Ɛpsilon

To H. E. Litchfield   10 February 1872

Down, | Beckenham, Kent.

Feb 16th.—/72

My dear Henrietta

The subject is doubtful & obscure. In the marriage of cousins there is obviously danger from evils, possibly latent on both sides, being developed in the offspring. As far as mere consanguinity is concerned, judging from the analogy of animals, I shd. think no direct evil would follow from the marriage of cousins.1 Nevertheless I shd. quite expect that if all the offspring of cousins throughout England could be compared with the offspring from parents not related, that the latter would be somewhat superior in size, & vigour   On the other hand, my recent observations lead me to conclude that if two cousins had long lived at some distance from each other, & had consequently been exposed to somewhat different conditions of life, this would counterbalance any slight evil from their consanguinity.—2 I do not know of any reason whatever to lead to the belief that the marriage of cousins on male or female side would be more injurious, one than the other.— Double cousins, (i.e. from 2 brothers marrying 2 sisters) would of course be more nearly related than ordinary cousins, & I shd. expect that their offspring would tend to suffer more.— Under our present state of knowledge the injury from the increase of any bad tendency common to the family seems to me more to be feared than that from mere consanguinity; though the good effects of crossing distinct families I look at as great & undoubted.

Yours affectionately | Ch. Darwin

1
CD discussed the advantages and disadvantages of the close interbreeding of domestic animals in Variation 2: 114–22; he discussed humans briefly in ibid., pp. 122–4.
2
CD may refer to his work crossing plants grown in different conditions (see, for example, Cross and self fertilisation, pp. 283, 443). In ibid, p. 461, he concluded, ‘From the facts given in this volume we may infer that with mankind the marriages of nearly related persons, some of whose parents and ancestors had lived under very different conditions, would be much less injurious than that of persons who had always lived in the same place and followed the same habits of life. Nor can I see reason to doubt that the widely different habits of life of men and women in civilised nations, especially amongst the upper classes, would tend to counterbalance any evil from marriages between healthy and somewhat closely related persons.’

Manuscript Alterations and Comments

1.5 that] interl
1.5 all] interl
1.8 long] interl
1.10 whatever] interl
1.10 to the … of 1.11] above del ‘think that’
1.17 distinct families] interl

Please cite as “DCP-LETT-8207,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-8207