How much effort would you be willing to put in for a cashew? Well, for capuchin monkeys, the answer is quite a bit.
Scientists at the University of Oxford and the University of Sao Paulo recently discovered that capuchin monkeys in northeast Brazil have been using stone tools for at least 700 years in their pursuit for food.
When the monkeys first arrived in the region a half million years ago, food options were scarce. They ended up resorting to stone tools to break the hard shells of the fruits and nuts that they needed to survive.
In doing so, they opened up the region to further capuchin habitation. Using rocks on cashew fruits is believed to have been the first stone tool use by the capuchins.
Scientists hypothesizes that if using tools was part of the capuchin colonizing process, then the behavior may be hundreds of thousands of years old.
Here’s Sean Greene, reporting for the Los Angeles Times :
Because of the patchiness of the capuchin fossil record, this idea is more speculative than anything else, Haslam said, at least until scientists can fully explore the monkeys’ archaeological record.
“We’re standing at the starting line of non-human archaeology, a field that now includes sites of chimpanzees, macaques and capuchins,” he said. “Who knows what we’ll discover as the work continues?”
Capuchins turned to technology because of the toxins lurking in the cashew fruit. The moon-shaped nuts that humans and capuchins like to each are encased in a shell hanging from the bottom of the fruit. That shell contains an irritating oil which includes toxins also found in poison ivy, with the nut found in the middle of the shell.
To overcome these plant defenses, the capuchins picked up a rock and did what any self-respecting monkey would do—smashed the fruit.
University of Oxford primate archaeologist Michael Haslam and his team found dozens of stone tools like hammers and anvils underneath fruit trees in Serra da Capivara National Park. The tools were dated to 700 years old, but given that they were used by colonizing capuchins, it’s possible that the practice goes back much further than that. Archaeologists think they may find more much older tools as digging continues.
This discovery represents the oldest non-human tools found outside of Africa, as well as the oldest known tools not belonging to humans or chimpanzees.
The capuchins’ select their tools based on size and material. The stones must be small enough that the capuchins can still control of them, but strong enough to crack hard shells of the fruits and nuts they want to eat. Hammers are made of hard quartzite, whereas anvils are made of heavier sandstone.
Researchers found the tools by searching near groves of cashew trees where the growing conditions have not changed much in the recent past. Scientists could distinguish the stones as tools based on the dark cashew residue left on their surfaces, which was then carbon dated to reveal the artifact’s 700-year history.
The model of the tools did not change throughout history, meaning that the capuchins managed to find an efficient prototype early on that did not need modifications.