Darwin A Case Study In His Own Theory: Inbreeding

New research suggests Charles Darwin may have been a human example of this own theory about plants: that inbreeding has negative effects on the health of offspring. Darwin married and had 10 children with his first cousin Emma Wedgwood. Only seven children survived past age 10 and three of the survivors may have been infertile. Host Guy Raz speaks with Tim Berra, professor of evolution at Ohio State University, about the "inbreeding coefficient" theory that Darwin proved through his work and his own life.

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GUY RAZ, host:

Charles Darwin famously wrote about how the most robust plants are the product of crossbreeding and that plant inbreeding, or self-fertilization, often carries a risk of producing a diseased species. Well, it turns out he didn't take his own advice. Darwin married his first cousin Emma Wedgwood.

And a new study in the latest issue of "BioScience" suggests that the reason three of his children died, and three others had no children, was because they were, well, somewhat inbred.

Tim Berra, professor emeritus of evolution at Ohio State University, led that study, and he joins me from member station WOSU in Columbus.

Welcome.

Dr. TIM BERRA (Professor Emeritus of Evolution, Ecology and Organismal Biology, Ohio State University): Hi, Guy. Nice to be here.

RAZ: Now, I understand that Darwin's work with plants made him suspicious about the effects of inbreeding in humans, is that right?

Dr. BERRA: Yes. Again, Charles Darwin is ahead of his time in virtually everything that he does. He was a brilliant person, and he was data-driven. He did these experiments in his greenhouse at Downe and showed that cross-fertilization was infinitely superior to self-fertilization. This worried him with regard to his family because his children had, you know, minimal problems but they often seemed to be ill. And Charles worried about this. Did his consanguineous marriage contribute to this?

RAZ: Professor Berra, explain how two people - say, you know, first cousins are more likely to produce children with genetic problems.

Dr. BERRA: There's a 6 percent probability that an individual who is a product of a consanguineous marriage will inherit an identical allele, or an alternative expression of a gene, that's identical, from each parent. And if there are deleterious alleles in this gene pool, they're going to get two copies, which will allow the expression of the gene, whereas one copy would not.

RAZ: Now, he didn't have data you talk about, but I've read that he suspected something might be wrong, and he was wrecked with some guilt about this.

Dr. BERRA: Yes, it bothered him. He did worry, particularly when Annie died. That was an incredible blow.

RAZ: She was 10 years old when she died.

Dr. BERRA: She was 10 years old, his first daughter - his favorite child, actually - and he never recovered from it. And he had three children who died before the age of 10, or at the age of 10. We know the cause of death of two of these. Annie died of tuberculosis, and Charles Waring died of scarlet fever. We know that consanguinity is a risk factor for susceptibility to infection. So that's one line that led us to question, was this related to his intermarriage with his Wedgwood family.

The other was that he had 10 children, six of which had long-term marriages. Well, of those six, three did not leave any offspring. Now if it were just one, you might, you know, dismiss it. But, yeah, two is suspicious; three out of six, that's pretty strong. And again, consanguinity is a risk factor for unexplained infertility.

RAZ: Now, a few of Darwin's children actually made out OK, right?

Dr. BERRA: Oh, yeah. It was not all genetic doom and gloom. Three of his sons were prominent scientists, and were elected fellows of the Royal Society and were knighted by Queen Victoria. Of course, Charles was much too controversial for Queen Victoria's taste; she wasn't about to knight him.

RAZ: That's Tim Berra. He's professor emeritus of evolution at Ohio State University.

Professor Berra, thanks so much.

Dr. BERRA: Well, thank you. It was fun.

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