Most obviously "it follows" from the theory of selection that "every variety which is selected into a species is favoured and preserved in consequence of being, in some one or more respects, better adapted to its surroundings than its rivals." This, in fact, is no more than a re-statement of the theory itself. But it does _not_ follow that "every species which exists, exists in virtue of adaptation" _peculiar to that species_; i.e. that every species which exists, exists _in virtue of having been "selected_." This may or may not be true as a matter of fact: as a matter of logic, the inference is not deducible from the selection theory. Every variety which is "_selected into_" a species must, indeed, present some such peculiar advantage; but this is by no means equivalent to saying, "in other words," that every variety which _becomes_ a species must do so. For the latter statement imports a completely new assumption--namely, that every variety which _becomes_ a species must do so because it has been "_selected into_" a species. In short, what we are here told is, that if we believe the selection principle to have given origin to some species, we must further believe, "as a necessary consequence," that it has given origin to all species.
The above reply, which is here quoted _verbatim_ from _Nature_, Vol. 38, p. 616-18, proceeded to show that it does not belong to "the first principles of the theory of natural selection" to deny that no other cause than natural selection can possibly be concerned in the origin of species; and facts were given to prove that such unquestionably has been the case as regards the origin of "local" or "permanent" _varieties_. Yet such varieties are what Darwin correctly terms "incipient" species, or species in process of taking _origin_. Therefore, if Professor Huxley's criticism is to stand at all, we must accept it "as a necessary consequence of the theory of selection," that every such _variety_ "which exists, exists in virtue of adaptation"--a statement which is _proved_ to be untrue by the particular cases forthwith cited. But as this point has been dealt with much more fully in the text of the present treatise, I shall sum up the main points in a few words.