The need for cooperation may facilitate call diversification

An important question in the evolution of language is what caused animal calls to diversify and to encode different information. Alarm calls are important to warn group members in dangerous situations. But in which contexts are quiet calls used? An international team of scientists led by Catherine Crockford of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, has now looked into the causes of call variation in less urgent contexts and found that chimpanzees use the quiet “hoo” call in three different behavioural contexts – alert, travel and rest. The need to stay together in low visibility habitat may have facilitated the evolution of call subtypes, with each call informing receivers how to respond in order for signaller and receiver to stay together.