What can chimpanzees tell us about the origin of human language? Not much, it turns out.
Fossils can offer invaluable insight into the ways early humans lived and evolved but not so much in terms of the development of human language. Instead, for all things speech-related, scientists turn to one of our closest living relatives – chimpanzees.
It was assumed that the noises chimps make are indicative of a kind of proto-language that can provide clues as to how early humans communicated with one another. However, recent research suggests their calls and grunts are "inconsistent" and not particularly language like.
"Chimpanzees give a range of different calls: hoots, pant-hoots, pant-grunts, pant-barks, rough-grunts, nest-grunts, alarm barks, waa-barks, wraas, screams, copulation screams, and soft panting play sounds (aka laughter)," said Michael Wilson, an associate professor at the University of Minnesota, in a statement. "Many of these calls grade into one another, and it can be difficult to categorize particular examples of some calls."
To try and make sense of the calls and separate the hoots from the wraas, Wilson and his team studied new and archival recordings of the chimpanzees living in Gombe National Park, Tanzania. He will be explaining their findings in a presentation at the 175th Meeting of the Acoustical Society of America taking place in Minneapolis, Minnesota, this week.
Chimpanzee vocal communication "raises questions about the evolution of signaling and social behavior," Wilson added. "Do chimpanzee pant-hoots inform other chimpanzees about good food patches, signal community membership, or individual identity, body size, or health?"
The team used a combination of simple statistical models analyzing particular vocal features (such as frequency range and duration of various call components) and, more recently, techniques adopted from speech technology, including machine learning.
The findings show that there are far fewer similarities between human and chimpanzee language than previously thought. Take one particular example: the food-associated rough-grunt calls, which earlier research found varied acoustically according to the quality of food, allowing one chimp to tell another exactly how nutritious a particular berry bush is. Lisa O'Bryan, one of Wilson's students, instead found that chimps produced a spectrum of different rough-grunt variants, which implies there is no consistency between acoustic features and the quality of food.
In essence, chimp vocal communication "isn't particularly language-like", said Wilson. "This is surprising, given that chimpanzees resemble us in so many other ways. But it seems that the key events in language evolution occurred well after the divergence of the chimpanzee and hominin (primate) lineages. In this case, language likely evolved due to uniquely human circumstances."
