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Monkeys Learn Stone Skills from Each Other

CAMBRIDGE, UK, March 26, 2007 (ENS) - Monkeys can learn skills from each other in the same way that humans do, according to a new study of capuchin monkeys in Brazil. While not conclusive, this research into the way monkeys use stones adds to a mounting body of evidence that suggests other species have something approaching human culture.

Dr. Antonio Moura, a Brazilian researcher from the University of Cambridge Department of Biological Anthropology, has discovered signs that a group of capuchin monkeys in northeastern Brazil bang stones together as a signaling device to ward off potential predators.

"One of the most interesting things is that they make a noise to scare off predators," Dr. Moura said. "They would seem to be communicating the danger to one another at the same time."

A strong case has already been made for great apes, such as gorillas and chimpanzees, having a capacity for social learning, but until now there has been no evidence of such culture among the New World primates of Central or South America, including capuchins.

Banging objects is an innate behavior in capuchin monkeys, but in all wild groups observed before this research the behavior had only happened in a foraging context. Banging stones is "an entirely new variant," Dr. Moura said.

This research in the Serra da Capivara National Park, in the Piaui state of northeast Brazil. There Dr. Moura observed episodes of stone-banging among a group of 10 monkeys.

Serra da Capivara National Park, a UNESCO World Heritage where ancient cave paintings have been found. (Photo courtesy Maria-Brazil)

As he approached, the monkeys would first search for a suitable loose stone, then hit it on a rock surface several times.

At first, the act was apparently an aggressive one directed at Dr. Moura as a potential predator, and as the group became used to his presence in the area the stone-banging decreased.

In many cases, adults and juvenile monkeys were seen banging the stones together without paying the researcher any attention at all. Dr. Moura says this suggests that the younger monkeys were learning the skill from their more experienced elders.

Captive monkeys released into the area also appeared to learn to bang stones from the others.

Dr. Moura describes this act of stone-banging as "a remarkable and novel" behavior which has yet to be observed in any other non-human primate species.

Capuchin monkeys are found in Central America and middle South America, in Brazil, Ecuador, eastern Peru, and Paraguay). (Photo courtesy Save Ecuador's Animals)

Biological anthropologists are divided over whether other species have the capacity to acquire skills by social learning, or whether the different skill sets exhibited by different groups of the same species are a result of environmental influences.

In this case, Dr. Moura could find no environmental cause for the capuchins acquiring this skill, so he suggests that they had learned it by observing and imitating one another.

"We already know that these monkey populations use stones as tools to dig holes or to forage and questions remain about why this happens in this area," Dr. Moura said. "Because it is quite dry and barren, it is possible they learn these skills from one another because they have to develop them quickly."

As well as using the noise to deter predators, Dr. Moura also reports that in many cases the act of stone-banging, which often took place on higher ground, dislodged other stones that could hit the predator below.

The main function of the act would appear to be that of a "loudspeaker," he said. Partly, this is to advise the predator that it has been spotted.

Because the capuchins spread out widely in the dry forested areas of northeast Brazil when they forage, the noise could be an alarm call, he speculates.

A capuchin monkey cracks a nut on an anvil using a large stone. (Photo by Marino G. de Oliveira, Funda��o BioBrasil)

This example of percussive stone technology adds to knowledge of other types of stone technology among wild capuchin monkeys of Brazil, such as the way they use stones as a hammer and anvil to crack nuts.

In 2004, a team of researchers, led by University of Georgia psychologist Dr. Dorothy Fragaszy, published the first direct scientific report of tool use among a population of wild capuchin monkeys. The monkeys used stones as hammers to crack palm nuts on other anvil stones. There had been reports of single instances of this behavior but never before of a whole population using tools routinely over a long period of time.

A multinational scientific research consortium including the University of Georgia, University of Sao Paulo, and the government of Italy has starting investigating this behavior with support grants from the National Geographic Society and the Leakey Foundation.

The use of stones provides biological anthropologists with a rare example of primates using stone technology, adding to the archaeological record of primate behavior. Most items, such as sticks, used by primates in cases where they may be exhibiting socially-learned skills are perishable.

Similar evidence of stone technology is found in the archaeological record of the earliest humans, and as more evidence emerges, scientists hope the ancient ancestry of human behavior will become clear.

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