http://www.washingtonpost.com/wp-dyn/content/article/2007/02/22/AR2007022201007.htmlChimps Observed Making Their Own Weapons
By Rick Weiss
Washington Post Staff Writer
Thursday, February 22, 2007; 2:48 PM
Chimpanzees living in the West African savannah have been observed
fashioning deadly spears from sticks and using the hand-crafted tools
to hunt small mammals -- the first routine production of deadly
weapons ever observed in animals other than humans.
The multi-step spear-making practice, documented by researchers in
Senegal who spent years gaining the chimpanzees' trust, adds credence
to the idea that human forebears fashioned similar tools millions of
years ago.
The landmark observation also supports the long-debated proposition
that females -- the main makers and users of spears among the
Senegalese chimps -- tend to be the innovators and creative problem
solvers in primate culture.
Using their hands and teeth, the chimpanzees were repeatedly seen
tearing the side branches off long straight sticks, peeling back the
bark and sharpening one end, the researchers report in today's on-line
issue of the journal Current Biology. Then, grasping the weapon in a
"power grip," they jabbed into tree-branch hollows where bush babies
-- small monkey-like mammals -- sleep during the day.
After stabbing their prey repeatedly, they removed the injured or dead
animal and ate it.
"It was really alarming how forceful it was," said lead researcher
Jill D. Pruetz of Iowa State University in Ames, adding that it
reminded her of the murderous shower scene in the Alfred Hitchcock
movie "Psycho." "It was kind of scary."
The new observations are "stunning," said Craig Stanford, a
primatologist and professor of anthropology at the University of
Southern California. "Really fashioning a weapon to get food -- I'd
say that's a first for any non-human animal."
Scientists have documented tool use among chimpanzees for several
decades, but the tools have been simple and used to extract food
rather than to kill it.
Some chimpanzees slide thin sticks or leaf blades into termite mounds,
for example, to fish for the tasty, crawling morsels. Others crumple
leaves and use them like sponges to sop drinking water from tree
hollows.
But while a few chimpanzees have been observed throwing rocks --
perhaps with the goal of knocking prey unconscious, but perhaps simply
as expressions of excitement -- and a few others have been known to
swing simple clubs, only people have been known to craft tools
expressly to hunt prey.
Pruetz and coworker Paco Bertolani of the University of Cambridge made
the observations near Kedougou in southeastern Senegal. Unlike other
chimpanzee sites currently under study, which are forested, this site
is mostly open savannah. That environment is very much like the one in
which early humans evolved and is different enough from other sites to
expect differences in chimpanzee behaviors.
Pruetz recalled the first time she saw a member of the 35-member troop
trimming leaves and side-branches off a branch it had broken off a
tree.
"I just knew right away that she was making a tool," Pruetz said,
adding that she suspected -- with some horror -- what it was for, as
well. But in that instance she was not able to follow the chimpanzee
to see what she did with it.
Eventually the research duo documented 22 instances of spear-making
and use, two-thirds of them involving females.
In a typical sequence, the animal first discovered a deep hollow
suitable for bush babies, which are nocturnal and weigh about half a
pound. Then the chimp would break off a nearby branch -- on average
about two feet long, but up to twice that length -- trim it, sharpen
it with its teeth, and poke it repeatedly into the hollow at a rate of
about one or two jabs per second.
After every few jabs, the chimpanzee would sniff or lick the tip, as
though testing to see if it had "caught" anything.
In only one of 22 observations did a chimp get a bush baby. But that
is reasonably efficient, Pruetz said, compared to standard chimpanzee
hunting practice, which involves chasing a monkey or other prey,
grabbing it by the tail and then slamming its head against the ground.
In the successful bush baby case, the chimpanzee eventually jumped on
the larger branch until it broke, exposing the limp bushbaby, which
the chimp then extracted. Whether the animal was dead or alive at that
point was unclear, but it did not move or make any sound.
Chimpanzee behavior is widely believed to offer a window on early
human behavior, and many researchers have hoped that the animals --
which are humans' closest genetic cousins -- might reveal something
about the earliest use of wooden tools.
Many suspect that wooden tools far predate the use of stone tools --
remnants of which have been found going back two-and-a-half million
years. But because wood does not preserve well, the most ancient
wooden spears ever found are only about 400,000 years old, leaving
open the question of when they first came into use.
The discovery that some chimps today make wooden weapons supports the
idea that early humans did too -- perhaps as much as 5 million years
ago -- Stanford said.
Adrienne Zihlman, an anthropologist at the University of California at
Santa Cruz, said the work supports other evidence that female chimps
are more likely to use tools than males, are more proficient tool
users, and are crucial to passing that cultural knowledge to others.
"Females are the teachers," Zihlman said, noting that juvenile chimps
in Senegal were repeatedly seen watching their mothers make and hunt
with spears.
"They are efficient and innovative, they are problem solvers, they are
curious," Zihlman said of females. And that makes sense, she said.
"They are pregnant or lactating or carrying a kid for most of their
life," she said. "And they're supposed to be running around in the
trees chasing prey?"
Frans B. M. de Waal, a primatologist at Emory University, said
aggressive tool use is but the latest "uniquely human" behavior to be
found to be less than unique.
"Such claims are getting old," he said. "With the present pace of
discovery, they last a few decades at most."
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