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Darwin Correspondence Project

To Nature   15 December [1879]1

fertility of hybrids from the common and chinese goose

In the “Origin of Species” I have given the case, on the excellent authority of Mr. Eyton, of hybrids from the common and Chinese goose (Anser cygnoides) being quite fertile inter se; and this is the most remarkable fact as yet recorded with respect to the fertility of hybrids, for many persons feel sceptical about the hare and the rabbit.2 I was therefore glad to have the opportunity of repeating the trial, through the kindness of the Rev. Dr. Goodacre, who gave me a brother and sister hybrid from the same hatch.3 A union between these birds was therefore a shade closer than that made by Mr. Eyton, who coupled a brother and sister from different hatches. As there were tame geese at a neighbouring farm-house, and as my birds were apt to wander, they were confined in a large cage; but we found out after a time that a daily visit to a pond (during which time they were watched) was indispensable for the fertilisation of the eggs.4 The result was that three birds were hatched from the first set of eggs; two others were fully formed, but did not succeed in breaking through the shell; and the remaining first-laid eggs were unfertilised. From a second lot of eggs two birds were hatched. I should have thought that this small number of only five birds reared alive indicated some degree of infertility in the parents, had not Mr. Eyton reared eight hybrids from one set of eggs. My small success may perhaps be attributed in part to the confinement of the parents and their very close relationship. The five hybrids, grandchildren of the pure parents, were extremely fine birds, and resembled in every detail their hybrid parents. It appeared superfluous to test the fertility of these hybrids with either pure species, as this had been done by Dr. Goodacre;5 and every possible gradation between them may be commonly seen, according to Mr. Blyth and Capt. Hutton in India, and occasionally in England.6

The fact of these two species of geese breeding so freely together is remarkable from their distinctness, which has led some ornithologists to place them in separate genera or sub-genera.7 The Chinese goose differs conspicuously from the common goose in the knob at the base of the beak, which affects the shape of the skull; in the very long neck with a stripe of dark feathers running down it; in the number of the sacral vertebræ; in the proportions of the sternum; markedly in the voice or “resonant trumpeting,” and, according to Mr. Dixon, in the period of incubation, though this has been denied by others.8 In the wild state the two species inhabit different regions. I am aware that Dr. Goodacre is inclined to believe that Anser cygnoides is only a variety of the common goose raised under domestication. He shows that in all the above indicated characters, parallel or almost parallel variations have arisen with other animals under domestication.9 But it would, I believe, be quite impossible to find so many concurrent and constant points of difference as the above, between any two domesticated varieties of the same species. If these two species are classed as varieties, so might the horse and ass, or the hare and rabbit.

The fertility of the hybrids in the present case probably depends to a limited degree (1) on the reproductive power of all the Anatidæ10 being very little affected by changed conditions, and (2) on both species having been long domesticated. For the view propounded by Pallas, that domestication tends to eliminate the almost universal sterility of species when intercrossed, becomes the more probable the more we learn about the history and multiple origin of most of our domesticated animals.11 This view, in so far as it can be trusted, removes a difficulty in the acceptance of the descent-theory, for it shows that mutual sterility is no safe and immutable criterion of specific difference. We have, however, much better evidence on this head, in the fact of two individuals of the same form of heterostyled plants, which belong to the same species as certainly as do two individuals of any species, yielding when crossed fewer seeds than the normal number, and the plants raised from such seeds being, in the case of Lythrum salicaria, as sterile as are the most sterile hybrids.12

Charles Darwin

Down, December 15


The year is established by the date of publication of this letter in Nature.
In Origin 6th ed., p. 240, CD described Thomas Campbell Eyton’s success in breeding together hybrids of the common and the Chinese goose, which were then, according to CD, generally ranked in different genera. The Chinese goose is a domestic variety of the wild swan goose (Anser cygnoides). The common European domestic goose is a variety of the wild greylag goose (Anser anser). On hare–rabbit crosses, see Correspondence vol. 19, letter from L. H. Morgan, [1 August 1871] and n. 5.
In Origin 6th ed., p. 240, CD wrote:

I am assured by two eminently capable judges, namely Mr. Blyth and Capt. Hutton, that whole flocks of these crossed geese are kept in various parts of the country; and as they are kept for profit, where neither pure parent-species exists, they must certainly be highly or perfectly fertile.

See Correspondence vol. 5, letters from Edward Blyth, 4 August 1855, 22–3 August 1855, and 8 December 1855, and Correspondence vol. 6, letter from Thomas Hutton, 8 March 1856.
See Brandt 1836, p. 5, G. R. Gray 1840, p. 73, and Dixon 1848, pp. 82, 87.
Edmund Saul Dixon. See Dixon 1848, pp. 85 and 142. CD’s annotated copy of Dixon 1848 is in the Darwin Library–CUL (Marginalia rev. ed.).
See Correspondence vol. 26, letter from F. B. Goodacre, 2 September 1878 and n. 2.
Anatidae is the family of ducks, geese, and swans.
Pyotr Simon Pallas. See Variation 1: 31 n. 46, and Pallas 1780, p. 100.
See ‘Three forms of Lythrum salicaria. CD had recently republished this and other papers on dimorphic and trimorphic flowers in Forms of flowers.


Brandt, Joannes Fridericus. 1836. Descriptiones et icones animalium rossicorum novorum vel minus rite cognitorum. Aves: fasciculus 1. St Petersburg: Academia Scientiarum.

Dixon, Edmund Saul. 1848. Ornamental and domestic poultry: their history and management. London: Office of the “Gardeners’ Chronicle”.

Gray, George Robert. 1840. A list of the genera of birds, with an indication of the typical species of each genus. London: Richard and John E. Taylor.

Pallas, Pyotr Simon. 1780. Mémoire sur la variation des animaux; première partie. Acta Academiæ Scientiarum Imperialis Petropolitanæ (1780 pt 2): 69–102.

‘Three forms of Lythrum salicaria’: On the sexual relations of the three forms of Lythrum salicaria. By Charles Darwin. [Read 16 June 1864.] Journal of the Linnean Society (Botany) 8 (1865): 169–96. [Collected papers 2: 106–31.]


CD has repeated a test of whether hybrids of the common and Chinese goose are fertile inter se. Reports his success, and comments on its significance for the theory of descent.

Letter details

Letter no.
Charles Robert Darwin
Sent from
Source of text
Nature, 1 January 1880, p. 207

Please cite as

Darwin Correspondence Project, “Letter no. 12391,” accessed on 31 March 2023,