"The truth is that adaptation explains the sinuosities of the movement of Evolution, but not the general directions of the movement, still less the movement itself. The road which leads to the town is obliged to follow the ups and downs of the hills; it adapts itself to the accidents of the ground, but the accidents of the ground are not the cause of the road nor have they given it its direction." [Footnote: Creative Evolution, p. 108 (Fr. p. 112).] The evolution of life cannot be explained as merely a series of adaptations to accidental circumstances. Moreover, the mechanistic view, where all is "given," is quite inadequate to explain the facts. The finalist or teleological conception is not any more tenable, for Evolution is not simply the realization of a plan. "A plan is given in advance. It is represented or at least representable, before its realization. The complete execution of it may be put off to a distant future or even indefinitely, but the idea is none the less formulable at the present time, in terms actually given. If, on the contrary, Evolution is a creation unceasingly renewed, it creates as it goes on, not only the forms of life but the ideas that enable the intellect to understand it. Its future overflows its present and cannot be sketched out therein, in an idea. There is the first error of finalism. It involves another yet more serious. If life realizes a plan it ought to manifest a greater harmony the further it advances, just as the house shows better and better the idea of the architect as stone is set upon stone." [Footnote: Creative Evolution, p. 108 (Fr. p. 112).] Such finalism is really reversed mechanism. If, on the contrary, the unity of life is to be found solely in the impetus (poussee formidable) that pushes it along the road of Time, the harmony is not in front but behind. The unity is derived from a vis a tergo: it is given at the start as an impulsion, not placed at the end as an attraction, as a kind of "... far-off divine event To which the whole creation moves."