Ape and human infants at comparable stages of development use similar gestures, such as pointing or lifting their arms to be picked up, new research suggests.
Chimpanzee, bonobo and human babies rely mainly on gestures at about a year old, and gradually develop symbolic language (words, for human babies; and signs, for apes) as they get older.
The findings suggest that “gesture plays an important role in the evolution of language, because it preceded language use across the species," said study co-author Kristen Gillespie-Lynch, a developmental psychologist at the College of Staten Island in New York.
The gesturing behavior was described June 6, in the journal Frontiers in Comparative Psychology. (8 Humanlike Behaviors of Primates)
The idea that language arose from gesture and a primitive sign language has a long history. French philosopher Étienne Bonnot de Condillac proposed the idea in 1746, and other scientists have noted that walking on two legs, which frees up the hands for gesturing, occurred earlier in human evolution than changes to the vocal tract that enabled speaking.
But although apes in captivity can learn some language by learning from humans, in the wild, they don't gesture nearly as much as human infants, making it difficult to tease out commonalities in language development that have biological versus environmental roots.
To do so, Gillespie-Lynch and her colleagues compared detailed video of an American baby girl in everyday life with two apes of the same age that were trained to communicate. Panpanzee, a chimpanzee, and Panbanisha, a bonobo, were living at the Language Research Center in Atlanta, where they received interactive training in sign language, gesturing and vocalizations; they also went through a daily testing session.
The researchers analyzed the young apes’ behavior when they were about a year old to about 26 months old to that of the human baby when she was 11 months old to almost 2 years old.