Researchers have found apes communicate more effectively and flexibly using gestures than they do with facial expressions and sounds, findings that may shed light on how human language developed.

A study published Monday looked at how two groups of chimpanzees and two groups of bonobos — a close relative of the chimp — use hand and limb gestures to communicate.

Conan, a chimpanzee, scratches his head at Chimp Haven in Keithville, La., on March 16. Researchers have found chimpanzees and bonobos use hand and limb gestures differently.
(Jim Hudelson/The Shreveport Times/Associated Press)

They found both species used facial and vocal signals similarly but communicated with gestures in very different ways from species to species and even from group to group.

"A chimpanzee may stretch out an open hand to another as a signal for support, whereas the same gesture toward a possessor of food signals a desire to share," said Amy Pollick, who along with fellow Emory University researcher Frans de Waal co-authored the study.

"A scream, however, is a typical response for victims of intimidation, threat or attack. This is so for both bonobos and chimpanzees, and suggests the vocalization is relatively invariant," Pollick said.

All primates use facial and vocal expressions, but only humans and the great apes — gorillas, orangutans, chimpanzees and bonobos — communicate with gestures, suggesting the practice is evolutionarily younger.

The study also found bonobos were more effective than chimpanzees in being understood when using combinations of gestures, facial and vocal methods of communication.

The researchers say the findings support the gestural origin hypothesis of language, which says that human languages first evolved through gestures before involving spoken words.

The research paper, Ape gestures and language evolution, first appeared online Monday in the journal Proceedings of the National Academy of Sciences.

Past studies had suggested that apes did not further develop spoken language as a result of genetic differences that limit their range of facial motions and hearing acuity.