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Darwin Correspondence Project

To W. D. Fox   26 April [1855]

Down Farnborough Kent

Ap. 26th

My dear Fox

Very many thanks for telling me exactly what I wanted to know.—

With respect to infant Poultry, I meant to have explained, that I wished you to fix how many days old, so as best to show the first downy plumage, the proportions, size & general character of the young birds of the several Breeds.— What is most important is that the age shd. be exactly the same for all; I first proposed a week at hap-hazard. The younger the bird the better in the more important respect of showing the characters of the young;1 on the other hand, whilst very young, I fear there wd. be great difficulty in measuring the cartilaginous bones. Will you fix for me, for really it would be simple guess-work in me, who am so totally ignorant of Poultry?

Secondly I had not thought of the greater difficulty of getting old dead Cocks than Hens.—2 I shd. like to hear sometime from you, whether my impression is right that old cocks are more characteristic, in proportions of body, than are old Hens?— Thanks for suggestion about measuring Feathers.— I shd. state that it is not my present intention to think of giving description of each breed; But I look only to certain points or questions, as the relative variation at different ages.—the effect of disuse on different parts: the result of my one comparison in this latter respect of the Ducks skeletons surprised me much,—more especially the great increase in weight in bones of feet, but I probably told you all about this.3

Should a Call Duck ever die, I shd. be very glad of one for skeleton: Can you tell me whether they breed freely with common tame Duck? How are the young of the Call Ducks: Perhaps you will compare the young with the young of the common for me.—

Have you wild Turkeys now: I shd. be glad of one for skeleton, shd. one die naturally, more especially if they are tamed birds of the wild Breed.—

Lastly, there is no point I am so eminently curious about, shd you ever hear anything which wd help me, is whether crosses between very different breeds, as bull-dogs & greyhounds &c are ever (or in successive generations), in the least degree less fertile than the pure parents.—4 I know it is said commonly that they are more fertile, but one statement makes me in the least degree doubt this.—5

Can you forgive so much trouble?

To save you rereading this, & to give me, whenever convenient, a better chance of having answer, I have put on other side, an abstract of my queries.—

Most truly yours | C. Darwin

I return Mr Galtons6 letter with many thanks. diag (1) To fix yourself age of infant Poultry. (2) Are old Cocks more characteristic in form than old Hens? (3) Do Call Ducks breed freely with common? character of the Ducklings? a

chance dead Bird for skeleton. (4) Chance-Dead wild Turkey (5) Any information on fertility of mongrels of very diverse races.—ramme


CD was investigating the stage at which the differences in plumage in various domestic breeds begin to develop. See letter to W. D. Fox, 19 March [1855].
Cock-birds were usually killed for the table while relatively young. Hens were kept for a number of years for their eggs.
See letters to J. D. Hooker, 11 [December 1854], and to W. D. Fox, 19 March [1855].
CD was seeking evidence from the animal kingdom that paralleled his experiments on the crossing of varieties of cultivated plants, as described in letter to M. J. Berkeley, 7 April [1855]. On his theory, crosses between two very distinct varieties ought to be slightly less fertile than those between matching parents; such had been indicated to be the case with plants (Gärtner 1849). His interest in the offspring of bulldogs and greyhounds stems from a famous case in the eighteenth century in which Robert Walpole, Earl of Orford, who kept hounds and other sporting breeds of dogs at his estate of Houghton, Norfolk, crossed a greyhound with a bulldog. The results were described by William Youatt in Youatt 1845, pp. 31–2, and by CD in Variation 1: 41 and 2: 95. CD’s copy of Youatt 1845, is in the Darwin Library–CUL.
CD summarised his few facts on the fertility and interbreeding of dogs in Variation 1: 29–33.
Probably John Howard Galton, who had corresponded with William Darwin Fox in 1838 in response to a query by CD about Galton’s strain of bloodhounds (Correspondence vol. 2, letter from W. D. Fox, [c. November 1838]). Galton was a cousin of Fox’s father Samuel Fox.


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 28 vols to date. Cambridge: Cambridge University Press. 1985–.

Gärtner, Karl Friedrich von. 1849. Versuche und Beobachtungen über die Bastarderzeugung im Pflanzenreich. Mit Hinweisung auf die ähnlichen Erscheinungen im Thierreiche, ganz umgearbeitete und sehr vermehrte Ausgabe der von der Königlich holländischen Akademie der Wissenschaften. Stuttgart: E. Schweizerbart.

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

Youatt, William. 1845. The dog. London.


Explains more clearly what he is looking for in his work on poultry: relative variation at different ages, the effect of disuse on different parts, breeding between wild and domestic, and degree of fertility of "mongrels of very diverse races".

Letter details

Letter no.
Charles Robert Darwin
William Darwin Fox
Sent from
Source of text
Christ’s College Library, Cambridge (MS 53 Fox 89)
Physical description
ALS 8pp

Please cite as

Darwin Correspondence Project, “Letter no. 1675,” accessed on 19 May 2022,

Also published in The Correspondence of Charles Darwin, vol. 5