Ɛpsilon

From J. J. Weir   27 December 1881

On Dec 27. 1881 Mr Jenner Weir wrote to Mr Darwin

“After some hesitation, in lieu of a Christmas card, I venture to give you the result of some observations on mules made in Spain during the last two years— — — — —. It is a fact that the Sire has the prepotency in the offspring, as has been observed by most writers on that subject, including yourself. The mule is more ass-like, and the hinny more horselike, both in the respective lengths of the ears and the shape of the tail; but one point I have observed which I do not remember to have met with, and that is, that, the coat of the mule resembles that of its dam the mare, and that of the hinny its dam the ass, so that in this respect the prepotency of the sexes is reversed”1

The hermaphroditism in lepidoptera, referred to below, is said by Mr Weier to occur notably in the case of the hybrids of Smerinthus populi-ocellatus2

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1
A mule is the offspring of a male donkey (Equus asinus) and female horse (Equus caballus), while a hinny is the product of a male horse and female donkey. CD had discussed prepotency in the transmission of characters in relation to sex in Variation 2: 65–8. He briefly referred to prepotency in crosses between species, and noted, ‘the ass is prepotent over the horse; the prepotency in this instance running more strongly through the male than through the female ass; so that the mule resembles the ass more closely than does the hinny’ (ibid., p. 67).
2
This paragraph, paraphrasing Weir, was added by Francis Darwin when preparing the extract of Weir’s letter for publication in ML 1: 396. The next letter published in ML 1: 397 (i.e., the letter ‘referred to below’) was the letter to J. J. Weir, 29 December 1881, which was CD’s response to this letter. Smerinthus populi (a synonym of Laothoe populi) is the poplar hawk-moth; Smerinthus ocellatus is the eyed hawk-moth. Natural hybrids of these species are common.

Please cite as “DCP-LETT-13582,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-13582