A research team led by scientists of the Max Planck Institute
for Evolutionary Anthropology scanned the skulls of neanderthals and found the
small middle ear ossicles, which are important for hearing, still preserved
within the cavities of the ear. To their surprise, the neanderthal ossicles are
morphologically distinct from the ossicles of modern humans. Despite the
differences in morphology, the function of the middle ear is largely the same
in the two human species. The authors relate the morphological differences in
the ossicles to different evolutionary trajectories in brain size increase and
suggest that these findings might be indicative of consistent aspects of vocal
communication in modern humans and neanderthals. These findings are also of
importance for shedding light on the emergence of human spoken language, which
can only be inferred indirectly from the archaeological and fossil record.
The three bones of the middle ear (hammer, anvil, stapes) make
up the ossicular chain. This bony chain, which is found in all mammals is
dedicated to the transmission of sound waves from the tympanic membrane to the
inner ear and helps in amplifying the energy of airborne sound in order to
allow the sound wave to travel within the fluid-filled inner ear. Moreover, the
ear ossicles are not only important for correct hearing but are also the
smallest bones of our body. Thus, it does not surprise that the ossicles are
among the most rarely found bones in the mammalian fossil record including the
one of human ancestors. Given their important role in audition this lack of
knowledge has ever been frustrating for researchers interested in studying
hearing capacities of extinct species.
Tiny bones still present
This also applies to our closest extinct relatives -- the
neanderthals whose communicative capacities including existence of human spoken
language is a major scientific debate ever since the first discovery of
neanderthal remains. A research team led by Alexander Stoessel from the Max
Planck Institute for Evolutionary Anthropology in Leipzig used high-resolution
computer tomography scans of neanderthal skulls and systematically checked for
ossicles that potentially became trapped within the cavity of the middle ear.
And indeed, the researchers found ear ossicles in 14 neanderthal individuals
coming from sites in France, Germany, Croatia and Israel, resulting in the
largest sample of ear ossicles of any fossil human species. "We were
really astonished how often the ear ossicles are actually present in these
fossil remains, particularly when the ear became filled with sediments"
says lead researcher Alexander Stoessel.
After virtually reconstructing the bones, the team -- which also
included scientist from the Friedrich-Schiller University in Jena and the
University College in London -- compared them to ossicles of anatomically
modern humans and also chimpanzees and gorillas which are our closest living
relatives.
Since ossicles are not only small but also complex-shaped the
researchers compared them by means of three-dimensional analysis that uses a
much larger number of measuring points allowing for examination of the
three-dimensional shape of a structure. "Despite the close relationship
between anatomically modern humans and neanderthals to our surprise the ear
ossicles are very differently shaped between the two human species" says
Romain David who was involved in the study.
Based on the results of the morphological comparison the
research team examined the potential reasons for these different morphologies.
In order to see if these differences may affect hearing capacity of
neanderthals and modern humans or reflects a tight relationship with the base
of the skull they also analyzed the structures surrounding the ear ossicles.
The outcome of this analysis was surprising, again since the functional
parameters of the neanderthal and modern human middle ear are largely similar
despite contrasting morphologies.
Similar communication skills in archaic humans
Instead, the team found the ear ossicles strongly related to the
morphology of the surrounding cranial structures which also differ between the
two human groups. The researchers attribute these differences to different
evolutionary trajectories that neanderthals and modern humans pursued in order
to increase their brain volume which also impacted the structures of the
cranial base which the middle ear is a part of. "For us these results
could be indicative for consistent aspects of vocal communication in
anatomically modern humans and neanderthals that were already present in their
common ancestor" says Jean-Jacques Hublin who is an author of this study
and continues "these findings should be a basis for continuing research on
the nature of the spoken language in archaic hominins."
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