Again, speaking of the principles of classification, Darwin writes:--
"We care not how trifling a character may be--let it be the mere inflection of the angle of the jaw, the manner in which an insect's wing is folded, whether the skin be covered by hair or feathers--if it prevail throughout many and different species, especially those having very different habits of life, it assumes high value [i.e. for purposes of classification]; for we can account for its presence in so many forms with such _different habits_, only by inheritance from a common parent. We may err in this respect in regard to single points of structure, but when several characters, let them be ever so trifling, concur throughout a large group of beings _having different habits_, we may feel almost sure, on the theory of descent, that these characters have been inherited from a common ancestor; and we know that such aggregated characters have especial value in classification[166]."
Now it is evident that this argument for the general theory of evolution would be destroyed, if Wallace's assumption of utility of specific characters as universal were to be entertained. And the fact of apparently "trifling" characters occurring throughout a large group of beings "having different habits" is proof that they are really trifling, or without utilitarian significance.
It is needless to multiply these quotations, for it appears to me that the above are amply sufficient to establish the only point with which we are here concerned, namely, that Darwin's opinion on the subject of utility in relation to specific characters was substantially identical with my own. And this is established, not merely by the literal meaning of the sundry passages here gathered together from different parts of his writings; but likewise, and perhaps still more, from the tone of thought which pervades these writings as a whole. It requires no words of mine to show that the literal meaning of the above quotations is entirely opposed to Mr. Wallace's view touching the _necessary_ utility of _all_ specific characters; but upon the other point--or the general tone of Mr. Darwin's thought regarding such topics--it may be well to add two remarks.