Social housing of primates is a fundamental welfare requirement backed by decades of research, yet isolation persists in some zoo, laboratory and rescue contexts, requiring policy and practice reform.
Primate social housing is not optional welfare improvement but a basic requirement for animals evolved for complex social lives. Solitary primates suffer - self-injurious behaviour, hair plucking, depression and immune suppression are measurable welfare outcomes of social isolation. The welfare research is unambiguous. The barriers to implementation are practical (space, compatibility management, introductions), economic (single housing is simpler to manage), and in research settings, scientific (claimed interference concerns). These barriers are not welfare justifications - they are management challenges that require investment to solve. Commitment to social housing for primates wherever possible is a welfare non-negotiable, not an aspiration.