Study Shows Chimpanzees Can Revise Beliefs Using Evidence

A study published in Science (October 30) reports that chimpanzees may share another trait long believed to be exclusive to humans: the ability to weigh evidence, revise beliefs, and change decisions based on new information.

• This follows the famous 1960 observation by Jane Goodall at Gombe National Park, Tanzania, where chimps were seen using tools—previously considered a uniquely human behaviour.

About the Study

• Location and team

• Conducted at the Ngamba Island Chimpanzee Sanctuary, Uganda.
• Led by researchers from the Netherlands, Uganda, the UK, and the US.
• Included behavioural observations of 15–23 chimpanzees.

• How the tests worked

• Five simple behavioural tests were used to see how chimpanzees revise their beliefs.
• The team applied a Bayesian model to predict how chimps should behave if they were rationally updating beliefs.
• Predictions were then compared with actual choices made by the apes.

Bayesian Reasoning in Chimps

• What is a Bayesian model?

• A statistical method that updates beliefs continuously as new evidence becomes available.
• Helps predict decision-making under uncertainty.

• Findings

• Chimpanzees didn’t simply imitate the latest clue or loudest signal.
• They assessed:
  • Relevance of the information
  • Reliability of each clue
• They maintained multiple possibilities and adjusted decisions as new evidence appeared.
• Their behaviour resembled rational, evidence-based reasoning, similar to humans.

Social Decision-Making in Chimpanzees

• Sharing information about food

• Experiments show chimps adapt their communication depending on the social context.
• They reveal hidden food only to individuals likely to help them.
• They withhold information from those known to be selfish or competitors.

• Comparison with humans

• Unlike human toddlers, chimps do not seem capable of actively hiding food or objects from rivals — a more complex strategic behaviour.

Source: TH