Neanderthal Eustachian tube morphology lowered population‐wide fitness and contributed to extinction

Abstract

Among modern humans, otitis media (benign otitis media with effusion and acute otitis media, AOM) is the second most common pediatric clinical conditions. Acute otitis media is a fatal disease that can result in meningitis and pneumonia if untreated. Osteological signs of this disease may be found in erosion patterns on the middle ear ossicles, ossification of the tympanic membrane, and a lack of mastoid pneumatization. Recent studies report that nearly all known Neanderthal ossicles exhibit erosion patterns consistent with chronic AOM. To account for the anatomical basis of this apparent disease susceptibility, we assessed the morphological configuration of the cartilaginous Eustachian tube (CET) and dilator tubae (DT) musculature among a modern human growth series ranging from newborns to adults (n=442) and a sample of Neanderthals (La Chapelle aux Saints 1, La Ferrassie 1, Forbes Quarry 1, Saccopastore 1, Guattari 1) and mid‐Pleistocene pre‐Neanderthals (Atapuerca 5 and Steinheim 1). We performed morphometric analysis of the bony upper respiratory tract boundaries. A total of 31 bilateral and midline 3D landmarks were used and coordinate data were subjected to Procrustes‐fitting for geometric morphometric analysis and calculation of univariate measures.Neanderthals exhibited tall narrow choanae and greater overall robusticity. La Ferrassie 1 and Forbes Quarry 1 possessed extremely infant‐like CET orientation relative to the Frankfurt Horizontal Plane while other specimens had adult‐like or intermediate orientation. Choanal orientation among all Neanderthals was horizontal as among human infants. This trait occurred alongside a relatively adult‐like elongation and vertical orientation of the DT whereas the pre‐Neanderthals were distinguished primarily by an extremely short DT relative to Neanderthals and modern humans.The morphological configuration of Neanderthals was unlike any modern human population or growth stage. Differences between these groups appear to be species‐level with Neanderthals retaining infant‐like horizontal orientation of both the choanae and (among some) CET into adulthood. Neanderthal children were probably susceptible to AOM for longer periods of development. While modern human children experience steep reduction in disease occurrence at approximately six years of age with changes in both CET length and orientation, Neanderthal children would have remained susceptible as there was no such growth change in CET orientation. This could have impacted population‐wide fitness when sympatric modern humans invaded Neanderthal habitats and competed for limited resources. AOM should thus be considered among the many potential factors involved in the extinction of the Neanderthals.Support or Funding InformationNational Science Foundation, Grant number 1128901This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.