For at least seven centuries, capuchin monkeys in Brazil have been opening cashews using sophisticated and effective tools, according to scientists at the University of Oxford. What's more, the primates may have been using them far longer than that.
Lydia V. Luncz, one of the authors of a study published in the journal Current Biology, told the Washington Post, that the layers of soil the study radiocarbon-dated only went back to 1266 A.D., but they expect the behavior began well before that.
The Oxford paper even suggests that human behavior may have changed based on our observation of the primate. The authors believe European arrivals to the New World may have first become aware that cashews were edible thanks to the monkeys – even more controversially, the finding “prompts us to look at whether early human behavior was influenced by their observations of monkeys using stones as tools,” according to the release announcing the study.
Cashews grow inside a shell that's too hard to open with bare hands and are covered in a fluid toxic enough to make people sick.
The fact that the capuchins use tools isn't new. They have been observed many times placing the cashews on flat pieces of stone, lifting heavy hammer stones and bringing them down hard against the cashew to break its shell. In fact, the stones are often left under cashew trees by capuchins, only to be picked up by the next monkey. "Like cutlery at a restaurant," the paper’s lead author, Michael Haslam, has said.
His research team mapped where monkeys had left modern tools, and dug looking for ancient stone tools.
The new findings are “incredibly important,” archaeologist Huw Barton of the University of Leicester in England told Science News. They “will help us reassess the earliest evidence of tool use by our own ancestors.”
Early European explorers would roast cashews in the shells and break them open after the shells softened.
Observed by scientists in Serra da Capivara National Park in the Brazilian state of Piaui, capuchins place the nuts on an anvil-like surface, then bash them open using a stone they’re able to hold in their cute little monkey hands.
How the large anvil stones came to rest at the foot of the Cashew trees is a mystery. “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 monkey’s live in that area. Humans don’t use rocks,”Luncz told the Post.
While this is not the first archaeological evidence of monkey tool use, it is the oldest. Haslam, Falótico and his colleagues reported the first evidence in May, in the Journal of Human Evolution: 10- to 50-year-old buried tools used by long-tailed macaques in Thailand. Before that, chimpanzees were the only primates other than humans with an ancient track record of tool use, dating back thousands of years.