What will an hypothesis of the derivation of species explain which the opposing view leaves unexplained?

Questions these which ought to be entertained before we take up the arguments which have been advanced against this theory.  We can only glance at some of the considerations which Darwin adduces, or will be sure to adduce in the future and fuller exposition which is promised.  To display them in such wise as to indoctrinate the unscientific reader would require a volume.  Merely to refer to them in the most general terms would suffice for those familiar with scientific matters, but would scarcely enlighten those who are not.  Wherefore let these trust the impartial Pictet, who freely admits, that, “in the absence of sufficient direct proofs to justify the possibility of his hypothesis, Mr. Darwin relies upon indirect proofs, the bearing of which is real and incontestable”; who concedes that “his theory accords very well with the great facts of comparative anatomy and zooelogy,—­comes in admirably to explain unity of composition of organisms, also to explain rudimentary and representative organs, and the natural series of genera and species,—­equally corresponds with many palaeontological data,—­agrees well with the specific resemblances which exist between two successive faunas, with the parallelism which is sometimes observed between the series of palaeontological succession and of embryonal development,” etc.; and finally, although he does not accept the theory in these results, he allows that “it appears to offer the best means of explaining the manner in which organized beings were produced in epochs anterior to our own.”

What more than this could be said for such an hypothesis?  Here, probably, is its charm, and its strong hold upon the speculative mind.  Unproven though it be, and cumbered prima facie with cumulative improbabilities as it proceeds, yet it singularly accords with great classes of facts otherwise insulated and enigmatic, and explains many things which are thus far utterly inexplicable upon any other scientific assumption.

We have said (p. 116) that Darwin’s hypothesis is the natural complement to Lyell’s uniformitarian theory in physical geology.  It is for the organic world what that popular view is for the inorganic; and the accepters of the latter stand in a position from which to regard the former in the most favorable light.  Wherefore the rumor that the cautious Lyell himself has adopted the Darwinian hypothesis need not surprise us.  The two views are made for each other, and, like the two counterpart pictures for the stereoscope, when brought together, combine into one apparently solid whole.