Why don’t we have the ability to “close” our ears, just like our eyes?
In: Biology
Evolution is not a game of optimization, it is a game of “good enough”. Survive until you can reproduce a couple of times and that’s enough. There was no evolutionary pressure strong enough to warrant the ability to shut our ears, so we don’t have that ability.
In fact, most of the reasons to shut your ears are man made. Cars, planes, trains, gunshots. In survival settings, shutting your ears is almost purely a downside. The loud noises are things wed definitely want to hear so we know to move. A falling tree, the roar of a predator, the sounds of violence, thunder. All calls to run for cover. Closing of the eyes has benefits. Protection from harsh light (like the sun, omnipresent), protection from dust and debris. The eyes are front facing, and more likely to be damaged.
The “ability to close our eyes” is also known as “eyelids”. We evolved eyelids because our eyes would dry out or get junk in them otherwise, which could permanentaly damage them. We generally do not have this issue with our ears, or the cases where we do (e.g. water in your ears) are minor enough to not cause natural selection to “solve” the problem
We actually do have some limited ability to “close our ears” via the tensor tympani muscle: https://en.wikipedia.org/wiki/Tensor_tympani_muscle
When we hear a loud sound, we have a reflex that moves our ear bones away from the ear drum, dampening sound. However, unlike eyelids, it does not eliminate sound completely
In order to work properly as lenses, our eyes need to have a wet surface, keeping this surface from drying out is one of the primary ourposes of eyelids. Ears don’t share this same requirement.
Believe it or not but earplug earrings are a thing. We might not have evolved a way to naturally close our ears, but we sure have invented the next best thing. Looks like the inventors probably had the same idea as you.
We kind of do, actually.
IDK the names for the bones or muscles in the ear, but there is a mechanism that will disengage one of your hearing bones from your eardrums if the noise gets loud enough. It’s not perfect and will not prevent all sound from entering your inner ear (the part that gets damaged by too loud noises), but your eyelids also don’t block out all light and you can still go blind with your eyes closed if there’s too much light.
Some people like my friend and I have learned the ability to “close” our ears, to help from loud sounds and just do it for fun. I didn’t believe it myself but I accidentally did it one day when I was yawning and then learned I could control it.
Unlike our eyes, which need to be protected from light and can be closed to rest, our ears are more about detecting sound and balance. They’re always ‘open’ to help us stay aware of our surroundings. Plus, closing them would interfere with our ability to maintain balance and hear important sounds.
We kind of do actually. There are at least two reflex arcs in our inner ear that desensitize our hearing (kind of like how we kick out our leg when the knee tendon is struck with a small hammer):
The first is the **cochlear reflex AKA the acoustic reflex**. [This reflex arc triggers in response to loud sound](https://en.wikipedia.org/wiki/Acoustic_reflex). The stapedius muscle contracts, stiffening the tiny bones in our ears that mechanically conduct sound from the eardrum and making sounds less intense to prevent damage to our hearing.
The **tensor tympani** [does a similar thing](https://en.wikipedia.org/wiki/Tensor_tympani_muscle), IIRC you can even activate it manually when you cringe or scrunch up your face, which is why you instinctively do that when you hear a very loud noise.
A reflex in the **inner ear cells of the basilar membrane** in the cochlea also helps [control the sensitivity of the basilar membrane](https://en.wikipedia.org/wiki/Basilar_membrane), preventing damage to the hair cells that transform mechanical sound waves to neural impulses.
We do but it’s not really under a functional level of voluntary control. It’s the rumbling you hear in your ears when you hear a very loud or sharp noise- your tensor tympani muscle sealing off as much of your ear drum as possible from the noxious stimulus.
Latest Answers