The date is established by the style of the printed stationery, which is a type that CD started using in May 1861, and by the fact that CD refers to having heard of fertile hybrids of Gallus sonneratii ‘many years ago’ (see also n. 3, below). In 1862, hybrids of G. sonneratii and G. bankiva (assumed to be the domestic fowl) were shown to have limited fertility at the Zoological Gardens in London (S. J. A. Salter 1863). CD reported these findings in Variation 1: 234, citing S. J. A. Salter 1863, which was published in the April issue of Natural History Review. After April 1863, one would expect CD to refer Eyton to John William Salter’s publication.

No further information on Eyton’s crossed pigs has been found. CD and Eyton had corresponded in 1856 about the offspring of an African pig, belonging to Rowland Hill, and a common pig (see Correspondence vol. 6, letter to T. C. Eyton, 21 August [1856]).

See Correspondence vol. 10, letter from T. C. Eyton, [after 19 May 1862?]; the ‘jungle fowl’ mentioned in that letter (to which this letter may be a reply) may have been Gallus sonneratii. In Natural selection, p. 435 n. 12, CD wrote, ‘several years ago I myself saw at the Zoological Gardens young birds, which were the offspring of hybrids inter se from a Sonnerat cock & Bantam Hen’. (Natural selection, the manuscript of CD’s ‘big book’ on species, was written between 1856 and 1858.) See also Variation 1: 234, where CD also cited Edward Blyth for information about Gallus sonneratii crossing with domestic hens in India.