Scientific understanding of animal sentience has advanced dramatically, expanding the circle of moral consideration to an increasingly broad range of species.
The expansion of scientific understanding of animal sentience is one of the most ethically significant scientific developments of the past half-century. Each decade, the circle of species considered potentially sentient has expanded: from mammals to birds (well-established), to fish (now strong scientific consensus), to decapod crustaceans (recent legal recognition in UK), and now to insects (actively researched). This expanding circle has direct welfare implications - species previously treated as incapable of suffering are now subject to welfare considerations. The precautionary principle - that where suffering is possible and avoidable, it should be avoided - becomes increasingly important as the frontier of sentience uncertainty encompasses billions of small invertebrates that would represent enormous welfare stakes if found to be sentient.