Morphology and function of Neandertal and modern human ear ossicles

Abstract

The diminutive middle ear ossicles (malleus, incus, stapes) housed in the tympanic cavity of the temporal bone play an important role in audition. The few known ossicles of Neandertals are distinctly different from those of anatomically modern humans (AMHs), despite the close relationship between both human species. Although not mutually exclusive, these differences may affect hearing capacity or could reflect covariation with the surrounding temporal bone. Until now, detailed comparisons were hampered by the small sample of Neandertal ossicles and the unavailability of methods combining analyses of ossicles with surrounding structures. Here, we present an analysis of the largest sample of Neandertal ossicles to date, including many previously unknown specimens, covering a wide geographic and temporal range. Microcomputed tomography scans and 3D geometric morphometrics were used to quantify shape and functional properties of the ossicles and the tympanic cavity and make comparisons with recent and extinct AMHs as well as African apes. We find striking morphological differences between ossicles of AMHs and Neandertals. Ossicles of both Neandertals and AMHs appear derived compared with the inferred ancestral morphology, albeit in different ways. Brain size increase evolved separately in AMHs and Neandertals, leading to differences in the tympanic cavity and, consequently, the shape and spatial configuration of the ossicles. Despite these different evolutionary trajectories, functional properties of the middle ear of AMHs and Neandertals are largely similar. The relevance of these functionally equivalent solutions is likely to conserve a similar auditory sensitivity level inherited from their last common ancestor.middle ear | homo | 3D shape | covariation T he hominin fossil record can only provide indirect information about auditory capacities of our extinct relatives. Inferences about the evolution of the human sense of hearing require understanding of the interplay between form and function in extant species. When auditory capacities are visualized as audiograms, plotting the sensitivity for different frequencies, anatomically modern humans (AMHs) differ from the W-shaped pattern found in most anthropoid primates. AMHs are characterized by a drastically lowered high-frequency cutoff and maintaining high sensitivity in the low to midfrequencies, resulting in a U-shaped audiogram (1-7). In primates, such hearing variability is assumed to be partly related to forms of vocalization and habitat acoustics (8-10). Diverse hearing capabilities are also related to the morphology of the diminutive middle ear ossicles housed in the tympanic cavity (11, 12). The malleus, incus, and stapes form the ossicular chain that connects the tympanic membrane to the oval window of the inner ear. These bones play an important role in audition by amplifying and regulating the sound waves transmitted to the cochlea (11,(13)(14)(15). In particular, the middle ear acts as a transformer that matches the impedances between the air and the pe...

Neanderthal language revisited: not only us

“…biorxiv.org/content/early/2017/10/03/106955]), breathing control, and acoustic sensitivity (audiograms) involved in modern speech. Since then, there is better evidence that the Neanderthal cochlear volume and audition were similar to modern humans and different from the chimpanzees [67], that despite differences in the morphology of the ear ossicles (probably due to differences in cranium) they were functionally very similar probably due to selective pressures for the maintenance of the same auditory profile [68 ], while the biomechanical modeling of the Kebara 2 Neanderthal hyoid showed that it is extremely similar to the modern human one in more than just shape [69 ].…”

“…biorxiv.org/content/early/2017/10/03/106955]), breathing control, and acoustic sensitivity (audiograms) involved in modern speech. Since then, there is better evidence that the Neanderthal cochlear volume and audition were similar to modern humans and different from the chimpanzees [67], that despite differences in the morphology of the ear ossicles (probably due to differences in cranium) they were functionally very similar probably due to selective pressures for the maintenance of the same auditory profile [68 ], while the biomechanical modeling of the Kebara 2 Neanderthal hyoid showed that it is extremely similar to the modern human one in more than just shape [69 ].Neanderthals had elaborate cultural adaptations that were virtually identical to AMH (until the latter developed the Upper Paleolithic toolkit after the demise of the Neanderthals), they flexibly adapted to their ecologies, buried their dead (apparently with mortuary ceremonies), built large structures, penetrated deeply into caves, and seem to have adorned themselves with drilled beads and feathers. They inhabited a climatic range (from Arctic to Mediterranean) requiring the extended ability to use culture as a buffer for ecological adaptation, and they interacted repeatedly with AMH over tens of thousands of years, exchanging genes, parasites and culture.…”

Reconstructing the Neanderthal Eustachian Tube: New Insights on Disease Susceptibility, Fitness Cost, and Extinction

“…This potentially autapomorphic configuration may have impacted the efficiency of middle ear aeration and hence, disease susceptibility during their childhood years. Evidence of osteological pathology congruent with OM has been reported in many Neanderthal specimens with perhaps the most compelling observation by Stoessel et al (2016) Quina H5, Le Moustier 1, Pech de l'Azé 1). All the mallei and incudes recovered (N = 17) exhibited substantial amounts of pitting lesions similar to such erosions found in modern Fig.…”

“…All the mallei and incudes recovered (N = 17) exhibited substantial amounts of pitting lesions similar to such erosions found in modern patients with chronic episodes of OM (Sade et al, ). Stoessel et al () also reported additional evidence of OM within the tympanic bone of La Quina H5. A study of Neanderthal ossicles from Amud, Israel by Quam and Rak () also confirmed the presence of pitting lesions.…”

“…patients with chronic episodes of OM (Sade et al, 1982). Stoessel et al (2016) also reported additional evidence of OM within the tympanic bone of La Quina H5. A study of Neanderthal ossicles from Amud, Israel by Quam and Rak (2008) also confirmed the presence of pitting lesions.…”