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This article is from
Creation 42(1):14–17, January 2020

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Our created ear

“The hearing ear and the seeing eye, the Lord has made them both” (Proverbs 20:12)

by

This article is adapted from the author’s contribution to the book Wonders of Creation: Design in a fallen world which he co-authored with Dr Stuart Burgess and Brian Edwards.
ear

Looking at the ear and how it works, it becomes immediately obvious that there is an awesome and very intricate process underlying our auditory sense. In fact, the human ear is one of the most intricate examples of miniature and sophisticated engineering on the planet.

My background is in mathematics applied to acoustic engineering, having performed research on the role of pressure waves with combustion. This includes very small variations in pressure, called acoustic waves, which travel through the air when we speak. Though small, they can even affect standing flames. That work involves the safety of jet engines which can under a certain phenomenon called ‘resonance’ (when one object vibrates in sympathy with another) amplify acoustic waves such that the vibrations grow and even destroy fan blades in the rotor. As we will see, resonance is an important property in hearing, and in particular in hearing the human voice.

How we hear

Sound is a pressure disturbance in the air. Small cyclical vibrations of pulsing pressure (called ‘acoustic waves’) travelling through the air enter the opening of the ear canal and reach the eardrum (‘tympanic membrane’—see fig. 1).

 semircular-canals
Figure 1. Diagram of the workings of the human ear. The semicircular canals (dark blue) in the inner ear concern balance and are not discussed here.

The resultant small vibrations of the eardrum are then transferred, through three tiny bones called ‘ossicles’ in the middle ear cavity, into the cochlea in the inner ear. Each stage of this system is staggering in its complexity. All mammals have a system with these basic features (see fig. 1). However, there are large differences between mammals, even in the ear canal.

As well as transmitting sound, the canal amplifies it, by resonance. The frequencies at which it resonates depend on its length, shape and volume. (Consider how the air column in a flute vibrates at different frequencies as we change its length by opening it at different points.)

In humans the canal is about 20 mm (0.8 ins) long, while those of cats and dogs are longer and bent at nearly a right angle to give them a horizontal and vertical component; they are designed for amplifying different frequencies to ours.

Different hearing range

Humans hear over a wide range (9 octaves) from about 20 cycles per second (Hertz = Hz) to nearly 20,000 Hz. Dogs hear from about 65–44,000 Hz (again over 9 octaves but shifted upwards compared to humans), while cats have one of the widest ranges of all—over 10 octaves, from 55 to 77,000 Hz.

Even in our twenties we begin to lose the capability of hearing very high frequencies (around 12,000 Hz and above). The human voice carries with it a raft of ‘harmonics’ (multiples of the fundamental frequency at which it is emitted—typically 125–400 Hz), which firstly extends the range at which it is heard, and ensures that each individual voice is unique. This includes the voice of Christ Himself, which all creation obeys. This was demonstrated when He commanded the wind and the waves to obey Him in Mark 4—the same person who spoke all into existence in Creation Week!

The harmonics of the human voice are particularly important between 2,000 Hz and 5,000 Hz since this is the region where different vowel sounds are distinguished. The even higher frequencies enrich the quality of the sounds, particularly in music. The ear canal is just the right length and shape to resonate with ‘speech’ frequencies (that is, the ear canal air vibrations are in sympathy with typical speech modes).

The sound of water

one-penny
Figure 2.

Remarkably, there is another fascinating fact that has emerged in recent research. It has been shown that all sounds from water are produced by the popping of tiny little bubbles of air trapped in the water,1 Each bubble vibrates at a frequency that depends on its size, so flowing water produces a range of audible frequencies. So, the sound of a babbling brook, a flowing waterfall, and the crashing waves on the ocean shore are made by billions of very small air bubbles that are vibrating against the mass of the water that encases them. These countless bubbles all have slightly differing frequencies, but all lie exactly in the range that the human ear amplifies by the acoustic resonance provided by the ear canal.

And these same frequencies are also in the region where human speech is distinctive. It may be significant that God says in His Word that “The voice of the Lord is over the waters; the God of glory thunders, the LORD, over many waters (Psalm 29:3).”

God communicates with clarity and precision through the Scriptures, but also in a more general way through His creation. Which of us has not been moved as we have listened to the beauty of a sparkling stream, the majesty of ocean waves, or the awesome power of a rainstorm?

Furthermore, the frequencies used by songbirds are again in the same range! The remarkable way our ear canal naturally resonates with and amplifies the frequencies of human speech and song, flowing water, and bird song are a further witness to the design inherent in our bodies.

The middle ear’s three ossicle bones

The acoustic signal causes the eardrum to vibrate. This pushes on the malleus (hammer) attached behind, which itself then pushes onto the incus (anvil) bone, which then moves the stapes (stirrup) horizontally (see fig. 1). The first two of these bones are some 5 mm (0.2 inch) long, with the stapes (the smallest bone in our body) smaller still. In fact, all 3 bones will fit with ease on a British 1p coin (c. 20 mm across; see fig. 2).

These are the only bones in the body that do not grow in size after birth. Believers in evolution try to argue that upper and lower parts of the jaw bones of a reptile moved to become the malleus and incus bones, but quietly ignore one of the biggest hurdles to such a story, namely that the jaws of reptiles never stop growing!

 working-of-human-ear
Fgure 3. Diagram of the workings of the human ear.

The ossicle bones need to amplify the signal, because it is now going to pass into a liquid medium in the inner ear (being incompressible, liquid is an impediment to sound). Each of the three are specially shaped to form a lever mechanism such that the stapes (attached to a membrane called the oval window in the cochlea – see fig. 3), moves approximately three times the distance travelled by the malleus. There is also a tenfold smaller area being vibrated in the oval window compared to the tympanic membrane of the ear drum,2 so that the energy transfer involved is almost 100% efficient.

The cochlea of the inner ear

The stapes acts like a pump on the oval window membrane and, cleverly, the membrane of the round window (see fig. 3) expands to compensate for the movement of the liquid inside the cochlea.

 choclea
Figure 4. The cochlea unwound with basilar membrane visible—reminiscent of a xylophone.

If we were to unwind the cochlea (see fig. 4), we would see an ingenious basilar membrane which tapers for higher frequencies inside the cochlea, rather like a xylophone, so the combined frequencies that come in from the oval window vibration are immediately split up into their component frequencies, each causing different parts of the basilar membrane to vibrate. This is in effect an instantaneous frequency analyzer, which would make any electrical engineer marvel. It is rather like having a miniature gremlin (with concert pianist skills!) playing a keyboard in your inner ear!

cilia
Figure 5. The cilia have a trapdoor operated by a spring attached to an adjacent cilium. Charged ions then move down the cilia and excite the nerves to the brain.

The final part of the hearing system involves the organ of Corti (see fig. 3), running along the top of the basilar membrane. This has tiny little hairs (stereocilia) on it (fig. 5) which send an electrical signal according to each frequency excited by the incoming signal. It is astonishing that each tiny ‘hair’, called a cilium (0.00025 mm thick—less than 1/70th of the thickness of the thinnest (flaxen) human hair!), when disturbed by the tectorial membrane (which touches the cilia above), causes the operation of literally a mechanical spring attached to the top of one hair. This spring is only a few nanometres thick and stretches to about 100 nanometres long; a nanometre is a millionth of a mm, which is getting towards the molecular scale. The other end pulls on a tiny trapdoor at the side of an adjacent cilium (fig.5)—one of the smallest examples of mechanical springs!

This open trapdoor then allows charged ions in the fluid-filled cochlea to excite ganglion nerves to send the signal to different parts of the cerebral cortex in the brain, depending on whether it is music or speech. For low frequencies there is about one nerve for each change in Hz. In the upper range it is about 2–3 Hz per nerve ending.

Noise damage

Sometimes the hearing mechanism is damaged by listening to repetitive sounds of one particular frequency, such as in certain industries if someone is not provided with ear protection. Listening to loud music can also do this, because the springs at the tip of the cilia for a particular set of frequencies can literally snap.

Some people have a genetic defect in their ears such that the cochlear system is not working. A brilliant Australian surgeon, Graeme Clark, developed the cochlear implant, which bypasses the cochlea system with a microphone attached to the spiral ganglion nerves. Initially this at least enabled basic speech to be heard, but later developments have led to implants with greater frequency resolution so that even music can be heard. Achieving this feat of exquisite engineering required clever minds. The implications are obvious—the original design was indeed superb!

Summary and conclusion

Such an exquisite system involving air vibrations, mechanical, chemical and electrical engineering is frankly astonishing, and confirms the intelligent design of the ear. Surely we can say with the Psalmist, “I praise you, for I am fearfully and wonderfully made. Wonderful are your works; my soul knows it very well” (Psalm 139:14).

References and notes

  1. Leighton, T., The acoustic bubble: Oceanic bubble acoustics and ultrasonic cleaning, Proceedings of Meetings on Acoustics 24:070006, 2015. Return to text.
  2. Areal ratio of tympanic membrane to stapes. See tinyurl.com/yyv5gay5. Return to text.

Helpful Resources

Readers’ comments

Peter K.
While this is an excellent piece of writing about God's amazing design, I have to point out that the frequencies from 2kHz to 5 kHz and beyond are mostly the consonantal key frequencies. The only harmonics of vowels that the brain needs to experience are the first and second harmonics. The brain does not need to use the other vowels' harmonics (3rd, 4th, 5th etc), which are too quiet to be heard in most situations anyway - each higher harmonic has less energy than the preceding lower harmonic. The only vowel with a significant (ie second harmonic) harmonic above 2 kHz is 'ee', often referred to as the high frequency vowel. Before more sophisticated hearing assessments were available, the baby brain stem hearing test used a 2 to 3 kHz stimulus as that proved access to the most consonant sounds - necessary for the decoding of speech. Isn't it also amazing that octaves use double the number of sound waves than the previous note? Middle 'C' is 256 sound waves per second, the 'C' above is 512 sound waves per second and so on. Halving the number goes down the octaves: 256, 128, 64, 32, 16, 8, 4, 2...... Why did God let people identify octaves by ear before they could count the number of sound waves??? Apologies to get pedantic about an otherwise excellent article. Peter Keen, Consultant Educational Audiologist, Keenhearing.
John Z.
Obviously, the ear and eye are both products of design, but, CMI, which organ do you feel is more complex?
Don Batten
It is difficult to compare the complexity. Both are incredibly complex and highly integrated for what they do. Vision is more information-rich than sound (compare the amount of computer memory needed for an hour of video vs an hour of sound), so it would appear to be more impressive, but as this article shows (a little bit), hearing is a marvelous thing too.
Timothy H.
I'm an engineer who's worked on the development of augmented reality headsets. The human hearing system is amazing in so many ways. Perhaps you've never thought about it, but you can localize sounds in 3D space with just two ears. It's easy to imagine how you could triangulate left to right, but how do we determine when sounds are coming from above or below us? We can also judge distance approximately. In fact, if someone is walking around in an adjacent room in your home, you can probably identify approximately where they are even though you can't see them, for instance as they approach the door way. And we do all this with just two "microphones".

This is part of a field called psychoacoustics. Your brain's audio processing builds a sophisticated model of your body, including head, shoulders and pinna. This model is often referred to as a head-related transfer function (HRTF). You brain uses this to evaluate the small changes in timing and frequency response between the ears, allowing it to further refine direction. Reflections off floors and ceilings are also decoded and can aid in sound localization.

Spatial audio systems, such as surround sound, video games, and virtual/augmented reality googles must reverse engineer all of this to produce realistic audio that sounds localized in space even though coming from fixed speakers.
Douglas Barrett W.
Great to hear from you - perhaps we will meet again at MEC.
David V.
Thank you for this wonderful article. Am I correct in thinking that Professor Clark is a Christian who believes in Creation? I seem to remember that he gave a public talk at one stage that discussed how unlikely it would be for the human hearing mechanism to have evolved.
Don Batten
Professor Clark apparently approves of the Graeme Clark Research Institute at Tabor College, Adelaide, which aggressively promotes theistic evolution. Thus it would appear that he is not 'on the page' when it comes to biblical creation (sadly). Maybe he has just never taken the time to think through the implications of theistic evolution, which undermines the whole message of the Bible—if you think about it.Evolution and the Christian Faith (Theistic evolution in the light of Scripture)
Dan M.
I design and build my own electro-mechanical handicap equipment such as wheelchair lifts, wheelchairs, and other safety equipment. So I know how hard it is to conceptualize and build something that works well. I spend thousands of hours at my computer designing these things on CADD and thankfully the Spirit gives me aha moments out of the blue when I get stuck. When I consider God's creation, (especially our own bodies) its intrinsic, mind-boggling design features, I'm blown away and it causes me to fall to my knees, (in the Spirit, I'm wheelchair-bound) and worship Him, (Psa 8:3-4). Our bodies are electro-mechanical super sophisticated machines themselves made up of trillions of interdependent cells that are miniature factories made up of machines at the molecular level incorporating many automatic chemical processes required for proper operation. Did I mention they are also heterosexually self-reproducing? This all evolved by unguided processes? When pigs land on the moon, (without our help)! It saddens me to think about all the heartfelt appreciation for our Creator because He loved us first that the secularists are missing out on. Not to mention salvation! After studying Creation science for twenty years and its implications, it is hard to believe how anyone could deny God's existence in lieu of evolution? It's irrational to me! One must be truly willfully ignorant to deny His authorship of the creation, (2Pe 3:5). When I witness all these obvious truths to my family members, they just sit there in silence, no response, (except anger) no repentance. They know it is the truth in their hearts, but they will not yield. How sad! I myself will praise you with my dying breath, Lord!
CHARLES NYANGAGA W.
How come we do not have more debates between young earth creationists and evolutionists and old earth creationists and non YEC ID theorists?
Don Batten
Off topic, but see: Debates
Melvyne C.
Very informative article, thank you. The intelligent design of the spring (Fig 5) is another example of irreducible complexity! Prof M Behe, an advocate of common descent with modification/intelligent design; seems to me, with his mouse trap analogy, to get stuck at the point of irreducible complexity, where prior machinery particles must still evolve in order to reach an irreducible state: which is not working fittness.
Surely, miraculous creation in six days remains the best answer for Judaeo-Christians! Moreover, God gave the law on origins publicly, as witnessed by over a million people. Not as theory to suit fallen disbelief.
Jonathan Sarfati
Some authors prefer the more dynamic term functionality threshold to the static irreducible complexity, although in many cases they amount to the same thing.
Tom G.
I have the ability to move some muscles in my ear which produce a thunder-like sound in my hearing. I am able to do this at will and can either do both together or independently. I have spoken to others who are able to do the same. Does it have a purpose? I.e. cancelling other sounds of certain frequencies.
Don Batten
You are one of the minority of people who can voluntarily contract a little muscle called the tensor tympani that is attached to the tympanic membrane (eardrum). This little muscle has several functions, including damping the noise generated by you own eating, etc., and protection against hearing damage from loud noises. You can read more about it here: www.sciencealert.com/some-people-can-make-a-roaring-sound-in-your-ears-just-by-tensing-a-muscle (copy and paste into your browser).
Geoff C. W.
Amazing!
Is there any known logic to the shapes of the ossicles? Does each bit of each bone have a purpose?
It might be better to say that liquids are ’virtually’ or ‘effectively’ incompressible. Submarine sonar and whale echolocation depend on the compressibility of seawater.
Thanks.
Jonathan Sarfati
The ossicle shapes optimize transmission of sound from gas to liquid. This really is amazing as you say.

An eminent scientist like Prof. McIntosh is well aware that water can be compressed. Some of his work relies on this too. But when it comes to sound transmission, at the pressures involved, it can be treated as incompressible.

PS: Prof. McIntosh himself replies

Geoff C W — thank you for your comment. You are of course strictly right. There is a small amount of compressibility possible in liquids (and once formed such sound waves do not diffuse away easily—which enables sound waves—e.g. sonar from whales and dolphins—to be sent over great distances). But compared to air, water is about 20,000 times less compressible, so for the minute forces in the middle ear and the ossicle acting on the oval window leading to the inner ear, as Jonathan Sarfati states, the liquid (which is not dissimilar to water in terms of dynamic behaviour) is essentially incompressible.

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