My dear Wallace

I am hard at work on sexual selection & am driven half mad by the number of collateral points which enquire investigation, such as relative number of the two sexes, & especially on polygamy. Can you aid me with respect to birds which have strongly marked secondary sexual characters, such as Birds of Paradise, Humming-birds, the Rupicola² or Rock thrush, or any other such cases. Many Gallinaceous Birds certainly are polygamous. I suppose that birds may be known not to be polygamous if they are seen during the whole breeding season to associate in pairs, or if the male incubates, or aid in feeding the young.

Will you have the kindness to turn this in your mind; but it is a shame to trouble you now that, as I am heartily glad to hear, you are at work on your Malayan travels.³ I am fearfully puzzled how far to extend your protective views with respect to the females in various classes.⁴ The more I work the more important sexual selection apparently comes out.

Can butterflies be polygamous? ie will one male impregnate more than one female? Forgive me troubling you & I daresay I shall have to ask your forgiveness again, & believe me, | My dear Wallace, | yours most sincerely | Ch. Darwin

P.S. Bates has had the kindness to set the Entomolg. soc. discussing the relative numbers of the sexes in insects & has brought out some very curious results.⁵

Is Orang polygamous, but I daresay I shall find that in your papers in (I think Annals. & Mag. of Nat. Hist.—⁶