Evidence of chimps' intelligence grows Published: April 18, 2007
CHICAGO: Observed in the wild and tested in
captivity, chimpanzees invite comparison with humans, their close
relatives. They bear a family resemblance that fascinates people, and
scientists see increasing evidence of similarities in chimp behavior
and skills, making some of them think on the vagaries of evolution.
For some time, paleontologists and evolutionary biologists have
known that chimp ancestors were the last line of today's apes to
diverge from the branch that led to humans, probably 6 million, maybe 4
million years ago. More recent examination shows that despite profound
differences in the two species, just a 1.23 percent difference in their
genes separates Homo sapiens from chimpanzees, Pan troglodytes.
And certain similarities between the two species, scientists say, go beyond expressive faces and opposable thumbs.
Chimps display a remarkable range of behavior and talent. They make
and use simple tools, hunt in groups and engage in aggressive, violent
acts. They are social creatures that appear to be capable of empathy,
altruism, self-awareness, cooperation in problem solving and learning
through example and experience. Chimps even outperform humans in some
memory tasks.
"Fifty years ago, we knew next to nothing about chimpanzees," said
Andrew Whiten, an evolutionary psychologist at the University of St.
Andrews in Scotland. "You could not have predicted the richness and
complexity of chimp culture that we know now." Jane Goodall, a young English woman working in Africa in the 1960s,
began changing perceptions. At first, experts disputed her reports of
chimps' using tools and social behavior. The experts especially
objected to her references to chimp culture. Just humans, they
insisted, had "culture."
"Jane suffered early rejection by the establishment," said Richard
Wrangham, a Harvard anthropologist. "Now, the people who say
chimpanzees don't have emotions and culture are the ones rejected."
The new consensus framed discussions in March at a symposium, "The
Mind of the Chimpanzee," at the Lincoln Park Zoo here. More than 300
primatologists and other scientists reviewed accumulating knowledge of
chimps' cognitive abilities.
After one session, Frans de Waal of Emory University in Atlanta said
that as recently as a decade ago there was still no firm consensus on
many of the social relationships of chimps. "You don't hear any debate
now," he said.
In his own studies at the Yerkes Primate Research Center at Emory,
de Waal found that chimps as social animals have had to constrain and
alter their behavior in various ways, as have humans. It is a part of
ape inheritance, he said, and in the case of humans, the basis for
morality. The provocative interpretation was advanced in his recent
book, "Primates and Philosophers."
Other reports shortly before the symposium had elaborated on the
abilities of chimps as toolmakers. Jill Pruetz, a primatologist at Iowa
State University, described 22 examples of chimps in Senegal making
stick spears to hunt smaller primates for their meat. Goodall was the
first to call attention to chimps as hunting carnivores, not strictly
vegetarians.
Pruetz observed chimps jabbing the spears into hollow tree trunks
where bush babies often dwell. Just one attempt was successful.
Previously, chimps had been seen using sticks mainly to extract
termites from their nests.
A team of archaeologists led by Julio Mercader of the University of
Calgary reported finding stones in Ivory Coast that chimps used 4,300
years ago to crack nuts. Today's chimps have often been videotaped
using rocks as a hammer to open nuts. The old stones with starch
residues from nuts, the researchers said, were the earliest strong
evidence of chimp tool use, and the finding suggested that chimps had
learned the skill on their own, rather than copying humans.
Other researchers combine field work showing chimp behavior in
natural habitats with laboratory experiments that are created to
disclose their underlying intelligence - what scientists call their
"cognitive reserve."
For example, chimps on their own would not sit at a computer
responding with rapid touches on the screen as a test of their
immediate memory. Videos of their doing just that at Kyoto University
in Japan especially impressed the symposium scientists.
Tetsuro Matsuzawa, a Kyoto primatologist, described a young chimp
watching as numbers one through nine flashed on the computer screen at
random positions. Then the numbers disappeared in no more than a
second. White squares remained where the numbers had been. The chimp
casually but swiftly pressed the squares, calling back the numbers in
ascending order - 1, 2, 3, etc.
The test was repeated several times, with the numbers and squares in
different places. The chimp, which had months of training accompanied
by promised food rewards, almost never failed to remember where the
numbers had been. The video included scenes of a human failing the
test, seldom recalling more than one or two numbers, if any. Humans can't do it," Matsuzawa said. "Chimpanzees are superior to
humans in this task." Matsuzawa suggested that early human species
"lost the immediate memory and, in return, learned symbolization, the
language skills."
Other experiments at Kyoto's primate center demonstrated the ability
of chimps to recognize themselves and focus attention on others. Masaki
Tomonaga, who conducted the tests, said that an infant made eye contact
with its mother at about two months and that sometime after the first
year was able to maintain a gaze as the mother moved about. Tomonaga
said such "gaze following" developed in humans about the same age,
"though infant humans generally have more complex interactions."
Misato Hayashi, also from Kyoto, described experiments with infant
chimps' manipulating nesting cups and square and cylindrical blocks.
They were slower to learn than humans, but the manual dexterity was
there. A human starts stacking blocks shortly after age 1, he said;
chimps are almost 3 before getting the hang of it.
In experiments with mirrors, researchers showed that chimps had an
awareness of themselves that is absent in monkeys but present in
dolphins and all the great apes. Similar tests by Emory scientists
showed some self-recognition among elephants. These behaviors were
reported by de Waal and his associate J.M. Plotnik.
At the symposium, researchers said the interest in learning more
about chimps was not just a case of knowledge for the sake of
knowledge. Their behavior and intelligence, scientists say, may offer
insights into the abilities of early human ancestors like
Australopithecus afarensis, the apelike "Lucy" species that thrived
more than 3 million years ago. A more urgent motivation for the
research, primatologists say, is that these are sentient beings and the
closest living relatives of humans, and their survival is threatened.
Elizabeth Lonsdorf, a primatologist at the Lincoln Park Zoo and a
symposium organizer, said researchers needed "to keep their eyes out
for ways to improve the care of chimpanzees."
Diseases like ebola and anthrax are taking their toll. Hunting
chimps for "bush meat" is increasing. Many of the forest habitats of
chimps in central Africa are being cut by loggers and land developers.
As a result, Lonsdorf said, "Groups of the animals are getting closer
together, which increased the threat of chimp violence and territorial
disputes."
Goodall recalled that when she went to Africa nearly a half-century
ago, at least a million chimps lived in the continent, and "now there
are perhaps only 150,000." In that time, they have impressed scientists
with physical and emotional reminders of their kinship to humans and
their occasional triumphs over them at a computer screen. IHT
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