To Herbert Spencer   23 [February 1860]¹

My dear Sir

I write one line to thank you much for your note. Of my numerous (Private) critics, you are almost the only one who has put the philosophy of the argument, as it seems to me, in a fair way.— Namely, as an hypothesis (with some innate probability as it seems to me) which explains several groups of facts.—

You put the case of selection in your Pamphlet on population in a very striking & clear manner.² You do not say whether I am to return it; I have not yet had time to read it, for my very small power of work of any kind is much overtaxed.—

If you require the pamphlet back, kindly send me one line: if I do not hear I shall understand that I am to keep it.

My dear Sir | Yours sincerely | C. Darwin