The science of animal pain has advanced dramatically in recent decades. Understanding what we know — and what remains uncertain — is essential for evidence-based welfare policy.
Animal pain science has moved from a position of deep skepticism about non-human pain to one of broad scientific consensus that at least vertebrates — and probably many invertebrates — experience pain with a subjective quality. Key evidence includes: nociceptors structurally similar to human pain receptors; opioid systems that respond to pain and analgesics; protective behaviours after injury; and conditioned avoidance learning. The greatest remaining uncertainty is the degree to which pain has a subjective, felt quality versus a purely functional role. This uncertainty argues for precautionary welfare policies that err toward protection rather than assuming absence of suffering.