Chimpanzees weigh evidence strength, not just novelty, in Uganda sanctuary study
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Chimpanzees at Ngamba Island Chimpanzee Sanctuary in Uganda switched food-box choices when shown stronger evidence, a study published in Science in October 2025 found. The apes discounted misleading clues and kept choices based on strong initial evidence. The results rule out simple recency bias, indicating rational belief revision.
Key Facts
- The study was led by Hanna Schleihauf of Utrecht University and published in Science in October 2025.
- Fieldwork took place at Ngamba Island Chimpanzee Sanctuary in Uganda, run in partnership with the Chimpanzee Trust.
- Across five linked experiments, chimpanzees switched choices more often when new evidence was clearly stronger than initial evidence.
- When a clue type proved unreliable, chimpanzees discounted that specific clue type rather than becoming generally more cautious.
Experimental Design
Researchers varied the type and strength of evidence chimpanzees received across five linked experiments. Weak clues included rattling sounds, while strong evidence included a direct view through a clear panel. The design tested whether chimpanzees simply followed the newest or most vivid clue, or genuinely compared evidence strength. Researchers also tested responses to repeated redundant clues and to clues later revealed as misleading.
Rational Belief Revision
Chimpanzees kept their original choice when the first evidence had been strong. They switched more often when the new evidence was clearly stronger than what they had started with. When evidence was later shown to have misled them, they discounted it going forward rather than continuing to weight it. Modelling against simpler explanations such as recency bias and random switching showed the data fit a rational belief-revision process.
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