Charles Darwin's worries about possible adverse effects of inbreeding in his family seem to have been justified, according to a study described in the May 2010 issue of BioScience. Darwin married his first cousin, Emma Wedgwood, and his mother, Susannah Wedgwood, was the daughter of third cousins. The study, which extended to 25 families including 176 children, found a statistical association between child mortality and the inbreeding coefficient of individuals in the Darwin/Wedgwood dynasty.
Charles Darwin demonstrated the phenomenon of inbreeding depression in many plants, and was aware of research into the effects of marriage between relatives on the health of resulting children. He feared that his marriage might have been responsible for some of his children's health problems and asked a member of Parliament to add a question about marriages to relatives to the British 1871 census form.
Three of Charles Darwin's 10 children died before reaching adulthood, one from childhood tuberculosis at age 10 and one from unknown causes as an infant. A third child, who died in infancy of scarlet fever, appears in a photograph to have developmental abnormalities. Inbreeding is an important risk factor in a number of human diseases, including infectious diseases. The authors of the study, Tim M. Berra, Gonzalo Alvarez, and Francisco C. Ceballos, suggest that the expression of deleterious genes "produced by consanguineous marriages could be involved in the high childhood mortality experienced by Darwin progeny." Furthermore, three of Darwin's six children with long-term marriages left no offspring. Unexplained infertility may also be a consequence of a consanguineous marriage. On the other hand, three of Darwin's sons were fellows of the Royal Society and were knighted by Queen Victoria.