title: Disproportionate Cochlear Length in Genus Homo Shows a High Phylogenetic Signal during Apes' Hearing Evolution.
abstract: Changes in lifestyles and body weight affected mammal life-history evolution but little is known about how they shaped species' sensory systems. Since auditory sensitivity impacts communication tasks and environmental acoustic awareness, it may have represented a deciding factor during mammal evolution, including apes. Here, we statistically measure the influence of phylogeny and allometry on the variation of five cochlear morphological features associated with hearing capacities across 22 living and 5 fossil catarrhine species. We find high phylogenetic signals for absolute and relative cochlear length only. Comparisons between fossil cochleae and reconstructed ape ancestral morphotypes show that Australopithecus absolute and relative cochlear lengths are explicable by phylogeny and concordant with the hypothetized ((Pan,Homo),Gorilla) and (Pan,Homo) most recent common ancestors. Conversely, deviations of the Paranthropus oval window area from these most recent common ancestors are not explicable by phylogeny and body weight alone, but suggest instead rapid evolutionary changes (directional selection) of its hearing organ. Premodern (Homo erectus) and modern human cochleae set apart from living non-human catarrhines and australopiths. They show cochlear relative lengths and oval window areas larger than expected for their body mass, two features corresponding to increased low-frequency sensitivity more recent than 2 million years ago. The uniqueness of the "hypertrophied" cochlea in the genus Homo (as opposed to the australopiths) and the significantly high phylogenetic signal of this organ among apes indicate its usefulness to identify homologies and monophyletic groups in the hominid fossil record.
authors.affiliation: Hominid Evolutionary Biology, AMIS-UMR 5288 CNRS, University of Toulouse (Paul Sabatier), Toulouse, France; Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa.
authors.forename: J
authors.initials: J
authors.lastname: Braga
authors.affiliation: Statistics and Probabilities Team, Institute of Mathematics of Toulouse, UMR 5219 CNRS-Université de Toulouse (Paul Sabatier), Toulouse, France.
authors.forename: J-M
authors.initials: JM
authors.lastname: Loubes
authors.affiliation: Hominid Evolutionary Biology, AMIS-UMR 5288 CNRS, University of Toulouse (Paul Sabatier), Toulouse, France.
authors.forename: D
authors.initials: D
authors.lastname: Descouens
authors.affiliation: Hominid Evolutionary Biology, AMIS-UMR 5288 CNRS, University of Toulouse (Paul Sabatier), Toulouse, France.
authors.forename: J
authors.initials: J
authors.lastname: Dumoncel
authors.affiliation: Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa.
authors.forename: J F
authors.initials: JF
authors.lastname: Thackeray
authors.affiliation: Institut d'Anatomie Normale et Pathologique, Faculté de Médecine de Strasbourg, Strasbourg, France.
authors.forename: J-L
authors.initials: JL
authors.lastname: Kahn
authors.affiliation: South African Nuclear Energy Corporation, Pelindaba, North West Province, South Africa.
authors.forename: F
authors.initials: F
authors.lastname: de Beer
authors.affiliation: Laboratoire Evolution et Diversité Biologique, UMR 5174 CNRS, University of Toulouse (Paul Sabatier), Toulouse, France.
authors.forename: A
authors.initials: A
authors.lastname: Riberon
authors.affiliation: South African Nuclear Energy Corporation, Pelindaba, North West Province, South Africa.
authors.forename: K
authors.initials: K
authors.lastname: Hoffman
authors.affiliation: Hominid Evolutionary Biology, AMIS-UMR 5288 CNRS, University of Toulouse (Paul Sabatier), Toulouse, France.
authors.forename: P
authors.initials: P
authors.lastname: Balaresque
authors.affiliation: Royal Museum for Central Africa, Tervuren, Belgium and Laboratory of Histology and Neuropathology, Université libre de Bruxelles, Brussels, Belgium.
authors.forename: E
authors.initials: E
authors.lastname: Gilissen
mesh_terms: D000818:Animals; D000885:Anthropology, Physical; D005075:Biological Evolution; D049628:Body Size; D051079:Catarrhini / Q000033:anatomy & histology* / Q000145:classification / Q000502:physiology; D003051:Cochlea / Q000033:anatomy & histology* / Q000502:physiology; D005580:Fossils; D006309:Hearing / Q000502:physiology*; D006801:Humans; D010802:Phylogeny