Monkey Business (article)
Two unrelated tamarin monkeys sit adjoining each other. Every fifteen seconds, a human research assistant brings a tray loaded with a marshmallow that is just out of reach of one of the monkeys. The only way that monkey can eat the treat is if his partner pulls a red handle that will put the marshmallow within reach.
You want how much for those grapes?
But pulling the handle doesn't bring any reward for the puller: pulling the handle only pays if the monkey who receives the marshmallow reciprocates by pulling in the future. Like many human situations, the monkeys must work together to obtain food and build trust while punishing failures to cooperate.
Another experiment that they discuss is monkeys learning to use (and budget) money. These are interesting studies, although I fail to see the real purpose in them, but none the less it is fun to see if the monkeys can learn the concepts. Also I would like to know if dogs would do something to benefit another dog, and then would except the same to be done for him.