Why shouldn't invertebrates feel pain

Great Debates
1

http://www.livescience.com/animalworld/ap_lobster_pain_050214.html

“It concluded that most invertebrates – including lobsters, crabs, worms, snails, slugs and clams – probably don’t have the capacity to feel pain”
So the question is why shouldn’t these animals feel pain, assuming this is true? Pain is a tool to keep us alive, and the beings that feel pain are more likely to avoid acts that threaten our survival and keep us alive long enough to reproduce and raise kids.

http://www.cnn.com/2006/HEALTH/conditions/02/03/btsc.oppenheim/

So why should invertebrates not have this function? What about their evolution would make them not benefit from physical pain? For them is it an all or nothing scenario where either they are either being eaten (fatal), fatally injured (fatal) or having nothing bad happen (nonfatal) to them that makes them not need pain? If they don’t feel pain then from an evolutionary perspective something about them makes them not need this ability but I don’t know what it is.

2

Assuming that the ability to perceive pain was acquired at some point, all that is necessary for other creatures, that do not perceive pain, to continue to exist is that they are sufficiently reproductively successful.

For most problems, there will be multiple solutions that are more or less equally workable; in order to perceive pain, you need a nervous system; this requires energy to build, run and just carry around - energy thus spent is not available for the purposes of reproduction, so you have sensitive offspring, but maybe less of them. And maybe this works, because being sensitive, more of them survive to maturity.
But what also works is pumping out large numbers of cheap, dumb offspring and hoping that chance will favour a few of them.

3

Basically what it comes down to is that these animals are just very complicated machines. We don’t program machines to feel pain no matter how complicated they are because it is pointless. If I want a machine to avoid damaging itself I program it so that it can’t damage itself. I don’t program it so that it can damage itself if it makes an effort and takes a bit of extra time. But that is all that pain is, it’s a way to make organisms take great effort before they damage themselves. That is a necessity for creatures that can override their built-in programming, but for creatures with no ability to override their programming you don’t program in pain, you program in avoidance.
Generally think that you are missing two main points.

The first is that you don’t need to be able to “feel” in order to respond to stimuli. For example even a cabbage can turn towards the sun, respond it can sense sunlight, but nobody would suggest that a cabbage can feel. As a more extreme example you can remove a chicken’s head altogether and it will still respond to the stimulus of gravity sufficiently to stand upright Creatures such as fish an invertebrates can respond to being eaten alive through simple reactions. They don’t need to be able to feel pain to do that.
The second point is that these creatures lack any semblance of self-awareness. An ant or a tuna isn’t aware that it is an ant or a tuna. As far as we can tell it isn’t even aware of what it is doing. It functions entirely by a series of stimulus-response reactions without any input from the brain aside from sensory processing.

When you combine those two pieces of knowledge it should become clearer why these organism have some need for pain. Humans need pain because we are self-aware. We don’t just function via stimulus-response, rather we evaluate situations and make decisions about appropriate behaviour. That allows us a great degree of freedom, but it also allows us to make damaging choices. You only need to look at a sportsman playing with an injury to see that that is true. Because we choose what actions to carry out we can also make choices that physically damage ourselves. To overcome that obvious flaw we evolved a pain response. Our brain can choose to run with an injury, but the body also gets a vote in the form of pain sensations. Pain is a way for the body to veto the ability of ‘higher’ animals to override instinct using the higher brain centres.

Animals like fish and ants don’t need pain because they can’t override their instincts to any great degree. When a fish reaches a certain age it starts swimming upstream, it doesn’t have any choice in the matter because it isn’t even aware it is swimming upstream. When an ant smells an intruder in the nest it attacks. It doesn’t have any ability to modify that behaviour or to decide that now is not a good time to attack. The reaction is pre-programmed and will occur whenever that stimulus is detected.

That means that pain can’t achieve anything in such creatures. They will do what they do in response to a pre-set stimulus. If they felt pain when they reacted that would just make them less effective, it wouldn’t prevent them form reacting. And they can’t learn not to react.

And the corollary of that is that pian is superfluous. If an animal always responds to stimuli with a specific reaction then the avoidance is the best reaction to avoid to damage. There is no point evolving pain as the reaction. If you want a human to avoid fire sunlight pain is a good solution because humans can and will override any instinct at all, including the instinctive desire to breathe. If you want a cockroach to avoid sunlight pain is very inefficient. It is far more efficient to simply program the cockroach to avoid sunlight. Cockroaches have absolutely zero ability to override such instincts and so it will work perfectly without any need for pain.

Pain evolved AFTER the evolution of the ability of the higher brain centres to override instinct. Prior to that it was unnecessary because instinct worked perfectly well at preventing damage.

I hope that made some sort of sense.

4

Wouldn’t pain fall under a stimulus? If you have ever cut a worm apart to fish, they wiggle like the dickens. If touched in the ground or bucket, they simply dig away faster. Would this not be an example of a pain (stimuli) response?

5

No, pain is a reaction. Heat is a stimulus, the pain is the response to that stimulus. A scalpel blade is a stimulus, the pain from a cut is a response to that stimulus.

Not as far as anyone has been able to ascertain, and there has been research done in this area. The worm may be responding to physical damage, but that response does not incorporate pain.
Think about it this way: You could create a virtual worm using any computer. It too would behave exactly the way you describe. Do you consider that evidence that computer code feels pain? Or is it simply evidence that computer code can respond to a stimulus in a pre-programmed manner?

6

The inistence that certain animals do not, and cannot, feel pain seems to me to carry about it some of the same whiff as the old insistence that the Earth is the center of the universe. “Lower” animals not feeling pain fulfills a need on our part, a need not to feel any guilt.

Sure, they look like they’re in pain.

Sure, their reaction is indistinguishable from pain.

But it can’t be pain because they don’t “need” pain? When did evolution occur because of “need”? Aren’t structures and systems inherited and modified randomly, and then nautral selection ruthlessly weeds out? What if the pain system comes from other uses, or exists as a side effect of something we do not yet understand, or is a byproduct of some other useful function (like nipples for men)? What if pain is immaterial to evolution, but (like junk DNA) hasn’t been weeded out?

Scientfically, we believe that everything we are comes from earlier ancestors, and most physical features and experiences humans have can be traced to precursors going far back into the past. Yet there are curious exceptions --always about things we’re emotionally sensnitive about, like behavior, intelligence, pain, and so on. THOSE things we always feel are exceptions, and we say they appeared suddenly, full-blown, in us.

Why then the belief that pain sprang fully-formed, like Aphrodite on the half-shell, into humans, or “higher” mammals, or whatever?

Why can’t pain have existed in “earlier” creatures? How would we know? Well, one way would be to observe them and see if they seem to be in pain. Which…is what we do seem to see. Hrm.

I’m not a scientist, but I know scientists are human too. I’ve seen them make some pretty unscientific assertions…an astronomer once told a Washington Post reporter that “It would be perverse of the universe” if his pet theory was wrong. Scientists confidently asserted women had inferior brains at one point. And scientists perform a LOT of “painful” testing on “lower” life forms – they have a considerable stake in not feeling guilty about inflicting pain.

It just seems too pat, too neat to say pain suddenly appeared without any precursors. And it seems like many of the systems we look at turn out to be much “older” than we thought.

I take their assertions that pain cannot exist in these animals with a very large grain of salt. Heck, just recently there was a story that lab mice have been singing complex songs in higher frequencies – presumably, in scientific labs around the world, for decades – and scientists just realized what had been going on.

I’m not saying that scientists are stupid in overlooking the obvious. But they’re human like everyone else. They certainly could be avoiding painful truths – there’s a history of that kind of thing.

Or maybe they’re just responding to stimulus. :wink:

Sailboat

7

Whether they “need” it or not, it does appear that fish do feel pain.

8

If you’re going to argue that lower animals don’t feel pain because they don’t need pain, then why do humans feel pain? Why don’t we just react to stimuli like boiling water with just a reaction to get away from it?

Pain is clearly a survival mechanism - it communicates the immediacy of the problem. Animals with less intelligence probably benefit from pain all the more because they can’t discern danger as well.

It reminds me of the things I was taught as a kid that later made me wonder “how the hell do they know that?” For instance - only people and bees can see color. Only humans conduct war. Only people can take another being’s point-of-view. Of course, they’re all wrong.

9

And the insistence that maybe they do feel pain suggests an inability to comprehend that they are not like us, with our minds and feelings.

“Looks like” is pretty poor indicator. Those reactions may be indistinguishable to casual, uneducated observation, but they aren’t to thorough neurological investigation.

“Seems” is an even poorer indicator than “looks like.”

I think you’re overlooking a huge body of research and evidence here. We can identify pain receptor nerves, types of pain, and pain centers in the brains of mammals. Invertebrates don’t even have brains as such. There’s nothing in their reactions to stimuli that isn’t satisfactorily explained by simpler mechanisms that are consistent with their infinitely rudimentary nervous systems. That the motions in those reactions resemble the motions of some pain reactions is just an indicator that those motions are effective, not that pain must be involved.

These critters are so neurologically simple compared to us that we can’t really relate to their sensations and behavior. In that sense, they are far better compared to machines than to mammals. Anthropomorhizing clouds rather than clarifies the matter.

10

Interesting, but the OP stipulated the question was whether **invertebrates felt **pain, no?

11

Yes, but DF was specifically responding to a post that “animals like fish and ants…”

The linked article in the OP specifies that there’s not much knowledge on invertebrate nervous systems.

Why is the default assumption that they don’t feel pain? I can accept that we don’t know for sure that they do, but Occam’s razor suggests they would.

12

This is an interesting distinction. How do biologists doing this research distinguish between behavior that is an autonomic response to stimuli vs. behavior due to pain from those stimuli? I certainly believe that the distinction exists, although I am not sure how scientists decide that one type of animal feels pain in the way that people do vs. other animals that do not. I am sure that most people would agree at the ends of the spectrum (AFAIK PETA is not protesting mistreatment of bacteria) but how do you draw the line? We have pleasure and pain centers in the brain; is there a “pain center” that can be objectively said to exist or not in other types of animals? And for those animals whose brain structure is fundamentally different, how do we know that pain does not exist for them, just because their mechanisms are different than ours?

Although I don’t disagree with your previous point, this argument does not prove that worms do not feel pain, it merely proves that it is possible to have worm-like behavior without pain. One could also write code that simulates certain aspects of human behavior, but that does not mean that humans are not conscious.

13

Huh?? How so?

The reactions that remind us of some of our pain reactions are much more simply and effectively explained as automatic responses to stimuli. Adding pain to the equation complicates the issue. Occam’s Razor suggest they don’t.

14

As I pointed out, we have no apparent need for pain. Our own reactions to adverse stimuli could much more simply be explained as automatic responses. And yet we feel pain. Occam’s razor suggests, therefore, that pain is a useful survival tool. What does it help with? It helps you learn faster to avoid adverse stimuli.

So animals that learn faster when presented with stimuli that would produce pain in humans, it seems the simplest explanation to me, are doing so because they have the same mechanism - they feel pain.

That’s why I say Occam’s razor would lead me to conclude that invertebrates with brains feel pain.

I think the OP stated it rather well. That’s why I think the onus is on those who claim they don’t feel pain.
Does it strike anyone else as ridiculous that because they think lobsters don’t feel pain, we should boil them alive? If there’s a chance they do, isn’t it more humane to err on the side of caution?

Hey - maybe they came up with their conclusion to fit their extant worldview!

15

No, no, no. Learning takes time and energy. Invertebrates don’t learn to avoid certain things - they reflexively avoid them - hardwired into them. Much simpler, much quicker, much more congruent with the behavior we see in them.

While we have some reflexive actions, automatic responses do not adequately explain much of what we do and can do. We reflexively withdraw a hand from a hot pan handle. Having experienced the pain, we learn not to touch hot things. As we learn how to identify which things are hot, we don’t have to touch them all to know to avoid them. Invertebrates can’t begin to do anything like that.

We can also choose to bear certain pain. Normally we’d withdraw from being pricked or stabbed with something, but we’ll consciously suffer a needle insertion that we know will benefit us. Again, invertebrates don’t do any such thing.

It’s apples and oranges. Invertebrates are neurologically much, much, MUCH simpler than mammals. They don’t learn - they simply react. The pain and learning thing is way, way, WAY beyond anything they do. You don’t need pain, nor even benefit from it, if you’re already going to withdraw from anything that’s likely to harm you.

As I said above, we cannot effectively relate to how simple invertebrates are. In this regard, they are much more like machines with sensors and preprogrammed responses than us or the animals we’re most familiar with.

I don’t think it’s possible to understand this aspect of invertebrates if you can’t step away from thinking that they are somehow like us in having minds and feelings. They simply don’t. They don’t have the neurology for it, they don’t have the need for it, they don’t in any way act like it. Some of their actions may remind us of some things we do, but that doesn’t mean they use the same processes in generating those actions. They are fundamentally extremely NOT like us.

16

That’s simply wrong. Higher invertebrates - including insects and lobsters - learn. They learn to avoid things they associate with having negative stimlui before. Even if the negative stimulus is removed, the behavior to avoid the thing that previously was associated with the stimulus remains.

17

Cite?

18

We do have need for pain, and some other living things don’t. Human behavior is very complex and our responses to pain are not all automatic. There may be some autonomic response to pain such as faster heartbeat, but people have an inifinite variety of behavioral responses to pain. If you are stuck with a needle you have a variety of responses you can choose, from gritting your teeth to saying “ouch” to slapping the nurse. In some other forms of life, though, reactions can be most simply explained as the consequence of chemical reactions rather than any conscious perception and reaction.

The thing about science is there is no default position that must be proven or disproven. There are hypotheses that must be tested. It sounds like you are putting forward pain in all creatures as dogma.

This is a good point, but different from the scientific question. This last question takes us to GD territory. Let’s face it. If there were a front-page story on the Official World Scientific Authority Journal on Crustacean Biology that said “No Question–Lobsters Feel Excrutiating Pain When Boiled,” lemme tell you, it wouldn’t make a dent in the Maine lobster industry.

19

Lobsters can learn from odors:
http://72.14.209.104/search?q=cache:0_Mamr9OJ7wJ:www.odu.edu/sci/biology/lobsters/abstracts.pdf+"lobsters+can+learn"&hl=en&gl=us&ct=clnk&cd=3&client=firefox-a

Lobsters figure out lobster traps:
http://www.ticam.utexas.edu/~organism/random-stuff/interesting-articles/Lobster_logicP.html

they inspect empty traps, and leave when traps do:
http://www.gma.org/lobsters/allaboutlobsters/researchquest.html

insects learn:
http://nationalzoo.si.edu/Animals/Invertebrates/News/socialinsects.cfm

fruit fly learns to avoid odors associated with pain:
http://www.nuffieldbioethics.org/go/browseablepublications/ethicsofresearchanimals/report_310.html

I haven’t been able to find a cite that lobsters learn from negative stimuli online, though I know I’ve seen it. I’ll continue looking later.

Nevertheless, your claims that invertebrates don’t learn is wrong.

20

We do have to be careful. Invertebrates are not a homogenous group. But in general, almost all invertebrates have very very simple nervous systems, and are absolutely incapable of learning.

Cephalopods are capable of learning though, and I wouldn’t be surprised to find many other examples of complex invertebrates that can learn.

But the vast majority of invertebrates really do perform absolutely stereotyped behaviors that involve no processing by anything like a “brain”. Insects don’t walk the way we do. Each leg performs a “walking” behavior independently of each other and independent of the insect’s brain. There’s no central processing going on.

And even in vertebrates there’s a lot of behavior that looks intelligent, but is really a very simple stimulus-response system, that only works for the organism in the context of it’s natural environment. If you artificially change the environment, you can see the organism responding to the stimulus in a very “stupid” way.

A classic example would be cuckoos laying their eggs in the nests of other birds. Bird parents appear to behave intelligently, bringing food back to the nest and feeding their babies. But put a cuckoo chick in the nest, and the parent birds will feed the cuckoo chick preferentially to their own babies. The parents are responding to the stimulus of an open mouth, and the cuckoo chick presents a stronger stimulus than the parent’s chicks. And so the parents happily continue to stuff worms into the cuckoo chick even after it has grown many times larger than the parents. They are unable to understand that something has gone wrong, because their responses to their chicks aren’t learned, they are stereotypical responses to stimuli. The stereotyped behavior works almost all the time, but when it breaks the birds have no way to fix it, no way to learn to behave differently.

So we have to avoid falling into two traps, one is the classic trap of anthropomorphizing animals and assuming that just because an animal behaves in a way that we can recognize (caring for its babies) that the animal has similar (although simpler) reasons for doing so. Put a rock in a hen’s nest, and it will brood the rock just like an egg. But the other trap is the trap of assuming that animals are completely different from us and must not have any thoughts or emotions similar to ours. Since humans are animals, our emotions and thought processes and self awareness are part of our animal heritage. A dog does doggy things completely differently than a human because he is a dog, but he also feels emotions similar to ours, a dog can love, hate, fear, feel pain, and feel happiness. Dog owners often have problems both when they expect their dogs to behave just like little people, but also when they expect them to act like machines.

Now, back to pain. We shouldn’t expect organisms that are incapable of learning to be able to feel pain. But this question doesn’t have to rely on theory, we can answer the question empirically. Humans and other vertebrates have special nerve cells for pain reception. We can see pain receptor cells, and nerves that carry pain signals in other vertebrates. So it is absolutely clear that animals with this equipment are capable of feeling pain. Other animals don’t have anything of the sort. Cut a leg off an ant and it doesn’t even seem to realize it is missing a leg. So it is clear that some animals feel pain, others don’t, but we don’t have to make broad sweeping declarations, we can figure out which is which on a case by case basis.