My dear Wallace

I am very much obliged for all your trouble in writing me your long letter, which I will keep by me & ponder over.² To answer it would require at least 200 folio pages! If you could see how often I have rewritten some pages, you would know how anxious I am to arrive as near as I can to the truth.³ We differ, I think, chiefly from fixing our minds perhaps too closely on different points, on which we agree: I lay great stress on what I know takes place under domestication.. I think we start with different fundamental notions on inheritance. I find it most difficult but not, I think, impossible to see how, for instance, a few red feathers appearing on the head of a male bird, & which are at first transmitted to both sexes, could come to be transmitted to males alone;⁴ XXX but I have no difficulty in making the whole head red if the few red feathers in the males from the first tended to be sexually transmitted.⁵ I am quite willing to admit that the female may have been modified, 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.—⁶ 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 & less bright colours of ♀ chaffinch,—the less red on the head & less clean colours of ♀ gold-finch—the much less red on breast of ♀ Bull-finch—the paler crest of Golden-crest Wren—&c—have been acquired by them for protection.—⁷ I cannot think so; anymore than I can that the considerable differences between ♀ & ♂ House Sparrow—or much greater brightness of ♂ Parus cæruleus (both of which build under cover) than of ♀ Parus, are related to protection.—⁸ I even misdoubt much whether less blackness of ♀ Blackbird is for protection.—

Again can you give me reason for believing that the modest differences between female Pheasants, the female Gallus bankiva, female of Black-Grouse—the PeaHen—female Partridge, have all special reference to protection under slightly different conditions.—⁹ I of course admit that they are all protected by dull colours, derived, as I think, from some dull-ground progenitor; & I account partly for their difference by partial transference of colour from the male; & 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, & it actually terrifies me & makes me constantly distrust myself.—

I fear we shall never quite understand each other. I value the cases of bright-coloured, incubating male fishes¹⁰—& 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.—¹¹

I fear this letter will trouble you to read it.— A very short answer about your belief in regard to the ♀ finches & gallinaceæ would suffice.—

Believe me | My dear Wallace | Yours very sincerely | Ch Darwin

XXX addendum

It is not enough that females sh^d be produced from the males with red feathers, which should be destitute of red feathers; but these females must have a latent tendency to produce such feathers, otherwise they would cause deterioration in the red head feathers of their male offspring.¹² Such latent tendency w^d be shown by their producing the red feathers when old or diseased in their ovaria.—