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Sorry monkey, apes are smarter

By BJS

Created 08/02/2006 - 08:26

The great apes are the smartest of all nonhuman primates, with
orangutans and chimpanzees consistently besting monkeys and lemurs on
a variety of intelligence tests, Duke University Medical Center
researchers have found.

"It's clear that some species can and do develop enhanced abilities
for solving particular problems," said Robert O. Deaner, Ph.D., who
led the study as part of his doctoral dissertation. "But our results
imply that natural selection may favor a general type of intelligence
in some circumstances. We suspect that this was crucial in human
evolution."

The study was published online August 1, 2006, in the journal
Evolutionary Psychology. Funding was provided by the medical center's
Department of Biological Anthropology and Anatomy.

Experts in psychology broadly define intelligence as general
problem-solving skills -- "domain-general cognition" in the parlance
of the field. This intelligence allows an animal to tackle new and
unpredictable situations. Domain-general cognitive ability is separate
from domain-specific abilities for solving certain environmental
challenges, such as a bird remembering where it cached food.

Intelligence testing of animals has repeatedly revealed that some
species perform better than others. This suggests that some animals
have better domain-general skills, Deaner said. However, scientists
have been hard-pressed to convincingly prove these differences could
be attributed to intelligence, he added.

"The trouble is that one species may outperform another in a
problem-solving test not because it's smarter, but because one species
is poorly suited to that particular testing situation," he said. For
example, one species may be more comfortable grabbing a joystick.

Deaner and his colleagues reasoned that they could refute this premise
-- that performance differences resulted from particular testing
situations -- by demonstrating that some primate species surpassed
others across a wide range of problem-solving tests. Primates are an
excellent comparison group because their similar perceptual and motor
skills means that the same tests are generally appropriate for all of
them, Deaner said. But developing a suitable data set to test this
idea was not easy.

"At first we thought gathering the data would require a lifetime,"
said Deaner, now an assistant professor of psychology at Grand Valley
State University in Allendale, Mich. "Ideally, one would test several
individuals from each of 20 or 30 species with dozens of cognitive
tests, but this certainly didn't seem practical. Then we realized the
data had already been gathered by an army of comparative
psychologists."

The team first pored through hundreds of published studies, then
assigned each testing situation or experiment to one of nine overall
paradigms. For example, one paradigm was patterned strings. During the
test, a primate is shown an array of crossing strings, only one of
which is tethered to a treat. The subject is allowed to pull only one
of the strings and must decide before pulling which string is actually
attached to the food. The paradigm taps the ability to form spatial
representations, considered crucial for intelligent behavior.

The results were clear: there were a few cases where one species
performed better than another one in one task and reversed places in a
different task, but, overall, some species truly outperformed others.
"Our research strengthens the long-standing notion that some animal
species truly are more intelligent than others," Deaner said. The
smartest species were clearly the great apes -- orangutans,
chimpanzees, and gorillas – which performed much better than monkeys
and prosimians.

"The fact that great apes performed better than other primates in
these laboratory tasks is reassuring," said Carel van Schaik, Ph.D., a
study co-author and director of the Anthropological Institute and
Museum at the University of Zurich. "After all, in absolute terms,
their brains are the largest and they show the most sophisticated
behavior under natural conditions -- deception and
culturally-transmitted behavior, including tool-use."

Though some species clearly outperformed others, there was no evidence
that any species performed especially well within a particular
paradigm. This result contradicts the theory that species differences
in intelligence only exist for narrow, specialized skills, Deaner
said. Instead, the results argue that some species possess a broad,
domain-general type of intelligence that allows them to succeed in a
variety of situations.

Team statistician Valen Johnson, Ph.D., a professor of biostatistics
at the University of Texas M. D. Anderson Cancer Center, created a new
statistical technique to examine the data for consistency across the
various tests. "It was tougher than it looks, because most species
were only tested in a few situations," Johnson said. "Conventional
methods wouldn't do the job."

> From Duke University [1]