Apes get upset when they lose, study shows

Chimpanzees and bonobos, like humans, are often upset when a risky decision turns out badly, according to a new study by US researchers.

If a gamble does not pay off, the apes display negative responses such as pouting, moaning, whimpering, screaming, scratching themselves and banging on the bars of their enclosure.

In the study, Alexandra Rosati and Brian Hare from Duke University in Durham, North Carolina dealt some surprises to semi-free-ranging common chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) from African ape sanctuaries.

The scientists said in their account for the online journal PLOS ONE they got interested in ape grumbling because negative emotional states have been shown to have a strong influence on human decision-making.

In one experiment, 38 apes had to decide between receiving a small portion of food immediately or a large one after a wait of one or two minutes. All of them had been pretested to make sure they understood the basic setup.

The chimpanzees chose the large reward in nearly two-thirds of the trials when it was delayed for one minute, and in slightly more than half when it was delayed for two. They were more patient than the bonobos but showed significantly more negative vocalising while waiting.

In a second experiment, the researchers compared chimpanzees' and bonobos' willingness to accept variability in payoffs.

Thirty-seven apes were given a choice between a risky option that provided, with equal probability, either a favourite snack or one they did not like, and a safe option that always delivered an intermediately preferred food type.

The chimpanzees were much more willing to take a risk, doing so almost two-thirds of the time, against only about 40 per cent for the bonobos. Both species had a much more intense emotional response to a bad outcome compared with a good outcome or playing it safe.

"Psychologists and economists have found that emotions play a critical role in shaping how humans make complex decisions, such as decisions about saving or investing money," noted lead researcher Rosati, now at Yale University.

She said the research showed apes' emotional responses to the outcomes of decisions to be similar to that of humans.

The researchers added that further studies were needed on whether these responses play a causal role in the apes' decision-making, as they do in humans.