As a species, we can say a lot about this issue, but we hardly have the exclusive rights to pain.
We have certainly seen a dog tending to a wound. Or a screaming deer in distress. But many animals suffer in silence, and we avoid asking them how they feel, so they don't spoil dinner.
But science keeps rearing its nagging head.
Do we feel our ways of eliminating insects differently when we learn that a fruit fly can feel pain? Or how about a lobster, waiting for that pot of boiling water?
The quietest victims in the animal world can be fish. We have been pulling them out of the sea for thousands of years, and recently, with such great efficiency that we can empty the oceans.
Once again, science is here to put our love of herring in a real bind.
A new study from the University of Liverpool published in Philosophical Transactions of the Royal Society B has found that fish feel pain in a "strikingly similar" way to humans. In fact, like us, they hyperventilate and stop eating when they are in pain. They even rub the part of their body that hurts.
For the study, Lynne Sneddon of the university's Institute for Integrative Biology reviewed the existing body of research, 98 studies in all, and concluded that they feel pain just as acute as we do.
"When subjected to a potentially painful event, fish show adverse behavioral changes, such as discontinuation of feeding and reduced activity, which are avoided when a pain reliever medication is provided," Sneddon notes in a statement from University.
To understand pain in other species, scientists look at nociceptors, specialized receptors that send signals to the spinal cord and brain when the body is damaged. Humans have them all over their skin, bones, and muscles. Nociceptors have also been found in many other species, including sea slugs, mollusks, and even those little fruit flies.
Fish have the same means of detecting pain signals. But scientists have long pondered whether they have the equipment to receive them. In other words, can a fish's single-layered forebrain process pain in the same way that a primate's much more complex mind does?
To find the answer, the researchers analyzed how the animals respond to potentially painful stimuli.
"When the fish's lips receive a painful stimulus, they rub their mouths against the side of the aquarium as if we were rubbing our toe when we hit it," says Sneddon.
Also, the old fisherman's adage that fish don't feel pain just doesn't add up from an evolutionary perspective. Pain is an efficient messenger that tells us we have a problem. An animal that cannot feel it will not receive that note, even if it is hurt.
"If we accept that fish experience pain, this has important implications for the way we treat them," says Sneddon. "Care must be taken when handling fish to avoid damaging their sensitive skin and their possibility of pain when catching them should be taken into account."
Christian Cotroneo, article in English