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Can You Hear Me Now? Good, Then Thank Your Irreducibly Complex Ears


Editor’s note: Physicians have a special place among the thinkers who have elaborated the argument for intelligent design. Perhaps that’s because, more than evolutionary biologists, they are familiar with the challenges of maintaining a functioning complex system, the human body. With that in mind, Evolution News is delighted to offer this series, “The Designed Body.” For the complete series, see here. Dr. Glicksman practices palliative medicine for a hospice organization.

the-designed-body4.jpgThermometer measures temperature and a barometer measures air pressure. But how do they do it? Each device is essentially a sensory transducer with a mechanism that enables it to sense a physical phenomenon and convert it into useful information. The devices the body uses to detect physical phenomena so it knows what is going on outside and inside of it are sensory transducers as well. Hearing is the sensation we experience when vibrating molecules within a medium, typically air (but sometimes water), form mechanical waves within a specific wavelength range and enter our ears.

Common sense tells us that without this special sense our earliest ancestors could never have survived. Evolutionary biologists claim that similar auditory mechanisms in other life forms prove that it was easy for chance and the laws of nature alone to invent hearing. But as in the development of human technologies, experience teaches that intelligent design is a more plausible explanation. Darwinists oversimplify the need for the presence of all the parts of the ear for it to hear well enough for human survival. They also fail to take into account how our brain converts what it receives into what we experience as hearing.

In truth, hearing is a mystery that nobody, not even evolutionary biologists, understands. Nobody really understands how we can hear, so nobody should claim to understand how the ear and hearing came into being. Yet that doesn’t stop Darwinists from telling us otherwise. Let’s look at what makes up the ear, how it works, and what the brain receives from it which it then converts into the sensation we call hearing.

Sound waves are oscillations, the back and forth movement of molecules within a medium, such as air. These vibrations are transmitted to adjacent molecules and spreads out in all directions. Sound is not due to the linear movement of air — that is called wind. Furthermore, since a vacuum has no air molecules it cannot transmit sound since there are no air molecules within it to vibrate. The physical nature of sound waves is that the air particles alternate between being packed together in areas of high concentration, called compressions, and spread apart in areas of low concentration called rarefactions. These compressions and rarefactions of air molecules form longitudinal pressure waves which, depending on the type of sound and the energy used to create them, have amplitude, wavelength, and frequency. Sound waves travel at about 330 m/sec, and since light travels at 300,000 km/sec, this means that light is literally about a million times faster than sound.

The human ear is a very complex sensory organ in which all of parts work together to produce and transmit mechanical waves of oscillating molecules to its cochlea. Although it is in the cochlea where the nerve impulses for hearing begin, the other parts of the ear play important roles that support cochlear function. The ear can be divided into three regions; the outer (external) ear, the middle ear, and the inner (internal) ear.

The outer ear consists of the pinna (ear flap), the ear canal, and the eardrum (tympanic membrane). The pinna acts like a satellite dish, collecting sound waves and funneling them down the ear canal to the eardrum. The pinna is made of flexible cartilage and is important for determining the location of different sounds. The ear canal produces wax which provides lubrication while at the same time protecting the eardrum from dust, dirt, and invading microbes and insects. The cells that line the ear canal form near the eardrum and naturally migrate outward toward the entrance of the ear canal, taking with them the overlying ear wax, and are shed from the ear. This provides a natural mechanism of wax removal. Sound waves enter through an opening in the skull called the external auditory meatus. They naturally move down the ear canal and strike the eardrum. The eardrum is a very thin cone-shaped membrane which responds to sound waves by vibrating to a degree that is determined by their amplitude, wave length, and frequency. It represents the end of the outer ear and the beginning of the middle ear.

The middle ear is an enclosed air-filled chamber in which the air pressure on either side of the eardrum must be equal to allow for adequate compliance, a measure of how easily the eardrum will move when stimulated by sound waves. The air in the middle ear tends to be absorbed by the surrounding tissue which, if not corrected, can lead to a vacuum effect, reduced eardrum compliance, and thus impaired hearing. The auditory tube in the middle ear connects with the back of the nose and pharynx. The muscular action of swallowing, yawning, or chewing causes the auditory tube to open, allowing ambient air to enter the middle ear, replacing what has been absorbed and equalizing the air pressure on both sides of the eardrum. Anyone who has flown in an airplane has experienced this vacuum effect as the plane descended and felt its resolution when a popping sound in the ear signified that air had entered the middle ear through the auditory tube.

The middle ear contains the three smallest bones in the body, the ossicles, which include the malleus (hammer), the incus (anvil), and the stapes (stirrup). The job of the ossicles is to efficiently transmit the vibrations of the eardrum into the inner ear which houses the cochlea. This is accomplished by the malleus being attached to the eardrum and the incus, the incus to the malleus and the stapes, and the stapes to the incus and the oval window of the cochlea.

The cochlea consists of three fluid-filled interrelated coiled chambers which spiral together for about two and half turns resembling a snail shell. Within the cochlea is the organ of Corti, the sensory receptor that converts the mechanical waves into nerve impulses. The vibrations, started by sound waves striking the eardrum and transmitted by the ossicles in the middle ear to the oval window of the cochlea, now produce fluid waves within it. The organ of Corti contains about 20,000 hair cells (neurons) running the length of the spiraled cochlea which when stimulated by these fluid waves causes them to bend and depolarize, sending impulses through the auditory nerve to the brain. Higher frequencies cause more motion at one end of the organ of Corti while lower frequencies cause more motion at the other end. The specific cochlear neurons that service specific hair cells along the organ of Corti respond to specific frequencies of sound which, when sent to the auditory cortex, are processed, integrated, and then interpreted as hearing. How the brain is able to perform this feat is as yet not fully understood.

Evolutionary biologists, using their well-developed imaginations, expound on how all the parts of the ear must have come together by chance and the laws of nature alone. However, as usual, they only try to explain how life looks and not how it actually works under the laws of nature to survive. Besides the development of all of its perfectly integrated parts, they never mention the problem the ear faces when it comes to transmitting the vibrations of the tympanic membrane to the organ of Corti with enough pressure to allow for adequate hearing to take place.

It is much easier to move through air than it is through water. That is because of water’s higher density. This means that it is much easier for sound waves in the air to move from the eardrum through the middle ear than it is for the oval window to move waves of fluid through the cochlea. Without some sort of innovation, this difference in air/water density would have so reduced the amplitude of the fluid waves in the cochlea that the hearing ability of our earliest ancestors would have been severely compromised and with it, their survival capacity.

So, what novelty of engineering did our ears develop to let them transmit sound waves through the outer and middle ear to the cochlear fluid with enough amplitude to allow for adequate hearing? It is important to remember that F= PA, Force is equal to Pressure times Area. This means that with a given force, the pressure on a given surface is inversely related to its area. If the area decreases, the pressure on the surface increases, and if the area increases, the pressure decreases.

It just so happens that the surface area of the tympanic membrane is about twenty times larger than that of the oval window. This means that the force generated by the vibrations coming from the tympanic membrane through the ossicles to the oval window naturally increases twentyfold on the cochlear fluid. It was this mechanical advantage of their larger tympanic membranes transmitting vibrations through their ossicles to their smaller oval windows of their cochleae that allowed our earliest ancestors’ ears to have adequate hearing so they could survive within the world of sound.

Evolutionary biologists seem to be completely ignorant of the fact that the parts used for hearing are not only irreducibly complex, but, to have functioned well enough so our earliest ancestors could hear well enough to survive, they must also have had a natural survival capacity. When it comes to the laws of nature, real numbers have real consequences.

But besides the cochlea there is another very important sensory transducer within the inner ear. Next time we’ll look at vestibular function and how it let our earliest ancestors stay balanced.

Photo credit: Eweht (Own work) [CC BY-SA 4.0], via Wikimedia Commons.