Page:Popular Science Monthly Volume 62.djvu/52

6 The great individual variation of these parts in the human being is not without significance and furnishes an excellent illustration of the biological truth that the perfection and constancy of an organ are directly proportional to its necessity in the life of the organism. Thus

in an arboreal primate, an exact appreciation of the contact surfaces of the tree-boughs among which it climbs and swings is of vital importance, and the slightest defect or deviation from the standard in the organs furnishing that intelligence would be apt to prove fatal; but

when such a being assumes a terrestrial life, so high a degree of sensitiveness in palms and soles is no longer necessary and the organ is allowed to lapse. Individual variations, no longer discouraged, tend to increase, and that which was once a necessary and vital arrangement