As a species, we may moan about it louder, but we hardly have the exclusive rights to pain.
We've certainly seen a dog nursing a wound. Or a deer calling out in distress. But many animals suffer in silence, and we're only too happy to refrain from asking them how they feel — lest it should ruin dinner.
But science keeps rearing its pesky head.
The most silent sufferers in the animal world may be fish. We've been plucking them from the sea for thousands of years — and recently, with such wholesale efficiency that we may empty the oceans.
Again, science is here to put our love for herring in a real pickle.
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 way that's "strikingly similar" to humans. In fact, like us, they hyperventilate and stop eating when they're hurting. They will even rub the part of their body that aches.
For the study, Lynne Sneddon, from the university's Institute of Integrative Biology, reviewed the existing body of research — 98 studies in all — and concluded that they feel pain just as sharply as we do.
"When subject to a potentially painful event, fishes show adverse changes in behaviour such as suspension of feeding and reduced activity, which are prevented when a pain-relieving drug is provided," Sneddon notes in a university release.
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 being damaged. Humans have them throughout their skin, bones and muscles. Nociceptors have also been found in many other species, including sea slugs, mollusks and even those tiny fruit flies.
Fish have the same means to detect pain signals. But scientists have long pondered whether they have the equipment to receive them. In other words, can the single-layered forebrain of a fish process pain the same way that the much more complex mind of a primate does?
To find the answer, researchers have looked at how animals respond to potentially painful stimuli.
"When the fish's lips are given a painful stimulus they rub the mouth against the side of the tank much like we rub our toe when we stub it," Sneddon says.
Besides, the old anglers' adage that fish feel no pain just doesn't add up from an evolutionary perspective. Pain is an efficient messenger that tells us that we've got a problem. An animal that can't feel it won't get that memo, even if hurts itself.
"If we accept fish experience pain, then this has important implications for how we treat them," Sneddon says. "Care should be taken when handling fish to avoid damaging their sensitive skin and they should be humanely caught and killed."