Freakonomics

"Adam Smith, the founder of classical economics, was certain that humankind's knack for monetary exchange belonged to humankind alone. 'Nobody ever saw a dog make a fair and deliberate exchange of one bone for another with another dog,' he wrote. 'Nobody ever saw one animal by its gestures and natural cries signify to another, this is mine, that yours; I am willing to give this for that.' But in a clean and spacious laboratory at Yale-New Haven Hospital, seven capuchin monkeys have been taught to use money, and a comparison of capuchin behavior and human behavior will either surprise you very much or not at all, depending on your view of humans."

Monkey Business