For Chimps, Tool Choice Is A Weighty Matter

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A juvenile chimpanzee in the Ivory Coast’s Tai Forest watches as her mother carefully places a soft coula nut onto a hard, flat rock. In her other hand, mom has a chunk of hard wood. Mom smashes the nut with her makeshift hammer, once, twice, three times. Having broken the outer shell, she plucks out the edible bits, reaching for another nut and starting the process again. The juvenile wants a snack too. Even though she’s learned the basic process by watching the older chimpanzees in her troop, she’ll be at least six years old before she’s proficient enough at this sophisticated form of tool use to crack nuts open herself. Not that she’ll stop trying, in the meantime.


Nut-cracking has been observed in wild chimpanzees in Guinea, Ivory Coast, Liberia, and Sierra Leone. With only one exception, chimpanzee groups in Central and East Africa have never been seen cracking nuts, despite the fact that all the necessary ingredients – nuts, stones, sticks, and roots – are all found in abundance in those parts of the continent. Nut-cracking, it seems, requires more than just the available tools and basic know-how. Even within nut-cracking groups, some individuals will go their entire lives without ever successfully cracking open a nut.

The mystery behind the apparent complication involved in learning to crack nuts prompted one research group, led by Cornelia Schrauf of the University of Vienna, to try to figure out how chimpanzees select their nut-cracking tools.

Successful nut-cracking involves selecting an appropriate surface to serve as the anvil. It should be hard and relatively flat. It should also be able to keep the nut from rolling away. Then, the chimp needs to select the appropriate hammer. It needs to be the right shape and size. It needs to be light enough to easily manipulate, but heavy enough to smash the nut in as few strikes as possible. In the Tai Forest, chimps select hammers made of stone for the hard panda nuts, but opt instead for wooden hammers when it comes to the softer coula nuts. If they’ve only got rocks around, they’ll use heavier, harder stones for panda nuts and lighter ones for coula nuts.

Researchers weren’t sure, however, if chimpanzees were actually using weight as the primary consideration for hammer selection, since weight correlates with other features of hammers, such as size, material, shape, and density.

Written By: Jason G. Goldman
continue to source article at blogs.scientificamerican.com

8 COMMENTS

  1. I already knew something about this, but somehow I don’t think it was nuts they were opening. It was something else, and they would use a stick to pull out the meaty parts of whatever it was.. Or maybe they just sucked the meaty parts out.

  2. “Is there a lesson to be learned here for human primates? “

    Yeah, that alpha chimps like Loi may be the boss not only because of power, but also cleverness. And that some individuals, like little Natsuki, have no aptitude for that macho-smashing stuff. Maybe she wanted to grow up to be a poet.

  3. Researchers weren’t sure, however, if chimpanzees were actually using weight as the primary consideration for hammer selection, since weight correlates with other features of hammers, such as size, material, shape, and density.

     
    Okay, one more nitpick before bed.

    The weight of an object is directly proportional to its size and density.  Since “size” appeared first in the author’s list, “shape” is therefore redundant to the matter of the hammer’s weight; but shape has plenty to do with its moments-of-inertia, which are undoubtedly involved in the hammering action (using an arm pivoted at a shoulder joint), due to the rotation of the hammer during the strike. Shape is probably more important in terms of how well the hammer fits the chimpanzee’s hand.
     
    “Material” is irrelevant to the matter of weight, because it has already been accounted for with “density”.  Perhaps “hardness” was what the author was attempting to get at.
     
    Typically careless science writing.  Just throw all those science-y terms in there.  One or two of them are bound to mean something.

  4. The other day at the animal shelter where I volunteer, a can of food dropped to the floor.
    The woman in charge said to the inquiring cat “you can’t open that, you’re not human, we use tools”.  Could a knocked me over with a feather.  But, she is very Christian and my boss, so I let it slide.  She needs to realize that other primates use tools, as do crows, and I think even a species of finch on the Galapagos wield sticks to nab goodies.   

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