Apeing our language
Chimp genome may shed light on surprising command of vocabulary.
Panbanisha knows how to get what she wants. The 19-year-old bonobo chimpanzee tells her carers when it's time for her favourite video: the one where the man in the gorilla suit drives to the restaurant and steals a taco.
Whereas wild chimps use screeches and hollers to make their point, captive-reared Panbanisha communicates through symbols and signs. Now, with the publication of the chimp genome, researchers are beginning to understand the myriad genes that contribute to these animals' communicative abilities. And it seems we may have underestimated the linguistic skills of our closest relative.
Wild chimpanzees, which live in groups of around 15 to 20, communicate using a rich variety of cries, hoots, grunts and barks. These vary subtly to convey different meanings, says primatologist Klaus Zuberbühler from the University of St Andrews, UK, who has studied the vocalizations of wild chimps living in Uganda's Budongo forest.
During a fight, chimps make slightly different screeches depending on whether they are the aggressor or the victim, says Zuberbühler. There are also different grunts for different amounts of food, and different barks for different predator threats.
“As soon as you focus on one type of vocalization, you're amazed by the amount of variation. These aren't just random sounds,” says Zuberbühler. “They are clearly intelligent animals.”
They have a deep understanding of the social world around them, he says, and use sound to transmit this information in the low visibility environment of the forest.
Chimps' linguistic skills are also evident from studies of captive chimps. In the 1970s, Washoe famously became the first common chimpanzee (Pan troglodytes) to learn American Sign Language and amassed a vocabulary of more than 100 signs.
More recently, researchers have taught chimps to communicate using symbols on a keyboard. Each symbol stands for a different word, and as the keys are pressed a computer-generated voice says the word out loud.
Chimpanzees can respond to questions posed by the keyboard, and also use it to convey information directly, says primatologist William Fields of Georgia State University, Atlanta.
One such bonobo (Pan paniscus), called Kanzi, spontaneously learned how to communicate using the keyboard after watching his mother being taught. “He's amazing,” says Fields.
At 24 years old, Kanzi understands spoken sentences such as “Kanzi, take the keys and put them in the refrigerator,” and responds appropriately. He can also produce sentences of his own using the keyboard, informing his keepers where he wants to go and what he wants to do.
Kanzi started learning symbols from humans at nine months of age, but his sister Panbanisha began at birth. Her vocabulary is richer as a result, says Fields.
If chimpanzees aren't as talented with the spoken word as they are with sign language and keyboards, that may be more to do with limitations in hearing than understanding. A 2003 study suggests that differences in a hearing gene called alpha tectorin renders chimps less sensitive to picking up the nuances of human speech1.
So how smart are chimps and what is it about their brains and genetic make-up that makes them so talented?
At least two genes may have helped the animals to develop the bigger brains thought necessary for language development. The genes, called ASPM and microcephalin are present in chimpanzees and humans, and mutations in either can cause humans to develop abnormally small brains and mental problems23.
Another gene, which occurs only in apes and humans, may also have helped to make chimps smarter. The gene, called GLUD2, codes for an enzyme that helps to regulate levels of glutamate, a protein that aids nerve-cell communication.
GLUD2 probably appeared around 23 million years ago, when the evolutionary trees of hominoids (apes and humans) and Old World monkeys split. It arose when its ancestor, the GLUD1 gene, was duplicated, inserted back into the hominoid genome, and underwent various changes in its DNA sequence4.
Round about the same time, the brains of our ancestors were increasing in complexity and size5. “So the appearance of GLUD2 may have contributed to the enhanced cognitive abilities and language skills of humans and apes,” says Henrik Kaessmann from the University of Lausanne, Switzerland, who studied the gene.
There is a fourth language-related gene, called FOXP2, which may be involved. The gene is found in a variety of species from mouse to monkey to man6. Humans carrying one mutated copy of the gene seem to have problems processing language and cannot make the fine tongue and lip movements that allow most people to speak clearly7.
The chimp FOXP2 gene is slightly different from the normal human form, so it's possible the animals have the cognitive capacity for language but are unable to express it vocally.
“Chimps may suffer from a problem in articulation,” says Fields. But by giving captive chimps the means to communicate through sign and symbol languages, we may, in part, have freed them of this constraint.
Some chimps have found other ways to get round the problem. Kanzi has started speaking, not by using his lips and tongue, but by using his throat. He can say words like ‘milk’, ‘grape’, and ‘peanut’ by altering the length of his vocal cords.
“We realized he was doing this when we heard him speaking with his mouth full of tomato,” says Fields. Kanzi had to be using his throat to make the sounds in order to speak clearly with a full mouth, Fields explains.
It's also possible that chimpanzees' 'language' in the wild is far more sophisticated than we give them credit for. We're only just beginning to distinguish the subtle differences between seemingly similar chimp calls, says Zuberbühler. Maybe the problem is not one of chimp communication, but of human understanding.
- Clark,A. G. et al. Science 302, 1960 - 1963 (2003).
- Kouprina, N., et al. PLoS Biol. 2, doi:10.1371/journal.pbio.0020126 (2004).
- Wang, Y. Q.& Su,B. Hum. Mol. Gen. 13, 1131 - 1137 (2004).
- Burki, F. & Kaessmann, H. Nature Genet. published online doi:10.1038/NG1431 (2004).
- Noback, C. R. & Montagna, W. The Primate Brain, (Meredith Corporation, New York, 1970).
- Enard, W. et al. Nature 418, 869 - 872 (2002).
- Hurst, J. A., Baraitser, M., Auger, E., Graham,F. & Norell, S. Dev. Med. Child Neurol. 32, 347 - 355 (1990).