We are told by numerous reports that crustaceans feel pain. These things crop up every few months, and some of you may know that I’ve written about it before, in Philosophy Now, that time in reaction to Lynne Sneddon’s research into fish. So my ears pricked up yesterday. Here’s a sample of the headlines:
Lobster pain may prick diners’ consciences (New Scientist)
Blow for fans of boiled lobster: crustaceans feel pain, study says (Guardian)
No backbone? Lobsters still feel pain (Times)
Prawns do feel pain, say scientists (Daily Mail)
The study was carried out by a team led by Robert Elwood at Queen’s University, Belfast. They’ve been spending their time “daubing acetic acid on to the antennae of 144 prawns.”
“Immediately, the creatures began grooming and rubbing the affected antenna, while leaving untouched ones alone, a response Prof Elwood says is “consistent with an interpretation of pain experience”. The same pain sensitivity is likely to be shared by lobsters, crabs and other crustaceans, the researchers believe.”
Prof Elwood says that the results are consistent with pain. This is true, but it’s a rather weak claim: the results are also consistent with the absence of pain. That an animal reacts physiologically and behaviorally to adverse stimuli does not imply that there are concomitant emotions or feelings of unpleasantness – or any consciousness at all. Even plants react to adverse stimuli. Nociception, the physiological mechanism behind animal responses to adverse stimuli, is important for those that possess it because it allows them to avoid damaging situations. Consciousness need not have anything to do with it.
But what is pain anyway? Here’s a reasonable definition, from the International Association for the Study of Pain:
“An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”
Defined in this way, pain is a subjective conscious experience. It follows that it is impossible to prove that animals feel pain, because animals cannot tell us how they are feeling. That the findings of scientific studies imply the presence of pain is an interpretation based on the assumed presence of consciousness.
If, on the other hand, you would rather define pain only in terms of physiology and behaviour, you can’t then suggest that crustaceans feel like we do, after conveniently dropping pain’s conscious aspect.
The aforementioned Lynne Sneddon is quoted as saying:
“Shrimps do not have a recognisable brain. You could argue the shrimp is simply trying to clean the antenna rather than showing a pain response.”
And Richard Chapman, from the University of Utah’s pain research centre said:
“Even a single-cell organism can detect a threatening chemical gradient and retreat from it. But this is not sensing pain.”
So crustaceans cannot feel pain because they do not have the right anatomical and physiological apparatus, ie. the apparatus that we know is involved with human pain sensation. In the Guardian article Prof Elwood gets the last word on this:
“Using the same analogy, one could argue crabs do not have vision because they lack the visual centres of humans”
His comment is misleading. The analogy is wrong. One of the reasons it might be inappropriate to use the word pain to describe animal responses is because of the emotional connotations of the word. Vision has no such connotations, so it doesn’t sound odd or controversial to say that a crab can see. We can therefore use the words vision and see without problems because they contribute relatively little to an anthropomorphic view of crabs.
In any case, crab vision – like the crab response to adverse stimuli – is radically alien to human vision, partly because crabs “lack the visual centres of humans”. To say that a crab can see is not to say that it is experiencing anything like we do.
Is it right to say that a robot with eyes – such as Domo – can see? Many would say yes, more for convenience than anything else. Saying so does not imply that you think the robot has any of the thoughts and emotions associated with conscious vision, because seeing does not imply them very strongly. I think that this is the way in which we would say that crabs can see.
Now, what if you program a robot to respond in the same way as we do to adverse stimuli? Does it experience pain? I think most people would say no, because pain, unlike seeing, has strong connotations of emotion and consciousness, which few would grant to robots.
Why should we infer pain in a prawn any more than we would infer pain in such a robot?
Is it OK if I slash my dog’s legs?
Spot-on, Mr Jar.