Can (some) crustaceans feel pain?

As a follow-up to my previous post on speciesism, it is of interest that a soon to be published paper in Animal Behaviour provides tentative evidence of pain in decapod crustaceans (which includes lobsters, crayfishes [crawfishes or crawdads], crabs, shrimps, and prawns). I came across this through a news report in New Scientist that showed up in my RSS feeds and it seemed worthy of mentioning.

Both the New Scientist report and the primary article are behind subscription walls, but here is the abstract of the paper:

Nociception or pain in a decapod crustacean?

Stuart Barr, Peter R. Laming, Jaimie T.A. Dick, and Robert W. Elwood
Animal Behaviour, in press

Nociception is the ability to perceive a noxious stimulus and react in a reflexive manner and occurs across a wide range of taxa. However, the ability to experience the associated aversive sensation and feeling, known as pain, is not widely accepted to occur in nonvertebrates. We examined the responses of a decapod crustacean, the prawn, Palaemon elegans, to different noxious stimuli applied to one antenna to assess reflex responses (nociception) and longer-term, specifically directed behavioural responses that might indicate pain. We also examined the effects of benzocaine, a local anaesthetic, on these responses. Noxious stimuli elicited an immediate reflex tail flick response, followed by two prolonged activities, grooming of the antenna and rubbing of the antenna against the side of the tank, with both activities directed specifically at the treated antenna. These responses were inhibited by benzocaine; however, benzocaine did not alter general swimming activity and thus the decline in grooming and rubbing is not due to general anaesthesia. Mechanical stimulation by pinching also resulted in prolonged rubbing, but this was not inhibited by benzocaine. These results indicate an awareness of the location of the noxious stimuli, and the prolonged complex responses indicate a central involvement in their organization. The inhibition by a local anaesthetic is similar to observations on vertebrates and is consistent with the idea that these crustaceans can experience pain.

Let me say this before the comments begin: I don’t think anyone is claiming that prawns can experience the same kind of pain, including emotional pain and anticipation of pain, that humans can. The point is simply that we cannot automatically dismiss all reactions to noxious stimuli in invertebrates as reflexive nociception. There could be something more to it.

On speciesism.

There has been a lot of discussion on the science blogs about “animal rights” recently. Most of the argument has centered around whether animals are necessary for research, but of course the animal rights movement includes issues such as factory farming, using animals for entertainment, the pet industry, and others. I am a scientist, in particular a zoologist, meaning that I study animals, and of course I agree that many medical advances would be impossible without research using animal models, short of using human models.

That said, I have been amazed at the lack of sophistication in the arguments I have seen. In fact, some of the positions expressed I have not actually encountered since the 8th grade, such as mocking vegetarians or invoking tu quoque arguments about those who oppose some or all animal research but eat meat. Moreover, some bloggers seem to believe that the animal rights movement is populated by only two varieties of people: those who blow up science labs, and those who argue that we should rename the Green Bay Packers because this makes reference to the meat industry. It’s “us versus them”, and they are all either criminal or silly such that the issue can be ignored. This “us versus them” mentality also is relevant in another capacity that I will discuss in a moment.

The issue of animal experimentation has been a contentious one since the 1800s, in particular with reference to vivisection. Many of the same arguments are still being used by both sides, with no resolution in sight. The question, from a philosophical point of view, is not whether animal research works. Yes, some opponents try to make a case on this front, and yes, there are problems with non-human models of human disease, but clearly one cannot do certain things — such as be a zoologist — without studying animals. It’s simply not effective to argue on the basis of whether it works, because obviously it does (with limitations) but this in itself provides no ethical justification. Experimenting on infants would presumably work even better, but I sincerely hope that no one would consider this alone as justification for the practice.

To many of the philosophers and scientists who have discussed this issue over the past 150 years, the central issue is the need to provide justification for inflicting suffering on some (non-human) individuals for the benefit of other (human) individuals. Both sides have invoked the standard moral philosophies, including utilitarianism and Kant’s categorical imperative, and again there has been no resolution. I would argue that neither side will convince the other on the basis of traditional moral philosophy either.

What it boils down to is a philosophical decision that human life is more important that non-human life. Many take this as a given, but a philosophy based on rationality demands that this be justified. Obviously the creationists have their explanation handy: Genesis 1:26-28. Non-religious arguments require a little more consideration than this.

And so I ask, on what basis do you draw the sharp moral line between “humans” and “animals”, “human rights” and “animal rights”, “us” versus “them”? What rational argument do you bring in defense of speciesism? Perhaps you argue that only humans are capable of suffering, or that our intellectual capabilities are of a different kind from those of other animals. As Dawkins has noted, neither is compatible with what we understand about evolutionary history.

I think that opening a discussion about the use of non-humans for human gain is useful. However, I think that simply rhyming off ways in which non-human research is beneficial and dismissing anyone who opposes some or all of it is not. It is a complex issue, and should be treated accordingly.

In one of the more balanced discussions I have seen on this topic, Madhusree Mukerjee made the excellent point that

Animal liberators need to accept that animal research is beneficial to humans. And animal researchers need to admit that if animals are close enough to humans that their bodies, brains and even psyches are good models for the human condition, then ethical dilemmas surely arise in using them.

And, of course, I am not the only biologist with an interest in knowledge about animals to note that the issue of speciesism is one that we cannot ignore.