Captive Gorillas And Orangutans Are Pretty Rational When It Comes To Making Decisions

Their ape-itude for decision making is very interesting.


Eleanor Higgs


Eleanor Higgs

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Eleanor is a content creator and social media assistant with an undergraduate degree in zoology and a master’s degree in wildlife documentary production.

Creative Services Assistant

Researcher stands outside an orangutan enclosure with a tray with two cups on it

 Orangutan training. Image Credit: M. Torben Weber, CC-BY 4.0 

How likely are you to play it safe? Choosing an unknown option might be reserved for those with money to burn on the Las Vegas strip – but the mechanisms behind choosing something potentially high risk-high reward is a subject that’s fascinated scientists. Human decision-making is often irrational and can lead to economically poor choices. Now, scientists are turning their attention to the animal kingdom to see if apes have the same cognitive biases when it comes to risky decisions.

The team carried out two experiments on orangutans and gorillas at Basel Zoo in Switzerland. In the first experiment, the animal was presented with two cups. One cup contained a safe option that was known to the animal, or they could choose a second cup as a risky option which might contain a higher reward than the safe option, or no reward at all. 


This first experiment succeeded the training period, where the animals had to learn from each experiment that the safe reward was always presented in the safe cup, whereas the risky reward could be presented in the risky cup. The animals had to learn, through feedback, the probability and the possible gain from the greater reward under the risky cup. 

In a second experiment, the safe reward was presented under a safe cup – however, the risky reward was always presented under one of several risky cups. This was designed to see if the animals could understand the relationship between the number of risky cups, and the chance of getting a reward if the risky cup was chosen. 

Graphic showing the experimental cup set up for each experiment

A: Experiment one design, chose between a safe reward or an unknown risk. B: Animals choose between the safe cup or one to four risky cups containing an unknown amount of reward.

After analysis, the team found that the orangutans and gorillas acted rationally, making decisions based on what they could gain and how likely they were to have a high reward. The animals also were more likely to choose the risky option as the potential reward increased. 

The team found that the orangutans were more likely than the gorillas to choose the risky cup in the first experiment. The researchers conclude that both the gorillas and the orangutans are more risk-prone in the second experiment, while they were risk-neutral in the first. They suggest that future work be carried on to explain the cognitive biases for this change between experimental designs. 


The paper is published in PLOS ONE.


  • tag
  • animals,

  • decision-making,

  • behavior,

  • primates,

  • apes,

  • gorillas,

  • orangutans,

  • cognitive bias