Wild capuchin monkeys in Brazil have been opening their favorite meal of cashew nuts using stone tools for at least 700 years, long before Christopher Columbus discovered the Americas and claimed it as the New World, findings of a new study have revealed.
In the research published in the journal Current Biology on July 11, primate archaeologist Michael Haslam, from the University of Oxford, and colleagues have found evidence that helps explain how monkeys managed to thrive on meals of hard-shelled fruits and seeds in the semi-arid region of Northeast Brazil.
"We find that primates with much smaller brains than humans have innovative ways of exploiting the food sources available to them," Haslam said.
The researchers have observed that young capuchin monkeys in the Serra da Capivara National Park in Brazil learn how to use stone tools from older monkey at cashew processing sites around the base of cashew trees.
The primates would use hammer stones on heavier anvil stones to pound open a nut and then discard the stones in piles at the processing sites where other monkeys would also select stones they can use.
The capuchins were also found to be particular with the materials they use — usually opting for smooth, hard quartzite stones as hammers and opting for flat sandstones for anvils.
Haslam and colleagues also made excavations at a food-processing site near cashew trees to see if the tool technology that the animals used has developed over time. Digging at the site eventually unearthed 69 stones that were used by previous generations of capuchin monkeys.
The stones have dark residues and mass spectrometry experiments revealed that these were caused by cashew nuts.
When the researchers carbon-dated the small pieces of charcoal that were found near the stones, they found that these were at least 600 to 700 years old.
This means that the stone tools that they found were already used prior to the Europeans' arrival in the New World. This converts to about 100 generations of capuchin monkeys.
"Wild capuchins at Serra da Capivara National Park (SCNP) use stones to pound open defended food, including locally indigenous cashew nuts and we demonstrate that this activity dates back at least 600 to 700 years," Haslam and colleagues wrote.
"Capuchin stone hammers and anvils are therefore the oldest non-human tools known outside of Africa."
The stones that were used by the monkeys were notably unchanged in shape and size over time. This suggests that the animals are conservative when it comes to using tool technology. Unlike humans, they prefer not to change the tools that they use.
