When presented with coin-like tokens, tiny yet savvy capuchin monkeys inhibit their natural impulses and make more calculated, rewarding decisions, according to new research.
While capuchin monkeys won't be heading to Wall Street anytime soon, the study provides the first demonstration that inherently worthless tokens, such as poker chips or coins, help monkeys to make more strategic decisions under certain situations.
Despite undergoing 35 million years of evolution independent of us, the monkeys' related skills appear to be on par with those of chimpanzees and 3-year-old children. Monkeys will wheel and deal for peanuts -- literally.
"Peanuts are the favorite food for all of the capuchins in our colony," lead author Elsa Addessi explained to Discovery News.
Addessi and co-author Sabrina Rossi, who are both at the National Research Council of Italy's Institute of Cognitive Sciences and Technologies, conducted the study, which is outlined in the latest issue of the Proceedings of the Royal Society B. Eight capuchin monkeys housed at the institute participated.
The researchers set up what is known as a reverse-reward test, where the monkeys had to select a smaller quantity of food or tokens in order to receive a larger reward. The reward consisted of chopped peanuts. Blue plastic poker chips, a small grey PVC cylinder, a brass plug, a metal nut, a black metal key and a silver metal band served as tokens.
At first the monkeys all went for the largest amounts, choosing the biggest peanut or token piles. They always did this when they saw food, but they were later able to curb this natural tendency with the tokens, which seemed to provide what the researchers said was "psychological distancing from the incentive features of food."
Two of the monkeys in particular, a male named Sandokan and a female named Robinia, repeatedly aced the tests. For example, when presented with 1 and 2 tokens, Sandokan chose 1 and received his peanut reward. He figured out the needed strategy too. When presented with 2 and 5 tokens, he selected 2, and again got his peanuts.
"The capacity of associating a symbolic stimulus (the tokens, in this case) with a reward and the capacity of reasoning on different types of symbolic stimuli in order to choose between them is an important prerequisite for the evolution of money use in humans, which was quite a slow process developing over thousands of years," Addessi said. "In this sense, we can say that the use of money evolved from non-human primate symbolic abilities."
Capuchin monkeys do not use tokens in the wild, so even if they can be taught things like very basic money skills and how to play an incredibly simple game of poker, these activities are restricted to human-orchestrated testing.
Nevertheless, "both good inhibition skills and the capacity of evaluating the quality and the quantity of two options before making a choice are fundamental for wild capuchins' survival in their environment," Addessi added.
During a prior study, Addessi even found that capuchins could indicate their food preferences based on token values, so a coveted Cheerio was worth more tokens than two pieces of Parmesan cheese. The results indicate the monkeys can reason about symbols.
James Anderson, a senior lecturer in the University of Stirling's Psychology Department, agrees with the new findings.
"Capuchins are renowned for their problem-solving abilities, so now the question is whether other species of monkeys can also show the same ability," he told Discovery News.
Michael Beran, a senior research scientist at Georgia State University's Language Research Center, told Discovery News, "It is important to see that smaller-brained primates can use symbols in this way and benefit from them the way that chimpanzees and humans do."
"Of course, as the authors noted, this does not mean the monkeys are as good as humans," Baren added, "but their data do support the idea of continuity across multiple species."