If the UK joins a handful of other nations to recognize the sentience of invertebrates, such as cephalopod mollusks and decapod crustaceans, by, for example, prohibiting the boiling of live lobsters, this will be based on evidence that emotions and felt experiences (i.e., sentience) are not limited to animals close to humans, such as the mammals.

Over a decade ago, the same debate revolved around fish. Do fish feel pain? …This debate was settled when fish were found to learn from encounters with negative stimuli by avoiding dangerous locations. The best explanation is that fish remember these locations because they felt and neuronally processed aversive experiences. The same logic has been followed for arthropods, such as crabs, which in experiments learn to avoid locations where they have been shocked…

For example, the face—the proverbial window on human emotions—expresses emotions through similar muscular contractions…indistinguishable between humans and chimpanzees. Obviously, increasingly distant species have increasingly different expressions of the emotions, but research has found that, for example, physiological changes, lowered temperature of the extremities, and activation of the amygdala during fear are notably similar in fearful rats and fearful humans…. 

Bees subjected to vigorous physical agitation (shaking) to simulate a predatory attack proved less willing to explore new tastes, and hence were negatively biased by their experience. They also showed reduced amounts of hemolymph dopamine, octopamine, and serotonin. Changes in these neurotransmitters mark anxiety or depression in humans.

 It is not hard to see that the denial of animal emotions, and by extension animal feelings, has been morally convenient during human’s history of animal exploitation. Conversely, their recognition is bound to shake up our moral decision-making…If crabs experience emotional states, then they have an interest in these states being positively valenced. Current research indicates that a wide range of animals have interests in avoiding felt pain, and that they would not consent to painful procedures if given the opportunity….

When the medical community recognized infant pain in the 1980s, it was because the evidence was so overwhelming that physicians could no longer act as if infants are immune to pain.

Excerpts from Frans BM de Waal and Kristin Andrews, The question of Animal Emotions, Science, Mar. 25, 2022