The scientific understanding of animal sentience has expanded dramatically, with strong evidence for conscious experience across many taxa.
The expanding circle of known sentience demands an expanding circle of moral concern. We now know that fish feel pain, that crustaceans show protective behaviors after injury, and that birds have functional equivalents to mammalian emotional systems. The appropriate response to uncertainty about sentience is a precautionary approach: when we are not certain an organism cannot suffer, we should err toward minimizing potential suffering rather than assuming none exists.