To J. D. Hooker   23 November [1856]¹

My dear Hooker

I fear I shall weary you with letters; but do not answer this, for in truth & without flattery, I so value your letters, that after a heavy batch, as of late, I feel that I have been extravagant & have drawn too much money & shall therefore have to stint myself on another occasion.—

When I sent my M.S. I felt strongly that some preliminary questions on causes of variation ought to have been sent you. Whether I am right or wrong in these points is quite a separate question, but the conclusion which I have come to, quite independently of geographical distribution, is that external conditions (to which naturalists so often appeal) do by themselves very little. How much they do is the point of all others on which I feel myself very weak.— I judge from facts of variation under domestication, & I may yet get more light. But at present, after drawing up a rough copy on this subject, my conclusion is that external conditions do extremely little, except in causing mere variability. This mere variability, (causing the child not closely to resemble its parent) I look at as very different from the formation of a marked variety or new species.— (No doubt the variability is governed by laws, some of which I am endeavouring very obscurely to trace).— The formation of a strong variety or species, I look at as almost wholly due to the selection of what may be incorrectly called chance variations or variability. This power of selection stands in the most direct relation to time, & in state of nature can be only excessively slow.— Again the slight differences selected, by which a race or species is at last formed, stands, as I think can be shown (even with plants & obviously with animals) in far more important relation to its associates than to external conditions.— Therefore, according to my principles, whether right or wrong, I cannot agree with your proposition that Time + altered conditions + altered associates are “convertible terms”. I look at first & last as far more important;—time being important only so far as giving scope to selection.— God knows, whether you will perceive at what I am driving.— I shall have to discuss & think more about your difficulty of the temperate & sub-arctic forms in S. hemisphere, than I have yet done.— But I am inclined to think I am right (if my general principles are right) that there would be little tendency to the formation of a new species, during the period of migration, whether shorter or longer; though considerable variability may have supervened.—

I will think whether to send notice to Linn. Journal about Owl seed; I almost doubt whether worth it.— Thanks for answer about Raspberry seeds.—² Where the Deuce can the Birds now get so many from? I have now found 9 kinds in Dung.—

I always thought from beginning to end, that D. C. had not done you justice; & independently of justice, that he was a goose not more to have used your materials³

Adios | My dear Hooker | Your’s | C. Darwin