Researchers have found that small Capuchin monkeys are able to understand the meaning of symbols and can use objects of no value to them as an exchange equivalent for obtaining food - that is, as money. This is stated in an article published in PLoS ONE magazine.
The authors of the article - scientists from the University of Rome La Sapienza and the Institute for Cognitive Research, as well as from the medical schools of Harvard and the University of Washington in St. Louis - note that earlier attempts to study the ability of monkeys for sign communication mainly turned to great apes.
In particular, there are known experiments in which chimpanzees were able to teach deaf people to use sign language for communication.
This experiment involved not great apes, but the capuchin monkeys (Cebus apella) living in South America, which diverged from human ancestors 35 million years ago.
The authors of the study note that there have been earlier experiments in which the "economic behavior" of non-human apes was studied. In particular, scientists were able to teach them to “buy” food from experimenters for objects of no value to them - “tokens”.
The article emphasizes that these experiments raise new important questions, so it remains unclear whether the monkeys really perceive the tokens as signs or they remain for them just a kind of "tools" for obtaining food.
“Monkeys can psychologically perceive tokens as symbols to represent food, just as humans perceive words or money. On the other hand, exchanging tokens for food may simply be the result of instrumental behavior. In this case, the behavior of monkeys exchanging tokens with experimenters may be analogous to the behavior of a pigeon foraging with a lever,”the scientists write.
They set out to find out exactly how monkeys perceive tokens: as symbols or as tools. To do this, it was necessary to find out whether their preferences for food coincided with the preferences for objects that symbolized different types of food.
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The experimenters trained five Capuchins to trade three types of tokens (which were a green token, a black plastic tube, and a copper hook) for three types of food. For example, an olive could be "worth" one green chip, and a piece of Parmesan could be "worth" one plastic tube.
Scientists have found out the preferences of monkeys in food - for each of them three types of food were selected, which differed in the degree of animal addiction to them. For example, a monkey named Paprika loved pistachios most of all, dried pineapple slices less, and even less seeds.
At the first stage of the experiment, the monkeys had to choose between two types of food out of three, while the "less favorite" food they could get more. As a rule, monkeys preferred "worse" food, but more.
At the next stage, the same experiment was carried out with signs indicating food. Then the scientists found out whether the choice of the monkeys in relation to food coincides with their actions in relation to the objects symbolizing the types of food.
As the results of the experiment showed, "the preferences of the Capuchins for symbolic objects were similar to the preferences for real food," the article says.
“These results show that Capuchins are indeed able to perceive tokens as symbols,” the scientists conclude.