Probably from the lack of familiarity with prevalent ideas and their history, the theologians are apt to suppose that scientific men of the present day are taking up theories of evolution in pure wantonness or mere superfluity of naughtiness; that it would have been quite possible, as well as more proper, to leave all such matters alone.  Quieta non movere is doubtless a wise rule upon such subjects, so long as it is fairly applicable.  But the time for its application in respect to questions of the origin and relations of existing species has gone by.  To ignore them is to imitate the foolish bird that seeks security by hiding its head in the sand.  Moreover, the naturalists did not force these questions upon the world; but the world they study forced them upon the naturalists.  How these questions of derivation came naturally and inevitably to be revived, how the cumulative probability that the existing are derived from preexisting forms impressed itself upon the minds of many naturalists and thinkers, Mr. Henslow has briefly explained in the introduction and illustrated in the succeeding chapters of the first part of his book.  Science, he declares, has been compelled to take up the hypothesis of the evolution of living things as better explaining all the phenomena.  In his opinion, it has become “infinitely more probable that all living and extinct beings have been developed or evolved by natural laws of generation from preexisting forms, than that they, with all their innumerable races and varieties, should owe their existences severally to Creative fiats.”  This doctrine, which even Dr. Hodge allows may possibly be held in a theistic sense, and which, as we suppose, is so held or viewed by a great proportion of the naturalists of our day, Mr. Henslow maintains is fully compatible with dogmatic as well as natural theology; that it explains moral anomalies, and accounts for the mixture of good and evil in the world, as well as for the merely relative perfection of things; and, finally, that “the whole scheme which God has framed for man’s existence, from the first that was created to all eternity, collapses if the great law of evolution be suppressed.”  The second part of his book is occupied with a development of this line of argument.  By this doctrine of evolution he does not mean the Darwinian hypothesis, although he accepts and includes this, looking upon natural selection as playing an important though not an unlimited part.  He would be an evolutionist with Mivart and Owen and Argyll, even if he had not the vera causa which Darwin contributed to help him on.  And, on rising to man, he takes ground with Wallace, saying: 

“I would wish to state distinctly that I do not at present see any evidence for believing in a gradual development of man from the lower animals by ordinary natural laws; that is, without some special interference, or, if it be preferred, some exceptional conditions which have thereby separated him from all other creatures, and placed him decidedly in advance of them all.  On the other hand, it would be absurd to regard him as totally severed from them.  It is the great degree of difference I would insist upon, bodily, mental, and spiritual, which precludes the idea of his having been evolved by exactly the same processes, and with the same limitations, as, for example, the horse from the palaeotherium.”