Like humans, monkeys can make irrational decisions when making choices

In the study, researchers found that rhesus monkeys preferred a highly-valued food item (a fruit) alone to the identical item paired with a food of positive but lower value (fruit and a vegetable).

The researchers suggest that this behavior is similar to what has been seen in previous studies with humans, where participants rated a 24-piece dinnerware set more highly than one with the same 24 pieces, plus 16 more pieces of which nine were broken.

According to the authors, decision-making processes in humans and other primates have evolved towards reducing the complexity in choices between large groups of assorted items, which may result in such irrational choices.

"People often judge a group -- of valuables, of foods, of other people -- by its average rather than by the sum of its parts. Our study shows that monkeys appear to do the same thing, which suggests that both monkeys and people inherited a particular way of simplifying the world around us, making choices easier, sometimes at the expense of 'rationality'" says Kralik.