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Darwin Correspondence Project

From L. H. Morgan   [1 August 1871]1

I mailed my letter without it | LHM.2


In view of these facts it seems to me, that we may legitimately claim these propositions—

1st. Hybridity can exist with a large proportion of all species—

2nd. That Hybridity shades off imperceptibly, from its difficult production to complete fertility between species

3d Although hybridity is usually found among allied species, it does not confine itself even to genera— The arrest of fertility seems to come from two causes, which are apt to go together, a repugnance to union & an inaptness on the part of the genus to coalesce— But it will be remembered that I cited some strange stories of animals that had laid aside this repugnance & in fact had gone to the other extreme— In animals not only of different genera but of different orders as the horse & cow— The variation in the sperm & germ cell was too great for adaptation   On the other hand roaming together over the surface of Western Europe we have the rabbit & hare closely allied species who have the repugnance towards an alliance, so great that in a state of nature they never unite— But when by artifice & confinement, this is overcome, the capacity to procreate is entirely undisturbed   The variation is slight, repugnance being the first barrier that nature has set up—

The facts are nearly all drawn from a book written by A. Godron to prove the permanence of species4   The leporide is from Paul Broca—5

The purpose of the paper was to show that on the ground of the permanence of species, hybridity had no significance whatever, but on Mr Darwins theory it was a necessary consequence & only one of the evidences of variation—6

Man is made up varieties struggling to be species— There is yet no good evidence of diminished fertility of the hybrid, though great efforts especially in this country has been made to prove it, but it is shown by the obvious change accompanied with the repugnance— As the white for the negro & the squaw for the white man—7


The date is established by the relationship between this letter and the letter from L. H. Morgan, 1 August 1871.
Morgan wrote this note at the top of a resumé of a paper by Edward Mott Moore that he had intended to enclose with his letter of 1 August 1871 (see letter from L. H. Morgan, 1 August 1871 and n. 1).
The resumé was written by Moore.
Moore refers to Dominique Alexandre Godron’s book on species and race, and particularly on the unity of the human species (Godron 1859); it includes several chapters on variation and hybridity.
‘Léporide’ was a name given by Paul Broca and other French naturalists to an alleged fully fertile cross between a hare and a rabbit; see Broca 1858–9, pp. 367–90. CD referred to Broca’s work, and to other reports of apparent crosses between hares and rabbits, in Variation and in the fifth edition of Origin but was sceptical of their existence (Variation 1: 105, 2: 98–9, 152; Origin 5th ed., p. 307). For the impossibility of naturally occurring hare–rabbit hybrids, and for more on Broca’s work in the context of contemporary debates on the nature of species, see J.-L.Fischer 1985.
The resumé is an abstract of a paper Moore delivered to the Club of Rochester (see letter from L. H. Morgan, 1 August 1871 and n. 1).
For the history of arguments about the fertility of the children of interracial unions in North America, see Desmond and Moore 2009, pp. 142–71. Répulsion instinctive, or natural aversion to interbreeding, was one of the tests Broca proposed to define different species. Broca used the apparent fertility of the supposed hybrids of rabbits and hares (distinct species) to argue that species could not be defined by the ability to produce fertile offspring, and to support his contention that human races represented more than one species. (See J.-L. Fischer 1985, especially p. 256.)


Broca, Paul. 1858–9. Mémoire sur l’hybridité en général, sur la distinction des espèces amimales et sur les métis obtenus par le croisement du lièvre et du lapin. Journal de la Physiologie de l’Homme et des Animaux 1: 432–71, 684–729; 2: 218–58, 345–96.

Fischer, Jean-Louis. 1985. "Espèce et hybrides: à propos des léporides". In Histoire du concept d’espèce dans les sciences de la vie, proceedings of the Colloque international, May 1985, organised by the Fondation Singer-Polignac, pp. 253–68. Paris: Éditions de la Fondation Singer-Polignac.

Godron, Dominique Alexandre. 1859. De l’espèce et des races dans les êtres organisés et spécialement de l’unité de l’espèce humaine. 2 vols. Paris: J. B. Baillière.

Origin 5th ed.: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. 5th edition, with additions and corrections. By Charles Darwin. London: John Murray. 1869.

Origin: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. By Charles Darwin. London: John Murray. 1859.

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


Sends abstract of a paper on hybridity read by Edward Moore to a natural history club in Rochester, NY. Argues the necessity of hybridity on CD’s theory.

Letter details

Letter no.
Lewis Henry Morgan
Charles Robert Darwin
Source of text
DAR 171: 240/1
Physical description
ALS 4pp

Please cite as

Darwin Correspondence Project, “Letter no. 7891F,” accessed on 16 September 2023,

Also published in The Correspondence of Charles Darwin, vol. 19