What is the function of the outer ear or pinna?

The human ear is divided into three major parts, outer ear, middle ear and inner ear. The first part is the outer ear where hearing does not take place. It is known as pinna in scientific terminology. Like a funnel it directs the sound waves towards the internal passage known as auditory canal. It should be noted that Nature has given more efficient pinna to some animals like antelope, deer and tiger etc, because they can be turned in any direction like aerial for receiving sound signals without turning the head.

Surprisingly, Charles Darwin had considered pinna to be rather superfluous organ in ‘The Origin of Species’, his world famous treatise on the theory of evolution. He had explained this hypothesis with the example of a sailor who had the left-hand side pinna severed by knife in a fight but was still able to hear through the hole. In Darwin’s view pinna night have been useful in the early stages of evolution but in the case of modern human beings the organs sticking out from the left and right sides of the head were clearly redundant.

Staunch followers of Darwin’s theory of evolution among the researchers did not think it necessary to make scientific study on pinna. Many years after Darwin’s death some researchers started questioning that if it was a rule of evolution to obliterate useless organs gradually then how pinna had escaped this fate. Now they understand its function. Both the pinnae perform the task of identifying the direction of sound by ascertaining the angle at which the sound waves make their impact. The frequency of sound waves plays the key role in this as there are a number of sounds of varying frequencies. If the frequency of any sound waves oscillate widely then locating the source of sound becomes impossible. This is the reason why it is extremely difficult to know the direction of insects like cricket from their chirping sounds.

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