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Darwin Correspondence Project

To Fritz Müller   11 February 1868

Down. | Bromley. | Kent. S.E.

Feb. 11. 1868

My dear Sir,

I am working on Sexual Selection, and am much interested in the Subject. You will remember my asking you about the colours of the Sexes in the lower animals and you gave me some information.1 I now want especially to know any cases of inequality in the number of the two Sexes in any of the lower animals; Especially of cases in which the females are in excess. I want to see the bearing of such facts on Sexual Selection   Any facts in relation to the males fighting or of the attachment of the male to the female would be very useful to me.

Have you ever observed anything in regard to the musical powers of male insects? In short I should be grateful for any hints whenever you might have the time and inclination to write to me on the Subject. I well know that your kindness is unbounded and I fear it makes me rather unreasonable.

My new Book has sold very well, the whole Edition of 1500 copies being disposed of during the first week.2

Believe me, my dear Sir | to be yours very Sincerely | Charles Darwin

I think you mentioned in one of your letters some Crustaceans in which the sexes were very unequal in number. Was it the extraordinary Crustacean with dimorphic males? I am going to look through your Book “Fur Darwin”.3 I know of course the case of the Gelasimus (which differs much in colour in the two sexes) mentioned in your letter of April 1. 1867, in which you say the male much the most abundant; but I think(?) you have mentioned other cases.—4


The information on the proportion of the sexes in Crustacea may have been in a missing portion of one of Müller’s letters. CD had written to Müller about the dimorphic males in Tanais, which Müller had first described in Für Darwin (F. Müller 1864); see Correspondence vol. 13, letter to Fritz Müller, 10 August [1865]. Müller’s reply, dated 10 October 1865, has a portion missing.
Gelasimus is now Uca. See Correspondence vol. 15, letter from Fritz Müller, 1 April 1867. The case of Gelasimus is mentioned in Descent 1: 315.


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 27 vols to date. Cambridge: Cambridge University Press. 1985–.

Descent: The descent of man, and selection in relation to sex. By Charles Darwin. 2 vols. London: John Murray. 1871.

Variation: The variation of animals and plants under domestication. By Charles Darwin. 2 vols. London: John Murray. 1868.


Is working on sexual selection and is interested in any anomalous sex ratios in lower animals and any sex-related characters.

Letter details

Letter no.
Charles Robert Darwin
Johann Friedrich Theodor (Fritz) Müller
Sent from
Source of text
The British Library (Loan MS 10 no 21)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 5860,” accessed on 30 November 2020,

Also published in The Correspondence of Charles Darwin, vol. 16