A FEATURE of the brain considered essential to human language has been found
in chimpanzees. The discovery provides further evidence of the profound
similarity between humans and our closest relatives. But experts can鈥檛 agree
whether the discovery means that chimps have hidden linguistic skills.
In normal human brains, a small mound of neural tissue called the planum
temporale (PT), located just above the ear, is larger on one side鈥攗sually
the left. This PT asymmetry lies in the middle of a brain area believed to deal
with the comprehension of language.
PT asymmetry was thought to be unique to
humans. But neurologist Patrick Gannon of Mount Sinai School of Medicine in New
York and his colleagues now say that in 17 out of 18 chimp brains they have
examined, the fingernail-sized piece of brain tissue was larger on the left side
(Science, vol 279, p 220). 鈥淚t鈥檚 significantly asymmetric,鈥� says
Gannon.
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Although primatologists agree that chimpanzees communicate to some extent
with gestures, attempts to teach them to 鈥渢alk鈥� using sign language have met
with limited success. The animals seem unable to grasp grammar and other
subtleties that separate language from other forms of communication.
In part, this was thought to be because chimps never evolved the necessary
brain structures. William Hopkins of the Yerkes Primate Center at Emory
University in Atlanta says: 鈥淭he big question has been: do chimps have the
architecture in the brain that supports language?鈥�
Gannon鈥檚 work suggests that they might. The possession of language may not be
such a fundamental distinction between humans and other apes: we may simply have
evolved more elaborate communication. 鈥淭his suggests maybe language isn鈥檛 as
special as we sometimes consider it,鈥� says Jeffrey Binder, a neurologist at the
Medical College of Wisconsin in Milwaukee.
Dieter Steklis, an expert on chimpanzee behaviour at Rutgers University in
New Brunswick, New Jersey, believes that attempts to teach chimps human sign
languages may have misled researchers about the animals鈥� linguistic abilities.
He says that they communicate with gestures in a more sophisticated way than
lower primates. Attempts to discover whether chimps possess a 鈥渓anguage鈥� should
concentrate on this communication, he suggests.
But other researchers question the significance of Gannon鈥檚 finding to
language. 鈥淲hat really matters is the wiring,鈥� says Steven Pinker, a
psycholinguist at the Massachusetts Institute of Technology. 鈥淚t鈥檚 like looking
at two computer chips. Unless you know how they are wired, you don鈥檛 know that
do the same thing.鈥�
Terrence Deacon, a neuroanatomist at Boston University, adds that the
discovery of PT asymmetry in chimps may simply mean that the assumption that
structure is vital for human language is wrong.
Gannon agrees that more work must be done to determine the precise role of PT
asymmetry. He and Hopkins are both imaging chimp brains to see if tasks like
gesture recognition activate the left PT.