The Monkey 'Epidemic' on a Panamanian Island: When Boredom Sparks a Simian Stone Age
In January 2022, Zoë Goldsborough, a PhD student at the Max Planck Institute of Animal Behavior, was reviewing tens of thousands of camera-trap images from Jicarón Island, Panama. Since 2017, 85 motion-triggered cameras had continuously recorded the island's white-faced capuchins (Cebus imitator). Then one frame stopped her cold: a young male capuchin with a howler monkey infant clinging to his back—calmly going about his day.
"This was so strange that I ran straight to my advisor's office to ask what it was," Goldsborough later recalled.
Key points
- Over 15 months (2022–2023), five young male capuchins abducted 11 howler monkey infants, each carried for up to 9 days. At least 4 infants died; researchers suspect none survived, as young males cannot nurse.
- The trend began with one subadult male, nicknamed "Joker", who carried four different infants. Five months of silence followed—then four other males from the same group picked up the behavior.
- This is not adoption, predation, or play. Cross-species adoption in animals is almost always by females caring for abandoned infants. Here the carriers were all males, the infants' parents were nearby (audibly calling from trees), the infants were not eaten, and carrying brought no obvious social benefit.
- Researchers concluded the capuchins were carrying "for carrying's sake"—a social tradition transmitted by imitation, akin to killer whales wearing dead salmon as hats or chimpanzees sporting grass-in-ear fashions—except this fad was lethal.
- Goldsborough et al., "Rise and spread of a social tradition of interspecies abduction," *Current Biology* (2025)
- Max Planck Institute of Animal Behavior press release (2025-05-19)
- Mongabay (2025-05-21); UC Davis Letters & Science Magazine (2024-04-18)
- bioRxiv: Development and social dynamics of stone tool use in wild capuchins (2025-11-04)
Why this island? Boredom as an engine of innovation
Jicarón's capuchins are the only Cebus population on Earth known to use stone tools—hammer stones and anvils to crack sea almonds, coconuts, hermit crabs, and land crabs (first noted by botanist Alicia Ibáñez in 2004). Stone tool use occurs only on Jicarón and Coiba islands, not the mainland—and, like the abductions, only among males.
Project co-founder Meg Crofoot offers a counterintuitive explanation: life on Jicarón is easy. No predators, few competitors, plenty of spare time. "This 'luxurious' life seems to set the stage for innovation. Necessity need not be the mother of invention—for a smart, social monkey in a safe, possibly under-stimulated environment, boredom and free time may be enough."
Islands provide three ingredients for cultural innovation:
1. Isolation — innovations aren't diluted by mainland contact or lost via emigration. 2. Low pressure — time and energy freed from predator avoidance and competition become an "exploration budget." 3. Social density with tolerance — enough observers for imitation, and enough tolerance of odd behavior to let novelty persist.
The male-only puzzle
A November 2025 bioRxiv study found stone tool use on Jicarón is entirely male-biased, meaning infants cannot learn it from mothers. A plausible hypothesis: if females are the dispersing sex in the Coiba archipelago, male-only traditions stay locked within groups, creating a male-only cultural transmission network—an instructive parallel to debates about gendered patterns in early human stone-tool cultures.
The dark side of cultural fads
The abducted infants were Coiba howler monkeys (Alouatta palliata coibensis), an endangered endemic subspecies. If the fad persists or spreads, it could become a conservation problem. As corresponding author Brendan Barrett put it: "Non-human animals can develop cultural traditions with no clear function—and destructive consequences for the world around them."
Why 'why here?' matters more than 'why?'
Barrett's key insight: any innovation is a low-probability accident; "why did it appear" is nearly unanswerable. But "why here" is structural: isolation + low pressure + social density + male philopatry explain why an innovation can take root.
Implications for AI and technology
Mainstream AI agent training is almost entirely demand-driven (tasks, reward functions, RLHF). The capuchins suggest innovation may not require necessity: boredom, idle time, and intrinsic motivation can generate spontaneous traditions—some useful (stone tools), some harmless (grass decorations), some harmful (interspecies abduction). Much like internet meme culture: high social density plus idle bandwidth produces viral traditions—some genuinely innovative (open source, Wikipedia), some noise, some toxic.
Epilogue
When these capuchins crack coconuts with stones, they echo a step our ancestors took 3 million years ago. When they carry another species' infant for no reason, they demonstrate something deeper: culture is born from purposelessness, spreads socially, hardens in isolation—and sometimes brings innovation, sometimes harm.
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