Ears for Hearing
Name: Ruhamah S.
Thursday, June 06, 2002
Do all animals need ears to hear?
A definition of "hearing" is "perception of sound made possible by vibratory
changes in air pressure on the ear drums" (Encarta Dictionary) so in that
sense ears are required to "hear." However the sound waves that change air
pressure on ear drums can also affect other parts of the body. Insects, for
example, do not have ears and ear drums like mammals and birds, but do
perceive sound waves.
This depends upon what you define as a "ear". If by that you mean the
ability to sense vibrations of the medium surrounding the animal, the answer
is NO. Fish, worms, and many other species do not have "ears" in the sense of
the anatomical structure most mammals possess. Even we humans can "feel"
frequencies of air movement less than 10 hertz, the typical cutoff frequency
of sound -- for example a large bass drum. Do we "hear" that? Is it sound? A
similar thing occurs with light. We can "feel" a hot burner on a stove from
several feet even though it is not "glowing". It is infrared radiation. Are
we "seeing" it? It is a matter of how you want to define the terms.
It depends upon your definition of ears. Most birds and mammals have ears
by tranditional definitions. However, reptiles, fish, amphibians and
invertebrates do not really have ears. We can follow the evolutionary
developmenbt through these animals and that is a real interesting topic!
I suggest you look up the frog and how
it hears. This will explain most amphibians. Fish and inveterbrates have
several methods in detecting vibrations (sound is really just vibrations).
This is a great library research project.
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Update: June 2012