When a person's behavior is out of control, people might say he is “going ape.” It appears, however, that our closest relatives can behave themselves better than we thought. New research in chimpanzees and monkeys could reveal clues about how self-control originated in humans.

Even children know that resisting instant gratification can lead to greater rewards. Past research showed that to cope with such delays kids can distract themselves by playing. Now psychologists Theodore Evans and Michael Beran of Georgia State University find that chimpanzees can also employ diversions to control themselves.

The scientists tested chimps with a candy dispenser that delivered a treat every 30 seconds. As soon as the apes reached for the accrued sweets, no more candy came—so if the chimps exercised restraint, they earned a greater reward. Sometimes the chimpanzees were given toys, such as magazines or toothbrushes. Evans and Beran found that the apes could resist temptation about 50 percent longer when they could amuse themselves with playthings, racking up 17 candies on average with toys and only 11 without toys.

Evans's other work has revealed self-control among more distantly related primates as well. For instance, tufted capuchin monkeys can show enough restraint to use celery stalks and pretzel rods to scrape peanut butter out of a cylinder, rather than devouring the edible sticks immediately.

The evolution of more sophisticated degrees of self-control might have been key to our ancestors’ developing time- and labor-intensive faculties such as tool making, Evans says. Further comparisons between humans and other primates could help us understand when and how our self-control became as complex as it did.