A surprising new study has revealed that diverse sounds produced by human speech not only evolved after Neolithic times, but also stem from biological alterations in the human bite as a result of eating softer diets.
The findings contradict the theory that the range of human sounds has not changed since Homo sapiens emerged about 300,000 years ago. Linguistic diversity was also commonly thought to evolve independently of biological changes.
In 1985, linguist Charles Hockett suggested that labiodentals – the class of speech sounds including ‘f’ and ‘v’ in English – might have evolved as diets became softer with the move away from hunting and gathering towards agriculture and industrialised food processing.
These changes, he said, altered the human bite so that new sounds were easier to produce.
Damian Blasi and Steven Moran, researchers from the Department of Comparative Linguistics at the University of Zurich in Switzerland, thought the proposal was intriguing.
“We thought it bizarre, unlikely, but ultimately fascinating,” says Blasi.
“So, we set out to test whether we could find such a link between diet, bite and labiodentals.”
Enlisting a highly interdisciplinary team to investigate, he and colleagues analysed the distribution of labiodentals in contemporary languages.
They studied how sounds changed through time in the diverse family of Indo-European languages – which includes English, Hindi and Spanish – then modelled the cost of producing labiodentals in a computational model of speech, and scoured paleoanthropological evidence.
Their investigations revealed that labiodental sounds arose recently, and that they did indeed stem from changes in diet and bite just as Hockett hypothesised.
“Soft diets led to a preservation of overbite and overjet, which characterises the majority of the bites that people have nowadays,” Blasi explains. These rendered labiodental sounds low cost, or “easy” to produce.
“Since our upper teeth protrude from our mouth, they can touch the lower lips with very little effort,” he says.
“Before, heavy wear diets produced an edge-to-edge bite so the upper teeth didn’t protrude, and hence it was harder to produce those sounds. Try it yourself – put your upper and lower teeth in contact then try to produce an ‘f’.”
The team’s research suggests that the sounds originated not long before the Bronze Age in Europe and Asia. They suspect they emerged from bilabials, another class of speech sounds which include, for instance, ‘b’.
The authors explore how labiodentals might be “useful” sounds for communicating.
“They are clearly distinguishable acoustically from other speech sounds and visually salient (think of someone saying the f-word),” Blasi says, adding that ultimately their benefit needs to be further investigated.
Although the study was consistent with Blasi’s broader research agenda, he says he was also “truly inspired” by Hockett’s humility.
“[Hockett] put together this idea but was rapidly dismissed by the very same people he was citing as support,” he says.
“So, he writes a reply that ends as follows: I cannot abandon my lovely hypothesis without a twinge of regret, but I console myself by recalling Einstein’s counsel, ‘if you are after the truth, leave elegance to the tailor’.
“And he was right after all.”
He and Moran consider the study “a small tribute to Hockett”.