Scientific understanding of animal sentience has expanded dramatically in recent decades, with implications for how we treat billions of animals in human care and in the wild.
Animal sentience science has undergone a revolution since the mid-20th century, when behaviorist orthodoxy denied inner lives to non-human animals. We now have strong evidence for emotional and pain experiences in all vertebrates, strong preliminary evidence in decapod crustaceans and cephalopods, and contested evidence in insects and other invertebrates. The scientific uncertainty does not justify ignoring potential suffering — the precautionary principle suggests taking sentience seriously whenever evidence is suggestive. Welfare decisions made under genuine uncertainty should minimize potential harm.