Genetics of Hearing
Tejas Yerramilli
Another one of our five senses, hearing is a complex tool that has allowed us to interact with one another through speech and music. Without hearing, homo sapiens would have gone extinct long ago due to predators. Supposing we did get past predators without hearing, however unlikely, humans would have still met their demise relatively early on. The reason for this sudden extinguishment of human life would have been our direct competitor many millennia ago – Neanderthals. About 45,000 years ago in Europe, Homo Sapiens and Neanderthals lived in close proximity, hunting for the same prey, eating the same things, and even sharing the same territory. In a battle between humans and Neanderthals, the latter would easily overpower us. With a shorter, much stockier anatomy, Neanderthals were a forced to be reckoned with. All this brings me back to my main point. Neanderthals are extinct. Why? Because humans got more resources, and faster. The reason for this was communication. With the power of listening to people near them, humans moved in one unit, rather than the Neanderthals moving independently. The power of hearing has guided us through about 200,000 years of evolution, and hearing isn’t going anywhere soon. Let’s look into the genetics of what makes hearing, hearing.
DISORDERS
50-60% of hearing loss in infants is caused by genetic reasons, and some of the more well-known ones are as follows.
Otosclerosis
Otosclerosis is a genetic disease that is characterized by hearing loss because of the ear being unable to amplify sound. The Punnett square below is a model of what it would look like, with the assumption that it would not be a heterozygote because of the rareness of the disease. Although the disease is rare, it is dominant (another important point is that although dominant, the mutation that causes Otosclerosis has reduced penetrance).
Otosclerosis is a very serious disease, as it can be chronic, lasting for years and sometimes a lifetime. The cause of this disease are the bones that vibrate and allow you to hear not being able to move to their full extent.
Usher’s Syndrome
Usher’s Syndrome is an extremely rare genetic disease which symptoms include hearing loss and an eye disease called retinitis pigmentosa, although we are going to focus on the hearing side of things. The hearing loss is caused by unusual development of sound receptor cells in the inner part of the ear, which transmit messages to the brain. Usher’s Syndrome is a recessive trait, and the abnormal cell formation is rare, which is probably why the disease itself is exceedingly uncommon.
There are 3 types of Usher’s Syndrome, each with their own set of symptoms. Type 1 results in being almost totally deaf at birth, with hearing aids most likely being futile. A person with type 1 Usher’s Syndrome might be a viable candidate for cochlear implants, with transmit sound directly from the ear to the brain.
Type 2 is a slight improvement, with having moderate-severe hearing loss at birth with hearing aids being an option that they could benefit from.
Type 3 is the least severe of the 3, with normal hearing at birth and some hearing loss in their mid-teens. People with type 3 could also benefit from a hearing aid.
Parts of the ear
Pinna – The pinna is part of the ear that is on the outside, or visible. It is responsible for taking sound waves and transmitting them to the ear canal.
Ear canal – This part of the ear acts like a passage to the ear drum.
Ear drum – Just like in a real drum, the ear drum is skin stretched across the area of the ear canal, and when sound waves reach it, the small bones vibrate and send a message to the inner ear.
Middle ear – The middle ear’s job is on the simpler side, with its core function being to transmit sound from the outer part of the ear to the inner ear.
Eustachian tube – This tube drains connects the middle ear to the throat, and drains fluid while maintaining the correct air pressure in your ears.
Inner ear – The inner ear functions in two key ways. The first one is changing the vibrations coming in into electrical signals for our brain to understand. The second, lesser known one, has to deal with balance. Your inner ear has fluid inside of it, and as that fluid moves, it helps tell your brain which direction you are facing. 
Curious Questions
Why is the ear shaped the way it is?
Our pinna or the visible part of our ear is shaped in its iconic yet relatively unusual way because of its ability to funnel sound in this shape. As seen above, the pinna is meant to transmit sound/vibrations to the ear canal, so even if it does look weird, the shape of our ears is justified.
Do you hear more with big ears?
Contrary to popular belief, the notion that having bigger ears lets you hear more things is a fallacy. Even if one person’s visible ear is bigger than another’s, the actual ear canal is usually extremely similar in size, making both individuals hearing approximately the same provided they have the same circumstances to begin with.
Are our ears unique?
Just like our thumb print, no two sets of ears are alike. Some people have big ears, small ears, earlobes a well. Surprisingly, there is a distinct difference in ears that usualaly goes unnoticed. Ear lobes can either be attached or detatched from the head, with detatched being more common as it is the dominent allele. In short, there are many things that make each human unique.
Conclusion
The ear and hearing have allowed us to communicate, get past predators, and much, much more. 50-60% of hearing loss in infants is genetic, and some well known ones are Otosclerosis and Usher’s Syndrome. The former is known for causing hearing loss by inhibiting the ear from amplifying sound, and the latter has 3 distinct types varying in sympotoms and severity. The ear is comprised of the pinna, ear canal, ear drum, middle ear, eustachian tube, and inner ear, all of them performing a critical role in how we hear. The pinna or visible ear is shaped in its peculiar form because its main function is to funnel vibrations or sound into the ear canal, and the ears shape is optimized for that task. Big ears do not neccesarly mean that you hear more things, as peoples ear canals are usually the same size. Our “ear prints” if you will, are completely unipqe to us because of the size of the ear, the earlobes, and many more things. Our ears and are extremely importatant to our well being, and hopefully this post gave you a little more insight as to how they work 😊.
Vocab –
Demise – A person’s death.
Neandrathals – an extinct species of human that was widely distributed in ice-age Europe between c. 120,000–35,000 years ago, with a receding forehead and prominent brow ridges. The Neanderthals were associated with the Mousterian flint industry of the Middle Paleolithic.
Stockier – Broad and sturdily built.
Characterized – Describe the distinctive nature or features of.
Chronic – Persisting for a long time or constantly recurring.
Abnormal – Deviating from what is normal or usual, typically in a way that is undesirable or worrying.
Functions – An activity or purpose natural to or intended for a person or thing.
Fallacy – A mistaken belief, especially one based on unsound argument.
Sources –
Learning Medicine 