skip to content

Darwin Correspondence Project

From Richard Sutton Ford   6 May 1839

Answers to “Questions about the Breeding of Animals”.1

Qy. 1 In crossing varieties of cattle & sheep, I have observed generally, that although the first cross has usually produced a satisfactory result—such in fact as might have been expected—a remarkable inconstancy has often attended subsequent crossings between this progeny and either of the parent stocks, as well as the breeding from the produce of the cross exclusively.

Qy. 4. In crossing between an old established variety, and a new, or mixed breed, the progeny will usually take more after the former than the latter. I may instance the effect produced by crossing our variously bred mares with an Arabian Stallion, in which the peculiarities of the sire have been remarkably impressed on the offspring, and continued through many generations, though of course becoming gradually weaker in each: nor am I inclined to attribute this to the power of the sex, although not aware that we have any examples of Arabian mares having been put to our native stallions. But in breeding sheep, which I have crossed both ways, between several of our old varieties and the new Leicestershire breed, I have not been able to determine, on the whole, that there was any preponderance of character in favour of either sire or dam, though in numerous cases the offspring has taken much more after the one parent than the other.

The colours of the progeny of domestic animals are extremely capricious. In crossing a black-sided, long-horned cow, with a red and white mottled bull, of the short-horned Durham breed, the produce in one year was a calf almost entirely red, and in the following year a white one. And I have now in my possession a brown horse, the sire and dam of which were both grey: nor do I mention these as being at all rare instances of the kind.

Qy. 12. The sexual passion of the males, in cattle and sheep at least, appears to be wholly indiscriminate, without regard to age, symmetry, or colour—the females, if not in almost perfect health, are never in season for the male— It may be remarked however, that a bull or ram, having served one female, will commonly prefer a fresh one to the same again; and sometimes when he has such choice, after having served the whole, he will continue to follow a particular one, though I think this is wholly incidental, and not the effect of partiality or design. Whether or not any preference of a more marked kind is shewn by these male animals in their wild state, I am unable to say—

Qy. 16 Most of our fine breeds of cattle & sheep (or what is termed by Breeders, “High Blood”) have been raised by breeding “in and in”; and when this has been pursued to a great extent—that is, through many generations—the result has been, feeble virility with effeminate appearance in the males; weak passion in the females, which even in sheep rarely produce twins; and diminutive size and great delicacy in the offspring during the first month; to which may be added, that a deficient supply of milk is usually a consequence of this high breeding. But whether these habits arise altogether from breeding in and in, or are more or less occasioned by the finest-boned and smallest-headed males being selected to breed from—such animals being most disposed to take on fat—I do not undertake to determine. Certain it is however, that in these extreme cases, the procreative powers of the stock have been in a great measure sacrificed in order to attain the greatest possible tendency to fatten.

I will here notice one curious and well established fact, which so far as I am aware is peculiar to cattle: If a cow produce at one birth, two male calves, or two females, in either case both animals will be fertile; but if she produce a male and a female calf at the same birth, though the male will possess the power of propagating his species, the female is invariably barren.

Qy. 18 That the dispositions of animals are not altogether the effect of training, but in some degree at least hereditary, may be gathered from the circumstance, that if the eggs of wild fowl—as of the wild-duck for example—be hatched under a tame duck, or dunghill hen, the produce will shew in a striking manner their wild habits: on the approach of intruders which would scarcely attract the notice of ducklings regularly descended from any of our tame breeds, they will endeavour to escape, or hide themselves; and on arriving at maturity, unless previously pinioned, and well guarded, they will desert their foster friends, and rejoin their original kindred, if such there be in the neighbourhood.

The maxim, “Like produces like”, is generally true; and I think this applies equally to temper, disposition, constitution and habits, as to form and size, though all these may be varied by incidental or artificial means. With respect to colour—we find that most animals in their wild, or native state, are true to that of their respective breeds; or if their colours vary, the variations are, with rare exceptions, very slight; and there may be a few species which even domestication does not appear to have altered in this respect—the Guinea fowl for example. But in general, tame animals are of an almost infinite variety of colours: whether this is to be accounted for on the principle laid down in Genesis Ch. XXX. v. 37 and following,2 or by the admixture of breeds which is continually taking place amongst them, I do not presume to decide; though I am of opinion that the latter cause must operate very powerfully; whilst I do not mean to deny the influence of the former.

On the subjects of most of these questions, many opinions are current which I believe to be vulgar errors. I have therefore not asserted above any thing as fact but what I think I have proved by my own experience.

R. S. Ford Swynnerton May 6th. 1839

CD annotations

scored brown crayon
scored pencil; ‘[backwards?]Did they take more after old Breed than new??’ added pencil
3.9 both ways… more after 3.12] scored brown crayon
scored brown crayon
scored pencil; ‘No because dogs & pidgeons’ added pencil
scored brown crayon
crossed pencil
scored pencil


See Correspondence vol. 2, Appendix V for the text of the questionnaire. See Vorzimmer 1969 for a discussion of the relationship of the Questions to CD’s notebooks on transmutation. Professor Vorzimmer points out that the form of most of the questions indicates that CD had already framed working hypotheses he expected the answers to confirm or refute.
The ‘principle’ is that coloration in offspring is affected by visual stimuli at the time of conception. See Genesis 30: 32–43.


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 27 vols to date. Cambridge: Cambridge University Press. 1985–.

Vorzimmer, Peter J. 1969. Darwin’s Questions about the breeding of animals (1839). Journal of the History of Biology 2: 269–81.


Answers to [Questions about breeding].

Letter details

Letter no.
Richard Sutton Ford
Charles Robert Darwin
Sent from
Source of text
DAR 186: 44
Physical description
AmemS 4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 509,” accessed on 17 September 2021,

Also published in The Correspondence of Charles Darwin, vol. 2