Scientists have identified evolutionary changes in the voice box that distinguish people from other primates that may underlie an ability essential to humanity: speaking.
Researchers said on Thursday that an examination of the voice box, known as the larynx, in 43 primate species showed that humans differ from great apes and apes in lacking an anatomical structure called the vocal membrane. – small ribbon-like extensions of the vocal cords.
Humans also lack balloon-like laryngeal structures called air sacs that may help some monkeys produce loud, resonant calls and avoid hyperventilation, they found.
The loss of these tissues, the researchers say, resulted in humans having a stable vocal source that was essential to the evolution of speech – the ability to express thoughts and feelings using articulate sounds. This simplification of the larynx allowed humans to have excellent pitch control with long, steady speech sounds, they said.
“We argue that the more complicated vocal structures in non-human primates may make it difficult to control vibrations precisely,” said primatologist Takeshi Nishimura of the Center for the Evolutionary Origins of Human Behavior at Kyoto University in Japan, author principal of the study. research published in the journal Science.
“Vocal membranes allow other primates to make louder, higher-pitched calls than humans – but they make voice clipping and noisy vocal irregularities more common,” said the evolutionary biologist and study co-author. W. Tecumseh Fitch of the University of Vienna in Austria.
The larynx, a hollow tube in the throat that connects to the top of the trachea and contains the vocal cords, is used for speaking, breathing, and swallowing.
“The larynx is the voice organ, which creates the signal we use to sing and speak,” Fitch said.
Humans are primates, just like monkeys and great apes. The evolutionary line that led to our species, Homo sapiens, split from that which led to our closest living relatives, chimpanzees, about 6 to 7 million years ago, with laryngeal changes occurring some time after.
Only living species were included in the study because these soft tissues are not likely to be preserved in fossils. This also means that it is unclear when the changes took place.
Fitch said it’s possible the laryngeal simplification originated in a human precursor called Australopithecus, which combined ape and human-like traits and first appeared in Africa around 3.85 million years ago. years, or later in our genus Homo, which first appeared in Africa around 2.4 million years ago. Homo sapiens originated over 300,000 years ago in Africa.
Researchers have studied the anatomy of the larynx in apes, including chimpanzees, gorillas, orangutans, and gibbons, as well as Old World monkeys, including macaques, guenons, baboons, and mandrills , and New World monkeys, including capuchins, tamarins, marmosets, and titis.
While this evolutionary simplification of the larynx was essential, it “did not give us speech by itself,” Fitch noted, pointing out that other anatomical traits mattered for speech over time, including a change in the position of the larynx.
The mechanisms of sound production in humans and non-human primates are similar, with air from the lungs driving vocal cord oscillations. The acoustic energy thus generated then passes through the pharyngeal, oral and nasal cavities and emerges in a form governed by the filtering of specific frequencies dictated by the vocal tract.
“Speech and language are closely related, but not synonymous,” said primatologist and psychologist Harold Gouzoules of Emory University in Atlanta, who wrote a commentary in Science accompanying the study. “Speech is the audible mode of expression based on sound – and humans, alone among primates, can produce it.”
Paradoxically, the increased complexity of human spoken language has followed an evolutionary simplification.
“I think it’s quite interesting that sometimes in evolution ‘less is more’ – that by losing a trait you could open the door to new adaptations,” Fitch said.