All hooting aside: Did a vocal evolution give rise to language?

By Oliver Whang

NEW YORK: The loss of certain muscles in the human larynx may have helped give our species a voice, a new study suggests. Read this sentence aloud, if you’re able.

As you do, a cascade of motion begins, forcing air from your lungs through two muscles, which vibrate, sculpting sound waves that pass through your mouth and into the world.

These muscles are called vocal cords, or vocal folds, and their vibrations form the foundations of the human voice.

They also speak to the emergence and evolution of human language.

For several years, a team of scientists based mainly in Japan used imaging technology to study the physiology of the throats of 43 species of primates, from baboons and orangutans to macaques and chimpanzees, as well as humans.

All the species but one had a similar anatomical structure: an extra set of protruding muscles, called vocal membranes or vocal lips, just above the vocal cords.

The exception was Homo sapiens.

The researchers also found the presence of vocal lips destabilised the other primates’ voices, rendering their tone and timbre more chaotic and unpredictable.

Animals with vocal lips have a more grating, less controlled baseline of communication, the study found; humans, lacking the extra membranes, can exchange softer, more stable sounds.

“It’s an interesting little nuance, this change to the human condition,” said Drew Rendall, a biologist at the University of New Brunswick who was not involved in the research. “The addition, if you want to think of it this way, is actually a subtraction.” That many primates have vocal lips has long been known, but their role in communication has not been entirely clear. In 1984, Sugio Hayama, a biologist at Kyoto University, videotaped the inside of a chimpanzee’s throat to study its reflexes under anaesthesia. The video also happened to capture a moment when the chimp woke and began hollering, softly at first, then with more power.

Decades later, Takeshi Nishimura, a former student of Dr Hayama and now a biologist at Kyoto University and the principal investigator of the recent research, studied the footage with renewed interest.

He found the chimp’s vocal lips and vocal cords were vibrating together, which added a layer of mechanical complexity to the chimp’s voice that made it difficult to fine-tune.

“People have been talking about evolutionary changes in our throats and oral cavity for many years, but this is the first time we took a close look at the larynx in a large selection of monkeys and apes,” said William Tecumseh Fitch, a biologist at the University of Vienna and one of the authors of the paper.

Asif Ghazanfar, a psychologist at Princeton University who was not involved in the research, said: “No one’s done a systematic evaluation like that. We didn’t have a large sense of what primates had it and what primates didn’t. We kind of had a guess, but this study nailed it.”

Harold Gouzoules, a psychologist at Emory University who wrote an accompanying commentary to the recent paper, said “Establishing causality here is essentially impossible,”“It might be a necessary step in the evolution of language, but whether it is absolutely critical remains to be seen.”

Dr Gouzoules said “Language is clearly more than the sum of its parts,” he said. “It’s just not likely that we’re ever going to have a completely satisfactory explanation.”