"As our knowledge advances, very slight differences, considered by systematists as of no importance in structure, are continually found to be functionally important; and I have been especially struck with this fact in the case of plants, to which my observations have of late years been confined. Therefore it seems to me rather rash to consider the slight differences between representative species, for instance those inhabiting the different islands of the same archipelago, as of no functional importance, and as not in any way due to natural selection[153]." [153] _Life and Letters_, vol. iii. p. 161. Now, with regard to this passage it is to be observed, as already remarked, that it refers to the formation of final judgements touching _particular cases_: there is nothing to show that the writer is contemplating _general principles_, or advocating on deductive grounds the dogma that specific characters must be necessarily and universally adaptive characters. Therefore, what he here says is neither more nor less than I have said. For I have always held that it would be "rather rash" to conclude that any given cases of apparent inutility are certainly cases of real inutility, _merely on the ground that utility is not perceived_. But this is clearly quite a distinct matter from resisting the _a priori_ generalization that all cases of apparent inutility must certainly be cases of real utility. And, I maintain, in every part of his writings, without any exception, where Darwin alludes to this matter of general principle, it is in terms which directly contradict the deduction in question. As the whole of this Appendix has been directed to proving that such is the case, it will now, I think, be sufficient to supply but one further quotation, in order to show that the above "latest expression of opinion," far from indicating that in his later years Darwin "inclined" to Mr. Wallace's views upon this matter, is quite compatible with a distinct "expression of opinion" to the contrary, in a letter written less than six years before his death. "In my opinion _the greatest error which I have committed_, has been not allowing sufficient weight to the direct action of the environment, i.e. food, climate, &c., _independently of natural selection_. Modifications thus caused, _which are neither of advantage nor disadvantage to the modified organisms_, would be especially favoured, as I can now see chiefly through your observations, _by isolation in a small area, where only a few individuals lived under nearly uniform conditions_[154]." [154] _Life and Letters_, vol. iii. p. 158. I will now proceed to quote further passages from Darwin's works, which appear to have escaped the notice of Mr. Wallace, inasmuch as they admit of no doubt regarding the allusions being to _specific_ characters.