The greater part of the adverse criticism, aimed at Darwinism applies only to the extravagant claims put forward by his overenthusiastic disciples; claims not to be found in the works of Darwin himself. As we shall see later, one of the greatest offenders in this respect was no less a person than the co-discoverer of the selection theory--Alfred Russell Wallace. Of all the mischievous misconceptions of Darwin’s theory none have worked so much harm as that which regards natural selection as the active and efficient cause of evolution. Although evolution is an established fact, our knowledge of its processes are incomplete and must always remain so until we have solved that most vexed of all biological problems, the “causes of variation.” As to the nature of these causes, natural selection is dumb. For its purpose, variation is simply assumed to be a fact, and Darwin’s acknowledged ignorance as to how variation is brought about is expressed in the term “spontaneous variation.” Until variation has played its part by producing new and various forms, selection has no function or office to perform. Then it simply decides which forms shall survive by destroying the rest. As Wigand has pointed out, selection does not do more than determine the survival of what is offered to it, and does not create anything new. As DeVries very strikingly puts it, “It is only a sieve, and not a force of nature, no direct cause of improvement, as many of Darwin’s adversaries, and unfortunately many of his followers also, have so often asserted. It is only a sieve which decides which is to live and which is to die.... With the single steps of evolution it has nothing to do. Only after the step has been taken, the sieve acts, eliminating the unfit.” Thus Prof. Cope’s point that Darwin’s theory does not explain the “origin” of the fittest, is well taken, or as Mr. Arthur Harris puts it, “Natural selection may explain the survival of the fittest, but it cannot explain the arrival of the fittest.” It was around this question of the “causes” of variation that the Neo-Lamarckians and the Weismannians fought their battle, the former insisting, as we have seen, that variation was caused by the hereditary transmission of acquired characters, while Weismann maintained that variation arose solely through the combining of two portions of differing germ-plasm contributed by two different individuals, and producing a new individual unlike either,--a “variation” from both. While whatever there was of victory fell to Weismann, neither side has experimentally proven its case, and we are still in the dark as to the “causes of variation.” Our ignorance is still cloaked in the convenient word “spontaneous;” to Darwin’s “spontaneous variation” we now add DeVries’ “spontaneous mutation.” It is another tribute to Darwin’s caution and insight that he recognized the possibility of variations arising either suddenly, as DeVries asserts they do, or gradually as DeVries denies.