title: Monkey vocal tracts are speech-ready.
abstract: For four decades, the inability of nonhuman primates to produce human speech sounds has been claimed to stem from limitations in their vocal tract anatomy, a conclusion based on plaster casts made from the vocal tract of a monkey cadaver. We used x-ray videos to quantify vocal tract dynamics in living macaques during vocalization, facial displays, and feeding. We demonstrate that the macaque vocal tract could easily produce an adequate range of speech sounds to support spoken language, showing that previous techniques based on postmortem samples drastically underestimated primate vocal capabilities. Our findings imply that the evolution of human speech capabilities required neural changes rather than modifications of vocal anatomy. Macaques have a speech-ready vocal tract but lack a speech-ready brain to control it.
authors.affiliation: Department of Cognitive Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.; Haidlhof Research Station, University of Vienna/University of Veterinary Medicine Vienna, Bad Vöslau, Austria.
authors.forename: W Tecumseh
authors.identifier: 0000-0003-1830-0928
authors.initials: WT
authors.lastname: Fitch
authors.affiliation: Artificial Intelligence Laboratory, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium.
authors.forename: Bart
authors.initials: B
authors.lastname: de Boer
authors.affiliation: Princeton Neuroscience Institute, Princeton University, Princeton, NJ 08544, USA.; Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA.
authors.forename: Neil
authors.initials: N
authors.lastname: Mathur
authors.affiliation: Princeton Neuroscience Institute, Princeton University, Princeton, NJ 08544, USA.; Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA.; Department of Psychology, Princeton University, Princeton, NJ 08544, USA.
authors.forename: Asif A
authors.initials: AA
authors.lastname: Ghazanfar
mesh_terms: D000818:Animals; D000882:Haplorhini / Q000033:anatomy & histology*; D007830:Larynx / Q000033:anatomy & histology*; D013060:Speech; D014828:Vocalization, Animal
keywords: Speech; formant frequency; language evolution; primate communication; vocal tract