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The significance of the irreducible complexity possessed by the human ear is this: The human ear is made up of several separate parts all coming together, and we are able to hear as a result of all these parts' working in harmony together. If one of these components is deficient, then we either become deaf or else our sense of hearing suffers serious damage. It is impossible for an organ possessing irreducible complexity to develop by stages, by chance, in a process of evolution. A brief résumé of how hearing actually takes place will enable this fact to be more clearly understood.
As is commonly known, the hearing process begins with vibrations in the air. These vibrations are enhanced in the external ear by about 17 decibels.1
Sound intensified in this way enters the external auditory canal. This is the passageway leading from the external ear to the eardrum. One interesting feature of the auditory canal, which is some three and a half centimeters long, is the wax it constantly secretes. This liquid contains an antiseptic property which keeps bacteria and insects out. Furthermore, the cells on the surface of the auditory canal are aligned in a spiral form directed towards the outside, so that the wax always flows towards the outside of the ear as it is secreted.
Sound vibrations that pass down the auditory canal in this way reach the eardrum. This membrane is so sensitive that it can even perceive vibrations on the molecular level. Thanks to the exquisite sensitivity of the eardrum, you can easily hear somebody whispering from yards away. Another extraordinary feature of the eardrum is that after receiving a vibration it returns to its normal state. Calculations have revealed that, after perceiving the tiniest vibrations, the eardrum becomes motionless again within up to four thousandths of a second. If it did not become motionless again so quickly, every sound we hear would echo in our ears.
The eardrum amplifies the vibrations that come to it, and sends them on to the middle ear region. Here, there are three bones in an extremely sensitive equilibrium with each other. These three bones are known as the hammer, the anvil, and the stirrup; their function is to amplify the vibrations that reach them from the eardrum.
But the middle ear also possesses a kind of "buffer," to reduce exceedingly high levels of sound. This feature is provided by two of the body's smallest muscles, which control the hammer, anvil, and stirrup bones. These muscles enable exceptionally loud noises to be reduced before they reach the inner ear. Thanks to this mechanism, we hear sounds that are loud enough to shock the system at a reduced volume. These muscles are involuntary, and come into operation automatically.
The middle ear, which possesses such a flawless design, needs to maintain an important equilibrium. The air pressure inside the middle ear has to be the same as that beyond the eardrum—in other words, the same as the surrounding atmospheric air pressure. But this balance has been thought of, and a canal between the middle ear and the outside world allowing an exchange of air has been built in. This canal is the Eustachian tube, a hollow tube running from the inner ear to the oral cavity.
The process whereby these mechanical motions begin to be turned into sound begins in the area known as the inner ear. In the inner ear is the cochlea, a spiral-shaped organ filled with liquid. The cochlea is linked to the stirrup bone by a membrane. By this connection, the mechanical vibrations in the middle ear are sent on to the liquid in the cochlea.
The vibrations which reach the liquid in the cochlea set up wave effects in it. The inner walls of the cochlea are lined with small hair-like structures, called stereocilia, which are affected by this wave effect. These tiny hairs move strictly in accordance with the motion of the liquid. If a loud noise is emitted, then more hairs bend in a more powerful way. Every different frequency in the outside world sets up different effects in the hairs.
But what is the meaning of this movement of the hairs? What can the movement of the tiny hairs in the cochlea in the inner ear have to do with listening to a concert of classical music, recognizing a friend's voice, hearing the sound of a car, or distinguishing the millions of other kinds of sounds?
The answer is most interesting, and once more reveals the complexity of the design in the ear. Each of the tiny hairs covering the inner walls of the cochlea is actually a mechanism which lies on top of 16,000 cells. When these hairs sense a vibration, they move and push each other, just like dominos. This motion opens channels in the membranes of the cells lying beneath the hairs. And this allows the inflow of ions into the cells. When the hairs move in the opposite direction, these channels close again. Thus, this constant motion of the hairs causes constant changes in the chemical balance within the underlying cells, which in turn enables them to produce electrical signals. These electrical signals are forwarded to the brain by nerves, and the brain then processes them, turning them into sound.
Science has not been able to explain all the technical details of this system. While producing these electrical signals, the cells in the inner ear also manage to transmit the frequencies, strengths, and rhythms coming from the outside. This is such a complicated process that science has so far been unable to determine whether the frequency-distinguishing system takes place in the inner ear or in the brain.
Everything we have examined so far has shown us that the ear possesses an extraordinary design. On closer examination, it becomes evident that this design is irreducibly complex, since, in order for hearing to happen, it is necessary for all the component parts of the auditory system to be present and in complete working order.
Take away any one of these parts—for instance, the hammer bone in the middle ear—or damage its structure, and you will no longer be able to hear anything. In order for you to hear, such different elements as the eardrum, the hammer, anvil, and stirrup bones, the inner ear membrane, the cochlea, the liquid inside the cochlea, the tiny hairs that transmit the vibrations from the liquid to the underlying sensory cells, the sensory cells themselves, the nerve network running from them to the brain, and the hearing center in the brain—all of these parts must exist in complete working order. The system cannot develop "by stages," because the intermediate stages would serve no purpose.
The claim that an organ as complex as the ear should have been constructed in stages by an unconscious process dependent solely on random chance, such as evolution, is both unscientific and irrational. BBC must be aware of this impossibility, since it frequently repeats that this is a miracle that is very difficult to believe, and says: "Evolution shapes our bodies. It is hard to believe that it could bring all this about."
References
- - Color Atlas of Human Anatomy, Harmony Books, New York, 1994, p. 70 ↩