Brazilian Monkeys Make Stone Hammers That Look a Lot Like Early Human Tools

M. Haslam
M. Haslam / M. Haslam

Animals are adorable when they do people things. It’s a scientific fact. But the list of “people things” just keeps on shrinking. Other animals can hold grudges, name their babies, read our expressions, and even read our mammogram results. The latest ding in our dominance comes courtesy of Brazilian capuchin monkeys, who, as it turns out, have been sharpening stones into human-style hammers for a long, long time. A report on the findings was published in the journal Nature.

Researchers in Brazil have had their eye on the bearded capuchin (Sapajus libidinosus) for some time now and have found that despite a varied diet, the little monkeys expend a lot of energy acquiring one particular food: cashews. To access the sweet meat inside the cashew’s tough shell, capuchins developed their own specialized tools, which they’ve been using now for at least 700 years.

The team now reports that those same monkeys may have been inadvertently messing with the timeline of human events. In addition to their cashew bashing, the researchers say, the capuchins will also pound one rock against another. This stone-on-stone percussion (as the researchers call it) chips away pieces of both rocks, sharpening them in the process—and producing results that look an awful lot like early human cutting tools.

The researchers couldn’t tell why the monkeys were smashing rocks. They did use some of the newly broken stones as hammers, but they didn’t use the sharpened parts. About half of the time after breaking a rock, a monkey mason would lick or sniff it, which suggests that they might be after essential minerals they can’t get any other way.

These findings have pretty substantial implications for both primate evolution and archaeological research. Before this, hominins (the group of primates that includes humans and our human-like ancestors) were the only known animals to make this type of tool.

“Our understanding of the new technologies adopted by our early ancestors helps shape our view of human evolution,” co-author Michael Haslam of the University of Oxford said in a statement. “The emergence of sharp-edged stone tools that were fashioned and hammered to create a cutting tool was a big part of that story. The fact that we have discovered monkeys can produce the same result does throw a bit of a spanner in the works.”

It also makes scientists wonder about certain caches of tools allegedly made by early humans. In an accompanying commentary in the same issue of Nature, paleontologist Hélène Roche called the research a “shattering discovery.” She noted that we have plenty of corroborating evidence showing that artifacts from the Early African Stone Age were indeed made by people. But there have been some questions about the origin of tools from the Late Pleistocene epoch (between 40,000 and 20,000 years ago), and the answer might well be “monkeys.”
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