How Monkeys Use Stone Tools

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Researchers are studying how monkeys use stones as a way of understanding the evolution of the use of tools.
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http://www.nytimes.com/2015/05/18/science/monkeys-provide-clues-to-how-tool-use-developed.html


Before human ancestors started making stone tools by chipping off flakes to fashion hand axes and other implements, their ancestors may have used plain old stones, as animals do now. And even that simple step required the intelligence to see that a rock could be used to smash open a nut or an oyster and the muscle control to do it effectively.

Researchers have been rigorous in documenting every use of tools they have found find in animals, like crows, chimpanzees and dolphins. And they are now beginning to look at how tools are used by modern primates — part of the scientists’ search for clues about the evolution of the kind of delicate control required to make and use even the simplest hand axes.

Monkeys do not exhibit human dexterity with tools, according to Madhur Mangalam of the University of Georgia, one of the authors of a recent study of how capuchin monkeys in Brazil crack open palm nuts.

“Monkeys are working as blacksmiths,” he said, “They’re not working as goldsmiths.”

But they are not just banging away haphazardly, either. Mr. Mangalam, a graduate student who is interested in “the evolution of precise movement,” reported in a recent issue of Current Biology on how capuchins handle stones. His adviser and co-author was Dorothy M. Fragaszy, the director of the Primate Behavior Laboratory at the university.

Using video of the capuchins’ lifting rocks with both hands to slam them down on the hard palm nuts, he analyzed how high a monkey lifted a stone and how fast it brought it down. He found that the capuchins adjusted the force of a strike according to the condition of the nut after the previous strike.

They bang the nut, check on it and bang it again. How hard depends on whether the nut needs to be cracked a little more, or a lot more. That is not creating fine jewelry but, he and Dr. Fragaszy concluded, it is a kind of dexterity.

Another study of tool use that came out almost at the same time categorized a variety of movements used by Burmese macaques, a world away, on two islands in Thailand. Amanda Tan, a graduate student at Nanyan Technological University in Singapore, working with her adviser, Michael D. Gumert, used videotapes of the macaques to identify 17 patterns of motion they used with different stones and different foods.

The researchers, who published their paper in Plos One on Wednesday, did not do the kind of force analysis conducted for the capuchin motion. But their findings present an intriguingly different example of the evolution of tool use.

The capuchins were cracking nuts. And although palm nuts are not their only food, they do not have a diet like that of the macaques, who used rocks to crack open 43 species of shellfish, as well as some seeds and plants.

They may have developed so many striking patterns involving different kinds of stones because of the variety of food, Ms. Tan said. One of the ways they use stones is called ax-hammering. “They use the sharp points of stones to chip open oysters that grow on rocks,” Ms. Tan said in an email.

Only macaques do this, she wrote, and it requires precision, “because they are using a small surface area of the tool to accurately chip open a small target.”

That kind of precision was presumably important to our ancestors making flaked stone tools, and the macaques may offer an example of how that kind of motion evolved.



Source:http://www.nytimes.com/2015/05/18/science/monkeys-provid
e-clues-to-how-tool-use-developed.html