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Darwin Correspondence Project

To J. J. Weir   17 March [1870]

Down. | Beckenham | Kent. S.E.

Mar 17th

My dear Sir

It is my decided opinion that you ought to send an account to some Sci Socy. & I think to the Royal Socy.— I wd. communicate it, if you so decide.—1 You might give as a preliminary reason the publication in the Transats. of the celebrated Morton case & the Pig case by Mr Giles..—2 You might also allude to the evident physiological importance of such facts, as bearing on the theory of Generation: whether it wd be prudent to allude to despised Pangenesis, I cannot say; but I fully believe Pan: will have its successful day.— Pray ascertain carefully the colour of the dam & sire.— see about duns in my Book. vol I p. 553 The extension of the mane & the form of hoofs are grand new facts.— Is the hair of your horse at all curly: for observe case given by me Vol. 2. p. 325, from Azara of correlation of form of hoof with curly hair?—4 See, also, in my Book; Vol I p. 55. Vol. 2. p 41 how excessively rare stripes are on faces of horses in England.— Give age of your Horse.—

You are aware that Dr Carpenter & others have tried to account for the effect of a first impregnation, from the influence of the blood of the crossed embryo;5 but with Physiologists who believe that the reproductive elements are actually formed by the reproductive glands this view is inconsistent.— Pray look at what I have said in Dom: Animals. Vol. I p. 402–405. Against this doctrine: it seems to me more probable that the gemmules affect the ovaria alone.— I remember formerly speculating, like you, on the assertion that wives grow like their husbands; but how impossible to eliminate effect of imitation & same habits of life &c.— Your letter has interested me profoundly.

In Haste. | Very sincerely your’s | Ch Darwin

PS. Since publishing I have heard of additional cases—very good one in regard to Westphalian pigs crossed by English boar, & all subsequent offspring affected given in Illust: landwirth: Zeitung 1868 p. 143.6

I have shown that mules are often striped though neither parent may be striped, due to ancient reversion— Now Fritz Müller writes to me from S. Brazil “I have been assured by persons who certainly never had heard of Ld. Morton’s mare, that mares which have borne hybrids to an ass, are particularly liable to produce afterwards striped ass-colts.”7 So a previous fertilisation apparently gives to the subsequent offspring a tendency to certain characters, as well as characters actually possessed by the first male.—

In the Reprint, (not called a 2d Edition) of my Domestic Animals, I give good additional case of subsequent progeny of Hairless dog, being hairy, from effects of first impregnation.—8

P.S. 2d.

The suggestion no doubt is superfluous, but you ought, I think, to measure extension of mane beyond a line joining front or back of ears & compare with horse.

Also to measure (& give comparison with horse) length, breadth & depth of Hoofs.—


It seems that Weir did not submit his account to the Royal Society of London (see letter from J. J. Weir, 17 March 1870, and letter to J. J. Weir, 14 June [1870]).
CD refers to George Sholto Douglas (Lord Morton) and Douglas 1820 and to Daniel Giles and Giles 1820. See also letter from J. J. Weir, 17 March 1870 and n. 1. CD discussed Giles’s pig in Variation 1: 404; the pig was a black and white Essex sow, and was bred first with a chestnut-coloured boar. Later, she was bred with a black and white boar, and some of the piglets were chestnut coloured.
CD discussed the dun colour in horses in Variation 1: 55–9.
CD refers to Félix d’Azara and Azara 1801.
CD refers to William Benjamin Carpenter.
CD refers to Illustrirte landwirthschaftliche Zeitung, 17 November 1868, p. 143 (see Variation 2d ed., 1: 436 n. 152). This journal was published in Leipzig: a copy may have been sent by Hermann Müller, who lived in Westphalia. No copy of the newspaper or article has been found in the Darwin Archive–CUL, and CD did not describe the case in the second edition of Variation, although he gave the reference above. The letter in which Müller gave this information has not been found.
On stripes appearing on mules and other animals owing to reversion to an ancestral type, see Variation 2: 42–3. CD cited the information from Fritz Müller in Variation 2d ed., 1: 436 n. 152.
See Variation (2d printing) 1: 404 n. 138, and Variation 2d ed., 1: 436 n. 152. The first edition of Variation was reprinted with some additions and corrections in early 1868 after the first printing had sold out (see Correspondence vol. 16, letter to John Murray, 9 February [1868]).


Azara, Félix d’. 1801. Essais sur l’histoire naturelle des quadrupèdes de la province du Paraguay. 2 vols. Paris: Madame Huzard.

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

Douglas, George Sholto (Lord Morton). 1820. A communication of a singular fact in natural history. [Read 23 November 1820.] Philosophical Transactions of the Royal Society of London 111 (1821): 20–2.

Giles, Daniel. 1820. Particulars of a fact, nearly similar to that related by Lord Morton. [Read 23 November 1820.] Philosophical Transactions of the Royal Society of London 111 (1821): 23–4.

Variation 2d ed.: The variation of animals and plants under domestication. By Charles Darwin. 2d edition. 2 vols. London: John Murray. 1875.

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


CD thinks JJW’s account [in 7137] is significant for a theory of generation and should go to some scientific society; suggests additional data is needed. Quotes cases of subsequent progeny apparently affected by a previous impregnation. Perhaps not prudent to allude to "despised" Pangenesis, which CD fully believes will have its day.

Letter details

Letter no.
Charles Robert Darwin
John Jenner Weir
Sent from
MR18 70
Source of text
American Philosophical Society (Mss.B.D25.)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 7138,” accessed on 21 June 2021,

Also published in The Correspondence of Charles Darwin, vol. 18