Naked Science Forum
Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: Lamprey5 on 12/02/2012 15:31:54
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A psychologist (Born) in the mid-19th century did experiments to try to find out if plants feel pain or not. He argued that not only do plants feel pain but they have extrasensory perception! From what I've read the study does not seem to be conclusive and sound. Does anybody know if plants feel pain?
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Plants do have mechanisms to detect and repair damage.
Some plants do have mechanisms to turn towards the sun, and perhaps also direct root systems towards water and nutrients.
Animals can have reflexes and local feedback loops in the nervous system independent of the brain. However, one could argue that one requires the central nervous system (brain) to perceive pain.
Plants lack a central nervous system, and don't appear to have a distributed nervous system. So, on that basis, one could argue that they do not have pain sensation.
Last year I had an electric fence around my garden and sun flowers. Periodically a leaf would touch the fence. The fence would eventually burn the leaf, but there was no indication that the plant was retracting from the fence,
Anyway, my conclusion is NO
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Leaves retracting when touched ... https://en.wikipedia.org/wiki/File:Mimosa_pudica_leaves_folding_when_touched_2.ogv
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Clifford suggests that to feel pain a central nervous system is required. He is not the only one to reach such a conclusion and it would certainly seem to be reasonable.
RD points out that plants can react to touch. But is that pure reaction or a pain defence mechanism? If so, what triggers the mechanism?
On a similar vein to RD's Mimosa example, the Venus Fly Trap also reacts to touch. Tiny hairs within the modified leaves which form the trap will trigger the closing of the trap when touched.
Then there are the cases of plants using chemical signals when attacked. For example, when caterpillars begin to eat the leaves of corn, the corn releases a chemical signal which attracts wasps. The wasps will then eat the caterpillars. Lima Beans, when attacked by spider mites release a chemical which alters the flavour of the bean, making it less attractive to the spider mite. This chemical is also released into the air to warn surrounding plants of the attack, so they can release this defence system before the spider mite attacks.
An experiment carried out at Exeter University showed that the Arabidopsis (a brassica related to the cabbage) warn each other of impending attack. Three healthy plants were isolated and the leaves of one were cut to simulate an attack. Not only did this plant begin a chemical reaction to protect itself, but the two undamaged plants, once they had received the signal from the 'attacked' plant began to react to protect themselves against perceived imminent attack.
Now I'm not sure any of this could be said to suggest that plants actually 'feel pain', but the fact that they react to attack and/or damage seems to suggest that plants are perhaps somewhat more advanced than we think. Plants have been around a couple of thousand million years or so longer than animals. They have protected themselves with modified leaves to form thorns and spikes, sharp edge leaves, chemical toxins and communications. They even bleed to protect damaged parts. Some plants even benefit from grazing.
So, do plants feel pain? Well, perhaps not in the same way that animals do, but perhaps they feel pain in a different way, but for the same purpose.
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Plants have been around a couple of thousand million years or so longer than animals. They have protected themselves with modified leaves to form thorns and spikes, sharp edge leaves, chemical toxins and communications. They even bleed to protect damaged parts. Some plants even benefit from grazing.
So, what would plants have been defending themselves against before animals?
Would there have been any benefits of thorns or toxins before animals?
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Plants appear to have taken these measures after animals emerged from the seas on to dry land. So insofaras protection against grazing animals is concerned, plants would have no more history than that of animals on the matter of defence, but maybe plants might have needed to protect themselves against parasitic plants. There is certainly evidence of plants using other plants to get their tops up amongst the high canopy trees in vine like fashion. Such plants would pose a threat to the host of strangulation and/or thirst. Plants may have been feeling pain and defending themselves against each other for a long time.
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Much of this revolves around how one would define pain, which even amongst humans is a highly subjective phenomenon. Extrapolating pain responses even onto other animals can be problematic, there are varying degrees of similarity in the nervous systems of different taxa of animals and it can be hard to judge how these differences translate into the feeling and processing of pain as it would in a human. In some ways there is an important psychological element to pain and its overall ability to indicate ‘suffering’ in either human, other animals or indeed plants, etc. Some organisms can be considered to be able to anticipate/fear instances of pain and respond accordingly, much as humans do, whereas other organisms are simply able to produce a response to physical intervantion/damage, yet still others are not capable of making any detectable pain response (although there may be observable physiological/endocrine responses which could be monitored, such as in the case of bivalves and similar animals).
In summary, I think I am inclined to say that plants are not capable of feeling pain in a manner that we as animals (particulary as hominids, and likewise other primates) would understand it. But there is always room in science for the revision of our accepted wisdom, were the evidence to come to light.
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i think they do feel pain but don't remember it because they don't have a brain. So they can react to pain (when they're being eaten they can 'call over the predators' of what is eating them, or they can send toxins to the bits that are being eaten and deter the eater. So they're purely reactive/hormonal/emotional, not logical.
The reason they feel pain is because it's the motivation to make an effort to keep healthy - putting energy into surviving rather than dying.
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Question. Humans need sensors to feel the sensations such as pain, need a nervous system to deliver the information that the sensors give it, a brain to identify the signal and figure out what to do, from its memory banks, give a signal to the nervous system to something like muscles, if the response is retracting your hand from the source of pain.
(Which is a rather mechanical view on it and somewhat can be simulated with robotics and computers)
How exactly are plants any different?
They sense they are damaged, being touched, eaten...etc. they end up responding, with chemical reactions and even warning other plants of the danger.
This would indicate that it does have a brain of sorts to comprehend how it should be defending itself at a given time.
Now for the bigger question, since we can't really put the sense of pain in robotics, we use a combination of sensors to simulate it being damaged. Mostly using loss of signal feedback, pressure sensors, vibration sensors etc...
Can we say plants don't have that kind of contraption in them?
Any questions or real answers with backing up would be appreciated
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A lot of interesting points have been raised in this thread, and it is tempting to try to respond to too many at once, so I will restrict myself to two points.
1. What do we mean by pain? With a few possible exceptions we all know what pain is. We humans define pain, and understand it in the context of our own experience. To feel that pain we need our nervous systems and our brains. They are part of our definition of pain, so without them this particular concept of pain is meaningless. We can extrapolate our feelings of pain to other animals. The nearer those animals are, physiologically and mentally, to us, the more accurate this extrapolation is likely to be.
What we cannot say with any degree of certainty is that creatures further removed from us; animal forms that lack brains, and even plants, do not have a “mechanism” by which they are able to suffer negative experiences in a way we are unable to comprehend.
2. We have seen, in this thread, examples of plants apparently adopting defensive strategies and warning other plants of danger. It is easy to anthropomorphise these examples and to treat them as though they were deliberate actions on the part of the plants. In fact, if we apply to them the precepts of evolution, they can all be explained without recourse to choice, personal or otherwise.