either at the same time or subsequently, for protection, by the accumulation of variations limited in their transmission to the female sex.  I owe to your writings the consideration of this latter point.  But I cannot yet persuade myself that females alone have often been modified for protection.  Should you grudge the trouble briefly to tell me whether you believe that the plainer head and less bright colours of [female symbol][73] chaffinch, the less red on the head and less clean colours of [female symbol] goldfinch, the much less red on breast of [female symbol] bullfinch, the paler crest of goldencrest wren, etc., have been acquired by them for protection?  I cannot think so; any more than I can that the considerable differences between [female symbol] and [male symbol] house-sparrow, or much greater brightness of [male symbol] Parus caeruleus (both of which build under cover) than of [female symbol] Parus are related to protection.  I even misdoubt much whether the less blackness of blackbird is for protection.

Again, can you give me reason for believing that the merest differences between female pheasants, the female Gallus bankiva, the female of black grouse, the pea-hen, female partridge, have all special reference to protection under slightly different conditions?  I of course admit that they are all protected by dull colours, derived, as I think, from some dull-ground progenitor; and I account partly for their difference by partial transference of colour from the male, and by other means too long to specify; but I earnestly wish to see reason to believe that each is specially adapted for concealment to its environment.

I grieve to differ from you, and it actually terrifies me, and makes me constantly distrust myself.

I fear we shall never quite understand each other.  I value the cases of bright-coloured, incubating male fishes—­and brilliant female butterflies, solely as showing that one sex may be made brilliant without any necessary transference of beauty to the other sex; for in these cases I cannot suppose that beauty in the other sex was checked by selection.

I fear this letter will trouble you to read it.  A very short answer about your belief in regard to the [female symbol] finches and Gallinaceae would suffice.—­Believe me, my dear Wallace, yours very sincerely,

CH.  DARWIN.

* * * * *

9 St. Mark’s Crescent, S.W.  September 27, 1868.

Dear Darwin,—­Your view seems to be that variations occurring in one sex are transmitted either to that sex exclusively or to both sexes equally, or more rarely partially transferred.  But we have every gradation of sexual colours from total dissimilarity to perfect identity.  If this is explained solely by the laws of inheritance, then the colours of one or other sex will be always (in relation to their environment) a matter of chance.  I cannot think this.  I think Selection more powerful than laws of inheritance, of which it makes use, as shown by cases of two, three or four forms of female butterflies, all of which have, I have little doubt, been specialised for protection.