Dawkins makes a convincing argument that far from having a reduced or absent capacity for pain, animals may feel it more than we do:

Without going into the interesting literature on Animal Suffering (see, for instance, Marian Stamp Dawkins’s excellent book of that title, and her forthcoming Rethinking Animals), I can see a Darwinian reason why there might even be be a negative correlation between intellect and susceptibility to pain. I approach this by asking what, in the Darwinian sense, pain is for. It is a warning not to repeat actions that tend to cause bodily harm. Don’t stub your toe again, don’t tease a snake or sit on a hornet, don’t pick up embers however prettily they glow, be careful not to bite your tongue. Plants have no nervous system capable of learning not to repeat damaging actions, which is why we cut live lettuces without compunction.

It is an interesting question, incidentally, why pain has to be so damned painful. Why not equip the brain with the equivalent of a little red flag, painlessly raised to warn, “Don’t do that again”? In The Greatest Show on Earth, I suggested that the brain might be torn between conflicting urges and tempted to ‘rebel’, perhaps hedonistically, against pursuing the best interests of the individual’s genetic fitness, in which case it might need to be whipped agonizingly into line. I’ll let that pass and return to my primary question for today: would you expect a positive or a negative correlation between mental ability and ability to feel pain? Most people unthinkingly assume a positive correlation, but why?

Isn’t it plausible that a clever species such as our own might need less pain, precisely because we are capable of intelligently working out what is good for us, and what damaging events we should avoid? Isn’t it plausible that an unintelligent species might need a massive wallop of pain, to drive home a lesson that we can learn with less powerful inducement?

At very least, I conclude that we have no general reason to think that non-human animals feel pain less acutely than we do, and we should in any case give them the benefit of the doubt. Practices such as branding cattle, castration without anaesthetic, and bullfighting should be treated as morally equivalent to doing the same thing to human beings.

full article: richarddawkins.net