What do a chimpanzee, a bonobo and a toddler all have in common? They all use gestures to communicate.
By studying hours of video of a female chimp named Panpanzee, a female bonobo named Panbanisha and a little girl with the initials GN, a team of psychologists hope to gain some insight into how spoken language evolved in humans.
Skeletons can be fossilized, but language cannot, the researchers noted in a study published this week in Frontiers in Psychology. To figure out how it came to be, they looked for similarities between the three closely related species to infer ways that our common ancestor would have communicated more than 5 million years ago.
"This is one line of evidence for the gestural foundation of human language evolution," the wrote.
The similarities between Panpanzee, Panbanisha and GN were striking. Among the universal gestures were:
* Reaching, in which subjects leaned toward a person or object they wanted without making contact.
* A "reach-touch" gesture, a sequence in which the subjects are able to make contact with the desired object (Cheerios, in one case).
* Pointing, which involves extending an arm with the index finger stretched out.
* A "point-touch" gesture, in which the index finger makes contact with something, such as a picture in a book.
* A "head-point" gesture, which has the head playing the role of the index finger.
* An "up" gesture, in which the subject raised her arms over her head to indicate she wanted to be picked up.
* A "go" gesture, which looks like reaching or pointing except that there's no specific target nearby.
"The most basic finding … is the similarity of gestures among bonobo, chimpanzee, and human child at comparable periods of development," the research team wrote. For all three species, these gestures were most often considered "communicative" because they were paired with eye contact, a vocalization or persistence.
The biggest difference was the GN was far more likely to combine her gestures with some type of vocalization; the older she got, the more likely these were to be words. By the time she was 18 months old, she was saying 513 words (on average) during her hour-long observation sessions.
"It's a new kind of evidence" that gestures evolved into human speech, said UCLA psychology professor Patricia Greenfield, one of the study authors. "It really speaks to the idea that gestures and vocal language, or speech, evolved together."
You can read the study online here.