Apes and Human Infants Display Similar Communicative Gestures

In a latest finding, psychologists from the University of California have detected striking similarities in the way a baby chimapanzee, a baby bonobo and a human infant communicate using gestures.

The psychologists identified similarities between the three after analyzing video footage of a female chimpanzee, female bonobo and a female human infant. A one-hour video of each was taken to compare the different types of gestures at various stages of communicative development.

Patricia Greenfield, professor of psychology at UCLA and co-author of the study stated that the similarity in the form and function of gestures between the three was really amazing.

The gestures made by the three species consisted of reaching, pointing with fingers or the head and raising arms to ask to be picked up.

A gesture would be called as communicative only if it had an eye contact with the person who is in conversation, and is accompanied by non-speech sounds or includes a visible behavioral effort to bring out a response. In all the three species, the gestures were accompanied with one or more behavioral signs that revealed their intention to communicate.

The apes included in this study namely Panpanzee, a female chimpanzee, and Panbanisha, a female bonobo, were raised together at the Language Research Center in Atlanta where they learnt to communicate using gestures, visual symbols (lexigram) and vocalizations.

"Lexigrams were learned, as human language is, during meaningful social interactions, not from behavioral training," said the study's lead author, Kristen Gillespie-Lynch.

On the other hand, the human infant grew up in her parents' home. The girl's symbols were spoken words and the apes' symbols were visuals. At 11 months the video analysis of the girl began and stopped when she was 18 months old. In the case of the two apes, the video analysis began at 12 months and continued till 26 months.

They noticed that as the species aged, they used fewer gestures and more symbols. When compared to the apes, the child transitioned more quickly, with no transition occurring in apes.

This study supports the "gestures first" theory of the evolution of language. Before the development of communication, the primary mode of communication was gestures, and as humans progressed, they rapidly used symbols which were later replaced by words, which dominated communication; whereas apes continued with gestures.

"Humans inherited a language of gestures and a latent capacity for learning symbolic language from the last ancestor we share with our chimpanzee and bonobo relatives - an ancestor that lived approximately 6 million years ago," the researchers conclude.

The study was published in the journal Frontiers in Psychology.