He knew from his own experiments with plants that inbreeding led to less vigorous offspring. What’s more, marriages of cousins were frowned upon in England and elsewhere in Europe due to their “supposed injurious consequences,” Darwin wrote in an 1870 letter to his neighbor. But, he added, “this belief rests on no direct evidence.”
It was a question Darwin was anxious to answer. Three of his 10 children – Anne Elizabeth, Mary Eleanor and Charles Waring – died during childhood. Six of the surviving seven went on to have long-term marriages, but three of those marriages bore no children, suggesting that his children suffered from infertility.
Scholars have documented Darwin’s worries that his own consanguineous marriage contributed to the poor health of his offspring, but he wasn’t able to resolve the question. Nearly 130 years after his death, a group of American and Spanish experts in evolution and genetics have done it for him.
Their conclusion? Darwin’s close genetic ties to his wife probably did play a role in the poor health of his children.
Not only were Darwin and his wife first cousins, but his mother’s parents were third cousins. The researchers calculated that for 6.3% of their genetic sequences, Darwin's children inherited the same DNA from their mother and father. That certainly increased their risk of developing health problems that only occur when the faulty genes are inherited from both parents. It probably explains the high rate of infertility among his adult children, the researchers write.
In addition, scientists discovered last year that inbreeding can make children more susceptible to infectious diseases. Anne Elizabeth died from childhood tuberculosis, and Charles Waring died of scarlet fever. The cause of death of Mary Eleanor, who lived only 23 days, is unknown.
“Charles Darwin’s fears of consanguinity appear to have been justified,” the researchers concluded. But they also noted that three of Darwin’s sons – George, Francis and Horace – became fellows of the Royal Society and were knighted. George went on to advocate against consanguineous marriages.
The report appears in the May issue of the journal BioScience.
-- Karen Kaplan
Photo: Charles Darwin suspected his children paid the price for his marriage to first-cousin Emma. Credit: Henry Chu/Los Angeles Times