From A. R. Wallace   16 August [1868]¹

Dear Darwin

I ought to have written before to thank you for the copies of your papers on “Primula” and on “Cross Unions of Dimorphic plants &c.”² The latter is particularly interesting and the conclusion most important; but I think it makes the difficulty of how these forms, with their varying degrees of sterility, originated, greater than ever. If “natural selection” could not accumulate varying degrees of sterility for the plant’s benefit, then how did sterility ever come to be associated with one cross of a trimorphic plant rather than another? The difficulty seems to be increased by the consideration that the advantage of a cross with a distinct individual is gained just as well by illegitimate as by legitimate unions. By what means then did illegitimate unions ever become sterile? It would seem a far simpler way for each plant’s pollen to have acquired a prepotency on another individual’s stigma over that of the same individual, without the extraordinary complication of three differences of structure and eighteen different unions with varying degrees of sterility!.

However the fact remains an excellent answer to the statement, that sterility of hybrids proves the absolute distinctness of the parents.

I have been reading with great pleasure Mr. Bentham’s last admirable address, in which he so well replies to the gross misstatements of the Athenæum;, & also says a word in favour of Pangenesis.³ I think we may now congratulate you on having made a valuable convert, whose opinions on the subject, coming so late & being evidently so well considered will have much weight.

I am going to Norwich on Tuesday to hear D^r. Hooker, who I hope will boldly promulgate “Darwinianism” in his address.⁴ Shall we have the pleasure of seeing you there?

I am engaged in negociations about my book.⁵

Hoping you are well & getting on with your next volumes⁶ | Believe me | Yours very faithfully | Alfred R. Wallace—