Fish don’t feel pain, says Brian Key.  How does he know? In the deep philosophical sense it remains a matter of some doubt as to whether other human beings really feel pain, and as Key notes, Nagel famously argued that we couldn’t know what it was like to be a bat at all, even though we have much more in common with them than with fish. But in practice we don’t really feel much doubt that humans with bodies and brains like ours do indeed have similar sensations, and we trust that their reports of pain are generally as reliable as our own. Key’s approach extends this kind of practical reasoning. He relies on human reports to identify the parts of the brain involved in feeling pain, and then looks for analogues in other animals.

Key’s review of the evidence is interesting; in brief he concludes that it is the cortex that ‘does’ pain; fish don’t have anything that corresponds with human cortex, or any other brain structure that plausibly carries out the same function. They have relatively hard-wired responses to help them escape  physical damage, and they have a capacity to learn about what to avoid, but they don’t have any mechanism for actually feeling pain with. It is really, he suggests, just anthropomorphism that sees simple avoidance behaviour as evidence of actual pain. Key is rightly stern about anthropomorphism, but I think he could have acknowledged the opposite danger of speciesism. The wide eyes and open mouths of fish, their rigid faces and inability to gesture or scream incline us to see them as stupid, cold, and unfeeling in a way which may not be properly objective.

Still, a careful examination of fish behaviour is a perfectly valid supplementary approach, and Key buttresses his case by noting that pain usually suppresses normal behaviour. Drilling a hole in a human’s skull tends to inhibit locomotion and social activity, but apparently doing the same thing to fish does not stop them going ahead with normal foraging and mating behaviour as though nothing had happened. Hard to believe, surely, that they are in terrible pain but getting on with a dancing display anyway?

I think Key makes a convincing case that fish don’t feel what we do, but there is a small danger of begging the question if we define pain in a way that makes it dependent on human-style consciousness to begin with. The phenomenology really needs clarification, but defining pain, other than by demonstration, is peculiarly difficult. It is almost by definition the thing we want to avoid feeling, yet we can feel pain without being bothered by it, and we can have feelings we desperately want to avoid which are, however, not pain. Pain may be a tiny twinge accompanying a reflex, an attention-grabbing surge, or something we hold in mind and explore (Dennett, I think, says somewhere that he had been told that examining pain introspectively was one way to make it bearable. On his next dentist visit, he tried it out and found that although the method worked, the effort and boredom involved in continuous close attention to the detailed qualities of his pain was such that he eventually preferred straightforward hurting.) Humans certainly understand pain and can opt to suffer it voluntarily in ways that other creatures cannot; whether on balance this higher awareness makes our pain more or less bearable is a difficult question in itself. We might claim that imagination and fear magnify our suffering, but being to some degree aware and in control can also put us in a better position than a panicking dog that cannot understand what is happening to it.

Key leans quite heavily on reportable pain; there are obvious reasons for that, but it could be that doing so skews him towards humanity and towards the cortex, which is surely deeply involved in considering and reporting. He dismisses some evidence that pain can occur without a cortex, and therefore happens in the brain stem. His objections seem reasonable, but surely it would be odd if nothing were going on in the brain stem, that ‘old brain’ we have inherited through evolution, even if it’s only some semi-automatic avoidance stuff. The danger is that we might be paying attention to the reportable pain dealt with by the ‘talky’ part of our minds while another kind is going on elsewhere. We know from such phenomena as blindsight that we can unconsciously ‘see’ things; could we not also have unconscious pain going on in another part of the brain?

That raises another important question: does it matter? Is unconscious or forgotten pain worth considering – would fish pain be negligible even if it exists? Pain is, more or less, the feeling we all want to avoid, so in one way its ethical significance is obvious. But couldn’t those automatic damage avoidance behaviours have some ethical significance too? Isn’t damage sort of ethically charged in itself? Key rejects the argument that we should give fish the ‘benefit of the doubt’, but there is a slightly different argument that being indifferent to apparent suffering makes us worse people even if strictly speaking no pains are being felt.

Consider a small boy with a robot dog; the toy has been programmed to give displays of affection and enjoyment, but if mistreated it also performs an imitation of pain and distress. Now suppose the boy never plays nicely, but obsessively ‘tortures’ the robot, trying to make it yelp and whine as loudly as possible. Wouldn’t his parents feel some concern; wouldn’t they tell him that what he was doing was wrong, even though the robot had no real feelings whatever. Wouldn’t that be a little more than simple  anthropomorphism?

Perhaps we need a bigger vocabulary; ‘pain’ is doing an awful lot of work in these discussions.