4. The doctrine in both its forms is deduced from a definition of the theory of natural selection as a theory, and the sole theory, of the origin of _species_; but, as Professor Huxley has already shown, it does not really follow, even from this definition, that all specific _characters_ must be "necessarily useful." Hence the two forms of the doctrine, although coincident with regard to species, are at variance with one another in respect of specific characters. Thus far, of course, I agree with Professor Huxley; but if I have been successful in showing that the above definition of the theory of natural selection is logically fallacious, it follows that the doctrine in both its forms is radically erroneous. The theory of natural selection is not, accurately speaking, a theory of the origin of species: it is a theory of the origin and cumulative development of adaptations, to whatever order of taxonomic division these may happen to belong. Thus the premisses of the deduction which we are considering collapse: the principle of utility is shown not to have any other or further reference to species, or to specific characters, than it has to fixed varieties, genera, families, &c., or to the characters severally distinctive of each. 5. But, quitting all such antecedent considerations, we next proceeded to examine the doctrine _a posteriori_, taking the arguments which have been advanced in favour of the doctrine, other than those which rest upon the fallacious definition. These arguments, as presented by Mr. Wallace, are two in number. First, it is represented that natural selection must occupy the whole field, because no other principle of change can be allowed to operate in the presence of natural selection. Now I fully agree that this statement holds as regards any principle of change which is deleterious, but I cannot agree that it does so as regards any such principle which is merely neutral. No reason has ever been shown why natural selection should interfere with "indifferent" characters--to adopt Professor Huxley's term--supposing such to have been produced by any of the agencies which we shall presently have to name. Therefore this argument--or rather assertion--goes for nothing.