On sterility of natural species and natural selection. Closely allied forms from adjacent islands offer best chance of finding good species fertile inter se.
Problem of minute variations and sexual selection.
March 19th. 1868
I should very much value a large Photograph of you, and also a carte for my album, though it is too bad to ask you for both, as you must have so many applicants.
I am sorry I shall not see you in town but shall look forward with pleasure to paying you a visit in the summer.
I am sorry about the Primulas, but I feel sure some equally good case will some day be discovered, for it seems impossibible to understand how all natural species whatever should have acquired sterility. Closely allied forms from adjacent islands would, I should think, offer the best chance of finding good species fertile ``inter se''; since even if nat. select. induces sterility I do not see how it could affect them, or why they should always be sterile, and varieties never.
I am glad you have got good materials on sexual selection. It
is no doubt a difficult subject. One difficulty to me is,
that I do not see how the constant minute variations, which
are sufficient for nat. select to work with,—could be
sexually selected. We seem to require a series of bold and
abrupt variations. How can we imagine than an inch in the tail
of the peacock, or
Pray let me see what your son says about the ``Sterility selection'' question. I am deeply interested in all that concerns the powers of Nat. selection, but though I admit there are a few things it cannot do I do not yet believe sterility to be one of them.
In case your son has turned his attention to Mathematical Physics, will you ask him to look at the enclosed question, which I have vainly attempted to get an answer to?
Believe me | Yours very faithfully | Alfred R. Wallace—
- f1 6024.f1See letter to A. R. Wallace, 17 [March 1868] and n. 3).
- f2 6024.f2See letter to A. R. Wallace, 17 [March 1868] and nn. 4 and 5.
- f3 6024.f3Wallace had misunderstood what CD's paper, `Specific difference in Primula', was about (see letter from A. R. Wallace, 15 March  and n. 6).
- f4 6024.f4In his letter of 17 [March 1868], CD wrote that he had traced the gradational steps by which the peacock's tail had developed.
- f5 6024.f5Wallace refers to his argument that hybrid sterility could be produced through the action of natural selection (see letter from A. R. Wallace, 1 March 1868 and enclosure). George Howard Darwin had written a critique of Wallace's work (see letter to A. R. Wallace, 17 [March 1868]).
- f6 6024.f6The enclosure has not been found, but see the letter from G. H. Darwin,  March  and n. 4.