Wishes to know whether differences in constitution (such as disease susceptibility) are related to differences in complexion. "Liability to such a disease as yellow fever would answer my question in the best possible way."
Down Bromley Kent
My dear Gray
It is a horrid shame to trouble you, busy as you always are, but there is one point on which I am very anxious to gain information & possibly it may be gained in the S. of your country & I can think of no one to apply to but you. Old writers often insist on differences of constitution going with complexion; & I want much to know whether there is any truth in this. It has occurred to me that liability to such a disease as yellow-fever would answer my question in the best possible way. Do you know anyone of a scientific mind to whom to apply to ask whether any observations have ever been made or published, whether Europeans (without of course any cross with negro-blood) of dark complexion & black hair are more liable or less liable to be attacked with yellow-fever, (or any remittent Fever) than persons of light complexion. If you could aid me in this it would be of much value to me. But do not trouble yourself to write merely to acknowledge this.—
I have just published a little notice in Gardeners Ch. on the fertilisation of Leguminous plants, which rather bears on our Fumariaceous discussion.
I sincerely hope that you are well & not working yourself to death
Pray believe me | My dear Gray | Yours most sincerely | C. Darwin
A sort of vague feeling comes over me that I have asked you all this before; if I have, I beg very many apologies.— I know I once wrote several letters to various parts of world for similar information.
- f1 2364.f1The year is given by CD's reference to having published a notice in Gardeners' Chronicle and Agricultural Gazette (see n. 3, below).
- f2 2364.f2No reply to CD's question has been found. Gray passed CD's query on to his friend George Engelmann, the botanist, in a letter dated 3 December (J. L. Gray ed. 1893, 2: 447):
Darwin asks me to find out if you medical men have ascertained or noticed any difference in liability to take fevers of warm climates, say yellow fever, between light-complexioned and dark-complexioned people of the Caucasian race. If you know personally anything about it, or where anything is published bearing on the point, kindly let me know.CD may have become interested in verifying a statement made by William Freeman Daniell in 1856 that ‘a sanguineous or choleric, or light complexioned man stands the African climate twice as well and as long again as the melancholic or dark complexioned man’ (Correspondence vol. 6, letter from W. F. Daniell, 8 October – 7 November 1856). See also Descent 1: 244–5.
- f3 2364.f3See letter to Gardeners' Chronicle, [before 13 November 1858]. CD refers to his correspondence with Gray about the mechanism of fertilisation in the Fumariaceae. See Correspondence vol. 6, letter from Asa Gray, 7 July 1857, and letters to Asa Gray, 20 July  and 29 November . See also letter from Asa Gray, 21 June 1858, and letter to Asa Gray, 4 July 1858. The apparent self-fertilisation of Leguminosae and Fumariaceae presented difficulties for CD's hypothesis that all organisms occasionally cross (Natural selection, pp. 53, 68–71).
- f4 2364.f4None of CD's earlier letters on this question have been found. The letter from W. F. Daniell (see n. 2, above) was probably a reply to one such letter.