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The author discusses each of nine theories that have been advanced to explain the predominance of right-handedness, and finds none of them wholly satisfactory. The advantages of specialization of one member would account for handedness; the original impulse to prefer the right to the left hand is sought. Handedness is accompanied by a peculiarity of our vision: Sighting is by the right or left visual line, not the median line. Contiguous areas of the brain have assumed dominance in the control and correlation of precise vision, fine manual procedures, including writing, and the closely related function, speech. This observation is of value in determining native left-handedness which has become masked by the attempt to adjust handedness to the condition of the majority. A test of the eye used in sighting will, in most cases, reveal the perferred hand. The author has designed an apparatus for this purpose, and finds that
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