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Darwin Correspondence Project

To F. S. Arnold   31 December [1878]1

Dec. 31st.

Dear Sir

I do not think that the two passages essentially contradict each other, but if I had to write them again I would owing to your criticism slightly modify them.2 The forms which most jostle each other I believe to be generally “varieties of the same species, & species of the same genus or of related genera”.— I would now insert “closely related genera”. In the other passage (p. 89) the forms which are able to live when exposed to severe competition are not varieties of the same species or sub-species but “belong to what we call distinct genera and orders”.— I would now add “quite distinct genera” or something to the same effect. But I know well that I often fail to think clearly & to express myself clearly.


The year is established by the relationship between this letter and the letter from F. S. Arnold, [2]6 December 1878.
See letter from F. S. Arnold, [2]6 December 1878 and n. 2. CD refers to passages in Origin 6th ed., pp. 86 and 89.


Origin 6th ed.: The origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. 6th edition, with additions and corrections. By Charles Darwin. London: John Murray. 1872.


Responds to criticism concerning varieties, species, and genera.

Letter details

Letter no.
Charles Robert Darwin
Francis Sorell Arnold
Sent from
Source of text
DAR 143: 21
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 11813,” accessed on 19 September 2021,