Comparing welfare states and welfare improvements across different species raises profound methodological and ethical questions at the frontier of welfare science.
Cross-species welfare comparison is philosophically and practically challenging but practically necessary for welfare prioritisation. Organisations allocating resources between helping fish versus pigs versus dogs must make implicit or explicit comparative judgements. The lack of agreed methodology means such decisions often rest on unstated assumptions. Recent work developing welfare range estimates for different species - considering evolutionary relatedness, neural complexity and behavioural flexibility - represents genuine progress even if conclusions remain uncertain.