Chimpanzees regularly string many different calls together into sequences, which are often three calls long and sometimes even longer. The finding suggests that the apes are more creative with their vocalisations than previously thought.
It also opens up the possibility of chimps combining calls to create new meanings, a skill thought to be unique to humans 鈥� although far more evidence would be required to show this.
Chimpanzees (Pan troglodytes) are our closest living relatives. They live in groups of a few dozen individuals and communicate with a mix of gestures and calls, including grunts, barks and screams.
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This is a far cry from the complex language that humans use. In particular, humans can combine words to create meanings not present in the individual words, such as 鈥渢his duck quacks in the ultrasonic鈥�.
By contrast, it isn鈥檛 clear that chimpanzees鈥� calls convey subtle or complex meanings. , like warning friends about snakes by startling them.
Crucially, there also seem to be limits to the ability of animals, including chimps, to combine calls in sequences. Some songbirds obey rules about the order that pairs of sounds should take, but nothing beyond that. This implies that they can鈥檛 convey anything subtler than things like 鈥渟nake alert鈥�.
C茅dric Girard-Buttoz at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and his colleagues recorded the calls of 46 adult chimpanzees in Ta茂 National Park in C么te d鈥橧voire. They obtained 900 hours of data, including 4826 utterances. While 3232 of these were single calls, 817 were paired calls and 458 were triplets. There were also longer sequences, but these were rare: there were only two instances of a sequence of 10 calls, for example.
The team found clear patterns in the call sequences. In paired calls, grunts and hoos tended to come first, while panted barks and other calls tended to come second.
This was also true for triplet calls. Within the triplets, some pairs were produced more often than would be expected by chance. Certain pairs of calls tended to come at the start, such as 鈥減anted hoo, panted bark鈥� and 鈥渉oo, panted hoo鈥�. What鈥檚 more, if the first two calls were a grunt and a panted grunt, the third was likely to be another grunt.
Read more: Bonobos and chimps 鈥榮peak鈥� with gestures
For Girard-Buttoz, this is reminiscent of the rules that structure human sentences. For instance, English sentences often start with a subject followed by a verb and an object, like 鈥渢he duck ate the elephant鈥�. 鈥淭here is some form of rules,鈥� says Girard-Buttoz. 鈥淎natomically, they can combine almost any call to any call in any order, but there are some more-recurring sequences.鈥�
Compiling such a large data set and hunting for patterns is 鈥渘ew and exciting鈥�, says Kirsty Graham at the University of St Andrews in the UK. She studies great ape gestures, and would like to see similar studies of gesture-based communication.
However, the key problem is that we don鈥檛 know whether the patterns in the chimps鈥� calls are meaningful to them. Girard-Buttoz says the next step is to find out if the combinations of calls have new meanings, differing from the meanings of the individual calls. 鈥淭hat鈥檚 what鈥檚 been done in some species. In chimpanzees, we don鈥檛 have that yet.鈥� One approach would be to play specific sequences to chimps and see how they react.
Julia Fischer of the German Primate Center in G枚ttingen thinks it would be necessary to show that the individual units have meaning and then the combination of units generates new meaning. Until this is demonstrated, she says there is no reason to think chimps have taken a step towards language.
Reference: bioRxiv
