Give me a hammer, and I'd probably end up bashing my thumb with it. When it comes to tool use, dexterity counts.
First off, these bearded capuchins open tough palm nuts by putting them on "anvils," including logs and boulders, and hammering at them, according to research by National Geographic explorer Dorothy Fragaszy of the University of Georgia at Athens.
Fragaszy and colleagues already knew the monkeys are choosy about their nut-cracking tools, for instance by selecting rocks that are heavier than themselves. (Related: "Hercules Monkeys Lift Stones to Crack Nuts.")
But she didn't know how the capuchins can skillfully get to their snack without smashing it to smithereens—until now. New observations in the southeastern state of Piauí, Brazil (map) reveal that the animals carefully regulate the force they use in nut-cracking.
After each strike, the monkeys evaluate the condition of the nut and then tailor the force of the next blow accordingly. (See National Geographic's monkey pictures.)
That's called dexterity, "a very surprising skill we never expected to find in a non-human animal," says Madhur Mangalam, also of the University of Georgia at Athens. (Read about how clever crows use one tool to acquire another.)
"We thought they'd try to break the nut with as much force as they can," adds Mangalam, who's a co-author with Fragaszy on a recent study published in the journal Current Biology.
Monkey Practice, Monkey Do
The monkeys' impressive skill also offers some insight into the evolution of human tool use, the scientists say.
Take stone knapping, or using one stone to strike another in order to shape it into an arrowhead or other useful object—a strategy used by many early humans.
"A novice knapper sort of bangs one stone against another and produces nothing very much that's usable," Fragaszy says. (Read how a wrong discovery led to the discovery of the oldest stone tools.)
A skilled knapper, on the other hand, controls the force of the stone "hammer"—much like capuchins.
Our ancestors' nut-cracking skills likely "allowed us to have a more complex skill of stone knapping," Mangalam adds. (See "Human Ancestors May Have Used Tools Half-Million Years Earlier Than Thought.")
Another thing the monkeys have in common with people: They both have to learn their expertise.
Capuchins take a couple of years to learn nut-cracking, which takes a lot of practice and playing with tools nuts and stones in different ways to get it right, Mangalam says.
Practice makes perfect—sounds anything but nutty to us.
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