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Darwin Correspondence Project

To [Henry Hussey Vivian?]   [April or May 1870?]1


I hope that you will excuse the liberty which I take in addressing you on a subject which I believe to be of scientific importance, & which you might greatly aid, if you shd think fit, to give the [illeg] after consulting those competent to form an opinion.— I have been led to study experimentally & theoretically during many years the good effects of crossing & the evil effect of close interbreeding; & the difference in vigour, & size & power [illeg] & health of the offspr[ing] in the 2 cases is in most cases extraordinary.— In Chap 17 of my work on the variation of Domestic Anim I have given a resume of my results,—2 & these might be consulted by any one who wishes to see what is at present [known] on the subject. In various European countries & the U. States the most contradictory opinions owing to the [continued] want of any reliable data have been found. whether the marriage of near relatives is in any way injurious to man..3

Some time ago I went to the of the Registrar general, suggesting that during the next Census, a return should be demanded, whether in each family the parents were related in blood;4 for it wd then it wd be possible by comparing the average numbers of the [surviving] children, of related & not related parents, to judge of the vitality of the children in the 2 cases, or of the fertility of the parents.

I have every cause to believe that the time will soon come, when this subject will be [emerging] as highly important for the welfare of mankind, though at present the subject has [8 words illeg].


The addressee and the date are conjectured from the relationship between this draft and the letter from H. H. Vivian, 10 May 1870.
Chapter 17 of Variation (Variation 2: 114–44) is titled ‘On the good effects of crossing, and on the evil effects of close interbreeding’. CD’s also published his work on crossing in Cross and self fertilisation (1876).
CD discussed consanguineous marriages in humans in Variation 2: 122–4.
CD may refer to his correspondence with William Farr, superintendent at the General Register Office (see Correspondence vol. 16, letter from William Farr, 21 May 1868). CD’s side of the correspondence has not been found. The registrar-general was George Graham.


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

Cross and self fertilisation: The effects of cross and self fertilisation in the vegetable kingdom. By Charles Darwin. London: John Murray. 1876.

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


Discusses the reasons for inserting questions on consanguineous marriages in the forthcoming Census.

Letter details

Letter no.
Charles Robert Darwin
Henry Hussey Vivian
Sent from
Source of text
DAR 96: 86
Physical description
Adraft 2pp

Please cite as

Darwin Correspondence Project, “Letter no. 7257,” accessed on 22 September 2021,

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