From Science:
You don’t need to be Dr. Doolittle to know what a chimpanzee means when she reaches out with her hand, palm-side up. It’s the begging sign, a gesture that speaks volumes even without any accompanying sound. Indeed, so evocative are the manual gestures of chimpanzees and bonobos that a team of researchers has rekindled an old hypothesis: that human language evolved from gesturing, rather than from vocal calls.
Chimps and bonobos use a variety of calls and gestures in their everyday lives. But many researchers assumed that both forms of communication were little more than reflexes, as when a chimp screams when it sees a snake. Frans de Waal, a primatologist at Yerkes National Primate Center in Atlanta, Georgia suspected there was something more to ape gestures. So he and colleague Amy Pollick videotaped the vocal, facial, and manual signals of two captive groups of bonobos and two groups chimpanzees. Of the 375 communicative signals the bonobos produced, nearly 79% were hand gestures, while 14% were facial and/or vocal signals.
The researchers then identified the specific social contexts of the various types of communication.
More here.