Primates are among the most social mammals on Earth. Solitary captivity causes severe psychological distress and is increasingly recognised as incompatible with acceptable welfare standards.
Solitary captivity is among the most severe forms of welfare deprivation for a primate. Animals evolved over millions of years for constant social contact, communication, grooming, play, and conflict resolution within social groups experience isolation as a profound and ongoing harm. The psychological manifestations — stereotypic self-directed behaviours, chronic stress hormones, immune dysregulation — are not minor adjustment difficulties but evidence of lasting psychological damage that does not fully resolve even when social housing is later provided. The fact that social housing also produces better research data provides a rare alignment of welfare and scientific interests. Facilities that still maintain routine solitary housing of primates for research or display should be considered to be operating below any reasonable contemporary welfare standard.