Apes have their own forms of communication but can grasp spoken English and understand symbolic language, according to a team of Georgia State University researchers.
"We have been wrong about what the ape brain can do," said Prof Sue SavageRumbaugh, who is teaching bonobo apes to understand spoken language. "There has been data for a long time suggesting that apes were capable of language. The evidence is there. We only have to look at it."
Apes, including gorillas, chimpanzees and bonobos, also known as pygmy chimpanzees, are our nearest evolutionary relatives. They share 99 per cent of the DNA found in humans, Prof Savage-Rumbaugh said, and act like us, feel like us and care like us.
Earlier work with chimps showed that apes could be taught hand symbols to achieve a limited form of communication with humans. Her work is different - the bonobos are expected to understand spoken words and to re-apply knowledge to show they comprehend the meanings of words.
She starts with a board with symbols for the words she uses such as food, water, milk, various rooms and places. The apes have a matching board which serves as a keyboard, allowing the bonobos to respond.
As she speaks she points to the symbols, and over time the bonobos pick up the words. She can then abandon her board and speak to them directly.
They were able to understand combinations of words and act accordingly, she said. She could ask them, for example, to get a tomato from the microwave or pour juice into milk rather than milk into juice. They listen and do what has been asked and can make their own requests, like asking for food and a hug after being scolded.
In one instance she wanted to say she had cut her finger and said: "Knife cut Sue". The bonobo responded by throwing a knife at the researcher.
They don't have a vocal tract, but if they did she believes they would be capable of limited speech. How would humans communicate other than by gestures and abstract sounds if they had the vocal capabilities of an ape, she asked.
"It is not only apes who have to listen to us. We have to listen to them" and recognise the language forms they use, she argued. "There is a good chance that they use symbolic language in the wild," she added, an assumption based on the speed with which they learn to communicate in captivity with humans.
A researcher from the College of William and Mary described similar work which attempts to understand how communication methods used by apes could be seen as an evolutionary step along the way towards human communication.
A dominant view of language is that espoused by Stephen Pinker and Noam Chomsky, who argue that language skills evolved very late, were available only to humans and were "hard wired", built into the genetic make-up of humans.
"My view on language is different," said Dr Barbara King, assistant professor of anthropology. "Language has a long evolutionary history. Language is about use. It is social." The argument was not only about whether apes had human-like language, it was also about what communications they used.
Animal "vocalisations" were a communications form that was repeated and understood by animal populations and could be learned by others in a group. "There is even some suggestion there is syntax in non-human vocalisations," she said. "We know little about ape vocalisation", but other forms such as facial features, gestures and body movements obviously occur. These exhibit "clear patterns and continuity" in terms of communication.
She also observes the behaviour of captive bonobo apes. "What I am finding is sequenced patterns," she said, which build up meaning and represent clear communication. A mother ape, for example, would perform movements and signs "repeatedly and predictably" in a form of "social information donation" taken up by the infant.
While she did not describe this level of communication as language, her work was an effort to place these actions in an evolutionary context and see if it represented a precursor of human language development.
"We can learn about language origins through looking at species other than our own."