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. I do and have always fully agreed; but you have got right round the subject, and viewed it from an entirely opposite and new side, and when you took me there I was astounded. When I say I agree, I must make the proviso, that under your view, as now, each form long remains adapted to certain fixed conditions, and that the conditions of life are in the long run changeable; and second, which is more important, that each individual form is a self-fertilising hermaphrodite, so that each hair-breadth variation is not lost by intercrossing. Your manner of putting the case would be even more striking than it is if the mind could grapple with such numbers—it is grappling with eternity—think of each of a thousand seeds bringing forth its plant, and then each a thousand. A globe stretching to the furthest fixed star would very soon be covered. I cannot even grapple with the idea, even with races of dogs, cattle, pigeons, or fowls; and here all admit and see the accurate strictness of your illustration.
Such men as you and Lyell thinking that I make too much of a Deus of Natural Selection is a conclusive argument against me. Yet I hardly know how I could have put in, in all parts of my book, stronger sentences. The title, as you once pointed out, might have been better. No one ever objects to agriculturalists using the strongest language about their selection, yet every breeder knows that he does not produce the modification which he selects. My enormous difficulty for years was to understand adaptation, and this made me, I cannot but think, rightly, insist so much on Natural Selection. God forgive me for writing at such length; but you cannot tell how much your letter has interested me, and how important it is for me with my present book in hand to try and get clear ideas. Do think a bit about what is meant by direct action of physical conditions. I do not mean whether they act; my facts will throw some light on this. I am collecting all cases of bud-variations, in contradistinction to seed-variations (do you like this term, for what some gardeners call "sports"?); these eliminate all effects of crossing. Pray remember how much I value your opinion as the clearest and most original I ever get.
I see plainly that Welwitschia (146/2. Sir Joseph's great paper on Welwitschia mirabilis was published in the "Linn. Soc. Trans." 1863.) will be a case of Barnacles.
I have another plant to beg, but I write on separate paper as more convenient for you to keep. I meant to have said before, as an excuse for asking for so much from Kew, that I have now lost TWO seasons, by accursed nurserymen not having right plants, and sending me the wrong instead of saying that they did not possess.
LETTER 147. TO J.D. HOOKER. Down, 24th {November, 1862}.
I have just received enclosed for you, and I have thought that you would like to read the latter half of A. Gray's letter to me, as it is political and nearly as mad as ever in our English eyes. You will see how the loss of the power of bullying is in fact the sore loss to the men of the North from disunion.
I return with thanks Bates' letter, which I was glad to see. It was very good of you writing to him, for he is evidently a man who wants encouragement. I have now finished his paper (but have read nothing else in the volume); it seems to me admirable. To my mind the act of segregation of varieties into species was never so plainly brought forward, and there are heaps of capital miscellaneous observations.
I hardly know why I am a little sorry, but my present work is leading me to believe rather more in the direct action of physical conditions. I presume I regret it, because it lessens the glory of Natural Selection, and is so confoundedly doubtful. Perhaps I shall change again when I get all my facts under one point of view, and a pretty hard job this will be. (147/1. This paragraph was published in "Life and Letters," II., page 390. It is not clear why a belief in "direct action" should diminish the glory of Natural Selection, since the changes so produced must, like any other variations, pass through the ordeal of the survival of the fittest. On the whole question of direct action see Mr. Adam Sedgwick's "Presidential Address to the Zoological Section of the British Association," 1899.)