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Darwin Correspondence Project

To George Gabriel Stokes [12 February 1863?]1

6. Queen Anne St | London. W.


My dear Prof. Stokes

Absence from home has prevented me from sooner thanking you most sincerely for the trouble which you have so kindly taken for me. I was rather crazy with curiosity to know what the chances were.—2

I believe your way of stating the problem is rather better for me.— I think I understand your two letters.3 The second way of calculating the case is much the best for me.—

I have made a copy for myself of your M.S. sentence & have altered the few words & figures which are necessary. I cannot suppose that I have made any blunder; so if I do not receive your sentence back, I shall understand that it is right.

with my sincere thanks | pray believe me | Yours truly obliged | Ch. Darwin


The date is conjectured from the address; CD stayed at 6 Queen Anne Street, London, between 4 and 14 February 1863 (see ‘Journal’ (Correspondence vol. 11, Appendix II)). In 1863, 5 and 12 February were Thursdays. The wording of the letter suggests that Stokes’s letter was forwarded from Down, making 12 February the most likely date.
Stokes was a mathematical physicist and Lucasian professor at Cambridge University (DNB). CD had apparently asked Stokes to determine the statistical chances of the same peculiarity recurring in a family. In Variation 2: 5, CD stated on Stokes’s authority that, given a peculiarity occurring on average in one individual in a million, and a population of sixty million, consisting of ten million families of six members each, ‘the odds will be no less than 8333 millions to 1 that in the ten million families there will not be even a single family in which one parent and two children will be affected by the peculiarity in question’. See also the manuscript of CD’s ‘big book’ on species (Natural selection, pp. 480–1 n.), in which Stokes is cited with regard to the extreme improbability of the same rare peculiarity appearing in father and child without some genetic connection.
The letters from Stokes have not been found.


Thanks GGS for calculation [to determine the chances of the same peculiarity recurring in a family, see Variation 2: 5]

Letter details

Letter no.
Charles Robert Darwin
George Gabriel Stokes, 1st baronet
Sent from
London, Queen Anne St, 6
Source of text
Cambridge University Library Add 7656: D76
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 4085,” accessed on 17 July 2019,

Also published in The Correspondence of Charles Darwin, vol. 11