Such was the scheme of evolution elaborated by Charles Darwin. His hypothesis leaves the origin of variations an unsolved mystery. It assumes what has never been proved, namely, the efficacy of “natural selection.” It rests on what has been definitely disproved by factual evidence, namely, the inheritability of the slight variations, now called fluctuations, which, not being transmitted even, by the hereditary process, cannot possibly accumulate from generation to generation, as Darwin imagined. Moreover, fluctuations owe their origin to variability in the external conditions of life (_e.g._ in temperature, moisture, altitude, exposure, soil, food, etc.), being due to the _direct_ influence or pressure of the environment, and not to any spontaneous tendency within the organism itself. Hence Darwin erred no less with respect to the spontaneity, than with respect to the inheritability and summation, of his “slight variations.” The subsequent history of Lamarckian and Darwinian Transformism is briefly told. That both should pass into the discard was inevitable, but, thanks to repeated revisions undertaken by loyal adherents, their demise was somewhat retarded. In vain, however, did the Neo-Darwinians attempt to do for Darwinism what the Neo-Lamarckians had as futilely striven to do for Lamarckism. The revisers succeeded only in precipitating a lethal duel between these two rival systems, which has proved disastrous to both. The controversy begun in 1891 between Herbert Spencer and August Weismann marked the climax of this fatal conflict.