New York, Feb 12 (IANS): A Duke University study has found that positive and negative frame of mind make a big difference for chimpanzees and bonobos too just as they do for humans.

People prefer something more when its positive attributes are accentuated than when its negative attributes are highlighted, even when the options are equal.

Thus, people will rate a burger as more tasty when it is described as "75 percent lean" than when it is described as "25 percent fat."

Both the statements in fact carry equal amount of truth.

"Historically, researchers thought these kinds of biases must be a product of human culture, or the way we were socialized, or our experience with financial markets," said co-author Christopher Krupenye, student in evolutionary anthropology at Duke University.

"But the fact that chimps and bonobos, our closest living primate relatives, exhibit the same biases suggests they are deeply rooted in our biology," Krupenye added.

In trials conducted in Congo, researchers presented 23 chimpanzees and 17 bonobos with a choice between two snacks -- a handful of nuts and some fruit.

In one series of trials, the researchers framed the fruit option positively -- by offering one piece of fruit, with a 50 percent chance of a surprise bonus piece.

In another series of trials, the researchers framed the fruit option negatively. This time they offered two pieces of fruit rather than one, but if the apes chose the fruit, half the time they were shortchanged and received only one piece instead.

Chimps and bonobos were more likely to choose the fruit over the nuts when they were offered a smaller amount of fruit but sometimes got more versus when they were initially offered more but sometimes got less -- despite receiving equal average payoffs in both scenarios.

The preference for the option framed as a prize rather than a penalty was especially strong in males.

The study appeared in the journal Biology Letters.