The Design in the Ear

Another interesting example of the irreducibly complex organs in living things is the human ear.

As is commonly known, the hearing process begins with vibrations in the air. These vibrations are enhanced in the external ear. Research has shown that that part of the external ear known as the concha works as a kind of megaphone, and sound waves are intensified in the external auditory canal. In this way, the volume of sound waves increases considerably.

Sound intensified in this way enters the external auditory canal. This is the area from the external ear to the ear drum. 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 which pass down the auditory canal in this way reach the ear drum. This membrane is so sensitive that it can even perceive vibrations on the molecular level. Thanks to the exquisite sensitivity of the ear drum, you can easily hear somebody whispering from yards away. Or you can hear the vibration set up as you slowly rub two fingers together. Another extraordinary feature of the ear drum is that after receiving a vibration it returns to its normal state. Calculations have revealed that, after perceiving the tiniest vibrations, the ear drum 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 ear drum amplifies the vibrations which 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 ear drum.

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, in such a way that even if we are asleep and there is a loud noise beside us, these muscles immediately contract and reduce the intensity of the vibration reaching the inner ear.

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 ear drum, in other words, the same as the atmospheric air pressure. But this balance has been thought of, and a canal between the middle ear and the outside world which allows an exchange of air has been built in. This canal is the Eustachean tube, a hollow tube running from the inner ear to the oral cavity.