Chimp (黑猩猩) Show
Hallmark of Human Culture, Study Finds Researchers have
discovered that chimpanzees not only teach each other new and useful behaviors,
but conform to their group’s preferred techniques for performing them--a
hallmark of human culture. Observers have previously reported
that wild chimps demonstrate more than three dozen different behaviors that have
no apparent ecological or genetic origin. This diversity suggests that there are
distinct ape cultures. The notion assumes that chimps transmit
culture--teaching and learning behaviors generation after generation. But the
theory is very difficult to test and prove in a controlled experiment outside of
a laboratory. So researchers at the University of St. Andrews in
Scotland and Emory University in Atlanta devised an experiment to test the
proposition. The results were published online August 21 in the science journal
Nature. Learning and Teaching The scientists
constructed a box in which a desirable food was hidden behind a trap. Captive
chimps could release the food by using a stick to move the trap in either of two
ways. Researchers dubbed these the "poke" and "lift" methods.
Scientists then isolated a high-ranking female of one group from her
companions and taught her the poke method to release food. A female of high rank
from a second group was taught the lift method. None of the
other members of the groups were allowed to watch the training.
Finally, researchers used a third group as a control, presenting them with
the box and sticks, but teaching them nothing about how to use them.
Scientists then let the chimp groups watch their matriarch (女家长) use the
technique she had learned. To get the food, each dominant female consistently
used the method she had been taught. The other chimps watched, often intensely,
for over 36 hours spread over ten days. During this period, 15
chimps in the two study groups successfully used one method or the other to get
food, and they picked up the behavior quickly. Median times for learning the
techniques in both groups were under a minute. In the meantime,
the six chimps in the control group were stymied. In more than four hours of
manipulating the sticks, they were unable to extract a single piece of
food. Some chimps in the "lift" group discovered the poke
method, and some in the "poke" culture discovered lifting. But they were a small
minority. When the apparatus was reintroduced two months later, the chimps
reverted to their own culture’s preferred method. This, the
researchers maintain, provides evidence of a "conformist bias". The animals
discount their own experience and instead adopt the behavior of the group, just
as humans do. "This is a very nice experimental setup," said
Diana Reiss, a research scientist with the Bronx, New York-based Wildlife
Conservation Society, who was not involved in the study. "It was controlled for
biases, and included a control group where there was no trained expert. The
setup eliminated the problem of learning by interacting with humans."
The researchers believe they have demonstrated for the first time an
ability among chimpanzees to transmit alternative technologies and alternative
methods of using tools. Monkey See, Monkey Do "When
all these different wild chimp behaviors were discovered in the field, there was
controversy." said Frans de Waal, a professor of primate behavior at Emory
University and study co-author. "Some scientists claimed it was social
learning. Others claimed there were other possible explanations--individual
learning, genetic differences, ecological variables, and so on."
"We did the experiment to prove that you could plant a behavior by
training one chimp and see it spread to other chimps by observation."
Giving the chimps two alternative methods of accomplishing the same task,
the researchers say, shows that chimps are capable of adopting local variants (
变形) of a technique, just as they would if the variant behaviors seen in the wild
are in fact socially transmitted. Not all experts agree with
this conclusion. Rob Boyd, a professor of anthropology at the University of
California, Los Angeles, said, "I have argued that any time true imitation
evolves, so will a tendency to copy the majority. So I would very much like it
to be true that the data supported this prediction." But Boyd
believes the study data fail to offer the necessary proof. He notes that while a
few chimps dropped their group’s rarer behavioral variant (using a stick to poke
or lift a trap to release food), the study "does not show that they switched to
the common variant, which is what I believe is necessary." Personifying
Animals Groups of chimps at the Yerkes National Primate
Research Center Field Station at Emery University, where the research was
carried out, have developed cultural differences on their own, without the
intervention of human teachers. One community, for example,
practices hand-clasp grooming (梳理毛发), in which two chimps each grasp one of the
other’s hands over their heads, grooming with the free hand. Other groups do not
engage in this behavior. Research with animal behavior, and
perhaps especially with the great apes, risks wrongly attributing human
characteristics to animals. But the researchers in this experiment say they have
been careful to avoid that trap. "We aim to avoid naive
anthropomorphism," said the lead author on the paper, Andrew Whiten of the
University of St. Andrews, "by developing a rigorous experimental design that
can unambiguously answer the question we pose." He adds that the
results were scored objectively from videotapes viewed by other scientists to
avoid bias. Whitten and his colleagues plan to do similar experiments with human
children as subjects. "If we see similar responses in the two
species." whiten said, "then a concern of interpretive anthropomorphism becomes
rather contrived." Some researchers have discovered that chimpanzees have a hallmark of human culture.