My Dear Sir

Many thanks for the kind manner in which you were good enough to receive my last communication, and also for your book which you so liberally present.—²

Since my last I introduced an Emberiza Schœniclus to my aviary, the only bird which noticed the new arrival was a Bullfinch ♂, he drove the Bunting about so unmercifully that I feared it must be removed, this Bullfinch is a very good tempered bird & I never before saw him molest any other bird, not even a specimen of the same species (schœniclus) also a captive with him, but which only differed by not yet having a black crown to the head. I cannot myself but think the black cap was the cause of so much animosity.—³

I may observe in passing that Bullfinches pair for life, nor do I recollect ever to have seen them separate, even in a wild state.

It has been to me a great puzzle to account for the separation of the sexes in many gregarious birds; & after years of seeking but one little fact has come before me bearing on the subject.

A very old bird catcher informs me that Goldfinches are thus sexually divided, he has found that if the flock is caught feeding on Teazle (Dipsacus Fullonum) they are all males, or nearly so—but if on Betony (Scrofularia) they are nearly all females.—⁴

This he accounted for by the fact that the male has a beak a little longer than the female & was thus able to obtain the Teazle seed which the shorter beak of the female failed to reach.—⁵

This solution appears to me to be the true one & I can easily imagine the differentiation proceeding till the male & female become as different in the beak as the New Zealand Neomorpha⁶

With regard to sexual selection in Lepidoptera.—

I do not think D^r. Wallace’s observations are by any means conclusive, the Bombyx of which he speaks is probably that which feeds on the Ailanthus,⁷ this is not a bright colored species, and in common with the European Bombyx mori the ♂ is eager for copulation immediately after its wings are expanded, indeed all Bombyces are so, our own species Saturnia pavonia ♀ minor Lasiocampa Quercus ♀ and others,⁸ attract the ♂ when placed in an opaque box, I have known cases in which the male of the first must have come down the chimney into a room where the female had emerged from the cocoon in a breeding cage.— Moreover they do not feed & it is therefore essential that the procreative act should be performed without delay.—

The ♀ I am inclined to think in the case of all Bombyces is quite passive in the matter.—

I will however write further to you very soon.—

I am | My dear Sir | Yours most gratefully | J Jenner Weir

C Darwin Esq^r | Down