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Darwin Correspondence Project

To J. D. Hooker   15 November [1856]1

Down Bromley Kent

Nov. 15th.—

My dear Hooker

I shall not consider all your notes on my M.S. for some weeks, till I have done with crossing; but I have not been able to stop myself meditating on your powerful objection to mundane cold period, viz that many fold more of the warm-temperate species ought to have crossed the Tropics that of the sub-arctic forms.—2 I really think that to those who deny modification of species, this would absolutely disprove my theory. But according to the notions which I am testing, viz that species do become changed & that time is a most important element (which I think I shall be able to show very clearly is the case) in such change, I think the result would be as follows. Some of the warm-temperate forms would penetrate the Tropics long before the subartic, & some might get across the Equator long before the sub-arctic forms could do so, (ie always supposing that the cold came on slowly) & therefore they must have been exposed to new associates & new conditions much longer than the sub-arctic. Hence I shd. infer that we ought to have in warm temperate S. hemisphere more representative or modified forms, & fewer identical species than in comparing the colder regions of the N. & S.— I have expressed this very obscurely, but you will understand, I think, what I mean.— It is a parallel case, (but with greater difference) to the species of the Mountains of S. Europe compared with the artic plants. The S. European alpine species having been isolated for a longer period than on the arctic islands. Whether there are many tolerably close species in the warmer temperate lands of the S. & N. I know not; as in La Plata, C. of Good Hope, & S. Australia compared to the North, I know not.— I presume it would be very difficult to test this; but perhaps you will keep it a little before your mind. For your argument strikes me as by far the most serious difficulty which has occurred to me.— All your critisms & approvals are in simple truth invaluable to me.—

I fancy I am right in speaking in this note of the species in common to N. & S as being rather sub-arctic than arctic.—

This letter does not require any answer: I have written it to ease myself & to get you just to bear your argument under the modification point of view in mind.—

I have had this morning a most cruel stab in the side on my notion of distribution of Mammals in relation to soundings.3

My dear Hooker | Yours most truly | C. Darwin


Dated by the relationship to the letter from J. D. Hooker, 9 November 1856.
A point presumably made by Hooker in person since it is not addressed in either the letter from J. D. Hooker, 9 November 1856, or the memorandum transcribed after that letter itemising Hooker’s queries about CD’s manuscript on geographical distribution.


CD finds JDH’s objections to a mundane cold period significant, and he endeavours to show how they do not rule out mutability.

He is writing on crossing.

Letter details

Letter no.
Charles Robert Darwin
Joseph Dalton Hooker
Sent from
Source of text
DAR 114: 182
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 1989,” accessed on 19 April 2021,

Also published in The Correspondence of Charles Darwin, vol. 6