I am worse than ever in bearing any excitement. Even talking of an evening for less than two hours has twice recently brought on such violent vomiting and trembling that I dread coming up to London. I hear that you came out strong at Cambridge (145/5. Prof. Owen, in a communication to the British Association at Cambridge (1862) "On a tooth of Mastodon from the Tertiary marls, near Shanghai," brought forward the case of the Australian Mastodon as a proof of the remarkable geographical distribution of the Proboscidia. In a subsequent discussion he frankly abandoned it, in consequence of the doubts then urged regarding its authenticity. (See footnote, page 101, in Falconer's paper "On the American Fossil Elephant," "Nat. Hist. Review," 1863.)), and am heartily glad you attacked the Australian Mastodon. I never did or could believe in him. I wish you would read my little Primula paper in the "Linnean Journal," Volume VI. Botany (No. 22), page 77 (I have no copy which I can spare), as I think there is a good chance that you may have observed similar cases. This is my real hobby-horse at present. I have re-tested this summer the functional difference of the two forms in Primula, and find all strictly accurate. If you should know of any cases analogous, pray inform me. Farewell, my good and kind friend.
LETTER 146. TO J.D. HOOKER.
(146/1. The following letter is interesting in connection with a letter addressed to Sir J.D. Hooker, March 26th, 1862, No. 136, where the value of Natural Selection is stated more strongly by Sir Joseph than by Darwin. It is unfortunate that Sir Joseph's letter, to which this is a reply, has not been found.)
Down, November 20th [1862].
Your last letter has interested me to an extraordinary degree, and your truly parsonic advice, "some other wise and discreet person," etc., etc., amused us not a little. I will put a concrete case to show what I think A. Gray believes about crossing and what I believe. If 1,000 pigeons were bred together in a cage for 10,000 years their number not being allowed to increase by chance killing, then from mutual intercrossing no varieties would arise; but, if each pigeon were a self-fertilising hermaphrodite, a multitude of varieties would arise. This, I believe, is the common effect of crossing, viz., the obliteration of incipient varieties. I do not deny that when two marked varieties have been produced, their crossing will produce a third or more intermediate varieties. Possibly, or probably, with domestic varieties, with a strong tendency to vary, the act of crossing tends to give rise to new characters; and thus a third or more races, not strictly intermediate, may be produced. But there is heavy evidence against new characters arising from crossing wild forms; only intermediate races are then produced. Now, do you agree thus far? if not, it is no use arguing; we must come to swearing, and I am convinced I can swear harder than you, therefore I am right. Q.E.D.
If the number of 1,000 pigeons were prevented increasing not by chance killing, but by, say, all the shorter-beaked birds being killed, then the WHOLE body would come to have longer beaks. Do you agree?
Thirdly, if 1,000 pigeons were kept in a hot country, and another 1,000 in a cold country, and fed on different food, and confined in different-size aviary, and kept constant in number by chance killing, then I should expect as rather probable that after 10,000 years the two bodies would differ slightly in size, colour, and perhaps other trifling characters; this I should call the direct action of physical conditions. By this action I wish to imply that the innate vital forces are somehow led to act rather differently in the two cases, just as heat will allow or cause two elements to combine, which otherwise would not have combined. I should be especially obliged if you would tell me what you think on this head.
But the part of your letter which fairly pitched me head over heels with astonishment, is that where you state that every single difference which we see might have occurred without any selection.