsque leurs feuilles se déploient et lorsqu’elles fleurissent.

Et elles peuvent aussi produire des parfums.

Et, oui, les animaux peuvent détecter ces sons, ces vues, et ces odeurs, et ils peuvent les utiliser, pour leur propre avantage (s’ils mangent la plante) ou pour un avantage mutuel (s’ils sont des pollinisateurs).

Les plantes peuvent également produire des signaux chimiques, pour la signalisation à l’intérieur de la plante, ainsi que pour la signalisation entre les plantes.

Les animaux (y compris les humains) peuvent produire des signaux internes, d’une partie de leur système immunitaire à une autre, ou d’une partie de leur cerveau à une autre partie, ou à leurs muscles ou à leur système immunitaire.

Les déplacements sismiques (tremblements de terre) peuvent être détectés par les animaux ainsi que par les machines.

Les phéromones peuvent être produites par les sécrétions humaines et elles peuvent être détectées et réagies (mais non sentis) par d’autres humains.

L’univers est plein de « signaux », dont la plupart ne sont ni détectés ni produits par des organismes vivants, végétaux ou animaux.

Les organismes vivants et les machines non vivantes peuvent « détecter » et réagir aux signaux, qu’ils soient internes ou externes ; mais seuls les organismes sentients peuvent les ressentir.

Pour ressentir des signaux, il ne suffit pas d’être vivant, de les détecter et d’y réagir ; il faut un organe du ressenti : un système nerveux.

La plupart des signaux produits par les organismes vivants ne sont pas non plus intentionnels ; pour qu’un signal soit intentionnel, il faut que le producteur puisse ressentir qu’il le produit ; cela aussi exige un organe du ressenti.

Le stress est un état interne qui signale des dommages dans un organisme vivant ; mais dans un organisme non sentient, le stress n’est pas un état ressenti.

Les papillons ont un organe du ressenti ; ils sont sentient.

Certaines espèces de papillons ont évolué une coloration qui imite la coloration d’une autre espèce vénéneuse, un signal qui dissuade les prédateurs qui ont appris que c’est souvent toxique.

Les prédateurs ressentent ce signal; les papillons qui le produisent ne le ressentent pas.

L’évolution darwinienne ne ressent pas non plus ; c’est juste un mécanisme non sentient par lequel les gènes qui encodent les traits qui aident un organisme à survivre et à se reproduire sont transmis à sa progéniture.

Les papillons, bien que sentients, ne signalent pas intentionnellement leur couleur dissuasive à leurs prédateurs.

Les plantes qui signalent par le son, la vue ou l’odeur, à elles-mêmes ou aux autres, ne le font pas non plus intentionnellement.

Tous les organismes vivants, à l’exception des plantes, doivent manger d’autres organismes vivants pour survivre. Les seules exceptions sont les plantes, qui peuvent effectuer la photosynthèse avec juste de la lumière, du CO2 et des minéraux.

Mais tous les organismes vivants ne sont pas sentients.

Il n’y a pas de preuve que les plantes soient sentientes, même si elles sont vivantes, et produisent, détectent et réagissent aux signaux.

Il leur manque un organe de ressenti, un système nerveux.

Les véganes nécessitent manger pour survivre.

Mais ils ne nécessitent pas manger les organismes qui ressentent.

Khait, I., Lewin-Epstein, O., Sharon, R., Saban, K., Perelman, R., Boonman, A., … & Hadany, L. (2019). Plants emit informative airborne sounds under stress. bioRxiv 507590.

Wilkinson, S., & Davies, W. J. (2002). ABA‐based chemical signalling: the co‐ordination of responses to stress in plantsPlant, cell & environment25(2), 195-210.

What Matters

Based on my last few years’ experience in teaching my McGill course on human cognition and consciousness, I now regret that I had previously been so timid in that course about pointing out the most fundamental bioethical point there is — the basis of all morality, of all notions of right and wrong, good and bad; indeed the basis of the fact that anything matters at all. I think it leads quite naturally to the nutritional points some want to convey, but starting from the bioethical side and then moving to the human health benefits. (Bioethics is not “politics”!)

Biological organisms are living beings. Some (not all) living beings (probably not plants, nor microbes, nor animals with no nervous system) are also sentient beings. That means they are not just alive, surviving and reproducing; they also feel.

And with feeling comes the capacity to be hurt. Chairs & tables, glaciers & shorelines, and (probably) plants & microbes can be damaged, but they cannot be hurt. Only sentient beings can be hurt because it feels like something to be hurt.

Most organisms are heterotrophic, meaning that they have to consume other organisms in order to survive. (The exceptions are autotrophs like green plants, algae and photosynthetic bacteria.)

This means that nature is full of conflicts of vital (life-or-death) interests: predator vs. prey. If the prey is sentient (i.e., not a plant), this means that the predator has to harm the prey in order to survive (by killing and eating it) — and the prey has to harm the predator to survive (by fighting back or escaping, depriving the predator of food).

It also has to be pointed out that there is no point trying to make conflicts of vital interest into a moral issue. They are a biological reality — a matter of biological necessity, a biological imperative — for heterotrophic organisms. And there is no right or wrong or choice about it: The survival of one means the non-survival of the other, as a matter of necessity.

But now comes the unique case of the human species, which is sentient and also, like all heterotrophic species, a predator. Its prey are plants (almost certainly insentient)  and animals (almost certainly sentient). But unlike obligate carnivores (like the felids), humans also have a choice. They can survive, in full health, as either carnivores or herbivores, or both. We are facultative omnivores.

The primates probably evolved from earlier herbivore/insectivore species, but there is no doubt that most primates, including the great apes, are also able to eat small mammals, and sometimes do. Our own species’ evolutionary history diverged from this mostly herbivore origin; we became systematic meat hunters; and there is no doubt that that conferred an adaptive advantage on our species, not just in getting food but also in evolving some of the cognitive traits and the large brain that are unique to our species.

Far fewer of our ancestors would have survived if we had not adapted to hunting. They did it out of necessity; a biological imperative — just as it was under pressure of a biological imperative that our ancestors, especially children, evolved a “sweet tooth,” a predilection for sugar, which was rare, and it was important to consume as much as we could when we could get it, because we had many predators and needed the energy to escape. By the same token, our predilection for aggression and violence, toward other species as well as our own, had been adaptive in our ancestral environment.

But in our current environment many of these ancestral predilections are no longer necessary, and indeed some of them have become (mildly) maladaptive : Our predilection for sugar, now abundant (whereas predators are almost nonexistent), when unchecked, has become an important cause of dental cavities, hyperactivity, obesity and diabetes (but not maladaptive enough to kill or prevent enough of us from reproducing to eliminate their genes from our gene pool). Our predilection for aggression and violence, when unchecked, is leading to ever more deadly forms of warfare and devastation (but not deadly enough, yet).

And in the same way, our unchecked taste for animal protein has led to industrial production of livestock, water depletion, air pollution, climate change, antibiotic overuse (creating superbugs), and a large variety of human ailments (on which others are more expert than I). But the point is that we have retained our hominid capacity to survive, in full health, without animal protein. We are, and always have been, facultative omnivores — with two metabolic modes herbivore and omnivore — that could adapt to different environments. 

So far, I’ve only mentioned the negative consequences of animal protein consumption for us along with the positive consequences of  not consuming animal protein, for us.
But let me not minimize the moral/bioethical aspect. Even if, setting aside the climatic aspects, the direct health benefits of our no longer eating meat are, for us, only mild to moderate, the harm and hurt of our continuing to eat meat are, for our sentient victims, monstrous.

And it should not be left unsaid that the clinical hallmark of a psychopath is the fact that if they want to get something, psychopaths are unmoved if getting it hurts others, even when what they want to get is not a vital necessity. That is why it is so important that people are fully informed of the fact that meat eating is not necessary for human health and causes untold suffering to other sentient beings. Because most people are not, and do not want to be, psychopaths.

Feeling vs. Moving

Sentience — which means the capacity to feel *something* (anything) — can differ in quality (seeing red feels different from hearing a cricket), or in intensity (getting kicked hard feels worse than getting lightly tapped) or in duration (now you feel, now you don’t).

But the difference between whether an organism has or lacks the capacity to feel anything at all , be it ever so faint or brief, is all-or-none, not a matter of degree along some sort of “continuum.”

Mammals, birds, reptiles, fish, and probably most or all invertebrates can feel (something, sometimes) — but not rhododendrons or Rhizobium radiobacter or Rutstroemia firma… or any of today’s robots.

There is no more absolute difference than that between a sentient entity and an insentient one, even if both are living organisms.

(Sedatives can dim feeling, general anesthesia can temporarily turn it off, and death or brain-death can turn it off permanently, but the capacity or incapacity to feel anything at all, ever, is all-or-none.)

Zeno's Paradoxes | Interesting Thing of the Day