Apes can make rational, economic decisions as humans do, research finds

They love to bet.
Nergis Firtina
Chimp with cash.
Chimp with cash.


The Institute of Biology at the University of Neuchatel (UniNE) in Switzerland discovered that orangutans and gorillas could make rational economic decisions. According to a new study, apes are similar to humans when it comes to making choices.

Led by Penelope Lacombe, Sarah Brocard, Klaus Zuberbühler, and Christoph Dahl, the study was conducted with orangutans and gorillas housed at Switzerland's Basel Zoo. The results were published in PLOS ONE on December 14.

"Rather than settling for a treat they are sure to receive, orangutans and gorillas prefer to bet on a bigger reward, even if they are not sure of getting it," says UniNE. As it seems, apes are prone to take risks like humans. Therefore, this risk-taking in monkeys was underlined by observing inhabitants of the Basel Zoo.

Apes can make rational, economic decisions as humans do, research finds
Orangutan training.

Orangutans are risk-takers

Individual apes were given two cups in the first experiment, one of which had a risk-free option and the other a more dangerous one. Choosing the safe course always resulted in receiving the same reward. Making the risky decision means either receiving a reward or not. However, the prize was more valuable regarding the secure reward.

Both orangutans and gorillas were found to understand how the experiment worked, and they preferred to select the riskier reward when they were more ravenous. Additionally, orangutans have a tendency to be risk-takers.

“We have shown that orangutans and gorillas can perceive variations in the number of rewards as well as variations in the probability of winning and make rational choices based on these variations. For example, they will preferentially bet and choose the "risky option" if they know that they have a better chance of winning, or if they can win a greater reward," explains Pénélope Lacombe, a doctoral student at UniNE and first author of the study.

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The preference is %78

Second, by altering how the monkeys were given the option to place a wager, primatologists could modify the monkeys' perception of the number of rewards or possibilities. Here, a set of orange cups are used in place of the pink "risky" cup, and the seekers hide the large reward under just one of these cups.

The probability of winning by selecting an orange cup is the same as the probability of winning by choosing the pink container previously. As a result of the configuration change, the monkeys used distinct betting methods. In one of the trials, the scientists discovered a 78 percent preference for "risky" solutions over all other possibilities.

“Our results show that although gorillas and orangutans rely on rational cues to decide whether to bet, they are subject to context-based cognitive biases that affect their choice,” says the paper.

Study abstract:

Human economic decision-making sometimes appears to be irrational. Partly, this is due to cognitive biases that can lead to suboptimal economic choices and context-dependent risk preferences pertinent question is whether such biases are part of our evolutionary heritage or whether they are culturally acquired. To address this, we tested gorillas (Gorilla gorilla gorilla) and orangutans (Pongo abelii) with two risk-assessment experiments that differed in how risk was presented. For both experiments, we found that subjects increased their preferences for the risky options as their expected gains increased, showing a basic understanding of reward contingencies and rational decision-making. However, we also found consistent differences in risk proneness between the two experiments, as subjects were risk-neutral in one experiment and risk-prone in the other. We concluded that gorillas and orang-utans are economically rational but that their decisions can interact with pre-existing cognitive biases, which modulate their risk-preference in context-dependent ways, explaining the variability of their risk preference in previous literature.