A so-called evolutionary simplification of the larynx led to human speech.
This trait is still present today.
Researchers are unsure at what point in history it evolved.
Scientists have spotted the evolutionary modifications in the voice box that make humans able to speak compared to other primates. They did this through an examination of the voice box, or larynx, in 43 species of primates.
No vocal membrane
To be exact, the scientists studied the laryngeal anatomy in chimpanzees, gorillas, orangutans, gibbons, macaques, guenons, baboons, mandrills, capuchins, tamarins, marmosets, and titis.
What they found was that humans differ from apes and monkeys in lacking an anatomical structure called a vocal membrane and balloon-like laryngeal structures called air sacs responsible for the loud calls performed by apes.
The lack of these elements is what causes a stable vocal source in humans that is critical to the evolution of speech. This simplification of the larynx is what gave humans excellent pitch control with stable speech sounds that result in modern-day speaking.
“We argue that the more complicated vocal structures in nonhuman primates can make it difficult to control vibrations with precision,” told The Guardian primatologist Takeshi Nishimura of Kyoto University’s Center for the Evolutionary Origins of Human Behavior in Japan and lead author of the new paper.
“Vocal membranes allow other primates to make louder, higher-pitched calls than humans – but they make voice breaks and noisy vocal irregularity more common,” said evolutionary biologist and study co-author W Tecumseh Fitch of the University of Vienna.
Humans, on the other hand, use the larynx for talking, breathing, and swallowing.
“The larynx is the organ of voice, which creates the signal we use to sing and speak,” Fitch added.
When did the larynx first appear?
Since the researchers only studied living species (because soft tissues are not preserved in fossils) , they could not determine at what point in history these evolutionary changes were made.
The so-called laryngeal simplification could have appeared with the Australopithecus, which first appeared in Africa roughly 3.85m years ago, or later in our genus Homo, which first appeared in Africa about 2.4m years ago.
The scientists do note that the evolutionary simplification of the larynx “did not give us speech by itself”, Fitch explained, stating that other additional changes such as the position of the larynx took place to lead to speech.
He further notes that it is interesting that the increased complexity of human spoken language was engendered by an evolutionary simplification.
“I think it’s pretty interesting that sometimes in evolution ‘less is more’ – that by losing a trait you might open the door to some new adaptations,” Fitch concluded.
Human speech and language are highly complex, consisting of a large number of sounds. The human phonal apparatus, the larynx, has acquired the capability to create a wider array of sounds, even though previous work has revealed many similarities between our larynx and those in other primates. Looking across a large number of primates, Nishimura et al. used a combination of anatomical, phonal, and modeling approaches to characterize sound production in the larynx (see the Perspective by Gouzoules). They found that instead of the human larynx having increased complexity, it has actually simplified relative to other primates, allowing for clearer sound production with less aural chaos.