A monkey chooses between groups of objects. Credit: Citation: Kralik JD, Xu ER, Knight EJ, Khan SA, Levine WJ (2012) When Less Is More: Evolutionary Origins of the Affect Heuristic. PLoS ONE 7(10): e46240.doi:10.1371/journal.pone.0046240

When making decisions about the value of an assortment of different objects, people approximate an average overall value, which though frequently useful can lead to apparently irrational decision-making. A new study published Oct 3 in PLOS ONE by Jerald Kralik and colleagues at Dartmouth College shows for the first time that non-human primates also make similar 'irrational' choices based on approximation.

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.

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Kralik JD, Xu ER, Knight EJ, Khan SA, Levine WJ (2012) When Less Is More: Evolutionary Origins of the Affect Heuristic. PLoS ONE 7(10): e46240.doi:10.1371/journal.pone.0046240

Public Library of Science: http://www.plos.org