Inbreeding doomed Darwin's children.

• Position: Genetics

Charles Darwin's family was a living human example of a theory that he developed about plants: that inbreeding could affect negatively the health and number of resulting offspring. The naturalist was married to his first cousin, Emma Wedgwood. They had 10 children, but three died before age 10, two from infectious diseases, and three of the six surviving children with long-term marriages did not produce any offspring--a "suspicious" sign that these Darwins could have had reproductive problems because of their lineage.

Studies have shown that susceptibility to infectious disease and unexplained infertility are risk factors of consanguineous marriage--unions of people related by birth.

An international scientific team led by biologist Tim Berra, author of Charles Darwin: The Concise Story of an Extraordinary Man, traced the genealogy of the Darwin and Wedgwood families for four generations. Darwin's mother and grandfather also were Wedgwoods, and his mother's parents were third cousins. The researchers used this data to run calculations in a specialized computer program to determine what is called an "inbreeding coefficient," or the probability that an individual received two identical copies of a gene resulting from marriages among relatives. The analysis showed a positive association between child mortality and the inbreeding coefficient for Charles Darwin's children and others in the Darwin-Wedgwood families, suggesting that matching damaging genetic traits from the blood-relative parents could have influenced the health of the offspring.

Darwin authored three botanical books showing that cross-fertilization was much more beneficial than self-fertilization for maintaining robust and plentiful plant species. He began to worry about...