that the amazement ought to be lessened when we reflect that beings almost infinite in number during an almost infinite lapse of time have often had their whole organization rendered in some degree plastic, and that each slight modification of structure which was in any way beneficial under excessively complex conditions of life has been preserved, whilst each which was in any way injurious has been rigorously destroyed.  The long-continued accumulation of beneficial variations will infallibly have led to structures as diversified, as beautifully adapted for various purposes, and as excellently co-ordinated as we see in the animals and plants around us.  Hence Darwin regards selection as the paramount power, whether applied by man to the formation of domestic beings or by nature to the production of species.  Employing a favorite metaphor, he said:  “If an architect were to rear a noble and commodious edifice without the use of cut stone, by selecting from the fragments at the base of a precipice wedge-form stones for his arches, elongated stones for his lintels, and flat stones for his roof, we should admire his skill and regard him as the paramount power.  Now, the fragments of stone, though indispensable to the architect, bear to the edifice built by him the same relation which the fluctuating variations of organic beings bear to the varied and admirable structures ultimately acquired by their modified descendants.”

Some critics of the Darwinian theory of the origin of species have declared that natural selection explains nothing, unless the precise cause of each slight individual difference be made clear.  Darwin rejoins that if it were explained to a savage utterly ignorant of the art of building how the edifice had been raised, stone upon stone, and why wedge-formed fragments were used for the arches, flat stones for the roof, etc.; and if the use of each part and of the whole building were pointed out,—­it would be unreasonable if he declared that nothing had been made clear to him, because the precise cause of the shape of each fragment could not be told.  This, in Darwin’s opinion, is a nearly parallel case, with the objection that selection explains nothing because we know not the cause of each individual difference in the structure of each being.  The shape of the fragments of stone at the base of the hypothetical precipice may be called accidental, but the term is not strictly applicable; for the shape of each depends on a long sequence of events, all obeying natural laws; on the nature of the rock, on the lines of deposition or cleavage, on the form of the mountain, which depends on its upheaval and subsequent denudation, and, lastly, on the storm or earthquake which throws down the fragments.