My dear Wallace

You cannot well imagine how much I have been pleased by what you say about Pangenesis.² None of my friends will speak out, except to a certain extent Sir H. Holland who found it very tough reading, but admits that some view “closely akin to it” will have to be admitted.³ Hooker, as far as I understand him, which I hardly do at present, seems to think that the hypothesis is little more than saying that organisms have such & such potentialities.⁴

What you say exactly & fully expresses my feeling, viz that it is a relief to have some feasible explanation of the various facts, which can be given up as soon as any better hypothesis is found.

It has certainly been an immense relief to my mind; for I have been stumbling over the subject for years, dimly seeing that some relation existed between the various classes of facts. I now hear from H. Spencer that his views quoted in my foot-note refer to something quite distinct, as you seem to have perceived.⁵

I shall be very glad to hear at some future day, your criticisms on the “causes of variability”.

Indeed I feel sure that I am right about sterility & natural selection. Two of my grown up children who are acute reasoners have 2 or 3 times at intervals tried to prove me wrong, & when y^r letter came they had another try, but ended by coming back to my side.⁶ I do not quite understand your case, & we think that a word or 2 is misplaced. I wish some time you w^d consider the case under the following p^t of view. If sterility is caused or accumulated through Nat. Sel., then as every degree exists up to absolute barrenness, Nat. Sel. must have the power of increasing it. Now take 2 species A & B & assume that they are (by any means) half-sterile i.e. produce half the full number of offspring. Now try & make (by Nat. Sel) A & B absolutely sterile when crossed, & you will find how difficult it is. I grant, indeed it is certain, that the degree of sterility of the individuals of A & B will vary, but any such extra-sterile individuals of, we will say, A, if they shd hereafter breed with other individuals of A will bequeath no advantage to their progeny, by which these families will tend to increase in number over other families of A, which are not more sterile when crossed with B.

But I do not know that I have made this any clearer than in the Chapt. in my Book—⁷ — It is a most difficult bit of reasoning, which I have gone over & over again on paper with diagrams.—

I shall be intensely curious to see your Article in Journal of Travel.⁸

Many thanks for such answers as you could give. From what you say I sh^d have inferred that Birds of Paradise were probably polygamous.⁹ But after all perhaps it is not so important as I thought.— I have been going through the whole animal kingdom in reference to sexual selection, & am just got to beginning of Lepidoptera, ie to end of Insects—& shall then pass on to Vertebrata. But my Ladies next week are going (ill-luck to it) to take me nolens-volens to London for a whole month.—¹⁰

I suspect Owen wrote article in Athenæum, but I have been told that it is Berthold Seeman—¹¹ The writer despises & hates me.—

Hearty thanks for your letter— You have indeed pleased me, for I had given up the great God Pan as a still-born Deity— I wish you could be induced to make it clear with your admirable powers of elucidation in one of the Scientific Journals.—

I think we almost entirely agree about sexual selection: As I now follow you to large extent about protection to females, having always believed that colour was often transmitted to both sexes: but I do not go quite so far about protection.—¹²

Always yours most sincerely | Ch. Darwin