Author: Ramlagan Nadia
Date: March 2008
"Fire on the roof, dial 911!" someone yells at the top of their lungs. This urgent cry,while usually causing panic and confusion, also generates awareness of present danger. Humans have become adept at warning each other through recognizable calls of alarm. Klaus Zuberbühler and colleague Kate Arnold of the University of St. Andrews have found that monkeys combine calls to make them meaningful in the same way that humans do. The study (published in Current Biology) has important implications for the current theory of human language evolution. According to theory, at some point in time the cache of human communcation grew large enough that it became more efficient to combine existing signals of communication, rather than to keep adding new ones. Their findings challenge the notion that combining signals was an essential step towards development of expressive language.
Zuberbühler explained, "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."
Belonging to a group of African monkeys called guenons, putty-nosed monkeys derive their name from their snow-white noses, which stand out in stark constrast to their dark brown to black faces. They can be found in the evergreen forests of Bioko, an island off the west coast of Africa, to northern Zaire and Nigeria. At Gashaka Gumti National Park, Nigeria, Zuberbühler and Arnold researched alarm calls uttered by free-ranging male putty-noses. A single male lives in a group with six to nine females and their offspring.
Equipped with recording devices and GPS tracking units, they were able to follow the movement of females in response to hearing certain recorded alarm calls. The females moved whenever the sounds signified the presence of a threat (for example an eagle or leopard), the identity of the caller, and if he intends to move to a new place. This vocalization of different types of information- all within one call, is much like how humans combine calls by creating sentences with a particular syntax, to make them meaningful.
"Most primates are limited in the number of signals they can physically produce due to 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," said Zuberbühler. "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 signalling may not be driven by too many signals but rather by too few."
Written by Nadia Ramlagan
Reviewed by Pooja Ghatalia
Published by Pooja Ghatalia.