The science of animal sentience - the capacity for subjective experience - is the foundation of animal welfare ethics and is advancing rapidly.
Sentience science is the empirical foundation of animal welfare ethics - without sentience, there is no welfare subject to protect. The expanding scientific consensus that sentience is widespread among animals, and not restricted to mammals and birds, has profound welfare policy implications. Each new species whose sentience is credibly established adds potentially billions of animals to the moral circle requiring welfare consideration. The methodology for sentience assessment - combining neuroanatomy, behavioral pharmacology, and cognitive bias testing - is becoming increasingly standardized, enabling more consistent evidence evaluation across taxa. The direction of travel in sentience science consistently expands rather than contracts the circle of morally relevant animals.