Darwin dynasty's ill health blamed on inbreeding

Darwin was so concerned about inbreeding that he lobbied unsuccessfully in 1870 for questions about first-cousin marriages to be added to the following year's national census form.

At the time, "blood marriages" were common, unions with first or second cousins accounting for 10 per cent of all marriages, often to keep money or influence in the family. Today, around a fifth of all marriages in the world are consanguineous