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Darwin Correspondence Project

From Alexander Wallace   14 March 1868

Beverley Road House, | Colchester.

March 14 68

Chas Darwin Esq

Dear Sir

In reply to your long and welcome letter of the 29 Febry—I must correct an error therein. You write “I infer that you suspect that entomologists who collect caterpillars for breeding would naturally choose the larger and finer ones, and would thus unintentionally breed most females.”1 Now having collected larvæ myself for many years and having been in company with many others similarly occupied, I can assure you that this view is quite incorrect. We should capture all both big and little larvæ of any particular kind of moth which we wanted—rejecting in toto those larvæ which were known to us as those of moths not wanted: of those unknown to us, we should certainly capture all we could till we had filled our boxes, & make no distinction as to big and little ones. I do not therefore think that therein can be found any real explanation of the reason why females are bred in greater number than males:—and I am by no means sure that such is really the case—viz that the females preponderate—

In my last letter I wrote my belief in the maxim omne vivum aut mas aut femina ex ovo,2 but I forgot to exclude all neuter races—from this circle— Your narrative of the sheep is curious—3 I noted with regard to the lambing season, a peculiar fact, which possibly may throw light—the summer of 1865 was remarkably dry & warm—the grass was everywhere parched & burnt up, and wonder was expressed in the newspaper that notwithstanding the great drought generally experienced and consequent scarceness of grass sheep did not suffer— the following spring was a great lambing season all over England. triplets were very common, my explanation of it was that being kept on moderate diet, the vigour of both male & female was increased & stimulated by the extra heat, but I am not aware whether any difference in the sexes was perceived that year.— If however it requires, as I believe it does a greater amount of vigour to beget a male than a female—then by placing sheep on the poor Highland pastures, you would according to my views put them in the best possible conditions for coition & for getting male offspring, as a fat sheep or beast is constitutionally of less vigour than a moderately lean animal— The question however requires light thrown on it from many other sources.

I confess I am much interested in the question of sex of offspring, as I have 6 boys, without a chance of a girl—much to the dismay of my wife4 & her friends:— When taking Race Horses into consideration, it were very desirable that to each parentage could be attached the sex of the offspring the time of year of foaling, the ages respectively of mare and sire— Racehorses are a variety perpetuated by constant breeding, and I apprehend that if a racing mare were put to horse of different strain—of good vigour & older than the mare—the result would be a colt—

I am quite of the opinion with regard to B Cynthia that chance favours the male in coition, that the ♂ nearest the ♀ at the time of calling, gets the entrée.—5

I shall be happy at any future time to contribute anything I know to your accumulated store

Believe me yours very truly | Alex Wallace

NB. I thank you for your information as to the changes of wheat barley & oats, Should your Son try it—I shall be glad to learn the result—6

CD annotations

2.1 In my … the result— 7.2] crossed pencil
End of letter: ‘Mr Butler at B. Museum7 believes fully that he has bred more males than females from caterpillar.’ ink; ‘Trimen says he did not collect great masses & certainly selected largest caterpillars or quickest bred—’8 pencil


Omne vivum aut mas aut femina ex ovo: everything alive is either masculine or feminine from the egg (Latin; see letter from Alexander Wallace, 28 February 1868).
CD’s discussion of sheep has not been identified, but he had recently received a letter and an article about a hardy breed of sheep, the lonk, and had written to inquire about the proportion of sexes in sheep (see letter from Jonathan Peel, 4 March 1868, and letter to Jonathan Peel, 6 March [1868]).
Wallace’s wife has not been identified.
Wallace had described sex ratios and mating behaviour in Bombyx cynthia (now Samia cynthia) in his letters of 25 February 1868 and 28 February 1868.
For Wallace’s original query regarding the transmutation of one grain species into another, see his letter of 28 February 1868. In a letter to J. B. Innes, 22 December [1862] (Correspondence vol. 10), CD had expressed disbelief about a similar account of the transmutation of oats into wheat. CD discussed these cereal plants in Variation 1: 312–20, but did not mention any accounts of transmutation of one grain into another. It is not known which of CD’s sons was planning an experiment.
CD had evidently met Arthur Gardiner Butler at the British Museum; he referred to Butler’s observations on butterflies in notes dated 17 March 1868 (DAR 81: 23).
Roland Trimen may have reported this information in person; he had last visited CD at Down on 27 and 28 December 1867 (see letter to J. P. M. Weale, 23 January [1868] and n. 12).


On proportion of sexes [of moths?] raised from larvae: AW does not select largest exclusively.

Account of lambing in 1864 after unusual drought.

Letter details

Letter no.
Alexander Wallace
Charles Robert Darwin
Sent from
Source of text
DAR 86: A26–7
Physical description
4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 6011,” accessed on 17 July 2019,

Also published in The Correspondence of Charles Darwin, vol. 16