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Page:Popular Science Monthly Volume 65.djvu/232

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228
POPULAR SCIENCE MONTHLY.

WHY IS THE HUMAN EAR IMMOBILE?
By Dr. WALTER SMITH,

LAKE FOREST COLLEGE.

THE ear has had a varied history. The evolutionist has a remarkable story to tell when he recounts the steps in the making of this organ. He traces the opening of the ear to the gill-slits of the fish forms of whose lineage we are. He shows (though this subject concerns us less at present, and is still discussed with some uncertainty as to details) how various structures in the region of this opening, which had originally a different purpose, were modified to become the series of little bones that propagate the vibrations of the air from the tympanic membrane to the fluid of the inner ear. He shows further, with greater or less completeness, how the cartilage shell grew on the outer side of the head, and was supplied with muscles, so that it could be moved about and even have its shape changed.

To get a good illustration of the mobile ear we only need to watch such an animal as the horse; the ear is as mobile as the eye, or more so. The poet speaks of the horse's ear and eye as twinned; but it is interesting to notice that each of the horse's ears can work independently. And it is evident that nature at one time meant, so to speak, that man's progenitors should possess ears of similar mobility. She gave them the projecting frame of cartilage and she attached to it the muscles for its movement. Then in the course of the generations she changed her mind and withdrew what she had bestowed. The cartilage shell, curiously wrought, is still there, and we regard it as adding to the beauty of the head; yet it is probably only a rudiment. The tip of the ear, when present, is a small outgrowth on the outer fold of the cartilage and is turned towards the center of the ear. The muscles of the ear, seven in number, are also rudimentary. Occasionally an individual is found who can move his ears; but even these movements are generally of an abortive kind, and are so unusual that the sight of them may distress those who are sensitive.

Why has man lost this power? Is it simply a case of retrogression? Or is it a loss for the sake of a greater gain, possible only through it? I think the reasons for this change in the organism can be indicated; one can, at least, point with assurance to a great mental gain in which it has resulted.

It will prove helpful to an appreciation of this gain to inquire first what man has lost in the passing of this mobility. The signifi-