To find out how vocal membranes affected spoken sounds, the researchers attached larynges from three deceased chimpanzees and six rhesus macaques that had been euthanized for other experiments to simulated lungs, according to the Times. They found that the vocal membranes and vocal cords vibrated together. ... Without these membranes, humans’ vocal source is more stable, allowing better pitch control and production of long and even-toned sounds, reports Will Dunham of Reuters. “A key thing that distinguishes human speech from animal sounds is our fine-grained control over the sounds we make,” [Associate Professor] Richard Futrell, who studies language processing in humans at the University of California, Irvine, and was not involved in the study, tells New Scientist.

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