Chimpanzee call variants offer insights into roots of language diversification

May 23 (UPI) -- Why and how did our ape ancestors first diversify their vocabulary, making the evolution of language possible? New research suggests the call variants deployed by chimpanzees can offer clues.

Previous studies have shown species that use different fight or flight responses for different predation threats also use different alarm calls. In other words, the diversification of danger can drive language diversification.

In the newest study, published this week in the journal Royal Society Open Science, researchers at the Max Planck Institute for Evolutionary Anthropology considered how language might diversify under less stressful conditions.

For clues, scientists looked to the 'hoo' call performed by chimpanzees.

"We found that chimpanzees have at least three acoustically different 'hoo' variants, each given in a different behavioural context: alert, travel and rest," researcher Catherine Crockford said in a news release.

Each variant calls for a different response. The alert 'hoo' instructs a caller's companion to approach, but to do so slowly and with caution. The travel 'hoo' calls for the signaler's companion to approach quickly, and to hurry up. The rest 'hoo' suggests the receiver stay put -- but remain nearby.

Researchers hypothesize that the call variants help to maintain social cohesion by allowing companions to stick together under a variety of circumstances or behavioral contexts.

"Chimpanzees benefit from cooperating with bond partners, and are thus particularly likely to gain from staying close to cooperation partners," said Crockford. "However, chimpanzees live in low visibility habitat, such that even when separated by short distances visual signals or non-specific vocal signals are likely to be unreliable in maintaining cohesion. Thus, encoding contextual information in quiet 'hoos' may facilitate cohesion -- and therefore cooperation."

Previous studies have shown that both chimpanzees and bonobos use a variety of hand gestures to augment their vocabulary, allowing for effective communication in a variety of social situations.