Monkey calls give clues to language origins
By Rebecca Morelle
Science reporter, BBC News
Campbell's monkey have distinct alarm calls
Scientists may be a step closer to understanding the origins of human language.
Two studies suggest that the ability to combine sounds and words to alter meaning may be rooted in a species of monkey.
A team found the Campbell's monkey can add a simple sound to its alarm calls to create new ones and then combine them to convey even more information.
The research is published in the journals Plos One and PNAS.
Human language is incredibly complex, but one commonly used feature is the process of adding another unit - a prefix or suffix - to a word to change its meaning. For example, adding "hood" to the word "brother" to form "brotherhood".
A team looking at Campbell's monkeys (Cercopithecus campbelli campbelli) in the Ivory Coast's Tai National Park found that these primates do a similar thing.
The researchers studied alpha males in six wild groups. These monkeys do not play a very social role but are alert to potential threats and disturbances and use their calls to highlight them.
The researchers discovered that the monkeys made several distinct alarm cries, among them calls described as "boom", "krak" and "hok".
The team found that booms were sounded when a falling branch had been spotted or to initiate group travel.
Kraks were only given after a leopard had been sighted.
While hoks were almost exclusively sounded when a crowned eagle swooped above the canopy.
But further analysis revealed that while booms were always unaltered, the monkeys sometimes added an "oo" to their kraks and hoks - and this transformed the information they were conveying.
Klaus Zuberbuehler, an author of the paper from the University of St Andrews, Scotland, said: "If you add this subtle additional oo unit to turn krak into krak-oo, then that call can be given to a whole range of other contexts. If you take the suffix away then it is almost exclusively a leopard alarm call."
While krak-oo appeared to be a general alarm call given to almost any disturbance, hok-oo was used for commotion specifically in the canopy, from the presence of neighbouring groups of monkeys to a glimpse of other flying animals.
Professor Zuberbuehler added: "What is interesting is that the same acoustic modifier is being used for these calls and that is really analogous to using a suffix in human language."
A second study focused on how Campbell monkeys combined their alarm calls, as they were more likely to use a longer sequence of calls than voice individual ones.
Professor Zuberbuehler said: "Sometimes the monkey can give 10, 15 or even 20 calls, and typically different types of calls can appear in these sequences... So we tried to understand what particular context would trigger these sequences."
The scientists found that a sequence made up only of booms was used to prompt the group to travel.
If a pair of booms was followed by some krak-oos, it was almost exclusively given when falling trees or branches had been seen.
But if two booms were followed by a mix of krak-oos and hok-oos, then that seemed to signal the presence of a neighbouring group of Campbell's monkeys or another lone male.
Professor Zuberbuehler said: "These are three different events that are nothing to do with each other, but they are basically made of the same call types."
He added: "This is the first time that we can demonstrate that these sequences convey something about the environment or an event the monkey has witnessed."
The researchers say that while the monkey's linguistic talents may be unique amongst primate species, if the findings prove to be more widespread then they could help to reveal more about the origins of language.
Professor Zuberbueler said: "Campbell's monkeys and humans separated from a common ancestor about 30 million years ago.
"This set of papers shows that in terms of the call morphology, there seem to be ancestral traits floating around the primate lineage that haven't been known before."