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Darwin Correspondence Project

From John Jenner Weir   17 March 1870

6 Haddo Villas | Blackheath, SE

17th March 1870

My Dear Sir

Some doubt having been thrown on the subject of the foals of Lord Martins mare mentioned in your work on Domesticated animals, has caused me to be ever on the look out for any similar case.—1

I heard the point disputed by Mr. Busk;2 Sir John Lubbock taking the opposite and, in my opinion, the true view.—

I mentioned to the latter the observations I am about to detail to you & he said they should be published, but I doubt whether they are worth it.—

My friend Mr. Lethbridge of Blackheath, has a horse bred by Lord Mostyn at Ruthin, from a mare which had previously had a foal by a Quagga, and he has been kind enough to afford me every facility for examining it.—3

The color of the horse is dun with dark mane, tail & lower part of the legs, it has “a dark stripe down the centre of the back, faint stripes on the forehead between the eyes, plainly striped on the inner side of the fore legs, and rather more faintly on the hind.— I could see no shoulder stripe.—

The mane grows much lower on the forehead than in Equus caballus, tæniopus, onager, hemionus or hemippus, but not so low as in Zebra, Burchellii or Quagga.—4

The hoofs are proportionately longer than in the horse, so much so that the Farrier who first shoed it and who knew nothing of its origin, said “Had I not seen I was shoeing a horse I should have thought I was shoeing a donkey”

Mr. Lethbridge tells me it is a very intelligent animal, rather mulish in some of its habits, making for instance more use of its ears by moving them, than a horse would.—

My Theory is this   I assume the truth of your doctrine of Pangenesis, & the existence of Gemmules.—5

Now the fœtus partakes of the specific character of both parents; in the case of a hybrid therefore of two species, and further the gemmules of two species must be existing & reproducing themselves, throughout the whole of the foetus & in every drop of its blood.—

The circulation of the blood of the dam & foetus being during the whole period of gestation identical, does it not necessarily follow that after parturition, the dam should still retain the gemmules which have been produced from the male element in the foetus.—

It appears to me that the fact could not be otherwise & that the female herself by being impregnated by a distinct species has become hybridized.—

My theory indeed leads to the queer paradox, that it is possible for offspring to have more than one male parent

It may be fanciful on my part but I cannot but think that my theory accounts for what has been so often noticed that persons long married grow like each other.—

Trusting you will not consider I claim anything more for myself than the application of your grand idea of Pangenesis.—

Believe me | My Dear Sir | Yours very faithfully | J Jenner Weir

C Darwin Esqr.

CD annotations

2.1 Sir … it.— 3.2] crossed pencil
4.1 My … the legs, 5.1] crossed ink; ‘Colour of parentsadded blue crayon
5.4 hind.—] ‘legs’ interl ink
5.4 I could see] del ink; ‘but no’ added ink
6.1 lower] ‘down’ interl ink
6.1 than in Equus] ‘the Horse,’ added above ‘Equus’; crossed indicating ‘but not’ to follow ‘the Horse,’
6.2 Burchelii] del ink
8.1 Mr.... animal] crossed pencil
9.1 My Theory … Pangenesis.— 15.2] crossed pencil
Top of letter: ‘Effect of 1st impregnation by Quaggas like Ld Martins’ pencil


In Variation 1: 403–4, CD cited a description by Lord Morton (George Sholto Douglas) of a chestnut Arabian mare who bore a hybrid to a quagga, and subsequently bore two partly dun-coloured, partly striped colts to a black Arabian horse.
George Busk.
Weir refers either to John Christopher Lethbridge or to his son Christopher Lethbridge, and to Edward Mostyn Lloyd-Mostyn, second Baron Mostyn. Ruthin is a town in Denbighshire, Clwyd, Wales. CD cited Weir for this information in Variation 2d ed., 1: 435–6.
Equus caballus: the horse; E. onager: the onager; E. hemionus: the Asian wild ass or kulan; E. hemippus: now E. onager. On E. taeniopus, see Harper 1940, who concludes that the name is best regarded as indeterminable. The zebra is E. zebra, and the quagga E. quagga. Equus burchellii is Burchell’s zebra.
For CD’s hypothesis of pangenesis, see Variation 2: 357–404.


Harper, Francis. 1940. The nomenclature and type location of certain Old World mammals. Journal of Mammology 21 (1940): 191–203.

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.


Describes the unusual appearance of a horse whose mother had previously borne a foal by a quagga. The effect of one mating on the subsequent pregnancy of another mating is explained by JJW using Pangenesis.

Letter details

Letter no.
John Jenner Weir
Charles Robert Darwin
Sent from
Source of text
DAR 181: 81
Physical description
10pp †

Please cite as

Darwin Correspondence Project, “Letter no. 7137,” accessed on 16 September 2021,

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