By now, you've probably learned—and hopefully unlearned—the myth that humans are the only living things to use tools. Dolphins, elephants, and even wasps can wield tools, though not with the same level of sophistication as we do.
But that doesn't mean they're all slouches with tools either. A new study in the journal Current Biology suggests that bearded capuchin monkeys are remarkably skilled at opening tucum nuts with their own makeshift hammer and anvil—basically, using a rock and a boulder or log to stabilize the nut. Rather than simply hitting a nut as hard as possible, capuchins use a deft touch and alternate their strike technique to avoid damaging the tucum nut's kernel, and to help conserve their own energy.
This was a bit of a surprise to the authors of the new study, Madhur Mangalam, a graduate student at the University of Georgia, and his advisor Dorothy Fragaszy. Mangalam and Fragaszy were particularly interested in how bearded capuchins managed to crack such a large, heavy, and tough nut as the tucum.
Once they'd managed to partially open the tucum nut's hard inner shell, the monkeys decreased the height and velocity of their next strikes about 85 percent of the time.
To find out, Mangalam and Fragaszy filmed 14 nut-cracking monkeys in Brazil's southern Parnaíba Basin. They used special video analysis software to measure two key variables: how high the monkeys lifted the utilized stones above their head, and how fast they brought those stones down onto the nuts.
Typically, the monkeys took two strikes to break through a tucum nut's soft outer hull and another two blasts to breach the inner shell, exposing the soft, presumably tasty kernel inside.
More importantly, capuchins appeared to vary their strikes according to how far along the nut was in the cracking process. For example, once they'd managed to partially open the tucum nut's hard inner shell, the monkeys decreased the height and velocity of their next strikes about 85 percent of the time. That, according to Mangalam and Fragaszy, means that the monkeys knew they were about to break through and eased off the throttle to avoid destroying the kernel inside.
In other words, bearded capuchins are pretty good with their hands—along with their brains. And not just in comparison with other wild animals; the monkeys' sophisticated approach to nut-opening "is similar in important ways to what is observed in humans cracking nuts with stone hammers," Mangalam and Fragaszy write. And that's quite an accomplishment for a monkey.
Beyond that, these findings could help others explore an essential and still-unique step in human evolution: developing the skill of shaping stones into arrowheads and other objects, a process called knapping. A comparison of the motions involved in knapping and the somewhat simpler ones involved in opening nuts, "might elucidate the differences in associated cognitive processes and/or biomechanical constraints between nonhuman primates and the hominids who first knapped stones," Mangalam and Fragaszy write.
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