Monkey Economy Works


From the Netherlands Organization for Scientific Research:

<<Market value of vervet monkey falls if monoploy is broken


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


Cécile Fruteau placed food containers with

highly-desired pieces of apple in two groups of South African vervet

monkeys. For the monkeys there was just one problem: only one in each

group could open the food container. This monkey had a low position in

the rank order and was therefore scarcely groomed. However, as soon as

she acquired the power to hand out apples she was valued more and was

groomed a lot by the rest of the group. Yet she could only enjoy that

privilege briefly; the researchers placed a second food container that

could be opened by another low-ranking female. From that moment onwards

the market value of the first monkey was halved, and she was therefore

groomed half as often. 

(Image: Xlandfair)

Long-term planning


experiments revealed that the female monkeys that could open the food

containers were groomed more than when they exerted no power over the

food production. The females concerned also did not have to groom the

other monkeys as long. They were therefore paid for their services as

food suppliers. Biological market theory predicts that the market value

of these female monkeys should vary according to the law of supply and

demand. The fact that the grooming time of the first monkey was halved

as soon as the second monkey gained the power to distribute apples,

confirms this idea; the price of goods – in this case the female

monkeys who could open the containers – was instantaneously adjusted to

the market.

Immediately after the opening of the food

containers, the researchers registered how long the females were

groomed for. The next occasion on which the females could open a

container was, however, several days later. The fact that the females

were still groomed more indicates that the vervet monkeys apply a

strategy that works in the long term. The choice of partners is also

influenced by long-term attitudes; the monkeys can value one monkey

relatively more than the others.

A change in price – grooming

for less long if there is another monkey that supplies apples – is only

possible if a negotiation process takes place. Many economists assume

that such negotiations can only take place if they are concluded with a

contract. However, the vervet monkeys do not have the possibility to

conclude such binding contracts and yet they still succeed in agreeing

to a change in price for a service.

The research of Eric van

Damme (Tilburg University) and Ronald Noë (University of Strasbourg) is

part of the Evolution and Behaviour research programme of the NWO

Division for Social Sciences.>>

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