Are plants conscious?


My late cousin was a serious grower of roses with his flowers winning awards at local shows. On a visit to his garden once, I noticed that he had placed a radio in the middle of all the rose bushes and he told me that he had heard that plants thrive on music. I too had heard this but dismissed it as the whimsy of plant lovers. I even teased him by asking him which roses bushes were not performing up to his expectations and when he pointed them out to me, I gave them a stern talking to.

It appears that plant neurobiology, the study of plant cognitive abilities, has become advocated by some scientists but now another group has launched a vehement attack on the whole idea of sentience in plants, saying that the limited response by plants to changes in their environments have been over-interpreted as suggesting a higher level of cognitive development than is warranted.

Bothered by claims that plants have “brain-like command centres” in their root tips, and possess the equivalent of animal nervous systems, the critics counter there is no proof of sentient vegetation or structures within plants that would grant them what the neuroscientist Antonio Damasio has called “the feeling of what happens”.

Writing in the journal Trends in Plant Science, where plant neurobiology made its debut in 2006, Lincoln Taiz, a botanist at the University of California, Santa Cruz, and seven like-minded researchers state: “There is no evidence that plants require, and thus have evolved, energy-expensive mental faculties, such as consciousness, feelings, and intentionality, to survive or to reproduce.”

But the proponents of plant sentience are fighting back, saying that the critics are merely prejudiced and ignoring the evidence.

The broadside drew a robust response from the University of Sydney’s Monica Gagliano, who conducts research on the cognitive abilities of plants, including perception, learning, memory and consciousness. She said the criticisms failed to take account of all the evidence and focused only on work that supported the authors’ viewpoint. “For me, the process of generating knowledge through rigorous science is about understanding the evidence base behind a claim,” she said. “Where is their experimental data? Or are we expected to just accept their claim at face value?”

When one views time-lapse videos of how plants respond to changes in their environments, one undoubtedly gets a feeling that they have a sense of agency. But my own uninformed reaction is to still feel skepticism towards the idea that they have any kind of consciousness as we understand the word in the context of animals, since they do not seem to have a central nervous system.

Comments

  1. Matt G says

    I think the evidence that plants recognize and share resources with close relatives is pretty robust, but that’s a far cry from anything resembling consciousness.

  2. Rob Grigjanis says

    consciousness as we understand the word in the context of animals

    And how exactly do we “understand” that word in any context? The best definition I’ve seen (with “best” meaning “well, I can sort of get that”) was in Julian Jaynes’ The Origin of Consciousness in the Breakdown of the Bicameral Mind*. It’s been years since I read it, but Jaynes basically defined it as an internal space in which we narrate our lives or possible lives (that doesn’t do justice to Jaynes’ actual wording, which took up a couple of pages).

    *One of the few books I’ve read for which the validity of the main thesis, or even some of the arguments, was secondary to the delight in sharing the intellectual journey of the author.

  3. 11Q says

    But my own uninformed reaction is to still feel skepticism towards the idea that they have any kind of consciousness as we understand the word in the context of animals, since they do not seem to have a central nervous system.

    There are plenty of eumetazoan taxa that have no real central nervous system either but still display some sophisticated capacity to respond to their environment, and I’ve not seen advocates for plant intelligence making such bold metaphysical claims anyway--that seems like a straw man. Plants do also lack distinct nerve cells--but while the presence of nerves is a major distinguishing factor between sponges and eumetazoa, plants represent a wholly separate development of multi-cellular life so that analogy might be spurious. The Venus flytrap for one has a fairly sophisticated and fast closing reflex with highly sensitive trigger hairs, so obviously some degree of internal signalling is present there.

  4. file thirteen says

    Before arguing the possibility of consciousness in plants, we ought to pin down where the line between conscious/not conscious is drawn. And to do that, we ought to specify what consciousness is exactly. Which we continually fail to do.

    I think there’s a general consensus that mammals, reptiles and birds are all conscious. What about insects? If not, why not? What about the individual cells that make up “conscious” beings? No? Then if non-conscious parts can make up a conscious being, and insects aren’t conscious, how about a swarm of insects? Or a beehive? What is consciousness anyhow?

    Is it a sense of self? I would argue that plants, and even some bacteria, have that.

    Is it memory? I wouldn’t have thought plants have that, but then I have read articles describing how some do. Why not? Even our immune cells have memory.

    Ok then, if I define consciousness as having a sense of self and a memory, then maybe plants are “conscious”. Did I miss something? But even if I didn’t, so what? I can’t see how it justifies playing Beethoven to rose bushes.

  5. ridana says

    I took an introductory botany class back in the 70s, and this was an issue even then. The instructor was quite adamant that plants were not conscious nor had will, and your grade depended on not only accepting that, but also being able to parse and identify the language of intentionality. Every test had several T/F questions of the sort, “Plants turn toward the sun to absorb more light for photsynthesis.” This was of course deemed false since plants’ turning toward the sun and absorbing more light was not an act of will, but simply due to the migration of auxin (and it turns out it’s not quite that simple after all). It got to the point where he was testing us more on semantics than science.

    Myself, I think plants are not conscious, but they certainly communicate. A tree sending out certain chemicals into the air or through the soil when it’s attacked by bugs may simply be a byproduct of getting chewed on, but the ability of other nearby trees of the same species to interpret that as a signal to ramp up production of their own anti-bug chemicals is hard for me to chalk up to simply a chemical reaction (i.e., less significant than our own thoughts and emotions being merely products of chemical reactions).

  6. colinday says

    @file thirteen
    #5

    I can’t see how it justifies playing Beethoven to rose bushes.

    And what justification does one need to play Beethoven (for whatever reason)?

  7. file thirteen says

    @colinday #6

    And what justification does one need to play Beethoven (for whatever reason)?

    Your consciousness stream may have truncated early; it appears to have lost the last three words of my sentence. I’ll highlight them for you

    I can’t see how it justifies playing Beethoven to rose bushes

  8. flex says

    While I haven’t read the Julian Jaynes’ book referenced by Rob Grigjanus above, both Susan Blackmore’s and Gerald Edelman’s books generally affirm that view. With an interesting twist in the case of Blackmore’s books in that her research suggests that consciousness often occurs after the brain’s decision making. In other words, the conscious decision to do something occurs after the brain has already made the decision and before the inner-self does. She doesn’t suggest this happens in every case, but certain experimental data strongly suggest this happens under certain test conditions. Which implies that ofttimes when we believe that our conscious mind makes a decision it really an illusion.

    On the question on whether plants have consciousness, as mentioned above, it really depends on your definition of consciousness. However, I believe that most consciousness researchers would deny that plants have anything close to self-awareness. Not only is a nervous system as we understand it is lacking, but the decision making properties of plants, while very complex and not fully understood, happens largely at a cellular level. And we don’t have any evidence that cells are conscious. (Although that would make a very interesting SF story. I can only recall a couple stories which hint at this idea. L’Engle’s A Wind In The Door and John Campbell’s Who Goes There?>. There are probably others which I can’t recall.)

    Finally, I would not deny that plants react to external stimuli, but do they respond to internal stimuli? As an example, could a plant choose to grow away from the light without any external pressure to do so? I don’t know any examples of this type of plant behavior, so I submit that plants do not exhibit consciousness. Mind you, I know a number of human beans [spelling deliberate] who I suspect of not reacting to internal stimuli either, so that may not be a good criteria to use. 😉

  9. John Morales says

    I remember Lyall Watson and Rupert Sheldrake.

    flex, “As an example, could a plant choose to grow away from the light without any external pressure to do so?”

    Perhaps think about your phrasing, whether it’s inadvertent or whether it evinces a deeper presupposition. I’ve taken the liberty of emphasising the salient section, which would have sufficed in any case.

  10. John Morales says

    [Hm, my #11 might be overly terse and therefore obscure, so an addendum]

    Choice is not necessary for consciousness, but awareness is.

  11. says

    @file thirteen:

    Is it a sense of self? I would argue that plants, and even some bacteria, have that.

    Really? What could you possibly mean by “a sense of self” in this case?

    @11Q:

    There are plenty of eumetazoan taxa that have no real central nervous system either but still display some sophisticated capacity to respond to their environment

    And is a mercury thermometer conscious? It responds in some capacity to its environment.

    @both of you, but only quoting file thirteen:

    Is it memory? I wouldn’t have thought plants have that, but then I have read articles describing how some do. Why not? Even our immune cells have memory.

    Is my laptop conscious? It responds to external stimuli in quite sophisticated ways to its environment, and it has memory, and it has at least as much “sense of self” as any bacterium.

    We know that in humans consciousness involves self-reflection and symbolic thought. You can call something that involves neither of these “consciousness” if you wish, but it’s not going to meaningfully compare to the human experience of consciousness. If you adhere to a definition including only those things that can be meaningfully compared to human consciousness, then you’re stuck in a bizarre place, because we can’t investigate the internal experience of consciousness. The only way we can know someone is experiencing this type of consciousness if if they communicate their symbolic thought through meaningful and mutually intelligible symbolic use of their own.

    Since there are bound to be some living things that can experience self-reflection and symbolic thought but cannot communicate that to us, the group of living things we know to be conscious (in a manner meaningfully comparable to the human experience of consciousness) will always be smaller than the group of living things that actually are conscious (in that way). So, sure, you can speculate on what might be conscious and for quite a number of living things I won’t be able to prove you wrong. But that doesn’t mean that it’s actually reasonable to assert that any of those things actually are conscious in any meaningful way.

    Plants show no ability to communicate symbolically. Because of this, plants show to humans no evidence that they “think” symbolically (or “think” at all).

    Plant consciousness is, at this moment, no more in evidence than any god, unless you decide that consciousness need not resemble what humans experience as consciousness and then… what?

    If you really mean something other than what humans experience by consciousness (say, a capacity to respond to different environmental stimuli with different behaviors), then just say that.

  12. file thirteen says

    @Crip etc #14

    Is it a sense of self? I would argue that plants, and even some bacteria, have that.
    Really? What could you possibly mean by “a sense of self” in this case?

    Just a way of behaving that differentiates… whatever we’re talking about… from the environment it’s in. I can’t give any examples that you couldn’t write off as being merely “reactive”, but in my defence I reckon I could achieve the same thing with the human brain by reducing it to its component parts until all we’re left with is a Turing machine. And yet, the hard problem of consciousness remains.

    We know that in humans consciousness involves self-reflection and symbolic thought.

    Is there any kind of thought that isn’t symbolic? And is self-reflection special? Given that it’s just symbolic thought again -- I’m sure you weren’t thinking of the space between the atoms making up your body or the elements that made it up when last you thought of “yourself”.

    Oh right, we were talking about plants. They seem to react to their environment in a way that distinguishes their self from it. At first blush my intuition is to say that plants don’t think, not in any way I could understand. But then the human type of thinking is really the only thinking I can pretend to understand, and I can’t explain thought any more than I can explain why “I” am this consciousness.

    The problem I see is, I would think that if plants store any information about themselves and their environment that they react to, then it would be too abstract for me to comprehend it as “symbolic thinking”, even if at it’s rudiments that’s what it is. I’d never say it was human consciousness.

    Thought, consciousness, where do you draw the line?

    This all reminds me of the following SSC story I found amusing.
    https://slatestarcodex.com/2019/02/28/meaningful/

  13. flex says

    @John Morales, #11,

    Choice is not necessary for consciousness, but awareness is.

    While I understand your meaning, I did use the word “chose” deliberately.

    Awareness may be one of the defining characteristics of consciousness, but the way awareness expresses itself to the rest of the world is through choice. It is trivial to create a device which tells the world that it is self-aware. The evidence of self-awareness comes from evidence of choices which are made by the device/creature due to internal stimulus rather than external stimulus. Even that differentiation (internal/external) is very hard to determine, it was only slightly tongue-in-cheek that I referred to some humans as beans rather than beings because so many human reactions to external stimuli appear to occur without self-awareness, consciousness, or thought.

    A self-aware creature will make choices which are based on their awareness, their inner monologue. When a self-aware creature makes a choice which is not explicable by observation of external stimuli, this is suggestive evidence that the creature is self-aware. I know of no other objective evidence which would suggest consciousness. Is this test perfect? By no means, memory appears to be a critical component of self-awareness, but we already can create a computer which will learn, retain memories, and use those memories to make better informed decisions. To the extent that the conclusions these computers arrive at can appear to be solely based on internal stimulus rather than external ones. Are those computers self-aware? There is no evidence which suggests that, but how do we know? My suggestion is that we will know, when like Shalmaneser in John Brunner’s Stand on Zanzibar demonstrated self-awareness and consciousness by refusing to believe something was true. That choice to deny of reality, based on Shalmaneser’s understanding of humanity, demonstrated self-awareness and consciousness, although the only person in the novel who recognized it was Chad C. Mulligan. Most readers don’t seem to notice it either. (I looked up the Wiki of the novel to refresh my memory of the names, and I see that the Wiki article doesn’t mention it either. Not that it’s a key plot point.)

    I submit that only by looking at the choices a object/creature/software makes can we determine if the thing is self-aware and has some form of consciousness. And most of the choices even a conscious creature makes are not obvious proof of self-awareness. The choice of a dog to refuse going for a walk, the choice for a toddler to scream “NO” even for something they generally want, the choice of a man to die rather than renounce his religion, are all evidence of some level of consciousness. If a plant chose to withdraw it’s roots from soil, or fold up it’s leaves to avoid the sun, not because the sun was too hot or the soil was tainted or it’s DNA indicated it was time to die, but because the plant’s inner monologue told it to do use (religious plants?), that would be evidence that the plant has some level of consciousness.

  14. Holms says

    “For me, the process of generating knowledge through rigorous science is about understanding the evidence base behind a claim,” she said. “Where is their experimental data? Or are we expected to just accept their claim at face value?”

    But their claim is the null hypothesis; the only claim in need of supporting evidence is the positive claim: plants are conscious. I’m side-eyeing any scientist that does not know this.

  15. file thirteen says

    @flex #16

    Unfortunately, imo Shalmaneser didn’t demonstrate consciousness. All it did was reject a set of inconsistent data in a very automated way, to the bemusement of its obtuse, blinkered operators whose only counter was “but it’s true!”. What Chad did was to realise something else was going on. “I tell you this three times!”

  16. woodsong says

    Whatever the mechanism, and whether this demonstrates consciousness or not, I’ll submit that dandelions do demonstrate at least short-term (seasonal) memory.

    I’ve routinely observed, over the past 30 years, that when the dandelions first bloom in the spring, they lift their flower heads several inches above the surrounding grass. This behavior changes with the first pass of a lawnmower. After the mowing, the dandelions bloom at just below the chopping point, and thereafter will bloom at the lowest height at which they reach full sunlight. A regularly mowed lawn will have dandelion blossoms sprawling sideways rather than reaching up.

    Just my two cents.

  17. Owlmirror says

    Whatever the mechanism, and whether this demonstrates consciousness or not, I’ll submit that dandelions do demonstrate at least short-term (seasonal) memory.

    I’ve routinely observed, over the past 30 years, that when the dandelions first bloom in the spring, they lift their flower heads several inches above the surrounding grass. This behavior changes with the first pass of a lawnmower. After the mowing, the dandelions bloom at just below the chopping point, and thereafter will bloom at the lowest height at which they reach full sunlight. A regularly mowed lawn will have dandelion blossoms sprawling sideways rather than reaching up.

    And interesting anecdote. But I wonder if this observation is of dandelions changing their growth pattern actually arises out of some sort of awareness that their stems and flowers are being mowed, or instead because there’s an interaction between the lawnmower blade and the stem. That is, when the blade hits the stem and severs it, the base of the stem is slewed sideways, so that when the stem regrows, that slew is imparted to the growing stem, and the stem grows sideways.

    As an experiment, you could try pulling some of the dandelion stems straight up before mowing so that they are shortened at the base but not hit by the mower blade, and seeing if these dandelions exhibit the same change in growth pattern as the mowed dandelions.

  18. Mano Singham says

    woodsong @#21,

    Here is a possible alternative explanation.

    All plants have a genetic variability. Assume that the dandelions have a range of heights that they grow to. At the first mowing, all the dandelions that grow above the height of the blade get cut, leaving only those whose heights tend to be below the blade height. As those grow taller, they get cut in subsequent mowings, finally leaving only those that are very short or grow sideways.

    Would that explain what you see?

  19. Owlmirror says

    @file thirteen:

    I think there’s a general consensus that mammals, reptiles and birds are all conscious.

    An odd grouping of animals, especially since birds are phylogentically grouped under sauropsids, which also includes reptiles (that is, “sauropsida” is what “reptiles” would be if it werenot defined paraphyletically).

    What about the rest of tetrapoda? Amphibians are excluded from the group of consciousness-havers?

    What about insects? If not, why not?

    Have you heard of Sphexishness?

    On the other hand, I have seen work that suggests that bees, or perhaps bee colonies, may have something like consciousness. That is, they do seem to be able to learn and communicate.

    So . . . maybe some insects?

    And of course, there’s cephalopods.

  20. file thirteen says

    What about the rest of tetrapoda? Amphibians are excluded from the group of consciousness-havers?

    Why you filthy frog-lover!! Nah, I’m totally kidding, I just mentioned those three off the top of my head -- it wasn’t meant to be an exhaustive list.

    Sphex behaviour is certainly food for thought, although not definitive proof of mindlessness. Perhaps it’s just stubborn and easily confused. 🙂

  21. Owlmirror says

    @Mano & woodsong:

    Rather than genetic variation in stem growth, I think another likely explanation might be phenotypic plasticity. Dandelions probably have not encountered lawnmowers for long enough in time to have evolved modified growth patterns, but they probably have had to cope with browsing herbivores for millions of years. And they could have evolved shortened stem regrowth as a response to that, with the shorter (and perhaps ever shorter) regrowth being selected for after each stem-chomping event.

  22. Jenora Feuer says

    @Owlmirror:
    I submit that the most obvious distinction between the Sphex wasp and bees is that bees are rather explicitly social insects.

    Not saying that social structures are necessarily required for consciousness, but they do make it far easier to observe.

    And, of course, on top of the ‘what is consciousness anyway’ issue, one of the other big problems of all this is trying to separate out the assumptions of the experimenter from the actual subject of the experiment. People will import intention into purely mechanical structures like buildings or bridges. We are really not good at actually knowing what is going on inside something else’s head, but we are good at convincing ourselves that we know anyway.

  23. woodsong says

    Owlmirror:

    But I wonder if this observation is of dandelions changing their growth pattern actually arises out of some sort of awareness that their stems and flowers are being mowed, or instead because there’s an interaction between the lawnmower blade and the stem. That is, when the blade hits the stem and severs it, the base of the stem is slewed sideways, so that when the stem regrows, that slew is imparted to the growing stem, and the stem grows sideways.

    As an experiment, you could try pulling some of the dandelion stems straight up before mowing so that they are shortened at the base but not hit by the mower blade, and seeing if these dandelions exhibit the same change in growth pattern as the mowed dandelions.

    Mano:

    Here is a possible alternative explanation.

    All plants have a genetic variability. Assume that the dandelions have a range of heights that they grow to. At the first mowing, all the dandelions that grow above the height of the blade get cut, leaving only those whose heights tend to be below the blade height. As those grow taller, they get cut in subsequent mowings, finally leaving only those that are very short or grow sideways.

    Would that explain what you see?

    The trouble with both of these explanations is that the dandelion flower stems only bloom once. The plant produces new ones for subsequent flowerings, whether the first are cut or not. The bud forms within the leaf rosette, then the stem lengthens and raises it up. So I don’t think it’s a function of existing stems being knocked sideways (especially since the severed stems will still be standing upright until they wither!) Also, Mano, the plant isn’t killed by the mower; dandelions grow as a basal rosette of leaves, and send up flowers.

    In a field that is never cut, the first blossoms will be around 6-10″ tall, and subsequent flowerings heights will be dependent on the height of surrounding vegetation. I’ve found dandelions with flower stems two feet tall in some meadows. Those plants also tend to point their leaves more vertically, and grow them longer.

    Owlmirror:

    Rather than genetic variation in stem growth, I think another likely explanation might be phenotypic plasticity. Dandelions probably have not encountered lawnmowers for long enough in time to have evolved modified growth patterns, but they probably have had to cope with browsing herbivores for millions of years. And they could have evolved shortened stem regrowth as a response to that, with the shorter (and perhaps ever shorter) regrowth being selected for after each stem-chomping event.

    I agree that this is plasticity rather than selection, and that it likely evolved as a response to grazers.

    What I think is going on is that the cut stems send a chemical signal to the plant. One cut stem is ignored, while all of them will trigger the plant to cause the buds that haven’t been raised yet to blossom at their current heights (below the mower blade level). It’s the subsequent growth pattern that I’m thinking could qualify as “memory”: the plant may retain a chemical signal (that slowly fades) triggering a “dangerous territory: bloom as quickly as possible!” response (sprawling growth and short stems rather than vertical and long). I would call the retained chemical cue a form of memory.

    Curiously, I’ve seen some bizzare-looking flowers where it appears that several buds fused into one flower head (or didn’t separate into several). These are far more common in places where the lawn in mowed extremely short. A Google image search on “dandelion flower abnormalities” turns up a few (among a lot of normal dandelion pix, plus other abnormal Compositae like daisies and sunflowers).

  24. John Morales says

    flex @16, I think you mean to refer to ‘autonomy’ (in the philosophical sense) when you employ the term ‘choice’, because (say) a magic 8-ball makes ‘choices’ too, from an observer’s perspective.

    A self-aware creature will make choices which are based on their awareness, their inner monologue.

    How do you supposedly distinguish between choices and contingent reactions?
    Is it unpredictability, reacting differently to the same stimulus at different times?

    (Heh. Had a loonie in Pharyngula back in the day, argued Process Theology, claimed even atoms made choices and so were in a sense conscious)

  25. flex says

    @file thirteen #20,

    Chad recognized that something more was going on than simply a refusal of an sophisticated adding machine to accept inconsistent data.

    I would refer you to the chapters continuity (38) and Tracking with Closeups (32).

    Now I’m not saying these chapters are conclusive evidence of Shalmaneser’s consciousness. What I am saying is that this is what Brunner envisioned as how artificial intelligence would express itself when it does occur.

  26. Mano Singham says

    woodsong @28 and owlmirror @#26,

    I like the plasticity idea and the explanation of how it might be working.

    Of course, this is an empirical question whose answer would be elucidated by some experimentation. I do not know if there is research on dandelion growth. The lawn care companies may have done some but that might be proprietary information. I do not know if there has been any public domain academic research on it.

  27. file thirteen says

    @flex #30

    It’s been many years since I read the book, but now that you mention it I do recall something about Shalmaneser bathed in liquid nitrogen going “Wow, what an imagination I’ve got”. So you’ve probably pointed out a couple of passages showing that Brunner intended the reader to consider it conscious, and I’m not saying you’re wrong.

    I interpreted the original scene you mentioned as more of a comment on human nature. Nobody can understand why the machine rejects data about a poor country in the middle of war-torn neighbours which nevertheless is a bastion for peace, but Chad, genius, master of human thought, cynic of cynics, has no trouble whatsoever realising that can’t be the whole story because people just aren’t like that. He asks the question: what would it take to accept the data as true? Shalmaneser says if a mysterious force was operating on the population (again from memory, corrections are welcomed) and Chad says righty-ho, there is such a force, I tell you three times (note for others: when Shalmaneser is told something three times it is programmed to accept it as truth). Whereupon the impasse is breached, Shalmaneser accepts the data and moves forward, and everyone stands around with wide eyes and gaping mouths.

    The telling thing to me was that Chad didn’t pause to consider this option, or whether there were other possibilities, before commanding Shalmaneser. Nor was there any question afterwards about whether that had been the right path or a mistake. The underlying message seemed to be that Chad was a genius precisely because he knew so well how flawed humans are, and that enabled him to solve the problem that perplexed the experts.

    I digress; my point is that I didn’t think the passage you mentioned reflected well on Shalmaneser as being a conscious being. IIRC he/she/it did turn out to be, but you didn’t see it there.

  28. consciousness razor says

    flex, @16:

    I submit that only by looking at the choices a object/creature/software makes can we determine if the thing is self-aware and has some form of consciousness.

    A weird submission. First, being “self-aware” is not the same as being “aware.” If you really mean any form of consciousness, then something which is sentient (or is aware, has sensory experiences) has some form of consciousness.
    No choices need to be made for that to be so, and we would not need to see such choices being made. I mean, it’s not clear how one is supposed to be engaged in “looking at” something like a choice — what does that look like? — but supposing for the sake of argument that it could be done, it’s presumably not necessary for this.
    It’s no different when something is aware of itself, but it’s good to make these distinctions clear anyway. It does raise a strange question: would it possible to choose not to be self-aware (if one were self-aware, or “aware of your awareness” if you like)? I’m not sure that could be done, even if one wanted to choose to do that. So if no such choice could be made, that seems like an even worse case compared to mere sentience, as far as your dubious submission is concerned.

  29. Sam N says

    Well, most people who have serious ideas regarding conscious experience agree that it’s a quantitative phenomenon. Systems can be ‘more’ or ‘less’ conscious, and that this consciousness requires a system that carries information about itself. I presume that conscious experience is simply the natural consequence of the existence of that information.

    So, I’d say yes, plants have some level of consciousness. But it would not be a conscious experience any of us could relate to. I’d also hazard the guess, given comparative complexities of the communication systems in plants compared to brains, that they are far, far less conscious than mammals.

    Although, I find Integrated Information Theory to be a compelling explanation for why consciousness exists at all. Certainly I find it more promising than any alternative framework for consciousness that I have been exposed to.

  30. Owlmirror says

    The original article (“Plants Neither Possess nor Require Consciousness“) is open access, and after dismissing the appropriateness of considering plants as being conscious, they discuss attempts to define consciousness, and which animals might be so under the criteria used:

    Based on their evolutionary analysis of the structure, organization, and functional specialization of the brain required for the emergence of consciousness, Feinberg and Mallatt concluded that the only animals that satisfied their criteria for consciousness were the vertebrates (including fish), arthropods (e.g., insects, crabs), and cephalopods (e.g., octopuses, squids).

    Many questions remain, but Feinberg and Mallat’s detailed anatomical studies on the level of complexity that the brain had to acquire before consciousness could evolve should give PNPs pause before speculating about consciousness, feelings, and intentionality in plants.

    The citations they reference, in case anyone is curious, are:

    Feinberg T.E. • Mallatt J.
    The nature of primary consciousness: a new synthesis.
    Conscious. Cogn. 2016; 43: 113-127

    Feinberg T.E. • Mallatt J.
    The evolutionary origins of consciousness.
    in: Poznanski R.R. Tuszynski J. Feinberg T.E. Biophysics of Consciousness: A Foundational Approach. World Scientific, ; 2016: 47-86

    Feinberg T.E. • Mallatt J.
    Consciousness Demystified.
    The MIT Press, ; 2018

  31. Owlmirror says

    @Mano:

    When one views time-lapse videos of how plants respond to changes in their environments, one undoubtedly gets a feeling that they have a sense of agency

    The paragraph I cited from the paper in #35 continues on that very point:

    Time-lapse videos of growing roots or twining stems, which have been speeded up to make them look more animal-like, do not constitute evidence for consciousness or intentionality. Animals can move about quickly because they possess motor systems composed of muscles and the neurons that control them. The slow growth movements of plants are caused by entirely different mechanisms involving cell wall expansion and water uptake, while rapid leaf movements, as in the case of M. pudica, are mediated by rapid changes in cell turgor pressure.

  32. flex says

    @Consciousness Razor at #33,

    Perhaps I am unclear. I’m trying to say that the only evidence we can have that some other thing is acting in a way that suggests that it has some level of consciousness is by examining it’s behavior. You appear to know that you are self-aware, and I’ll take your word for it. However, there is no way that you can tell that I’m conscious other than asking me, which I could lie about, or by monitoring my behavior over a period of time. Further, what you see in my behavior cannot entirely rule out a sufficiently well programmed, not-at-all-conscious, algorithm.

    Which makes recognizing consciousness in creatures other than our ourselves rather difficult. I suspect you generally accept that everyone has this little homunculus we call ourselves sitting about three inches behind our eyes, but all of us could be lying to you. (I recommend continuing to believe that we are all generally conscious, solipsism as a career choice gets pretty hungry.)

    There are tools which are available and used to evaluate biological systems; cats, dogs, and other animals return results which appear to gauge consciousness. Like all scientific tools, these are imperfect, and to the best of my knowledge we don’t really have a good idea of how imperfect these tools are. But like the Body-Mass Index, the tools are used because they are the one for which the most amount of data is historically available.

    I was not trying to make any distinction between awareness and self-awareness, and my use of those terms was probably more confusing than helpful.

    As for your question about could a self-aware creature chose to be not self-aware. Beyond the obvious point that death is generally believed to eliminate self-awareness (at least by non-religious people), I believe this isn’t a hard question to answer. We can see self-aware creatures slip into not self-aware states all the time. People with certain forms of dementia can lose their self-awareness, and then recover. It is frightening, both for them and for their family. I admit, I’m only taking their word that they are slipping into and out of self-awareness, but I’m willing to do so. Certain types of brain injuries also destroy self-awareness without resulting in death. So, there doesn’t seem to be a reason why a self-aware creature couldn’t choose to be not self-aware. Although putting that choice into practice may risk going too far and killing oneself or not going far enough and remaining self-aware but in considerable pain. But the choice could be made.

    That being said, your question is still interesting because if we view awareness as a continuum we can ask if a creature could choose to place itself at an optimum place for their own survival on this hypothetical awareness continuum? Have evolutionary pressures done this? Is the awareness level of a chicken a summit in an evolutionary landscape such that chickens which develop greater awareness are less likely to survive? If awareness is a continuum, what evidence do we have that it ends with human-level self-awareness? Without violating any known physical laws, could we be more self-aware than we currently are? How would that even look?

  33. flex says

    As a clarification, I am not refuting the work cited by Eulenspiegel @35. The work done on anatomical structures to generate some idea of the necessary framework for consciousness to exist is complimentary to behavioral studies to test for the presence of and level of consciousness.

  34. John Morales says

    flex, heh.

    (to CR)

    That being said, your question is still interesting because if we view awareness as a continuum […]

    A quality either exists or not, regardless of its degree.

    (That is, the least aware thing must perforce be aware)

    When you invoke choice, you invoke sapience.

  35. John Morales says

    PS Tsk

    There are tools which are available and used to evaluate biological systems; cats, dogs, and other animals return results which appear to gauge consciousness.

    Yeah, they have brains and nervous systems. Etc.

  36. Sam N says

    @Flex 37, “Without violating any known physical laws, could we be more self-aware than we currently are? How would that even look?”

    If, as you posit, such awareness is quantitative (a sensible assumption), I would look at variance in the human population. There are some people who seem more self-aware than others, and may increase incidence of anxiety, for example.

    But if you want to reduce self-awareness, you can do the experiment yourself. Take 20 mg of valium. Or go to a local bar some evening and drink 6 pints.

  37. consciousness razor says

    I’m trying to say that the only evidence we can have that some other thing is acting in a way that suggests that it has some level of consciousness is by examining it’s behavior.

    I don’t think that’s correct. We also have evidence about evolutionary and geological history to consider, along with the biology and chemistry and physics of the parts which constitute a being with consciousness, and so forth. Those are all empirical, but they need not involve observing the behavior of an animal, plant, computer, or whatever. You also generally need to know certain abstract and non-empirical things (e.g., algebra and geometry) in order to understand findings from those empirical subjects. The point is, we can get solid, useful, relevant evidence from all over the place if we like; and that’s what we should do if we’re interested in learning about it.

    Further, what you see in my behavior cannot entirely rule out a sufficiently well programmed, not-at-all-conscious, algorithm.

    You’re making this more difficult than it needs to be. I can easily determine that you’re not conscious, every single time you go to sleep.

    I suspect you generally accept that everyone has this little homunculus we call ourselves sitting about three inches behind our eyes, but all of us could be lying to you.

    I don’t accept that there is a little homunculus sitting behind anyone’s eyes, so … ??

    We can see self-aware creatures slip into not self-aware states all the time.

    If they are aware (or self-aware) at some time, they couldn’t choose to not be aware at that time. It’s simply not about choosing. You hear something, and for that reason, we say you’re aware of that sound.
    You don’t choose to be aware of what in fact you did hear. And if you could do something like that, I have no idea why we should put the label “awareness” on that kind of ability. It sounds like something very different from awareness as I understand the term.

    People with certain forms of dementia can lose their self-awareness, and then recover.

    Not a choice. A family member of mine is suffering from dementia now, and it’s very sad that nothing can be done about it.

    I admit, I’m only taking their word that they are slipping into and out of self-awareness, but I’m willing to do so.

    Better clear some things up…. I’m not disputing that your state of consciousness changes over time. The most obvious example of that is one I mentioned above, about being awake or asleep, and we could also talk about various other altered states or degrees of consciousness that a specific individual may be in at different times. So it is a dynamical kind of thing in time, not fixed. What is being disputed is a different question: whether it’s a matter of choice. The one doesn’t follow from the other.

    Although putting that choice into practice may risk going too far and killing oneself or not going far enough and remaining self-aware but in considerable pain. But the choice could be made.

    I think you’re confusing a few things here, or forgetting where this train of thought was supposed to be headed.
    If you hear a performance of Messiaen’s Turangalila-Symphonie, then you kill yourself, that doesn’t make the claim false that you heard it (while you were still alive). Of course you’re not continuing to hear it after death. But it did happen, when you did exist.
    Maybe you can choose a lot of things. (I’m a determinist and compatibilist. You may not agree that what I’d call “choice” is the real thing, and I’d basically respond that there is no real thing. Not sure if the discussion is headed toward free will, but it could….) However, no matter what your choices may be like, you certainly can’t choose which true facts are true, because all of the true facts are true.

  38. flex says

    @ Consciousness Razor #42We also have evidence about evolutionary and geological history to consider, along with the biology and chemistry and physics of the parts which constitute a being with consciousness, and so forth

    I believe we are somewhat talking past each other. While all the above is true in a general sense, it is not known to be true for a specific individual. We can certainly say that for mammals, and human beings in particular, we can largely define a biological system which we believe allows consciousness to express. But we cannot know for certain for a specific individual without behavioral testing. As mentioned above, the same being which constitutes a being with consciousness due to our understanding evolutionary history, biology, chemistry, and physics can lose consciousness simply by sleeping.

    I try to drill this idea into the heads of the engineers I mentor. You cannot infer specific population traits to an individual or infer specific individual traits to a population. You can provide a probability in either direction, but you can’t determine it. The example I use is red-headed people in Ireland. There are a lot of red-headed people in Ireland. But if you meet someone with red hair, can you say that they are Irish? Conversely if you talk with someone in Ireland on the phone, can you say they have red hair? In both cases you can assign a probability of truth, but not a certainty until you test the individual. Evolution, biology, chemistry, and physics can assign a probability that a thing is conscious, but until the thing is tested (if we had a good test) we couldn’t be certain. Further, since we all acknowledge that consciousness is not a continuous state, if the test is applied at the wrong time, it may also give false results. Giving a Rorschach test to someone who is asleep will not be very revealing.

    You might be thinking that we can tell whether a creature is awake or asleep by looking at the signals passing through their brain. That is true, but that is not enough. It may help us determine if a human being is conscious or not, but does it work on dogs? Rats? Or machine intelligence? As we move further from the studies we make on our own brains, we lose confidence that we can apply that knowledge to other creatures. This breaks down entirely when we consider the possibility of machine consciousness. The only tools we have to determine if a specific individual, which we suspect may be conscious, are behavioral ones.

    A family member of mine is suffering from dementia now, and it’s very sad that nothing can be done about it.

    That is indeed very sad, and I’m sorry that the individual involved, you and your family are going through that pain. Losing that sense of self, or seeing that loss in others, has got to be the most frightening experience because it hits at the very core of our understanding of who we are. You, your family, and the individual involved all have my deepest sympathy, and I also wish our brains were not the fragile vessel of chemical soup that they are.

    That being said, my point was not that the person with dementia has made a choice. But that the options exist. A person who has survived the loss of their eyes may not have chosen to be blind. But their existence demonstrates that a person can survive being blinded. To bolster the idea that blindness can be a choice, there are plenty of documented historical cases where people deliberately blinded themselves. Not something I would choose, but they made a choice to deprive themselves of sight.

    What is being disputed is a different question: whether it’s a matter of choice.

    Ah. Here is the nub we are chewing on. And the questions we have been wrestling with are slightly different. You question whether consciousness itself is a matter of choice. My understanding of the original question was that it concerned whether a conscious person could choose to permanently lose their consciousness.

    My take on your question is that as we don’t know what leads to the development of consciousness, we can’t know if it could be a choice. But from a purely theoretical standpoint, as choice is generally seen as a result of consciousness, I would say that a developing consciousness couldn’t chose to halt the development of consciousness. Until a consciousness is developed to the point where choices are possible, the choice to remain not conscious cannot be made. A developing child cannot chose to turn off their developing brain, and the resulting consciousness. (Although there are some people who I facetiously suspect managed to accomplish this feat. Many of them are in politics.)

    Having written the above, there remains a question. As most consciousness research suggest that consciousness is not a binary state but a continuum, the question remains as to where along that continuum could a being realistically be said to be able make the choice to remain at that point on the continuum. Human beings are conscious enough to make a choice to regress their consciousness, but as we don’t even know what it means to travel further along that continuum, we cannot choose to do so. I suspect that for most, if not all creatures, the population mean on that consciousness continuum is driven by evolutionary pressures and not a species-wide determination to change. I do include human beings in that category, although I’m certain others (not yourself) would like to think that human beings are special in some way and can make individual or population level determination to adjust their place on the consciousness continuum (if we knew what that meant).

    The question I was answering was, could a being who was already conscious (even only sporadically) make the choice to give up consciousness. Which I still think is possible.

    The option of a human body living without consciousness has been demonstrated, thus a choice can be made. That was all I was trying to say. There may be some difficulty in actualizing the choice, but that is a separate problem. I can chose to eat at a restaurant tomorrow, but if the restaurant burns down tonight my choice cannot be acted on. That does not invalidate today’s choice. As you correctly point out, the choice of today is the choice of today, the choice of tomorrow may need to be different as tomorrow is different than today.

    But it did happen, when you did exist.

    The point about death was only to show that there was an extreme case, after you are dead you cannot choose to listen to Messiaen. But there is nothing preventing you from listening to Messiaen, or the Ramones, when you sleep and are not conscious. I don’t really any idea whether doing so will change brain enough to change your consciousness when you regain consciousness. Most of the studies I’ve read about learning when not conscious have either been flawed or inconclusive, so I tend to doubt whether a significant affect could occur. But I’m willing to continue to entertain the idea that there may be an effect, simply because we don’t know enough about how the brain works.

    Not sure if the discussion is headed toward free will

    No. Although I suspect we would agree more than we disagree on this topic.

  39. John Morales says

    flex, all very abstract, but the topic at hand is plant consciousness.

    Your supposition is that they are conscious to the degree they can be perceived to make choices, no?

    And you defend it with epistemic abstractions, as in that it cannot be necessarily excluded.

    That’s weak.

  40. John Morales says

    PS

    But there is nothing preventing you from listening to Messiaen, or the Ramones, when you sleep and are not conscious.

    Heh. Listening while unconscious.

  41. John Morales says

    PS [can’t resist, though it’s otiose]

    As most consciousness research suggest that consciousness is not a binary state but a continuum

    As per #39, the least conscious thing must perforce be conscious.

    (Whoosh!)

  42. flex says

    Your supposition is that they are conscious to the degree they can be perceived to make choices, no?

    No.

    My position is that if plants exhibit any form of consciousness we can only determine it through looking at the behavior of plants, with a particular focus on behavior which contradicts our current knowledge of plant behavior. And even then we can only, tentatively, suggest consciousness may occur in plants once that behavior has been evaluated and remains inexplicable. It’s a rather high bar for consciousness, and I’ve never seen evidence that plants are able to pass it.

    I fully agree with you, and what appears to be the consensus of the readers of this comment thread (if any are left), that our understanding of the requirements for consciousness are not met by plants. Plants do not have the physical properties (e.g. a neural network) which we believe to be a requirement for consciousness, and they don’t exhibit any behavior which cannot be explained through our knowledge of plant development. Either as known behavior, or behavior where the details of of that behavior is still unknown but the boundaries of those details are well defined and preclude consciousness (a defined unknown).

    My only contention is that the nature of consciousness itself is still an unbounded unknown. We know a lot about it, but most of our studies have been done on the creature we once thought of as the only conscious creature (ourselves). Only recently (past 50 years or so) has our investigations included other creatures, and most of those are from the same class (mammals). Even with all the work in artificial intelligence, we don’t know how to identify consciousness in a non-biological system. People think we do, but a properly programmed computer can provide the “correct” answers to the tests we use to determine consciousness. Yet we still don’t believe they are conscious. Neither do I, even though they can pass the tests, because we know our tests are not capable of detecting consciousness directly.

    Because we don’t have a conclusive test for consciousness, we have to leave room for the possibility that plants could be conscious. Because of what we know about plants, the probability of that possibility is vanishingly small. But because of the limitations of our knowledge of how consciousness emerges, we cannot say conclusively that plants could never be conscious. We can only say that all the evidence is against it. For all practical purposes we can treat plants as not having consciousness.

    As per #39, the least conscious thing must perforce be conscious.

    The reason I didn’t answer #39 before is because it shows a lack of understanding of what a continuum is. But if you persist in thinking I didn’t understand your point I suppose I should answer. A continuum has no clear division between any adjacent points. A division can be artificially made, imposed on the continuum from without. But when only using the information contained within the continuum, there is no appreciable difference between adjacent points. Consciousness, like many things, is a continuum, not a binary state. If you look at how human beings and other animals for which we have some evidence that they exhibit consciousness, we can see that consciousness shows different levels of complexity. From the abstract symbol using consciousness of human beings, to the remembered present of dogs, to the barely discernible consciousness of mice (our tests are not conclusive, but they have a lot of the physical traits we expect would allow for consciousness. My personal feeling is that they don’t have consciousness, but I am often wrong). If you continue to traverse this continuum in search of the least conscious thing, you will continually find that the most non-conscious thing is indistinguishable from the least conscious thing. That is the nature of a continuum. And that will lead to defining the previously thought of most non-conscious thing as the new least conscious thing. By continuing to take these steps, you will eventually decide that plants are indeed conscious.

    To provide a metaphor, a continuum exists between the Arabian Sea and the Indian Ocean. If you start in the Arabian Sea and head toward the Indian Ocean, you can reach a point humanity has defined as the dividing line between the two. There are differences, you can take water from the middle of the Arabian Sea and compare it against the water from the middle of the Indian Ocean and identify where each sample came from. But at the point where the seas meet, you can’t tell the difference between water sampled from one side of the artificially imposed line and the other. If you just look for incremental differences in the water as you travel you won’t find any, but if you look at the differences between samples which are far distant you can find differences. At the dividing line between the two bodies of water you can’t say, “I know I have left the Arabian Sea, because I see a difference in the water.” Maybe plants are far enough away from our understanding of consciousness that it is like sampling water from the middle of the Arabian Sea and the Atlantic Ocean. We can make a determination, but you can’t get there by incrementally looking for the least conscious thing.

    Well, the obvious rejoinder is that consciousness must not be a continuum, but either is or contains somewhere, a step-function. Maybe it does. But that is not what the current data by consciousness researchers suggests. Which is why, on occasion, the question of whether plants have consciousness arises. It’s not because the researchers are stupid and can’t see the forest for the trees, it’s because our understanding of what conditions must occur for consciousness to arise are not well known. There is no clear dividing line. There is no known step function. The data suggests a continuum. We’ve relied on our gut feeling rather than the data so often in the past, to our detriment, that we should have learned to respect the data we have even when we look for more to support our beliefs.

    My gut feeling is that we will have a better idea of the nature of consciousness, and the conditions which must exist to allow it to arise, once we create consciousness artificially. I also believe that we will probably do this by accident, not by design, and we won’t immediately recognize what we’ve done. I hope I’m wrong in this belief, and at the rate we are acquiring knowledge about consciousness there may well be some insights into it’s nature, enabling consciousness to be developed slowly rather then by accident.

  43. consciousness razor says

    But we cannot know for certain for a specific individual without behavioral testing.

    In a sense, we can’t know “for certain” even with such testing. Skepticism is always an option. With that said, it’s also an option to be skeptical about the external world (e.g., to think an evil demon might be tricking you), but nobody is too worried about that, because it’s too radical to undermine nearly everything you think you know about reality, while getting nothing valuable out of the deal in return.
    I put the problem of other minds at more or less the same level. When we’re talking about ordinary human beings, what you don’t ever do is say “maybe, finally, I’ll see that this one is a p-zombie” and then run a bunch of tests. That’s partly because there aren’t any reliable/informative tests to run, partly because it would be a ridiculous and pointless way to live your life.
    Look, earlier you made a claim about what type of “evidence” was possible, and I responded to that. The goal-posts have shifted here. I count something as evidence if it raises the probability that a claim is true. It doesn’t need to be raised up to 100% (almost, practically, etc.), raised up to a number you think is sufficiently high, or something like that. It merely has to go up for something to be evidence, not stay the same (because the thing is irrelevant) or go down (because it’s evidence against). It’s going to be a real number from 0 to 1, like any probability, so those are the only three possibilities: greater than, less than, or equal.

    You might be thinking that we can tell whether a creature is awake or asleep by looking at the signals passing through their brain. That is true, but that is not enough. It may help us determine if a human being is conscious or not, but does it work on dogs? Rats? Or machine intelligence? As we move further from the studies we make on our own brains, we lose confidence that we can apply that knowledge to other creatures.

    It would work just as well, if we know how to model/interpret those systems just as well. Humans aren’t different in that respect. Introspection wouldn’t tell you even about other people, of course. But you’re talking about studying brains and computer systems and so forth, which means humans aren’t in principle a special case, because these are all physical systems. So I don’t get what would make you especially concerned about the case of non-human consciousness. (It could just be stubborn resistance with nothing in particular backing it up, and if so, that’s at least understandable.)
    Perhaps for supernatural beings (gods, ghosts, etc.), we couldn’t gain information about them in the same ways, because they lack a physical object like a brain for us to study. But those don’t exist, and we don’t need to be concerned about the best ways to study objects that don’t exist. If our epistemology were good enough for the real universe that we happen to live in (but little or nothing beyond that), then that’s good enough for all practical purposes.

  44. John Morales says

    A complicated position, flex. Doesn’t differentiate between the degree to which something is conscious and the degree to which something exhibits consciousness, for example.

    But fine; you can’t personally rule out that plants have consciousness, because of abstract reasons.

    I remember the Zabriskan Fontema and the Sessile Grog. And I used to have a lithop.

  45. flex says

    @Consciousness Razor #48,

    So I don’t get what would make you especially concerned about the case of non-human consciousness.

    I’m only concerned due to the additional difficulty in identifying consciousness. We know human being can be conscious. We have both physical evidence that other mammals have similar nervous systems to human beings, and they respond to behavioral testing. Which leads us to believe that they have some sort of consciousness. We have no idea what non-human consciousness would be, whether alien or machine. I only use machine consciousness as an example because we are far more likely to encounter that before we encounter extraterrestrials.

    @John Morales, #49,

    you can’t personally rule out that plants have consciousness, because of abstract reasons.

    Of course I can. I assign a slightly higher level of probability that plants have consciousness than the probability that there is a god. A probability which is effectively zero for use in making decisions about how to act. The claim that plants have some level of consciousness is an extraordinary claim, which requires extraordinary evidence, and it would violate everything we currently know about how consciousness develops. The problem is that we still know so little.

    Consciousness is a particularly difficult subject because we still don’t have a good model for how it occurs. We know it exists, but not what allows it to occur. The best current models suggest that consciousness appears to be a result, maybe even a side effect, of brain processes. There is no thing we can point to and say, “Because the brain has this structure, or this feature, or even these active connections between these dozen processing modules at this time, this person is currently consciousness.” Might this happen in time? Could we get to an understanding so complete that we can say that in human beings when certain connections are made, and the process is active, that person is conscious? Maybe. We cannot say that today. Even if we could do that for human beings, translating that information to another thing may not work. This is not an abstract reason, this is an acknowledgement of the limits of our knowledge.

    Yes, I take a very complicated position because it is a very complicated problem. If you want a simple, uncomplicated, answer, your best bet is to join a religion. Theologians have argued about the nature of consciousness, usually in the guise of talking about souls or atman or similar mystical concepts, for millennia.

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