Synapse, CA
03-07-07
Chimps Branch Out in Tool-Making
By Dan Paskowitz
Science Editor
The use of tools was for a long time considered one of the crucial characteristics
distinguishing human beings from other animals. Jane Goodall’s research first
challenged this view by showing that wild chimpanzees modify objects from their
environment and use them as tools (for example, the use of stripped sticks to
rouse ants or other insects in their nests and extract them for food). This
observation has since been extended to a number of other species, such as
dolphins. The making and use of weapons for hunting, however, has been
thought to be a uniquely human trait. Researchers from Iowa State University
and Cambridge have now demonstrated that chimpanzees make spears and use
them to hunt prey, further blurring the behavioral distinctions between ourselves
and our closest relatives.
The researchers observed a community of 35 chimpanzees living in a dry habitat
in Fongoli, Senegal, over a period of 18 months. Chimpanzees elsewhere hunt
red colobus monkeys without using tools, but these preferred prey are absent
from Fongoli, where bushbabies are hunted instead. These small, nocturnal
primates sleep in tree hollows and other cavities during the day. To make tools
for hunting them, the chimpanzees broke off tree branches, trimmed them of side
branches and leaves, stripped them of bark, further trimmed the narrow end, and
in some cases, sharpened it to a point with their teeth. The resulting tools
resembled spears and averaged about 70 centimeters in length. These were
forcibly and rapidly jabbed downwards several times into hollow trunks or
branches, in a manner described by one of the authors as reminiscent of the
shower scene in Psycho. No bushbaby was killed or caught in most of the 22
such episodes observed, but in one case, the chimpanzee proceeded to reach
into the cavity and pull out an apparently dead or unconscious bushbaby.
While previously observed chimpanzee hunts have been dominated by adult
males, the newly observed tool-hunting behavior was conducted mainly by
females and juveniles. The authors proposed that since females are not usually
included in hunts for monkey meat by groups of male chimpanzees, they have
turned to a solitary but tool-dependent method instead. This suggestion of
female-driven technology development is consistent with the observation that
female bottlenose dolphins use tools, but males do not. The authors also
proposed, intriguingly, that we may have underestimated the speed of tool
development by our hominid ancestors. The Fongoli chimpanzees use wood
tools rather than stone for hunting. If our ancestors did the same, most of the
evidence for this would have been lost, since wood fossilizes relatively poorly.
Our stone-dominated picture of human tool development may therefore be
missing much of the story. The new report can be found online at www.currentbiology.com/content/future and will appear in the March 6 issue of Current
Biology.