Dear Mr. Darwin,

Thank you very much for the copy of your new work which you have been so kind as to send me.¹ I have not yet read very much of it, for my reading power is so limited that it does not suffice even for getting through the chief books bearing on my immediate topic, and what I read on any other topic is read, as it were, by stealth.

What I have read, however, has surprised me by the immense accumulation of evidence, interesting in itself and doubly interesting by its implications, which you have brought to bear on the questions you discuss. I had no idea that such multitudinous proofs of the action of sexual selection were forthcoming.

I am glad that you have so distinctly expressed your conviction on the more special question you treat.² It will, I doubt not, raise afresh the agitation on the general question; since many who have in a considerable degree reconciled themselves to the conception of evolution at large, have never had represented to them, in a positive way, these ultimate implications of it. Many such will doubtless fight against them; and out of the fighting there is sure to come further progress.

I very much wish that this book of yours had been issued somewhat earlier, for it would have led me to introduce some needful explanations into the first volume of the Principles of Psychology, lately published.³ One of these explanations I may name. Though I have endeavoured to shew that instinct is compound reflex action, yet I do not intend thereby to negative the belief that instincts of some kinds may arise at all stages of evolution, by the selection of advantageous variations. I believe that some instincts do thus arise; and especially those which are operative in sexual choice.

I am, | Very Sincerely Yours | Herbert Spencer