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