Ɛpsilon

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

Sir

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].

Draft

1
The addressee and the date are conjectured from the relationship between this draft and the letter from H. H. Vivian, 10 May 1870.
2
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).
3
CD discussed consanguineous marriages in humans in Variation 2: 122–4.
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.

Manuscript Alterations and Comments

1.1 liberty] after del ‘great’
1.1 subject 1.2] pencil above del pencil ‘point’
1.2 to be] above del ‘is’
1.2 scientific] above del ‘much’
1.2 , & which] after del ‘for science’
1.2 greatly] after del ‘fur’
1.3 you shd think fit, to give the [illeg]] interl; ‘shd’interl pencil; ‘think’ altered from ‘thought’ pencil; ‘, to give the [illeg]’ pencil
1.3 consulting] after del ‘due’; altered from ‘consultation’ pencil
1.3 those competent] after del pencil ‘with’
1.3 an opinion 1.4] ‘opinion’ after interl and del ‘sound’
1.4 I have been] above del ‘The course of my studies has’
1.4 to study] after del ‘me’
1.4 experimentally] after interl and del pencil ‘& am still studying’
1.4 theoretically] interl
1.5 & the evil] after del ‘distinct breeds, or in the case of plants, distinct individuals’
1.5 close] interl
1.5 ; & the difference 1.6] ‘difference’ above del illeg
1.6 & size] after del illeg interl; ‘size’ circled pencil
1.6 & power] below del illeg
1.6 & health] pencil interl
1.6 the offspr[ing] in the 2 cases is] above del ‘if cross-bred again’
1.7 in most] after del illeg; ‘most’ pencil above del ‘many’
1.7 In Chap 17] after interl & del ‘In many instances the effect on the’
1.7 Chap 17] below del ‘the 2d volume’
1.7 Chap 17 of my] ‘Chap 17 of’ added above ‘my’
1.7 variation of] interl
1.7 Domestic] interl after del ‘Domestic’
1.8 I have given] after del interl illeg
1.8 & these … subject. 1.9] added; ‘these might’ after del ‘which’; ‘at present’ after del ‘[known]’
1.9 various] pencil below del ‘all’ below del pencil ‘many’
1.9 European] ‘an’ added pencil; after del pencil ‘parts of’
1.10 countries] interl pencil
1.10 owing to … data 1.11] interl; ‘[illeg]’ interl
1.11 found] below del ‘formed’
1.11 near relatives] above del ‘cousins’
2.1 Some] after del ‘& no data have *as yet [interl] ever been collected. by which [8 words illeg] convinced that this is an important subject for [illeg] of mankind. &’; ‘S’ pencil over ‘s’
2.1 went to the] above del ‘suggested’
2.1 of the] after del pencil ‘office’
2.1 suggesting] interl
2.1 during] after del ‘if’
2.2 a return] after del ‘th’
2.2 should be demanded] above del ‘had to be made’
2.2 in each family the parents were] above del ‘each man was a’
2.3 related] altered from ‘relative’
2.3 in blood] ‘in’ after del ‘of’
2.3 but wd] after del ‘to his wife’
2.3 but wd] above del ‘&’
2.3 by] over ‘to’
2.3 average] interl
2.4 the [surviving]] above del ‘their’
2.4 of related & not related] above del ‘with the average number of’
2.4 to judge of the] interl after del ‘which were related with the number of [illeg] parents not related; & this wd serve as a guide to the’
2.4 vitality] after interl & del illeg; after del ‘to the’
2.5 , or of the fertility of the parents] added pencil
3.1 soon] interl pencil
3.2 highly] above del ‘an’
3.2 for the welfare] after del ‘point’
3.3 the subject] below del ‘it’
3.3 [illeg] to] pencil above del pencil illeg

Please cite as “DCP-LETT-7257,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-7257