Overview
- Researchers at UC San Diego published a peer-reviewed paper on Oct. 20–21, 2026 reporting that macaque groups exposed to a 2020 simian retrovirus outbreak were less likely to take food that looked contaminated.
- In controlled tests of 55 Japanese macaques, animals chose fruit on a clean surface far more often than fruit placed on a surface with real macaque feces sealed under epoxy to preserve only visual contamination cues.
- Macaques from outbreak-exposed groups ate the contaminated-appearing food in 47 percent of trials versus 79 percent for the unexposed group, and the change tracked group exposure rather than whether an individual had been infected.
- A complementary analysis of 54 individuals across seven rearing backgrounds found former pet macaques raised by humans were more likely to eat contaminated-looking food than sanctuary-born, mother-reared macaques, linking early-life experience to avoidance differences.
- Authors say the results support an experience-dependent 'behavioral immune system' in non-human primates, raise animal-welfare questions about species-appropriate rearing, and call for follow-up work on social transmission and how long learned avoidance persists.