Scientists have identified evolutionary modifications in the speech box that distinguish humans from other primates that may underlie an indispensable human ability: speaking.
Examinations of the speech boxes, or larynx, of 43 primate species show that humans differ from apes and monkeys by the lack of an anatomical structure called the vocal membrane: the small ribbon-like extension of the vocal cords, researchers said Thursday.
They found that humans also lack balloon-like throat structures called air sacs, which may help some apes and monkeys make loud, resonant calls and avoid hyperventilation.
According to the researchers, the loss of these tissues led to a stable source of voice in humans, which was crucial to the evolution of language – the ability to express thoughts and feelings using a clear voice.
This simplification of the larynx enables humans to achieve excellent pitch control with long, steady speech, they say.
“We think that the more complex vocal structures of non-human primates make precise control of vibrations difficult,” said primatologist Takeshi Nishimura of the Center for the Evolutionary Origin of Human Behavior at Kyoto University, who published in the journal Lead author of the study. science.
W Tecumseh Fitch, an evolutionary biologist at the University of Vienna and study co-author, said: “Acoustic membranes allow other primates to make louder, higher-pitched calls than humans — but they make vocal breaks and noisy sounds irregular. more common.”
The larynx is a hollow tube in the throat that connects to the top of the windpipe and contains the vocal cords used for speaking, breathing, and swallowing.
“The larynx is the vocal organ, and it creates the signals we use to sing and speak,” Fitch said.
Humans are primates, as are monkeys and apes. Changes to the larynx occurred sometime after the evolutionary lineage that led to our species Homo sapiens split from the evolutionary lineage that led to our closest relative, the chimpanzee, some 6 to 7 million years ago.
The study only included living species because these soft tissues are not easily preserved in fossils. It also means it’s not clear when the change occurred.
Fitch said the simplification of the larynx may have arisen in a human precursor called Australopithecus, which combines features of apes and hominids and first appeared in Africa about 3.85 million years ago, or later in our genus Homo. , the genus first appeared in Africa about 2.4 million years ago. Homo sapiens originated in Africa more than 300,000 years ago.
The researchers studied the throat anatomy of great apes, including chimpanzees, gorillas, orangutans, and gibbons, as well as Old World monkeys, including macaques, chimpanzees, baboons, and mandrills, as well as capuchins, marmosets, marmosets, and Laryngeal anatomy of New World monkeys including otitis.
While this evolutionary simplification of the larynx is key, Fitch notes that it “doesn’t allow us to speak by itself,” noting that other anatomical features have also been important for speech over time, including changes in the position of the larynx.
The mechanism of sound production is similar in humans and non-human primates, with air from the lungs driving the oscillations of the vocal cords. The sound energy produced in this way then passes through the pharynx, mouth and nasal cavity and emerges in a form controlled by a specific frequency filter dictated by the vocal tract.
“Speech and language are closely related, but not synonymous,” said Harold Gouzoules, a primatologist and psychologist at Emory University in Atlanta, who wrote a review in the journal Science that accompanies the study.
“Speech is a form of language expression based on audible sounds — in primates, only humans can produce it.”
Paradoxically, the complexity of spoken human language has increased with evolutionary simplification.
“I think it’s very interesting that sometimes ‘less is more’ in evolution — losing a trait might open the door to some new adaptations,” Fitch said.