Footnotes

'THE PROPORTION OF THE OFF-SPRING OF 1ST COUSIN MARRIAGES AMONGST THE INSANE, IDIOTIC, DEAF & DUMB &C ' – Darwin ponders the potential injurious effects of marriage between first cousins and (by unstated implication) the risks posed by his own marriage to his first cousin, Emma Wedgwood; the question being the subject of his son George's paper 'Marriages between First Cousins in England and their Effects', Journal of the Statistical Society, June 1875, 38:2, pp.165-9 (in which reference is made to the information supplied by Rayner).

A further statistical analysis, with reference to George's paper, has recently been undertaken by Tim M. Berra, Gonzalo Alvarez and Francisco C. Ceballos, in 'Was the Darwin/Wedgwood Dynasty Adversely Affected by Consanguinity?', BioScience, Volume 60, Issue 5, 1 May 2010, pp.376-383 (https://doi.org/10.1525/bio.2010.60.5.7), in which not just Darwin's marriage but the inter-marriage prevailing within his family is assessed: 'Charles Darwin, who was married to his first cousin, Emma Wedgwood, was one of the first experimentalists to demonstrate the adverse effects of inbreeding and to question the consequences of consanguineous mating. He documented the phenomenon of inbreeding depression for numerous plant species, and this caused him to worry about the health of his own children, who were often ill... Our answer to the question posed by the title of this article is yes. Charles Darwin's fears of consanguinity appear to have been justified given the context of the Darwin/Wedgwood marriages'. (They also point out, however, that three of Darwin's sons were knighted, and that the Darwins have been fellows of the Royal Society in father-to-son sequence longer than any other family, from Erasmus Darwin, elected 1761, to Sir Charles Dalton Darwin, elected 1922; a span of 201 years over five generations and seven fellows.) The first of our letters is recorded by the Darwin Correspondence Project.