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Samples - Monkeys in the marketplace (for website Darwin Year 2009)


In many aspects, monkeys are a lot like us. They even show economic behaviour: they trade, they bargain, and they raise their prices when whatever they are ‘selling’ is in high demand. Researchers at the Universities of Tilburg(Netherlands) and Strasbourg(France) are studying this economic behaviour. They discovered that it follows the rules and principles of human markets.

Nienke Beintema

According to Charles Darwin, the main driver for evolution is competition. When individuals compete for food, for a mate or for space, it is the strongest one that wins and that gets the most offspring in the end. The ‘survival of the fittest’ thus leads to species that are better adapted to the demands of their environment.

“At the same time we see mutual exchanges between individuals,” says Cécile Fruteau, a researcher formerly affiliated with TilburgUniversitybut now working in Strasbourg. Fruteau has spent many months studying wild groups of sooty mangabeys and vervet monkeys, two closely related monkey species in Africa. “Individuals give each other things, like food items, or they do each other a favour, for instance by grooming. Why would they do that if they are each other’s competitors?” One explanation, as she points out, is that individuals help others because they are family. By helping a family member, they increase its chance of survival, and hence, indirectly, they increase the survival of their own genes. After all, some of these are shared by the family member. But then again – exchanges also happen between unrelated individuals. “One theory states that individuals help others, because they expect others to help them in return,” Fruteau continues. “This is called reciprocal altruism. It is a theory that makes a lot of sense, and it is very likely to be true. But it is very hard to test in nature. In monkey societies, for instance, there are many different individuals that all interact with each other. It is very hard to keep track of who owns what to whom. Moreover, monkey societies are very dynamic. Their social structures change all the time. It’s impossible to prove that reciprocal altruism holds true.”

Fruteau and her two supervisors, prof. dr. Ronald Noë (Strasbourg) and prof. dr. Eric van Damme (Tilburg), aim to explain the exchange of so-called commodities – goods and services – in another way. Prof. Noë is a primate ethologist, and prof. Van Damme is an economist. “By exchanging commodities in a deliberate way, monkeys show economic behaviour,” says Fruteau. “In fact, they operate on a biological market. We use the term ‘market’, because just like on human markets, the value of commodities depends on the levels of supply and demand. Something that is more popular, and less available, will cost more.”



Then, which are these commodities in monkey societies? Which goods and services are traded? “An interesting one is grooming,” says Fruteau. “One monkey grooms the other in exchange for being groomed in return. Or in exchange for food, for sex, or for being allowed to hold a female’s baby.” Baby-holding, apparently, is a popular activity among female monkeys. They are so eager to hold another female’s baby that they are prepared to ‘pay’ for it by grooming the baby’s mother. “Baby access is more expensive than grooming,” notes Fruteau, “so a female needs to spend more time grooming than she actually gets to hold the baby.”

Just like on human markets, the price of a commodity is dependent on supply and demand. “If there are a lot of males around,” says Fruteau, “a male may groom a female, hoping that she will choose him for a mate. But if males are scarce, females will start to groom males in return for sex.”

In order to put a ‘price tag’ on some of these activities, Fruteau decided to do an experiment. She put tasty apples in a box, which the monkeys themselves could not open. From a distance and out of sight, she used a remote control to open the box, but only when one particular female would touch the box. “We know that social status is important in monkeys,” says Fruteau. “I chose a low-ranking female to be the one to be able to open the box. It didn’t take very long for the monkeys to figure out that this one female had a special power. Soon the monkeys started to please that female. They started grooming her, hoping that she would open the box for them.” And she did, after a certain amount of grooming. But then Fruteau appointed a second female who could also open the box. Now there were two ‘key-holders’, who were competing for the favours of the others. “It worked just like a supermarket,” says the researcher. “There was more supply, so the prices were lower. Each female would get groomed only half of the time, compared to the grooming time when there was only one ‘key-holder’. This was fascinating to see. The monkey market followed the same rules and principles that our human economy has.”

Funny things

Fruteau did her research with monkeys in the wild. She studied the sooty mangabeys in Ivory Coastand the vervet monkeys in South Africa. “It took lots of time to habituate them to my presence,” she says. “At first they always tried to trick us. They would suddenly disappear into the forest, and it would take me a long time to find them back. But after a while it got easier.” She had to follow the monkeys throughout their territory, which in the case of the mangabeys could be as large as 20 square kilometers. “It was tough,” she says. “Sometimes you’re stressed and tired and the monkeys don’t behave the way you want them to. But then you realise that you’re actually very lucky to be with them. They are great, and they do funny things all the time. Sometimes you see a group gathered around a pond, the youngsters are jumping from liana to liana, the mothers are grooming each other and keeping an eye on their children. It’s like a human family at the swimming pool.”

More information:

Ronald Noë’s website on biological markets: < http://ronald.noe.googlepages.com/markets-main >

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