The moral circle is expanding to include invertebrates as evidence for their capacity to suffer grows, challenging welfare science and advocacy to engage with the largest animal populations on Earth.
The expanding moral circle to include invertebrates is one of the most significant - and scientifically supported - developments in contemporary animal ethics. If even a small fraction of the world's invertebrate population experiences states that matter morally, the aggregate welfare significance is enormous given their astronomical numbers. The scientific evidence is strongest for decapod crustaceans and is growing for insects. Cephalopods were already legally recognised as sentient in the UK Animal Welfare Act 2006. For welfare science and advocacy, the practical implication is not to treat all invertebrates identically to mammals, but to apply a proportionate, evidence-sensitive precautionary approach: where evidence of sentience is stronger, welfare protections should be correspondingly stronger. This is an area where the welfare consensus is moving rapidly.