CD encloses letter from Asa Gray, although it is critical of JDH.
Role of struggle in forming species in retreat from advancing glaciers.
Down Bromley Kent
My dear Hooker
I send enclosed, received this morning.— I send my
own,, also, as you might like to see it; please be sure return it.— As the facts about N. range are quite invaluable for me
for my theory of transport to America. If your letter is Botanical
private, I shd
Many thanks for your note received this morning, & now for another “wriggle” According to my notions, the sub-arctic species would advance in a body, advancing so as to keep climate nearly the same, & as long as they did this, I do not believe there would be any tendency to change, but only when the few got amongst foreign associates. When the tropical species retreated as far as they could to the equator, they would halt, & then the confusion would spread back in the line of march from the far north & the strongest would struggle forward &c &c (But I am getting quite poetical in my wriggles) In short I think the warm temperate would be exposed very much longer to those causes which I believe are alone efficient in producing change than the sub-arctic; but I must think more over this, & have a good wriggle I cannot quite agree with your proposition that because the sub-arctic have to travel twice as far, they wd be more liable to change. Look at the two Journeys which the Arctics have had from N. to S. & S. to North, with no change, as may be inferred, if my doctrine is correct, from similarity of Arctic species in America & Europe & in the Alps.— But I will not weary you; but I really & truly think your last objection is not so strong as it looks at first. You never make an objection without doing me much good.—
Hurrah a seed has just germinated after 21
Adios | C. Darwin
Owls & Hawks have often been seen in mid Atlantic.
- f1 1991.f1Dated by the relationship to the letter from Asa Gray, 4 November 1856 (see n. 2, below).
- f2 1991.f2A letter to Hooker from Asa Gray, sent by Gray to CD enclosed in the letter from Asa Gray, 4 November 1856.
- f3 1991.f3Letter from Asa Gray, 4 November 1856.
- f4 1991.f4See letter from J. D. Hooker, [16 November 1856].
- f5 1991.f5This experiment was recorded in CD's Experimental book, p. 17 (DAR 157a).