Among the unanswerable, perhaps the weightiest of the objections, is that of the absence, in geological deposits, of vestiges of the intermediate forms which the theory requires to have existed.  Here all that Mr. Darwin can do is to insist upon the extreme imperfection of the geological record and the uncertainty of negative evidence.  But, withal, he allows the force of the objection almost as much as his opponents urge it,—­so much so, indeed, that two of his English critics turn the concession unfairly upon him, and charge him with actually basing his hypothesis upon these and similar difficulties,—­as if he held it because of the difficulties, and not in spite of them;—­a handsome return for his candor!

As to this imperfection of the geological record, perhaps we should get a fair and intelligible illustration of it by imagining the existing animals and plants of New England, with all their remains and products since the arrival of the Mayflower, to be annihilated; and that, in the coming time, the geologists of a new colony, dropped by the New Zealand fleet on its way to explore the ruins of London, undertake, after fifty years of examination, to reconstruct in a catalogue the flora and fauna of our day, that is, from the close of the glacial period to the present time.  With all the advantages of a surface exploration, what a beggarly account it must be!  How many of the land animals and plants which are enumerated in the Massachusetts official reports would it be likely to contain?

Another unanswerable question asked by the Boston reviewers is, Why, when structure and instinct or habit vary,—­as they must have varied, on Darwin’s hypothesis,—­they vary together and harmoniously, instead of vaguely.  We cannot tell, because we cannot tell why either should vary at all.  Yet, as they both do vary in successive generations,—­as is seen under domestication,—­and are correlated, we can only adduce the fact.  Darwin may be precluded from this answer, but we may say that they vary together because designed to do so.  A reviewer says that the chance of their varying together is inconceivably small; yet, if they do not, the variant individuals must perish.  Then it is well that it is not left to chance.  As to the fact:  before we were born, nourishment and the equivalent to respiration took place in a certain way.  But the moment we were ushered into this breathing world, our actions promptly conformed, both as to respiration and nourishment, to the before unused structure and to the new surroundings.

“Now,” says the “Examiner,” “suppose, for instance, the gills of an aquatic animal converted into lungs, while instinct still compelled a continuance under water, would not drowning ensue?” No doubt.  But—­simply contemplating the facts, instead of theorizing—­we notice that young frogs do not keep their heads under water after ceasing to be tadpoles.  The instinct promptly changes with the structure, without supernatural interposition,—­just as Darwin would have it, if the development of a variety or incipient species, though rare, were as natural as a metamorphosis.