An ongoing debate among scientists, on why chimpanzees and other nonhuman primates cannot speak or sing like humans, has focused mainly on evolutionary changes in human brain development. Attention has now expanded to anatomical changes of the voice box that may have played a role in our capacity to produce complex sounds.
A team of researchers from Japan and Europe has now revealed that evolution of the human larynx contributed to the stable voices we use to communicate. Unexpectedly, these changes do not include the addition of structures but rather the loss of specific vocal folds or cords in the larynx.
“Paradoxically, the increased complexity of human communication involved a simplification of our vocal anatomy,” says lead author Takeshi Nishimura of KyotoU’s Center for the Evolutionary Origins of Human Behavior, or EHUB.
Most primates have thin, ribbon-like vocal membranes rising out of their vocal folds. The loss of these air sacs seen in chimpanzees and other apes seems to have provided a stable voice quality and controllable voice pitch that we humans use when singing or speaking.
Nishimura adds, “Studies by the late Dr Sugio Hayama, on which our work was largely based, showed that evolutionary modifications in the larynx were necessary for the evolution of spoken language. We took his work to the next level, demonstrating that the simpler the vocal fold morphology, the easier it is to control its vibrations.”
Senior author Tecumseh Fitch of the University of Vienna explains that the thin vocal membranes found in the larynx in the team’s large selection of monkeys and apes are specific to nonhuman primates. Based on computer modeling showing how vocal membranes allow nonhuman primates to create their characteristic vocalizations, the team posits that the melodious quality of the human voice directly results from losing these membranes during evolution.
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