Compared to other primates, humans have exceptional pitch control and an ability alien to other species: speaking. But why are humans the only animals that possess a voice? And why do humans have more voice control than nonhuman primates?
Scientists believe evolutionary changes in the human voice box aided our ability to have long and stable speeches. For example, researchers found out that a human’s larynx is different from apes and monkeys after examining the voice box in 43 species of primates.
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A voice box evolved for speaking
The team of researchers, led by Takeshi Nishimura, associate professor at Kyoto University’s Center for the Evolutionary Origins of Human Behavior, has said that the human voice box evolved for speaking as a means to communicate.
The team found that humans have more superficial laryngeal anatomy than other primates. This allows humans to maintain long and stable speech sounds and express complicated changes in speech sounds, the team said. The team’s findings were published in the U.S. journal Science.
The team analyzed the throats of specimens of 43 species of primates through a computed tomography scan.
It found that all primates except for humans had vocal membranes, in addition to vocal cords. In addition, this study of laryngeal anatomy in primates showed that humans also don’t have balloon-like structures called air sacs. These air sacs help some primates produce loud and resonant sounds. They also help monkeys, and apes avoid hyperventilating — breathing abnormally fast.
The scientists noted that the gradual loss of these structures led to stable vocal systems in humans. And this gave humans a remarkable evolutionary ability to control their pitch and speak. Such speech allows humans to voice their thoughts using complex and clear sounds.
Nishimura said that complex vocal structures in other primates could make it harder to control their pitches. And our more straightforward articulated design may have worked in our favor.
“We argue that the more complicated vocal structures of nonhuman primates can make it difficult to control vibrations precisely,” said Nishimura.
Tecumseh Fitch, an evolutionary biologist at Austria’s University of Vienna, also said that complex vocal structures allow other primates to make higher calls than humans. “But they make voice breaks and noise vocal irregularity more common,” Fitch said.
Evolution of a larynx
“The larynx is the organ of voice, which creates the signals we use to sing and speak,” Fitch said. Apart from talking, humans also use the larynx for breathing and swallowing.
However, it is still unclear when modern humans lost the complex vocal membranes found in other primates. And this study only focused on living primates because laryngeal soft tissues are not likely to be preserved in fossils.
Scientists say humans split from their closest relatives, the chimpanzees, about 6-7 million years ago. And the laryngeal evolution occurred some time after that.
Fitch believes that the evolution of the human voice box may have started with the human predecessor, Australopithecus. Australopithecus had both human-like and ape-like features, and he first appeared in Africa about 3.85 million ago. The laryngeal changes may also have occurred in a later genus, Homo, which first appeared about 2.4 million years ago in Africa. In comparison, homo sapiens (wise man) appeared about 300,000 years ago.
Bottom line; scientists are still speculating about the laryngeal evolution timeline in humans.
Other factors that aided complex speech in humans
The laryngeal simplification may have aided pitch control, but other factors have also played a crucial role. For example, Fitch noted other anatomical changes, such as the change in the position of the larynx, also led to speech over time. In addition, specific genes and a different brain structure may also be behind a human’s ability to speak.
“Speech and language are related, but not synonymous,” said Harold Gouzoules. He is a psychologist and primatologist from Emory University in Atlanta.
Sound production in all primates, both humans and nonhumans, is similar. Here, air from the lungs causes vibration of the vocal cords. Then this acoustic energy moves through the pharyngeal, oral, and nasal cavities producing specific frequencies influenced by the vocal tract.
It’s pretty fascinating that an evolutionary simplification led to the complexity of human speech. As Fitch rightly puts it, “By losing a trait, you might open the door to some new adaptations.”