Our ability to hear is a marvel of physical design, the interlocking work of various sensing apparatuses and interpreting mechanisms. Scientists today have been examining where our hearing ability comes from and the answers are as surprising as they are ancient.
Your 300 Million Year Old Ear
One of the oldest systems in your ear is the vestibular system in the inner ear which helps us maintain balance and enact tightly coordinated motions. The vestibular system is comprised of three main semicircular ducts that help us align ourselves spatially. The ducts are aligned perpendicular to each other, mimicking the mathematical concept of x, y and z axes – ascribing height, width and depth to space. The ducts are flanked with ololiths that log linear movements of the body.
The vestibular system coordinates multiple bodily functions to maintain our sense of balance. Subtle signals from the vestibular system give our eyeballs a “steady cam” ability to provide us with smooth visual perception even when we are in motion. Vestibular input lets our eyes compensate for our motion and steadies our view. As futuristic as the vestibular devices get, they are, in fact, incredibly ancient – probably originating in prehistoric underwater life forms and then adapting and evolving as creatures began to move out of water and onto land.
Recent study at McGill University in Montreal and John Hopkins University in Baltimore show that the vestibular system has layered functions. The oldest impulses of the system correlate with its origins in underwater movement – slow sweeping spatial skills and balance that probably developed 300 million years ago in sea life.
A second newer skill set is also present in our vestibular system today – an ability to make sharp split-second decisions about movement and balance. This sort of ability undoubtedly evolved for land use where the risk of falling over and the need for sharper quicker motions is both more possible and more present in air rather than in water. The McGill research group noted the dual functioning of the vestibular system with respect for how older functioning is augmented by newer, land-based skills that evolved.
When Something Sounds Fishy
Our ear’s connection to ancient marine life doesn’t end there. Inside the middle ear we have three tiny bones, colloquially they are the hammer, the anvil and the stirrups, that form a bone chain to the inner ear, giving our hearing added accuracy and range. These three bones have direct correlation to jaw bones present in reptiles and fish. Ancestral fish like zebrafish have preserved these ancient jawbone arrangements in their jaw structure today.
It is evident that as the evolution of mammals occurred small bones that once held functions in the jaw slowly became removed from the jaw and repurposed as hearing apparatus. This sort of dynamic evolutionary change is called “exaptation”. Over the past century a fossil record has been unearthed that clarifies the journey of the bones from reptilian jaw to mammalian ear. Critical links uncovered in this evolutionary chain make it one of the best documented incidences of evolutionary exaptation.
In mammals the three inner ear bones are known as ossicles. Problems within the ossicles can lead to hearing loss just like damaged hair cells in the inner ear. Malformed bones can limit how sound is transmitted and perceived.
Because of the similarity of ancient jaw bones and modern middle ear ossicles, some research into the ossicle bones is first modeling study within fish and reptiles where the analogous jaw structures are present. At the Keck School of Medicine at the University of Southern California, researchers are studying conductive hearing loss by first following genetic mutations in zebrafish.
By studying the history of the ears’ components, researchers today are finding new approaches to our knowledge of hearing and balance and expanding our understanding of the work our ears do. In a long history of preservation and adaptation, studying the origins of human hearing is poised to lead us into the future of hearing care.
Hearing Health Care Center
When you have an issue with your hearing, it’s time to set up an appointment with Hearing Health Care Center. Our amazing staff is on hand to help you find the solutions you need for lifelong better hearing. We bring comprehensive understanding and thorough testing to your hearing care. Set up an appointment today!