Scientists think that Homo sapiens began talking somewhere between 50,000 to two million years ago, a massive range underscroring the fact that how and when human language emerged is still a mystery. Various theories chalk it up to the creation of stone tools, cave art, and the need to band together, but there’s no accepted explanation for our ability to gossip with such complexity. To gain a clue, University of Minnesota recently looked to the vocalizations of chimpanzees in an attempt to draw a parallel between their chatter and our own.

In a presentation Tuesday at the 175th Meeting of the Acoustical Society of America in Minneapolis, Minnesota, the team discussed what they learned about human language by studying the sounds that make up chimpanzee communication: “hoots, pant-hoots, pant-grunts, pant-barks, rough-grunts, nest-grunts, alarm barks, waa-barks, wraas, screams, copulation screams, and soft panting play sounds (a.k.a. laughter),” study lead Michael Wilson, Ph.D. explained in a statement released Tuesday. Chimp vocalizations, the team found, were far less similar to human speech than they anticipated, hinting that it’s the parts of us that are uniquely human that have driven our linguistic abilities.

“It seems that the key events in language evolution occurred well after the divergence of the chimpanzee and hominin (primate) lineages,” says Wilson. “In this case, language likely evolved due to uniquely human circumstances.”

Little Chimp Climbing on Back
Chimpanzee vocalizations aren't quite parallel with human language, say scientists.

Humans and chimps share 98 percent of their DNA, making these apes an excellent place to start when digging for the origin of our behaviors. Wilson and his team applied speech technology techniques and machine learning to recordings of wild chimps at the Gombe National Park in Tanzania and a group of captive chimps in Texas, in an attempt to draw links between certain sounds and certain perceived “meanings.” If the chimps did indeed use vocalizations to convey nuanced messages in the way humans do, they hypothesized, then further studies on chimps might shed light on the roots of human language.

Below is a recording of a chimp named Edgar: He’s the alpha male in the Gombe group and inclined to loud calls called “pant-hoots.” These calls begin as a soft grunt and build up to a full scream before softening back to a hoot. It’s thought that pant-hoots, which often chorus through the chimp social groups, are used to indicate the spatial location of chimps in the part and the location of food.

Edgar, the alpha male of the Mitumba community, gives a full pant-hoot call. 

There’s no question that pant-hoots are a form of chimp communication, but the team’s acoustic analysis of the call components, frequency, and frequency range led the scientists to conclude that “chimpanzee vocal communication isn’t particularly language-like.”

Similar analyses, applied to the other types of chimp sounds, pointed to the same conclusion. “In contrast to some previous studies, which reported that rough-grunts vary acoustically in ways that could inform other chimpanzees about food quality, she [student Lisa O’Bryan] found that within rough grunt-sequences to a given food type, chimpanzees produce a range of rough-grunt variants — suggesting there is no consistent match between acoustic features and food quality,” Wilson explains.

The ability to have variation and complexity in meaning is what differentiates communication from language, write the researchers. While chimps vocalizations and physical gestures allow chimps to communicate at least 19 messages to each other, these communication systems lack advanced syntax, references to the past and future, and compositional variations, which the researchers say are crucial to what we consider language.

According to this study, those properties of language are still uniquely human — in particular, unique to both the size and neural complexity of our brains. While the brains of ancient humans were similar in size to chimps, modern human brains are 3.5 times larger, and they have neural capabilities that some scientists believe make language possible in humans and not in other primates. Chimps may share a wealth of other human behaviors and habits, but the gift of gab remains, for now, distinctly human.