Ape And Human Infant Gestures Are Similar And Communicative
June 8, 2013

Ape And Human Infant Gestures Are “Predominantly Communicative”

April Flowers for redOrbit.com — Your Universe Online

In a study devoted to comparing the different types of gestures of a female chimpanzee, a female bonobo and a female human infant at comparable stages of communicative development, psychologists analyzed video of the three to find remarkable similarities among the species.

This study, published in the open-access journal Frontiers in Psychology, represents the first time such data has been used to compare the development of gestures across species. The bonobo, formerly known as the “pygmy chimpanzee,” and the chimpanzee are the two species most closely related to humans in the evolutionary tree.

"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.

All three species made gestures that included reaching, pointing with fingers or the head, and raising the arms to ask to be picked up. The researchers said that it was “striking” that all the gestures of all three species were "predominantly communicative.”

For a gesture to be classified as communicative, it had to include eye contact with the conversational partner, be accompanied by vocalization (non-speech sounds) or include a visible behavioral effort to elicit a response. The research team applied the same standard to all three species, finding that for all three, gestures were usually accompanied by one or more behavioral signs of an intention to communicate.

The same facial expressions and basic gestures occur in human populations worldwide, according to Charles Darwin´s 1872 book, The Expression of the Emotions in Man and Animals. This commonality implies that these traits are innate. The UCLA research team has taken Darwin´s conclusions a step farther. Their findings provide new evidence that the origins of language can be found in gestures and new insights into the co-evolution of gestures and speech.

The apes in the study were raised together at the Language Research Center in Atlanta. The chimp (Pan troglodytes) was named Panpanzee, and the bonobo (Pan paniscus) was named Panbanisha. At the Center, the apes learned to communicate with caregivers using gestures, vocalizations and visual symbols (mainly geometric shapes) called lexigrams.

"Lexigrams were learned, as human language is, during meaningful social interactions, not from behavioral training," said Kristen Gillespie-Lynch, an assistant professor of psychology at the City University of New York and a former UCLA graduate student in Greenfield's laboratory.

The human child, who grew up in her parent´s home with her older brother, made mostly verbal symbols. The apes, in comparison, made mostly visual symbols. The researchers videotaped the girl from age 11 months to 18 months. The apes were recorded from 12 months of age until 26 months old. For all three, one hour of video was analyzed per month.

The study findings support the “gestures first” theory of the evolution of language. Communicating with gestures was dominant in all three species during the first half of the study, while all three participants increased their symbol production during the second half. The child started using words while the apes began using lexigrams.

"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. Gesture plays a role in the evolution, and the development, of language, the pattern suggests.

Gesture was the primary mode of communication for all three species at the beginning stage of communication development. The research team noticed that the human infant progressed much more rapidly in the development of symbols, with words beginning to dominate her communication in the second half of the study. The apes, on the other hand, continued to rely predominantly on gesture.

"This was the first indication of a distinctive human pathway to language," Greenfield said.

As they aged, all three increased their use of symbols over gestures. This change was far more pronounced for the human child, whose transition from gesture to symbol could be a developmental model of the evolutionary pathway to human language and thus evidence for the "gestural origins of human language."

Though gestures are the first step in language evolution, the team found evidence to suggest that the evolutionary pathway from gesture to human language included "co-evolution of gestural and vocal communication,” meaning that most of the child´s gestures were accompanied by non-language vocalizations. The apes´ gestures rarely were.

"This finding suggests that the ability to combine gesture and vocalization may have been important for the evolution of language," Greenfield said.

The findings led the team to conclude that 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. That common ancestor lived about six million years ago.

The researchers report that the evolution of human language built on capacities that were already present in the common ancestor of the three species.

"Our cross-species comparison provides insights into the communicative potential of our common ancestor," Gillespie-Lynch said.