Scientists have identified evolutionary modifications in the voice box that distinguish people from other primates that may support an indispensable ability for humanity: speaking.
An examination of the voice box, or larynx, in 43 species of primates showed that humans differ from monkeys and apes in their lack of 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, ringing calls and avoid hyperventilation.
The loss of this tissue, according to the researchers, led to a stable sound source in humans that was crucial to the development of speech – the ability to express thoughts and feelings using articulated sounds.
This simplification of the larynx, they said, enabled humans to have excellent pitch control with long, stable speech sounds.
“We argue that more complex vocal structures in non-human primates can make it difficult to precisely control vibrations,” said primatologist Takeshi Nishimura of the Center for the Evolutionary Origins of Human Behavior in Japan, lead author of the research. Published in Science.
“Vocal membranes allow other primates to make louder, higher-pitched calls than humans – but make vocal breaks and loud vocal irregularities more common,” said evolutionary biologist and study co-author W Tecumseh Fitch from the University of Vienna.
The larynx is a hollow tube in the throat attached to the top of the windpipe and containing the vocal cords, used for speaking, breathing, and swallowing.
“The larynx is the organ of the voice that creates the signal we use for singing and speaking,” Fitch said.
Humans are primates, as are monkeys and apes. The evolutionary lineage that gave rise to our species, Homo sapiens, separated from that which gave rise to our closest living relative, the chimpanzee, approximately 6-7 million years ago, with laryngeal changes occurring sometime after that.
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 occurred.
It’s possible, Fitch said, that the laryngeal simplification may have originated in a hominid called Australopithecus, which combined ape-like and human-like traits and first appeared in Africa about 3.85 million years ago, or later in our species, which first appeared in Africa around 3 years ago. 2.4 million years. Homo sapiens arose 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, gynos, baboons and mandrills, and New World monkeys including capuchins, tamarins, marmosets and goats.
While this evolutionary simplification of the larynx was pivotal, it “did not give us speech per se,” Fitch noted, noting that other anatomical traits are important for speech over time, including the 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 generated in this way then passes through the cavities of the pharynx, mouth and nose and appears in a form governed by filtering specific frequencies dictated by the vocal tract.
said primatologist and psychologist Harold Gozole of Emory University in Atlanta, who wrote Commentary on the sciences accompanying the study.
“Speech is the audible, sound-based method of linguistic expression—and humans, alone among the 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 by losing a trait you may open the door to some new modification,” Fitch said.
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