Doubts Cast on Oldest Fossil Case of Deafness

I recently wrote an article on this site about the possible occurrence of Surfer’s Ear in Neanderthals. During that article we mostly discussed what might have caused these external auditory exostoses (EAEs), but I didn’t discuss what implications these might have had for the Neanderthal’s hearing.

Until this month (October 2019) if you had looked up the oldest suspected case of deafness in the fossil record you would have probably found a 430,000 year old Neanderthal skull called ‘Cranium 4’. This skull, from a site in Northern Spain, showed very pronounced exostoses that appeared to almost completely obstruct the auditory canal. Based on this, the authors of the original study back in 1997 suggested that this individual was probably deaf.

SierraAtapuerca
Panorámica de la Sierra de Atapuerca, Northern Spain. Near the site where the skull was recovered. Source: Wikimedia Commons

Then, this October, a new study was published taking a fresh look at Cranium 4. Since 1997 CT scanning and computer modelling techniques have moved on a bit, which allowed researchers to create a much more detailed 3D model of the skull’s inner ear. They then plugged the figures generated from this model into a computer program designed to predict hearing ability. This program has been used previously on other skulls recovered from the same location, which lacked these ear exosteses, and were therefore interpreted as having unaffected hearing. In those cases the program agreed with the human researchers, and suggested these individuals probably had hearing very similar to that of modern humans.

They then turned the program on Cranium 4. To everyone’s surprise the program suggested that the growths in its ears probably had very little, if any, effect on this individual’s hearing. The exosteses seem to have reduced the cross-section of the ear canal by about 52%. By comparing to this to the modern day medical literature the researchers suggest the program was correct, and this would have had very little impact on hearing.

If accurate then these results are very interesting, and they have important implications for future studies on other fossil skulls. Applying this technique to other fossil skulls could change our understanding of these individuals’ lives and health. So watch this space!

 

Reference:

Mercedes Conde-Valverde, et al. A revision of the conductive hearing loss in Cranium 4 from the Middle Pleistocene site of Sima de los Huesos (Burgos, Spain)Journal of Human Evolution, 2019; 135: 102663

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