Page:The Zoologist, 4th series, vol 2 (1898).djvu/420

388 now practically extinct from so many areas, their former presence is proved by the hard- wooded and spinous trees and shrubs which have almost alone survived. And thus natural selection has acted on the original flora and fauna in which this obscurely understood evolutionary response to environmental conditions played such a vast and primary part. Natural selection is not the act of creation, but the effect of competition; it guides the battles, and directs the forces it did not provide. There seems indeed some prospect of "natural selection" being relegated by some writers to the old armoury of teleology. Thus a recent writer has remarked that it is held by "Wallace and others among our deeper-thinking naturalists, that the workings of natural selection are incomprehensible unless we regard them as guided by a controlling intelligence." A much more weighty argument is "that the conception of the struggle for existence has derived its force, not wholly from actual observation of what occurs, but very largely from inference as to what, it is believed, must occur."

We may, however, quit these realms of suggestion, and observe how even in our scanty geological records we see exhibited some phases of the commencement of a struggle for existence. Thus, after a period of animal evolution which may be computed by millions of years, and in which fish abounded, perhaps not yet altogether under a severe stress of selection and survival, the Mesozoic period arrives, when, in the words of Oscar Schmidt, "the Placoids and Ganoids, hitherto predominating in the ocean almost without a foe, now found overwhelming enemies in the true Sea-lizards or Enaliosaurians, especially the Ichthyosaura and Plesiosaura." Here we see natural selection, with its iron and implacable rule, a real factor