Like humans, apes too play it safe when odds are uncertain

Apes prefer to play it safe when the odds are uncertain, according to a new study.

 

Humans are known to play it safe in a situation when they aren't sure of the odds, or don't have confidence in their judgments.

 

And new evidence from a Duke University study is showing that chimpanzees and bonobos, our closest living primate relatives, treat the problem the same way we do.

 

Graduate student Alexandra Rosati and Brian Hare, an assistant professor of evolutionary anthropology, asked 16 chimps and 14 bonobos to make choices between two bowls of treats. Though no dice or chips are involved, this kind of experiment is considered a "gambling game," Rosati said.

 

The apes could choose between a safe bet that would always provide a food they liked somewhat less, peanuts, or a variable bet in which the payout could be either a highly-preferred big piece of banana or less-desirable cucumber slice.

 

The apes "gambled" by making a choice of one bowl or the other. They knew the odds before they chose because the experimenter showed them bowls with two potential outcomes, but then gave them only one.

 

Depending on the contents of the bowls, there could be a 100 percent chance of receiving a banana, a 50% chance, or a 0% chance.

 

The apes readily distinguished between the different probabilities of winning: they gambled a lot when there was a 100% chance, less when there was a 50% chance, and only rarely when there was no chance.

 

In some trials, however, the experimenter didn't remove a lid from the bowl, so the apes couldn't assess the likelihood of winning a banana.

 

The odds from the covered bowl were identical to those from the risky option: A 50% chance of getting the much sought-after banana. But apes of both species were less likely to choose this ambiguous option.

 

They were willing to take the chance on the covered bowl when they knew the only alternative was food they didn't like (the cucumber), or no food at all. But, like humans, they showed "ambiguity aversion" -- preferring to gamble more when they knew the odds than when they didn't.