What happens in an animal’s body when it encounters something harmful? Do animals feel pain? How do different species process pain?
Ed Yong’s book An Immense World explores the complex question of whether and how animals feel pain. From naked mole rats that don’t react to acid to fish that show signs of distress after injury, the animal kingdom presents a wide range of responses to potentially harmful stimuli.
Keep reading to discover the surprising science behind how different creatures experience pain and what this means for our ethical treatment of animals.
Animals’ Experience of Pain
It’s a question that concerns many of us: Do animals feel pain? Because they can’t tell us how they’re feeling, it’s hard to know whether various species are experiencing pain. Yong discusses what we know about animals’ pain and the related matter of nociception.
Nociception—the physical recognition of harm—takes place in the peripheral nervous system. If you’re bitten on the hand by a cat, for example, nociception occurs in your hand and your spinal cord, which tells your hand to quickly pull away from the cat’s mouth. Yong says that almost all animals, including humans, have nociceptors—neurons that pick up on harmful external and internal stimuli such as toxins, extreme temperatures, or inflammation in the body. But animals vary in the number of nociceptors they have, how easily activated they are, their size, and how quickly they transmit information.
For example, naked mole rats, which sleep in large piles in underground burrows to keep warm, have nociceptors that don’t respond to acids, meaning they don’t experience acids as harmful. This is because carbon dioxide builds up in the rats’ burrows every time they exhale, so they’ve evolved to tolerate it in much higher doses than other animals. (Shortform note: Scientists believe that understanding more about how nociception works biologically in animals, especially in simpler invertebrates, could lead to better ways of treating pain.)
Pain is more than just nociception. Yong explains that pain is the conscious experience of harm, also known as suffering. Pain occurs when signals from the nociceptors travel up the spinal cord to the brain, which creates the sensation of pain. In humans, the brain is always involved in producing pain.
We don’t know whether various animals have consciousness in the same way that humans do. Consciousness stems from nervous systems, which require processing power. Not all animals have enough processing power to experience consciousness. This would seem to mean that these creatures also can’t experience pain.
On the other hand, says Yong, it’s possible that animal nervous systems work differently than human ones when it comes to processing pain. Some animals that don’t have very complex nervous systems still exhibit complex behaviors that appear to demonstrate their ability to feel pain.
For example, studies show that injecting fish in the lips with bee venom causes them to lie on the bottom of their tank, rocking from side to side, and to rub their lips against objects, long after the injections occurred. According to the scientists who conducted these studies, this shows that fish likely feel pain.
| The Ethics of Animals’ Pain Examining whether and to what degree various animals feel pain can help humans understand the ethical implications of killing animals for food. In his famous 2004 essay, Consider the Lobster, author David Foster Wallace (known primarily for the novel Infinite Jest) examines the ethics of boiling lobsters alive during food preparation. While Wallace doesn’t reach any definitive conclusions, he considers it significant that lobsters exhibit behavior consistent with pain, scrambling desperately to escape upon being placed into pots of boiling water. He notes that even if lobsters experience only a primitive form of suffering, humans may be obligated to prevent such suffering; the same argument could apply to all animals we eat. Indeed, many people believe that we shouldn’t eat meat because it causes animals unnecessary suffering. They argue that industrial livestock farming ignores animal welfare and inflicts pain upon sentient beings. For example, cows are transported to slaughterhouses in crowded, poorly ventilated trucks where they can suffer from heat stroke; once they arrive, they await slaughter in pens where they can often hear, see, and smell other animals being killed. Yet studies show that cows experience fear and anxiety; they also perceive the stress of other cows and become more fearful as a result. In other words, cows feel anxious and fearful prior to slaughter. During slaughter, cows are hit with a stun gun, then hung upside down to bleed to death. If they are improperly stunned the first time, they may experience severe pain as they are repeatedly hit with the metal bar of the stun gun—or they may bleed to death while still conscious. Despite Wallace’s unease, a simple crustacean might not have a nervous system complex enough to experience pain; its behavior might simply be a product of nociception. On the other end of the spectrum, cows are highly intelligent and have similar nervous systems to humans, meaning they’re capable of processing pain in a similar way. |
