Image (c) Ronald Noë
(PhysOrg.com) — A monkey that has acquired the sole power to hand out apples is generously rewarded with grooming sessions by the other monkeys in its group. But as soon as another monkey can hand out apples as well, the market value of the first monkey is halved. The monkeys therefore unerringly obey the law of supply and demand. Dutch-sponsored researchers Ronald Noë, Cécile Fruteau and Eric van Damme demonstrated this in their article that was published online on 7 July by the renowned journal PNAS (Proceedings of the National Academy of Sciences).