Page:Popular Science Monthly Volume 51.djvu/352

intelligent adaptations come into existence flash upon us like a revelation. We look as with vision renewed upon the pine cone in the forest, upon the flower shining amid the expanse of green, upon the sudden lightning of the firefly, and the manifold hues of insect and bird. For, little as we have attended to them before save as the commonplaces of our knowledge, we now see that they are paths of least resistance objectively embodied—protoplasmic tools with which, in the silence of the unconscious world the organic system is slowly but surely reaching its ends. And as we ponder it becomes clear to us that the same system is at work in the making of tools and the fashioning of organs—that, though the one process is conscious, the other unconscious, they are deep down in the heart of them the expressions of but a single method. Everywhere we find the evidences of this likeness—in the awl of the shoemaker and the tool of the boring insect; the earth-trap of the native African and the pitfall of the ant lion; the web of the spider and the net of the fisherman; the digging stick of the Australian, the foot of the mole, and the spade of the navvy; in the single oar of the boatman and the sculling tail of the fish; the sticky tongue of the anteater and the slime pot of the human catcher of birds; in the kayak of the savage and the floating pupa skin of the gnat; the scale armor of the armadillo and the soldier's cuirass; in the climbing hooks of the tiger beetle, the claws of the bat, and the grappling irons used in naval warfare; on the one hand, in the pulley, screw, and wedge; in chisels used in stonecutting, gravers with which wood is carved, axes for felling trees; in screwdrivers, lifting jacks, Nasmyth hammers, battering rams; the cord and weight of the window sash, the wheels of carriages, and the rollers whereon heavy masses are moved from place to place; on the other hand, in the muscles, sinews, and joints of animals; in the wing of the bird, the paddle of the porpoise, the hand of man, the mandible of the ant, the horns of the cow, the lance of the swordfish, the stinging cells of certain cœlenterata, the channeled poison tooth of the snake, or the defensive antennæ of the spider; even in the vertebrate eye itself. For all these, being objective paths of least resistance, are signs of a law that, pervading the realm of living things, has its roots in the inorganic world, since it springs from the very nature of motion as a result of differential stress. And when adequate account is taken of the presence of end in organic activities, of its absence from movements which are inorganic—account, that is to say, of the fundamental difference between living protoplasm and inorganic matter—then the whole of evolution, viewed apart from its secondary processes, may be summed up in the simple formula—movement in the direction of least resistance.