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[Josh Greenman <josh.greenman AT gmail.com>]

http://www.nytimes.com/2010/01/12/science/12monkey.html

January 12, 2010
Chimps and Monkeys Could Talk. Why Don’t They?
By NICHOLAS WADE

Walking through the Tai forest of Ivory Coast, Klaus Zuberbühler could
hear the calls of the Diana monkeys, but the babble held no meaning
for him.

That was in 1990. Today, after nearly 20 years of studying animal
communication, he can translate the forest’s sounds. This call means a
Diana monkey has seen a leopard. That one means it has sighted another
predator, the crowned eagle. “In our experience time and again, it’s a
humbling experience to realize there is so much more information being
passed in ways which hadn’t been noticed before,” said Dr.
Zuberbühler, a psychologist at the University of St. Andrews in
Scotland.

Do apes and monkeys have a secret language that has not yet been
decrypted? And if so, will it resolve the mystery of how the human
faculty for language evolved? Biologists have approached the issue in
two ways, by trying to teach human language to chimpanzees and other
species, and by listening to animals in the wild.

The first approach has been propelled by people’s intense desire —
perhaps reinforced by childhood exposure to the loquacious animals in
cartoons — to communicate with other species. Scientists have invested
enormous effort in teaching chimpanzees language, whether in the form
of speech or signs. A New York Times reporter who understands sign
language, Boyce Rensberger, was able in the mid-1970s to conduct what
may be the first newspaper interview with another species when he
conversed with Lana, a signing chimp. She invited him up her tree, a
proposal he declined, said Mr. Rensberger, who is now at M.I.T.

But with a few exceptions, teaching animals human language has proved
to be a dead end. They should speak, perhaps, but they do not. They
can communicate very expressively — think how definitely dogs can make
their desires known — but they do not link symbolic sounds together in
sentences or have anything close to language.

Better insights have come from listening to the sounds made by animals
in the wild. Vervet monkeys were found in 1980 to have specific alarm
calls for their most serious predators. If the calls were recorded and
played back to them, the monkeys would respond appropriately. They
jumped into bushes on hearing the leopard call, scanned the ground at
the snake call, and looked up when played the eagle call.

It is tempting to think of the vervet calls as words for “leopard,”
“snake” or “eagle,” but that is not really so. The vervets do not
combine the calls with other sounds to make new meanings. They do not
modulate them, so far as is known, to convey that a leopard is 10, or
100, feet away. Their alarm calls seem less like words and more like a
person saying “Ouch!” — a vocal representation of an inner mental
state rather than an attempt to convey exact information.

But the calls do have specific meaning, which is a start. And the
biologists who analyzed the vervet calls, Robert Seyfarth and Dorothy
Cheney of the University of Pennsylvania, detected another significant
element in primates’ communication when they moved on to study
baboons. Baboons are very sensitive to who stands where in their
society’s hierarchy. If played a recording of a superior baboon
threatening an inferior, and the latter screaming in terror, baboons
will pay no attention — this is business as usual in baboon affairs.
But when researchers concoct a recording in which an inferior’s threat
grunt precedes a superior’s scream, baboons will look in amazement
toward the loudspeaker broadcasting this apparent revolution in their
social order.

Baboons evidently recognize the order in which two sounds are heard,
and attach different meanings to each sequence. They and other species
thus seem much closer to people in their understanding of sound
sequences than in their production of them. “The ability to think in
sentences does not lead them to speak in sentences,” Drs. Seyfarth and
Cheney wrote in their book “Baboon Metaphysics.”

Some species may be able to produce sounds in ways that are a step or
two closer to human language. Dr. Zuberbühler reported last month that
Campbell’s monkeys, which live in the forests of the Ivory Coast, can
vary individual calls by adding suffixes, just as a speaker of English
changes a verb’s present tense to past by adding an “-ed.”

The Campbell’s monkeys give a “krak” alarm call when they see a
leopard. But adding an “-oo” changes it to a generic warning of
predators. One context for the krak-oo sound is when they hear the
leopard alarm calls of another species, the Diana monkey. The
Campbell’s monkeys would evidently make good reporters since they
distinguish between leopards they have observed directly (krak) and
those they have heard others observe (krak-oo).

Even more remarkably, the Campbell’s monkeys can combine two calls to
generate a third with a different meaning. The males have a “Boom
boom” call, which means “I’m here, come to me.” When booms are
followed by a series of krak-oos, the meaning is quite different, Dr.
Zuberbühler says. The sequence means “Timber! Falling tree!”

Dr. Zuberbühler has observed a similar achievement among putty-nosed
monkeys that combine their “pyow” call (warning of a leopard) with
their “hack” call (warning of a crowned eagle) into a sequence that
means “Let’s get out of here in a real hurry.”

Apes have larger brains than monkeys and might be expected to produce
more calls. But if there is an elaborate code of chimpanzee
communication, their human cousins have not yet cracked it. Chimps
make a food call that seems to have a lot of variation, perhaps
depending on the perceived quality of the food. How many different
meanings can the call assume? “You would need the animals themselves
to decide how many meaningful calls they can discriminate,” Dr.
Zuberbühler said. Such a project, he estimates, could take a lifetime
of research.

Monkeys and apes possess many of the faculties that underlie language.
They hear and interpret sequences of sounds much like people do. They
have good control over their vocal tract and could produce much the
same range of sounds as humans. But they cannot bring it all together.

This is particularly surprising because language is so useful to a
social species. Once the infrastructure of language is in place, as is
almost the case with monkeys and apes, the faculty might be expected
to develop very quickly by evolutionary standards. Yet monkeys have
been around for 30 million years without saying a single sentence.
Chimps, too, have nothing resembling language, though they shared a
common ancestor with humans just five million years ago. What is it
that has kept all other primates locked in the prison of their own
thoughts?

Drs. Seyfarth and Cheney believe that one reason may be that they lack
a “theory of mind”; the recognition that others have thoughts. Since a
baboon does not know or worry about what another baboon knows, it has
no urge to share its knowledge. Dr. Zuberbühler stresses an intention
to communicate as the missing factor. Children from the youngest ages
have a great desire to share information with others, even though they
gain no immediate benefit in doing so. Not so with other primates.

“In principle, a chimp could produce all the sounds a human produces,
but they don’t do so because there has been no evolutionary pressure
in this direction,” Dr. Zuberbühler said. “There is nothing to talk
about for a chimp because he has no interest in talking about it.” At
some point in human evolution, on the other hand, people developed the
desire to share thoughts, Dr. Zuberbühler notes. Luckily for them, all
the underlying systems of perceiving and producing sounds were already
in place as part of the primate heritage, and natural selection had
only to find a way of connecting these systems with thought.

Yet it is this step that seems the most mysterious of all. Marc D.
Hauser, an expert on animal communication at Harvard, sees the
uninhibited interaction between different neural systems as critical
to the development of language. “For whatever reason, maybe accident,
our brains are promiscuous in a way that animal brains are not, and
once this emerges it’s explosive,” he said.

In animal brains, by contrast, each neural system seems to be locked
in place and cannot interact freely with others. “Chimps have tons to
say but can’t say it,” Dr. Hauser said. Chimpanzees can read each
other’s goals and intentions, and do lots of political strategizing,
for which language would be very useful. But the neural systems that
compute these complex social interactions have not been married to
language.

Dr. Hauser is trying to find out whether animals can appreciate some
of the critical aspects of language, even if they cannot produce it.
He and Ansgar Endress reported last year that cotton-top tamarins can
distinguish a word added in front of another word from the same word
added at the end. This may seem like the syntactical ability to
recognize a suffix or prefix, but Dr. Hauser thinks it is just the
ability to recognize when one thing comes before another and has
little to do with real syntax.

“I’m becoming pessimistic,” he said of the efforts to explore whether
animals have a form of language. “I conclude that the methods we have
are just impoverished and won’t get us to where we want to be as far
as demonstrating anything like semantics or syntax.”

Yet, as is evident from Dr. Zuberbühler’s research, there are many
seemingly meaningless sounds in the forest that convey information in
ways perhaps akin to language.