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Darwin Correspondence Project

To Richard Spruce   1 April 18691

The facts which you state are extraordinary, and quite new to me.2 If you can prove that the effects produced by ants are really inherited, it would be a most remarkable fact, and would open up quite a new field of inquiry. You ask for my opinion; if you had asked a year or two ago I should have said that I could not believe that the visits of the ants could produce an inherited effect; but I have lately come to believe rather more in inherited mutilations. I have advanced in opposition to such a belief, galls not being inherited. After reading your paper I admit, Firstly, from the presence of sacs in plants of so many families, and their absence in certain species, that they must be due to some extraneous cause acting in tropical South America. Secondly, I admit that the cause must be the ants, either acting mechanically or, as may perhaps be suspected from the order to which they belong, from some secretion. Thirdly, I admit, from the generality of the sacs in certain species, and from your not having observed ants in certain cases (though may not the ants have paid previous visits?), that the sacs are probably inherited. But I cannot feel satisfied on this head. Have any of these plants produced their sacs in European hot-houses? Or have you observed the commencement of the sacs in young and unfolded leaves which could not possibly have been visited by the ants? If you have any such evidence, I would venture strongly to advise you to produce it …

I may add that you are not quite correct (towards the close of your paper) in supposing that I believe that insects directly modify the structure of flowers. I only believe that spontaneous variations adapted to the structure of certain insects flourish and are preserved.3


The date is provided by Alfred Russel Wallace, the editor of Spruce 1908, from which this transcription of part of CD’s letter is taken.
Spruce had written, ‘The inimitable researches of Mr. Darwin have rendered it (to my mind) almost certain that many of the deviations from symmetry in the form and direction of the parts of a flower have been brought about by the direct mechanical agency of insects’ (Spruce 1908, 2: 408).


Spruce, Richard. 1908. Notes of a botanist on the Amazon & Andes, being records of travel … during the years 1849–1864. Edited by Alfred Russel Wallace. 2 vols. London: Macmillan and Co.


RS’s facts are remarkable. A year or two ago CD would not have believed ants could produce an inherited effect, but he has "lately come to believe rather more in inherited mutations". However, CD is not satisfied that the sacs are inherited and urges RS to produce any other evidence he might have.

Letter details

Letter no.
Charles Robert Darwin
Richard Spruce
Sent from
Source of text
Spruce 1908, 2: 385

Please cite as

Darwin Correspondence Project, “Letter no. 6691,” accessed on 23 September 2021,

Also published in The Correspondence of Charles Darwin, vol. 17