Scientists have uncovered evolutionary changes in the human voice box that distinguish us from other primates and may underpin an essential human ability: speaking.
On Thursday, scientists said that an analysis of the voice box, or larynx, in 43 species of primates revealed that humans vary from apes and monkeys by lacking a vocal membrane: short, ribbon-like extensions of the vocal cords.
They discovered that humans lack balloon-like laryngeal structures known as air sacs that may aid certain apes and monkeys in producing loud and resonant cries and avoiding hyperventilation.
According to the researchers, the loss of these tissues resulted in a steady vocal source in humans, which was essential to the formation of speech – the capacity to transmit thoughts and emotions through articulate sounds.
According to the researchers, this simplicity of the larynx allowed humans to have superb pitch control with extended, consistent speech sounds.
Primatologist Takeshi Nishimura of Kyoto University’s Centre for the Evolutionary Origins of Human Behavior in Japan and lead author of the study published in the journal Science stated, “We argue that the more complicated vocal structures of nonhuman primates can make it difficult to control vibrations precisely.”
“Vocal membranes allow other primates to make louder, higher-pitched cries than humans, but they also increase the frequency of voice breakdowns and noisy vocal irregularities,” said evolutionary scientist and research co-author W Tecumseh Fitch of the University of Vienna.
The larynx, a hollow tube in the throat that houses the vocal cords and is attached to the top of the windpipe, is used for speaking, breathing, and swallowing.
“The larynx is the vocal organ, producing the signal we utilize to sing and speak,” Fitch explained.
Humans, along with monkeys and apes, are primates. Approximately 6m to 7m years ago, the evolutionary lineage that led to our species, Homo sapiens, diverged from the lineage that led to our closest living relatives, chimpanzees, and laryngeal modifications occurred sometime after that.
Because these soft tissues are rarely preserved in fossils, only live animals were included in the study. This also indicates that it is uncertain when the alterations occurred.
It is probable that the laryngeal simplification developed in Australopithecus, a human ancestor that mixed ape-like and human-like features and first appeared in Africa approximately 3.85 million years ago, or in our genus Homo, which first appeared in Africa approximately 2.4 million years ago. Homo sapiens originated in Africa more than 300,000 years ago.
Laryngeal anatomy was investigated in apes such as chimpanzees, gorillas, orangutans, and gibbons, as well as Old World monkeys such as macaques, guenons, baboons, and mandrills, and New World monkeys such as capuchins, tamarins, marmosets, and titis.
While this evolutionary reduction of the larynx was crucial, it “did not give us speech by itself,” Fitch said, noting that other physical features, including a change in the larynx’s position, contributed to speech over time.
Air from the lungs drives the oscillations of the vocal cords in both humans and nonhuman primates, producing a similar process for sound generation. This acoustic energy then goes via the pharyngeal, oral, and nasal cavities and emerges in a form determined by the vocal tract’s filtering of specific frequencies.
“Speech and language are closely connected, but not synonymous,” noted primatologist and psychologist Harold Gouzoules of Emory University in Atlanta, who accompanied the study with a commentary published in Science.
“Speech is the audible sound-based method of expressing language, and humans are the only primates capable of producing it.”
Paradoxically, the complexity of human spoken language rose after an evolutionary reduction.
Fitch remarked, “I find it fascinating that occasionally in evolution, ‘less is more – that by losing a feature, the door may be opened to new adaptations – is true.”
