Washington Post
02-23-07
Chimps make, use hunting spears
By RICK WEISS
WASHINGTON POST
WASHINGTON - Chimpanzees living in the West African savannah have been
observed fashioning spears from sticks and using the hand-crafted tools to hunt
small mammals - the first routine production of deadly weapons ever observed in
mammals other than humans.
The multistep 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 Thursday's online issue of the journal Current
Biology. Then, grasping the weapon in a "power grip," they jabbed into treebranch 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 classic Alfred Hitchcock movie "Psycho."
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 nonhuman 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 for it.
Pruetz and co-worker 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.
Adrienne Zihlman, an anthropologist at the University of California at Santa Cruz,
said the work supports other evidence that female chimps are more likely than
males to use tools, 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.