The researchers then played examples of phrase structure grammar, a recorded sequence that clumped A and B together, such as A-A-A-B-B-B. But when the researchers violated the more complex grammar rule, the monkeys would not respond by looking at the speaker.
"It's quite clear that these animals are able to pick up sequential regularities in a sound," said Fitch. "But they're not able to pick up a rule at this phrase structure grammar level."
No Magic Bullet
Fitch says animals and humans share mechanisms related to language, including auditory systems, vocal production systems, and aspects of the conceptual system. But while animals have complex thoughtsfor example, they may know their way through a junglethey're unable to express them vocally.
Still, there is plenty of evidence, Fitch says, that many non-human primates, as well as birds, actually have structures and rules that govern their vocalization.
"Birds don't stick things together willy-nilly," he said. "They have particular orders in which they string together calls to make more complex songs. The question then is, What is the level of complexity in these rules?"
Fitch says a fundamental aspect of human language is the ability to use phrase structure, but he stresses that there is no one "magic bullet" that gives us language.
"I don't believe that such magic bullets exist," he said. "Language is a complex mosaic including many important abilities, and any attempt to reduce it to just one will be simplistic and unsatisfactory."
In his article, Premack suggests that other reasons, apart from an animal's inability to understand complex grammar, explain why they have not evolved languages. He says recursive language, which is one way to achieve more complex phrase structure, is not the key factor to consider.
"There has been too much tendency to think that because animals don't have recursion they don't have language," Premack said. "But the reason why they don't have non-recursive language or any other language is because they lack a whole bunch of simpler things."
He says one reason that animals don't have language is because they don't have voluntary control of sensory-motor systems, specifically voice and face, which are essential for speech and sign.
Another reason, he says, is that animals don't teach the way humans do.
"Although human mothers do not teach children grammar, they definitely teach them words," said Premack. "Humans are the only species that teach. Evolution, being endlessly clever, might produce words that don't require teaching, but until it does, it is not clear how any species other than humans could evolve language."
Animals are also not as flexible as humans. While bees may be able to send messages through dance, humans have dozens of ways of sending messages.
Imitation may be yet another factor. While many species can copy a role model's choice of object or location, they can't copy the motor action. This second-level of imitation, Premack maintains, is needed for the evolution of language." "Recursive language is very powerful and it enables us to talk in the fancy way we do," he said. "But suppose we only had non-recursive language. You could still ask questions, use descriptions, and make requests, only it would not be half as wonderful as the system we have."
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