Of course, if a species with warning colours were, in part, completely isolated, and its colours or markings were accidentally different from the parent form, whatever set of markings and colours it had would be, I consider, rendered stable for recognition, and also for protection, since if it varied too much the young birds and other enemies would take a heavier toll in learning it was uneatable.  It might then be said that the character by which this species differs from the parent species is a useless character.  But surely this is not what is usually meant by a “useless character.”  This is highly useful in itself, though the difference from the other species is not useful.  If they were in contact it would be useful, as a distinction preventing intercrossing, and so long as they are not brought together we cannot really tell if it is a species at all, since it might breed freely with the parent form and thus return back to one type.  The “useless characters” I have always had in mind when arguing this question are those which are or are supposed to be absolutely useless, not merely relatively as regards the difference from an allied species.  I think this is an important distinction.—­Yours very truly,

ALFRED R. WALLACE.

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HERBERT SPENCER TO A.R.  WALLACE

64 Avenue Road, Regent’s Park, London, N.W.  September 28, 1895

Dear Mr. Wallace,—­As I cannot get you to deal with Lord Salisbury I have decided to do it myself, having been finally exasperated into doing it by this honour paid to his address in France—­the presentation of a translation to the French Academy.  The impression produced upon some millions of people in England cannot be allowed to be thus further confirmed without protest.

One of the points which I propose to take up is the absurd conception Lord Salisbury sets forth of the process of Natural Selection.  When you wrote you said you had dealt with it yourself in your volume on Darwinism.  I have no doubt that it is also in some measure dealt with by Darwin himself, by implication or incidentally.  You of course know Darwin by heart, and perhaps you would be kind enough to save me the trouble of searching by indicating the relevant passages both in his books and in your own.  My reading power is very small, and it tries me to find the parts I want by much reading.—­Truly yours,

HERBERT SPENCER.

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To the following letter from Mr. Gladstone, Wallace attached this pencil note:  “In 1881 I put forth the first idea of mouth-gesture as a factor in the origin of language, in a review of E.B.  Tylor’s ‘Anthropology,’ and in 1895 I extended it into an article in the Fortnightly Review, and reprinted it with a few further corrections in my ‘Studies,’ under the title ’The Expressiveness of Speech or Mouth-Gesture as a Factor