for National Geographic News
While monkeys are able to understand the most basic grammatical rules, new research shows they can't master the more complex grammars that are central to human language.
A new study of cotton-top tamarins (Saguius oedipus), a rare South American monkey, confirms previous findings that monkeys are able to grasp the rules of "finite state grammars"basic grammar that, for example, controls the types of words that go next to each other in a sentence.
But the study, described in the journal Science last week, shows that monkeys don't understand more complex "phrase structure grammars," in which words in a sentence can be separated but still depend on each other. (The "if then " construction is a classic example of such grammar.)
The research suggests that the ability to perceive phrase structure is one of the main differences between animal communication and human language.
"Phrase structure is an important component of language," said Tecumseh Fitch, a lecturer at the school of psychology at the University of St. Andrews in Scotland, who led the study. "Sentences are not just lists of words, but they have a complex structure over and above that, which enables us to communicate causal connections, opinions about statements, and complex social ideas."
In an accompanying article, David Premack, a professor emeritus in psychology at the University of Pennsylvania in Philadelphia, explores the reasons why animals have not evolved languages of any kind. He points to more "humble" explanations than phrase structure as reasons for why animals don't have languages.
"Animals lack things like teaching, imitation, and voluntary control of sensory-motor systems," said Premack. "If you don't have those things, you are not going to evolve any kind of language."
The tamarins are a highly endangered species found only in the rain forests of Colombia. They live in trees and are quite vocal. When a tamarin is separated from the group, he makes a whistling contact call that sounds like a songbird.
For their research, Fitch and his colleague Marc Hauser, a Harvard University psychology professor, studied a colony of tamarins housed at Harvard in Cambridge, Massachusetts.
The researchers first exposed the monkeys to examples of grammar known as finite state. A recorded sequence repeated the letters A and B like this: A-B-A-B-A-B. When the researchers violated the grammar by playing, for example, A-B-B-A, the monkeys would look toward the loudspeaker.
"That shows that without training, they've been able to figure out a rule at the finite state grammar levelthey've been able to sense that pattern," said Fitch.
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