Monday, September 10, 2012

Do plants feel pain?

"Does it hurt my vegetables when I eat them?"
"Is it ok that I prune my bushes?"

These questions, and many like them, pop up whenever I've given a talk or been interviewd about the WHAT A PLANT KNOWS. Truth is, I didn't fully anticipate this take on plant senses, but it seems that the book has, so to say, struck a nerve, with many readers who are concerned for the welfare of their plants.

But indeed, the question of plant sentience is perhaps only an extension of our interest in understanding consciousness in general, and by extension, suffering.

Neuroscientist Daniel Bor recently wrote a great piece in Slate entitled When Do We Become Truly Conscious? that can help us come to terms not only with animal suffering, but plant (lack of) suffering as well.

In analyzing when a a human becomes conscious, Bor writes:
"The evidence is clear that a fetus can respond to sights, sounds, and smells, and it can even react to these by producing facial expressions. The evidence is equally clear, however, that these responses are generated by the most primitive parts of the brain, which are unconnected to consciousness, and therefore these actions don’t in any way imply that the fetus is aware."
If we replace "fetus" with "plant" and make a few edits for scientific clarity, we get:

The evidence is clear that a plant can respond to sights, sounds, and smells, and it can even react to these by changing development [many example of this in WHAT A PLANT KNOWS!]. The evidence is equally clear, however, that these responses are generated in the abscence if a brain, and thus is unconnected to consciousness, and therefore these actions don’t in any way imply that the plant is aware.

Obviously in philosophical debates such as these, semantics play a key role. Bor and I don't use the word aware  in the same way.In WHAT A PLANT KNOWS I posit the thesis that plants are indeed aware of their environment. But they are not conscious, at least not in the way that Bor uses awareness and consciousness:
"In adult humans, for normal consciousness to occur, it is now generally agreed that two sets of regions need to be intact, functional, and able to communicate effectively with one another: the thalamus, a kind of relay station in the middle of the brain that connects many regions with many others; and the prefrontal parietal network, our most high-level, general purpose section of cortex. If either the thalamus or prefrontal parietal network is substantially damaged, the patient is likely to enter into a vegetative state, with virtually no sign of consciousness."
Psychologists, physicians and neurobiologists alike have come to a consensus that suffering, which is subjective, is located in the prefrontal cortex, while pain centers are located deep within the human brain that radiate out from the brainstem. The International Association for the Study of Pain meshes pain and suffering and defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” So if suffering from pain necessitates highly complex neural structures and connections of the frontal cortex, it follows that plants obviously don’t suffer – they have no brain.

So munch away on your celery stalks; take pride in your ability to chop tomatoes; and prune your oak so that it doesn't obstruct a path. Your plants may "know" what's happening, but frankly my dear, they don't give a damn.

3 comments:

  1. Thanks for the peace of mind.

    What types of life forms exist on the cusp of being able to feel pain? Are there creatures where it could possibly go either way?

    Do mice have the neural complexity to feel pain? What about salamanders? Beetles?

    Do far less complex animals who do feel pain possess a prefrontal cortex per se, or just something comparable?

    What life form has the greatest capacity for suffering is this even possible to determine?

    Sorry to bombard you, but I just became very interested in the topic all of a sudden.

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  2. "Your plants may "know" what's happening, but frankly my dear, they don't give a damn."

    That's a nice way of putting it.
    Plants respond chemically without a consciousness, whereas animals do not.

    A definition of 'animal': "a living organism that feeds on organic matter, typically having specialized sense organs and nervous system and able to respond rapidly to stimuli."

    Clarifying an organism as an animal could be done by returning TRUE for each condition for the definition.

    "feeds on organic matter"
    "specialized organs"
    "nervous system"
    "able to respond rapidly to stimuli"

    If most or all all conditions are TRUE then the organism is an animal.
    Else FALSE and the organism is not an animal but exhibits some animalistic behaviours.

    For a human;
    "feeds on organic matter" TRUE
    "specialized organs" TRUE
    "nervous system" TRUE
    "able to respond rapidly to stimuli" TRUE
    TRUE, TRUE, TRUE, TRUE = 100% TRUE.
    Humans are animals.

    Now, for plants;
    "feeds on organic matter" MOST DO NOT = FALSE
    "specialized organs" TRUE (nutrient circulation)
    "nervous system" FALSE
    "able to respond rapidly to stimuli" TRUE (Mimosa pudica)
    FALSE, TRUE, FALSE, TRUE = 50% TRUE.
    Plants are not animals, but have specialized organs and are able to respond rapidly to stimuli.

    For "specialized organs", consider the difference between a rock and any plant. I would consider the plant more alive than the rock as it can transport nutrients throughout itself to survive, whereas rocks cannot.

    Rocks do circulate water; rivers and streams in caves. But does the water prolong the existence of the rock? No, it is erosion and destroys the rock.

    Therefore I would say that by plants having this circulatory system the condition is TRUE.

    As plants are, based on definition I mentioned, only 50% animal, they are not 100% animal and are therefore not animals.

    I will continue to enjoy the taste and health benefits of vegetables!

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