As fascinating as this is, I think it's also quite curious that the humans so regularly try to barter with the monkeys. If a monkey ran off with my phone, I dou

As fascinating as this is, I think it's also quite curious that the humans so regularly try to barter with the monkeys. If a monkey ran off with my phone, I doubt I'd have the presence of mind to offer it food, and I'd certainly never consider that it rejected my offer because it wanted different food. My guess would be the locals probably help visitors out by telling them that the monkeys will return their items in exchange for food and how to go about making their offer. I would therefore imagine some kind of co-evolution of the local monkey and human cultures. Indeed, I wonder if much of the complexity of this behavior is actually a result of accidental human design - older individuals would likely be more easily recognized by locals who may ascribe to them certain preferences of food type and quantity, something like "yeah small john over there won't give you back your wallet for less than 5 grapes." Clearly it's still very complex behavior on the monkeys' part but it might be simpler than them independently figuring out economics.