There are so many doubtful points on the problems relating to sterility that they will never agree.
4 Chester Place | R. Park. N.W | Until April 1
My dear Wallace
My son has failed in your problem & says that it is ``excessively difficult'': he says you will find something about it in Thompson & Tait Nat Philos (Art. 649). He has, however sent the solution, if the plate rested on a square rim, but he supposes this will not answer your purpose; nevertheless I have forwarded it by this same post.— It seems that the rim being round makes the problem much more difficult.—
I enclose my photograph, which I have received from Down.
I sent your answer to George on his objections to your argument on sterility but have not yet heard from him.— I dread beginning to think over this fearful problem, which I believe beats the plate on the circular rim; but I will sometime. I foresee, however, that there are so many doubtful points, that we shall never agree.
As far as a glance serves it seems to me, perhaps falsely, that you sometimes argue that hybrids have an advantage from greater vigour, & sometimes a disadvantage from not being so well fitted to their conditions.— Heaven protect my stomach whenever I attempt following your argument.—
Your's most sincerely | C. Darwin
- f1 6058.f1The year is established by the relationship between this letter and the letter from A. R. Wallace, 19 March 1868.
- f2 6058.f2CD refers to George Howard Darwin. See letter from G. H. Darwin,  March  and n. 4.
- f3 6058.f3See letter to A. R. Wallace 17 [March 1868] and n. 7.
- f4 6058.f4For George's critique of Wallace's argument that hybrid sterility could result from natural selection, see the enclosure to the letter to A. R. Wallace, [21 March 1868]. For Wallace's reply to George's comments, see the letter from A. R. Wallace, 24 March .