A Marxist Analysis
In an article titled “Monkey Business” in the New York Times Magazine, Stephen J. Dubner and Steven D. Levitt describe some interesting experiments with capuchin monkeys and money. Although some of the results seem provocative, the most revealing sentence in the essay is this one: “It is sometimes unclear, even to Chen himself, exactly what he is working on.”
(The opening quotation from Adam Smith is from Book I, Chapter II of An Inquiry into the Nature and Causes of the Wealth of Nations; the topic is examined at greater length in his Lectures on Jurisprudence, specifically the lecture of March 30, 1763.)
I’ve heard of animals grasping the concept of trade even outside of interaction with humans. The most notable example is Bonobos (also known as pygmy chimpanzees). They will often exchange food for sexual favors.