Chimpanzees can change an initial food-location choice when later evidence supports an alternative more strongly, while tending to keep their choice when the counterevidence is weaker. A 2025 peer-reviewed Science study tested this evidence-sensitive belief revision in controlled tasks; it does not show that chimps reason like humans in every domain.
Key takeaways
- Chimpanzees were more likely to revise an initial choice when later counterevidence was stronger than the evidence supporting the first choice.
- In the first two experiments, researchers tested 15 chimpanzees; those experiments were preregistered, according to the University of St Andrews Research Repository.
- Later experiments examined how chimpanzees handled alternatives, repeated versus new information, and clues that undermined earlier evidence.
- The authors interpret the findings as metacognitive evaluation of evidence, but the controlled tasks do not establish unrestricted human-like reasoning.
The evolution of rationality: How chimps process conflicting evidence
The study tested whether chimpanzees selectively revise an initial belief about where food is hidden when later evidence points elsewhere. In the first two experiments, chimps were more likely to change their choice when the alternative was supported by stronger evidence, and tended to retain it when the new evidence was weaker.
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What did the chimpanzee study actually test?
Researchers hid food at one of two locations, gave each chimpanzee an initial clue and choice, then presented a different clue favoring the alternative before asking for a second choice. The question was whether the animals responded to the relative strength of the clues, rather than simply following the newest one.
The evidence types differed by experiment: one contrasted direct visual evidence (seeing the food) with auditory evidence (hearing it); the other contrasted auditory evidence with indirect visual traces. The researchers classified the clues as stronger or weaker based on prior research, and initial choices supported those classifications. The primary research manuscript describes the test of selective belief revision.
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Did chimps weigh stronger evidence over weaker evidence?
Yes. In the first two experiments, chimpanzees were more likely to choose the location supported by stronger evidence, whether that evidence appeared before or after the weaker clue. This pattern is inconsistent with a simple rule of always preferring the newest information.
The relative strength of a clue depended on the comparison being tested: direct sight of food was stronger than hearing it in one experiment, while hearing it was stronger than indirect visual traces in the other. The study reports that 15 chimpanzees took part in these first two preregistered experiments, according to Schleihauf and colleagues’ paper record.
Did chimpanzees represent more than one possible explanation?
A later experiment examined whether chimpanzees considered more than the strongest-supported location. Researchers tested whether subjects could retain an alternative possibility when the option with the strongest evidence was no longer available. The authors interpret the results as evidence that chimpanzees represented and weighed alternatives. This behavioral result does not prove that the animals formed verbal propositions or consciously articulated hypotheses.
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Can chimps tell new evidence from repeated evidence?
A later experiment contrasted genuinely new information with a redundant repeated cue. Chimpanzees were more likely to revise a choice after independent new evidence than after repetition of information from the same source. The authors interpret this as evidence that the animals distinguished the informational value of new evidence from redundant repetition.
What happens when evidence about the evidence changes?
The final experiment tested whether chimpanzees changed a choice when new information weakened the connection between an earlier clue and the food. The researchers describe this as second-order evidence: information about the evidential value of another clue. The authors interpret the findings as showing sensitivity to whether earlier evidence remained reliable. See the primary manuscript for the experiment details.
Are chimpanzees rational?
The study supports a constrained form of evidence-sensitive belief revision in these tasks, not a claim that chimpanzees are rational in every human sense. The authors state that chimpanzees responded to counterevidence in ways predicted by a formal model of rational belief revision: they remained committed when evidence for the alternative was weaker and revised their belief when it was stronger. This is the authors’ interpretation of behavior in a controlled food-location task, not proof of language-like conscious reasoning.
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The authors also interpret the broader findings as metacognitive evaluation of conflicting evidence. That conclusion should be distinguished from what the experiments directly measured: choices made after researchers controlled the clues. The University of St Andrews Research Repository identifies the work as a peer-reviewed Science article by Hanna Schleihauf, Emily Sanford, Bill Thompson, Snow Zhang, Joshua Rukundo, Josep Call, Esther Herrmann, and Jan Engelmann.
What did the study not prove?
- It did not show that chimpanzees use human-like language to describe beliefs or hypotheses.
- It did not establish conscious verbal deliberation or unrestricted scientific reasoning.
- It did not show that chimpanzees reason like humans in every setting.
- It did not estimate what percentage of the chimpanzee population is rational.
Behavior can support an inference about a cognitive process without providing direct access to an animal’s private thoughts. These experiments tested carefully controlled food-location choices, so broader claims should remain cautious.
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What does chimpanzee reasoning tell us about human evolution?
The study suggests that some forms of evidence-sensitive reasoning may have older roots than humans. In the tested tasks, chimpanzees compared clues, responded to new versus repeated information, and changed choices when evidence for an earlier clue was undermined.
This does not mean human rationality evolved fully formed in chimpanzees. The study supports a limited evolutionary implication: some processes involved in evaluating evidence may predate uniquely human language-based reasoning. The repository record lists the paper in Science, volume 390, issue 6772, pages 521–526, published October 30, 2025, with DOI 10.1126/science.adq5229. Nature’s November 11, 2025 news analysis provides secondary context.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How is this study different from ordinary animal learning?
Learning that a cue predicts food is different from selectively revising a choice when conflicting clues differ in strength or reliability. The study tested whether chimpanzees responded to stronger counterevidence, distinguished new from redundant information, and reacted when evidence undermined an earlier clue.
The animals made choices in a structured environment, and researchers controlled the evidence presented. The results therefore support evidence-sensitive decision-making in the tested context, not a claim about every kind of chimpanzee decision.
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Frequently Asked Questions
Can chimpanzees change their minds when they get new evidence?
Yes. In controlled food-location tasks, chimpanzees were more likely to change their choice when later evidence supported the alternative more strongly than the evidence behind their initial choice.
Do chimps weigh strong and weak clues differently?
In the first two experiments, chimpanzees were more likely to choose the location supported by stronger evidence, even when that evidence came later. The study tested 15 chimpanzees in those experiments, according to the paper record.
Did the study prove that chimpanzees think like humans?
No. It tested choices in controlled food-location tasks. The authors interpret the findings as evidence of metacognitive evaluation, but they do not establish human-like language or general-purpose reasoning.
What does “second-order evidence” mean in this study?
It means information that bears on whether an earlier clue is reliable. The researchers tested whether chimpanzees changed a choice when new information weakened the link between an earlier clue and the food.
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Chimpanzees can revise a food-location choice when stronger evidence contradicts an initial clue, while tending to retain it when counterevidence is weaker. The study supports the authors’ interpretation of bounded, evidence-sensitive metacognition—not unrestricted, human-equivalent rationality.
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