Researchers have found similarities between the early behavior of humans, chimpanzees and bonobos. Chimpanzees and bonobos are closely related to humans on the evolutionary tree. The study shows that babies of all three species develop more or less the same kind of communicative language skills while growing up.
"The similarity in the form and function of the gestures in a human infant, a baby chimpanzee and a baby bonobo was remarkable," said Patricia Greenfield, a Distinguished Professor of Psychology at UCLA and co-author of the study. Researchers used video footage of the babies growing up that helped them analyze their behavior and development.
The researchers studied gestures such as pointing fingers and raising arms when the babies want to be picked up, and found them to be strikingly similar in the three different species.
Previously, Charles Darwin had said that facial expressions and certain gestures were similar regardless of a human's geographical location. The present study takes this idea a bit further by finding that certain gestures among closely-related ape species are innate. The study provides a new insight into the development of gestures and speech.
The female chimpanzee called Panpanzee, (Pan troglodytes), and Panbanisha, a female bonobo (Pan paniscus) were raised together at the Language Research Center in Atlanta.
At this Center, the apes learned to communicate with their caretakers using gestures, voices and visual symbols (mainly geometric shapes) called lexigrams.
"Lexigrams were learned, as human language is, during meaningful social interactions, not from behavioral training," said the study's lead author, Kristen Gillespie-Lynch, an Assistant Professor of Psychology at the City University of New York.
The human girl grew up at her home where video recordings were taken from when she was 11 months old and ended when she reached 18 months. The video footage for the apes started when they were about 12 months old and ended at 26 months.
The video analysis showed that babies of the three species learn gestures first and later develop speech skills based on symbols (for apes) and words (for human baby).
"Gesture appeared to help all three species develop symbolic skills when they were raised in environments rich in language and communication," said Gillespie-Lynch, who conducted the research while she was at UCLA.
Another important finding was that the human baby would gesture with vocalizations while such behavior was absent in other apes.
"This finding suggests that the ability to combine gesture and vocalization may have been important for the evolution of language," Greenfield said in a news release.
The study is published in the journal Frontiers in Psychology.