Washington, March 11 : A new study has revealed that monkeys convey meaning by combining distinct alarm calls in particular ways.
"In linguistics, morphemes are usually defined as 'the smallest meaningful units in the grammar of a language,'" said Klaus Zuberbuhler of the University of St. Andrews-for instance, a word such as "cat" or a prefix such as "un".
"Our research has revealed some interesting parallels in the vocal behaviour of forest monkeys and this crucial feature of human language," Zuberbuhler added.
He said that his research built on previous studies that showed that male putty-nosed monkeys (Cercopithecus nictitans) produce different alarm-call series in response to a number of disturbances, including leopards and crowned eagles.
The researcher said that the call series consisting of "pyows" are a common response to leopards, while series of "hacks" and "hacks" followed by "pyows" are given to eagles. They further said that males assemble "pyows" and "hacks" into unique "pyow-hack" sequences.
Working with University of St. Andrews researcher Kate Arnold, Zuberbuhler has now found evidence that the various "hacks" and "pyows" of male putty-nosed monkey contain at least three types of information-the event witnessed, the caller's identity, and whether he intends to travel.
The researchers said that all such signals were recognized by other monkeys.
According to them, the new findings challenge the commonly-held notion that the transition from non-combinatorial to combinatorial communication was an essential step in the evolution of human language.
Scientists had even thought that such language may have emerged relatively late in human evolution, Zuberbuhler said, based on the notion that signals would be combined only once the number of them had grown sufficiently.
The theory also suggested that at some point, it becomes more economical to combine existing elements, rather than add new ones to a large repertoire.
"Our research shows that these assumptions may not be correct. Putty-nosed monkeys have very small vocal repertoires, but nevertheless we observe meaningful combinatorial signalling," Zuberbuhler said.
In fact, according to him, most primates are limited in the number of signals they can physically produce because of their lack of tongue control.
"The only way to escape this constraint may be to combine the few calls (they have) into more complex sequences. In other words, it may be 'harder' for non-human primates to evolve large repertoires than to evolve the ability to combine signals. Hence, the evolution of combinatorial signaling may not be driven by 'too many' signals but rather by 'too few'," he said
The study appears in the March 11th issue of Current Biology, a publication of Cell Press.