A team of scientists from the University of Oxford have been studying capuchin monkeys in Brazil that open cashew nuts using stone tools.

The results of their study suggests that the primates have been using the method for at least 700 years, long before the “discovery” of the Americas by Christopher Colombus. And it appears that the monkeys might have been using the stone tools even longer ago, writes Darryl Fears for The Washington Post.

capuchin monkeys
Image source: Wikimedia Commons

Capuchin monkeys tool use began at least 700 years ago

“We think we’re just at the beginning,” said study author Lydia V. Luncz. Scientists found that the 1300s were the radio-carbon-dated time in the soils in which the tools were discovered, however it looks like the practice may have started long before. “We definitely expect this to go beyond 700 years,” she said.

As amazing as this seem it is actually not that groundbreaking to find evidence of tool use among primates. Study lead author Michael Haslam previously published a paper on wild macaques using tools in Thailand, but this is the first time that evidence has been found outside Africa and Asia.

This latest paper was published Monday in Current Biology. It makes the slightly controversial suggestion that the evidence “prompts us to look at whether early human behavior was influenced by their observations of monkeys using stones as tools.”

The scientists propose that new arrivals to the area could have learned that cashews were edible by watching the monkeys. If this seems far-fetched, it’s important to note that the small nut that you buy in the shops is now the natural state of the cashew.

Deliberate tool use fascinates scientists

In the wild the nut is found inside a bright-red apple with a tough shell, with a toxic fluid around it. It is not known how people found out that the cashew was edible, but for many years they would cook the cashew apple over a fire and then break it open to eat.

In contrast the capuchin monkeys break open the apple using stones. “They are very deliberate with this,” Luncz said.

The monkeys have also been observed tapping different nuts in order to find a good one. Once they are happy with their choice, they place it on a larger stone which acts as an anvil.

“They don’t want to hit their feet or their fingers” in the same way that chimpanzees and macaques sometimes do in other places, Luncz said. “They strike down on it. They very carefully peel the shell away and expose the kernel. And they love it. They really get into it. It’s rich in protein, and it’s a great food source for them, definitely worth the effort.”

Further research needed into primate archaeology

The study shows that capuchin monkeys entered the stone age hundreds of years ago, but have hardly innovated since. This is similar to behavior exhibited by West African chimps.

“It’s just a handful of primates [species] living today out of 350 that show this kind of behavior,” Luncz said. She believes that “we need to look back at other species that used tools” given the fact that the human use of tools has been widely researched.

There are several mysteries that require further research, such as how the large anvil stones got to their current position under the cashew trees. “I don’t know the answer to that,” Luncz said. “At some point [the monkeys] must’ve carried them there. Maybe they dragged them. I have not observed one of those sites established from scratch. But it must be monkey made because only monkeys live in that area. Humans don’t use rocks.”