Are you likelier to buy an expensive diet pill when you hear it has helped 40 percent of people or failed to help 60 percent? That's easy. People are much more likely to go with a choice framed positively, even when the odds are 50–50. New research shows that our ape cousins share these tendencies, suggesting the response is rooted in our biology rather than in how we are socialized in our culture and economy.

The susceptibility to positive framing is what scientists call an irrational bias, and it is very powerful. To better understand why our psyche responds so deeply, Christopher Krupenye, a Duke University graduate student in evolutionary anthropology, and his colleagues Alexandra Rosati of Yale University and Brian Hare of Duke gathered 40 of our closest living relatives—23 chimpanzees and 17 bonobos—and offered them options for choosing food: either one or two fruits versus a constant number of peanuts. Sometimes the apes were shown one piece of fruit each time they made the selection, but half the time they were given two: positive framing. In other trials, the apes were initially presented two pieces of fruit, but half the time they got only one: negative framing. Regardless of the framing, the apes ended up with an identical quantity of fruit. Yet they were more likely to choose fruit when they were offered the single fruit with its frequent “bonus” than the double fruit with its frequent “loss.”

Because these framing effects are shared with our nonhuman relatives, Krupenye says, the results suggest that these biases are hardwired into our biology and may have conferred some evolutionary benefit as apes foraged for food. Yet a hardwired tendency does not have to be a sentence. Although susceptibility to framing is in our blood, being aware of the bias can help us avoid making poor decisions. Next time you encounter a well-framed ad, try figuring out what the negative framing would be and see if you are still tempted. Chances are, you can use your brain to outwit your biology.

The sexes are not equally swayed by spin

As with humans, apes are likely to make decisions depending on whether their choices are presented positively or negatively. Yet in the Duke study discussed at the left, male apes were more affected than females by how their choices were framed. A body of research has shown that gender also affects how humans respond to framing. The studies show a range of intriguing and sometimes contradictory sex differences, which may have to do with the arenas (health, money, food) in which the choices are being made and how those interact with typical gender roles.

• In matters of life and death, such as the effectiveness of screening for cancer, women are more responsive to negative presentation (how many people will die) as opposed to positive (how many will survive). Men respond more to positive framing.

• In one money-negotiation study, in which people accepted or refused a share of $10 (“I give you $6” versus “I take $4”), women were unaffected by framing, but men were likelier to reject a negative presentation (“I take…”) and show physical responses akin to feeling competitive and defensive.

• In another study, women were more likely than men to choose positively framed 80 percent fat-free chocolate rather than the identical 20 percent fat chocolate.

• In some research, men were more persuaded than women by a negatively framed message about what they would lose by not complying with tax regulations (fines and jail) versus what they would gain by complying with regulations (no fines, no jail).