Charles Darwin's family suffered from the deleterious effects of inbreeding, suggests a new study that serves as ironic punctuation to the evolutionary theorist's life work.
Pioneer of the theory that genetic traits affect survival of both individual organisms and species, Darwin wondered in his own lifetime if his marriage to first cousin Emma Wedgwood was having "the evil effects of close interbreeding" that he had observed in plants and animals.
Three of their children died before age 10, two from infectious diseases. The survivors were often ill, and out of the six long-term marriages that resulted, only half produced any children. According to researchers at Ohio State University and Spain's Universidad de Santiago de Compestela, that alone is a "suspicious" sign that the Darwins suffered from reproductive problems.
Inbreeding can cause serious health problems, because it increases the chances of successful gene expression for diseases otherwise rare or muted in an individual's pedigree.
The new study, detailed in the journal Bioscience, fed genealogical data on the Darwin-Wedgwood link into a specialized computer program, which spit out a "coefficient of inbreeding," or the probability that an individual received two identical copies of a gene resulting from marriages among relatives. (Some genetic disorders are caused by recessive genes, which means they require two copies of a gene in order for the trait to manifest.)
Results revealed that inbreeding was a possible factor in the offspring's poor health. Darwin's children suffered from a "moderate degree" of inbreeding, the researchers concluded. When expanded to other branches of the family tree and four consecutive generations, the analysis found an even stronger association between child mortality and incestuousness.
Darwin's mother and grandfather were also Wedgwoods, and his mother's parents were third cousins.
The study relied solely on birth and death records. In the late 19th century it was still fashionable for wealthy families to intermarry over generations. As would be expected of prominent families, their genealogical records were also in excellent condition.
When genealogical records are not available, scientists interested in genetic heritage must rely on DNA and radiological analysis of bone samples — a type of research recently utilized for mummies.
In fact, this past February, an international team announced that a high degree of inbreeding was the likely explanation for boy pharoah King Tutankamun's early death and frail, club footed frame. And research published last year showed the termination of the Habsburg dynasty that ruled Spain for nearly 200 years may have been a result of frequent inbreeding.