Chimps make hammers to crack nuts

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Chimps Fashion Hammers to Crack Nuts

 

By PAUL RECER

..c The Associated Press

 

WASHINGTON (May 23) - A band of chimpanzees in West Africa routinely swing

crude stone hammers to crack open nuts, a sophisticated use of tools the apes

have been teaching to each new generation for more than a century.

 

Using carefully selected stones weighing up to 33 pounds, the chimps pound

the tough shell of the panda nut to extract a high-energy kernel that is an

important part of the animal's diet, researchers report Friday in the journal

Science.

 

''It is a very skillful behavior that takes up to seven years for them to

learn,'' said Melissa Panger, a George Washington University researcher and

co-author of the study. ''It looks easy, but if you sit down and try it is a

very difficult task.''

 

The panda nuts fall to the ground inside an outer husk. Inside the husk is a

golfball-sized nut covered by a shell that can require up to a ton of

pressure to break open. Yet, if the animals pound too hard, the nut shatters

and is inedible, Panger said.

 

''What is remarkable is that they are controlling the force precisely,'' she

added.

 

Inside the shell are three nutritious kernels. During nut-smashing season,

some chimps spend two or three hours a day opening as many as 100 panda nuts.

The nuts can provide up to 3,000 calories a day, researchers said.

 

The chimps establish nut-cracking stations, usually centered on a battered

root of a hardwood tree that they use as an anvil.

 

Panger said the chimps leave the hammer stones beside the anvils and some of

the tools have apparently been used for generations. Some animals have been

seen carrying pounding stones from one anvil to another, just as a repairman

might carry tools from place to place, she said.

 

Nut cracking demonstrates a degree of sophisticated learning because it

required the animals to select hammer stones at a distant rock outcropping

and then carry them to the anvil. Panger said selection of the stones

requires some thought by the chimps: The crude hammers have to be flat on one

side, heavy enough to smash the nuts and have a place to grasp.

 

''They have to use it without crushing their fingers,'' said Panger. ''Some

of these hammers have been used so many times that they have deep pits,

suggesting that they have been used for many generations, over and over

again.''

 

Mothers teach their children to bang on nuts, and some young chimps have been

seen hitting nuts with smaller stones, imitating their parent.

 

The researchers said the nut-smashing technique is known to only some bands

of West African chimpanzees. It has not been seen among chimps in central

Africa, although the apes there have nuts and stones available to them.

 

This suggests that nut smashing is a cultural, learned behavior that has not

spread widely among the apes.

 

''There has to be knowledge of the size and hardness of the rock,'' said

Julio Mercader, another George Washington University researcher and the first

author of the study. ''And that knowledge is transmitted from chimp to chimp

and from generation to generation.''

 

In their research, Mercader and Panger used archaeological methods to dig

around an anvil site. They found stone chips that had apparently broken off

stone hammers in past generations. Age dating of deposits at one site showed

that the apes had used it as nut-cracking station for at least 110 years,

Panger said.

 

She said it is likely that early hominids, the direct ancestors of modern

humans, also had nut-cracking sites in Africa and that sharp chips flaking

from the stone hammers may have helped humans learn tool making.

 

''If they were hammering and unintentionally make some of these sharp-edged

flakes, then the leap to making a cutting tool is not as great,'' she said.

 

Robson Bonnichsen, a stone tool expert at Oregon State University in

Corvallis, said humans first began shaping stone tools about 2.5 million

years ago and that chips from that work have a distinctive shape, which

researchers would not confuse with the pieces of stone randomly broken from

stone hammers by chimps.

 

Bonnichsen said the research by Panger, Mercader and their co-author,

Christophe Boesch of Max Planck Institute in Germany, gives important new

insights into tool use by primates.

 

''This is really interesting,'' he said. ''I applaud their work.''

 

AP-NY-05-23-02 1546EDT