An examination of the voice box, or larynx, in 43 primate species showed that humans differ from monkeys and apes in lacking an anatomical structure called the vocal fold: tiny ribbon-like extensions of the vocal cords, researchers said Thursday. They found that humans also lack balloon-like laryngeal structures called air sacs that may help some monkeys and apes make loud, audible calls and avoid hyperventilation. The loss of this tissue, according to the researchers, led to a stable source of sound in humans that was crucial to the development of speech – the ability to express thoughts and feelings using articulated sounds. Simplification of the larynx, they said, allowed humans to have excellent pitch control with long, steady speech sounds. “We argue that the more complex vocal structures in nonhuman primates may make precise vibration control difficult,” said lead author Takeshi Nishimura of the Center for Evolutionary Origins of Human Behavior in Japan, lead author of the study. Published in Science. “Vocal membranes allow other primates to make louder, higher-pitched calls than humans — but they make vocal breaks and loud vocal abnormalities more common,” said evolutionary biologist and study co-author W Tecumseh Fitch of the University of Vienna. The larynx is a hollow tube in the throat that connects to the top of the trachea and contains the vocal cords, used for speaking, breathing and swallowing. “The larynx is the voice organ that creates the signal we use for singing and speaking,” Fitch said. Humans are primates, like monkeys and apes. The evolutionary lineage that gave rise to our species, Homo sapiens, diverged from that which gave rise to our closest living relative, the chimpanzee, about 6-7 million years ago, with laryngeal changes occurring shortly thereafter. Only living species were included in the study because these soft tissues are not suitable for fossil preservation. This also means that it is not clear when the changes were made. It’s possible, Fitch said, that the simplification of the larynx may have come from a hominid called Australopithecus, which combined ape and human features and first appeared in Africa about 3.85 million years ago, or later in our species. which first appeared in Africa about 3 years ago. 2.4 million years ago. Homo sapiens appeared more than 300,000 years ago in Africa. The researchers studied the anatomy of the larynx in monkeys including chimpanzees, gorillas, orangutans and gibbons, as well as Old World monkeys including macaques, guinea pigs, baboons and mandrills, and New World monkeys including capuchins, tamarins, marmosets and goats. . While this evolutionary simplification of the larynx was crucial, “it didn’t give us speech per se,” Fitch noted, noting that other anatomical features are important for speech over time, including change in the position of the larynx. The mechanisms of sound production in humans and non-human primates are similar, with air coming from the lungs causing the vocal cords to vibrate. The sound energy thus produced then passes through the cavities of the pharynx, mouth and nose and appears in a form governed by the filtering of specific frequencies dictated by the vocal tract. said zoologist and psychologist Harold Gozol of Emory University in Atlanta, who wrote a Science Commentary accompanying the study. “Speech is the auditory, sound-based method of linguistic expression – and humans, alone among primates, can produce it.” Paradoxically, the increasing complexity of human spoken language follows an evolutionary simplification. “I think it’s interesting that sometimes in evolution it’s ‘less is more’ — that losing a feature can open the door to some new modification,” Fitch said.
