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Charles Darwin’s family tree tangled with inbreeding, early death

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charles darwin inbreeding wedgwood child deathCharles Darwin‘s studies of heredity, adaptation and evolution included many experiments into the effects of crossbreeding and inbreeding in both plants and animals. Such consanguineous pairing often resulted in weaker, more sickly descendants.

Ironically, his own lineage and marriage could have been experiments as well. At the age of 29, he proposed to his first cousin, Emma Wedgwood, the daughter of his mother’s brother. Darwin realized the dangers of inbreeding and wondered if his close genetic relation to his wife had had an ill impact on his children’s health, three (of 10) of whom died before the age of 11. In a letter to friend, Darwin noted his concern for his children, writing that "they are not very robust."

Darwin’s marriage to his cousin was not the only mixing of blood in the two lines. The Darwin-Wedgwood family in fact had several instances of close family matches, and a new analysis, published online May 3 in the journal BioScience, shows that some of Darwin’s concerns about his offspring’s health might have been valid.

The analysis, led by Tim Berra, professor emeritus in the Department of Evolution, Ecology and Organismal Biology at the Ohio State University in Mansfield, found that Darwin’s kids did have "a moderate level of inbreeding" and in the family’s children, there was "a significant positive association between child mortality and inbreeding."

When two individuals mate, genetic material from both parents is passed on to the progeny. So even if one parent carries a harmful recessive trait, the other parent is likely to have a healthier version, which will manifest itself in the offspring. If both parents, however, carry a recessive allele—which is more likely to happen if they share much of their genetic material, as close relatives do—then they raise the chances that their child will have only the bad genes.

Berra and his colleagues’ assessment of 25 nuclear families across four generations of Darwins and Wedgwoods found a slightly lower-than-average child mortality rate compared with the general population of the time. But in those nuclear families with higher levels of inbreeding, offspring had an estimated 5.4 percent reduction in fitness. And the autosomal genomes of Charles Darwin’s children were likely more than 6 percent identical (that is, homozygous). That number represents about four times the amount of overlap than children of second cousins would be expected to have.

Although none of Darwin’s children had obvious documented physical or mental deformities, the three who died appear to have suffered from infectious disease, which is more likely to be contracted in those with higher levels of inbreeding, Berra and his colleagues noted. One died at 23 days old, and another, who was not developing normally, died at 18 months. The third likely died of tuberculosis, for which inbreeding increases the contraction risk.

Many famous and powerful families have been renowned for their pairing of close relatives, including the Hapsburgs and some ancient Egyptian pharaohs, and marrying relatives—both close and distant—was in general more common historically when groups were smaller and more isolated. But by Darwin’s time it was already assumed that "consanguineous marriages lead to deafness & dumbness, blindness [etc.]," Darwin wrote in a letter to parliamentarian John Lubbock in 1870. Darwin had been hoping the government could accumulate broad population-based data about the frequency of cousins marrying and the health of their offspring, and he requested questions to this effect be included in England’s census.

Darwin’s request was denied, but his concern lives on today. More than half of the states in the U.S. have explicit limits on first-cousin marriages.

Image of Charles Darwin and his son William Darwin taken in 1842, courtesy of Wikimedia Commons

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  1. 1. Highlite 1:56 pm 05/3/2010

    So, the dude was a freak? Ahha, well, this shows a clear and undeniable tendency to devalue life. This, in my eyes, taints his perspective on evolution. Not that I am a creation advocate, I also doubted for years that Darwin was correct, now I feel that way even more.

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  2. 2. candide 2:39 pm 05/3/2010

    Regardless of your opinion of Mr. Darwin MANY other scientists have added to and support Evolution.

    Instead of "feeling" about evolution try doing some work with data and facts, the basis of Science. You can "feel" and "believe" that the world is flat, but it does not change the fact that it isn’t.

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  3. 3. Crucialitis 4:35 pm 05/3/2010

    What do you expect?
    It’s not like you had highways and cars with which to move far away from your family. It’s also unlikely that you would be able to acquire land to start your new family on unless you were well connected and an all-too-well-known specific gender/ethnicity combination.

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  4. 4. JLaurel 5:00 pm 05/3/2010

    What’s this nonsense? Darwin lived during the height of the British Empire. People not only moved around, but Britain actually had colonies in all corners of the world and the empire comprised about 1/4 of all land on this planet.

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  5. 5. Crucialitis 5:07 pm 05/3/2010

    Just because there are colonies doesn’t mean your average serf-level citizen is globe trotting about. It certainly took longer than a few hours to cross the ocean, let alone your municipality, on anything not steam driven.

    Even with those luxuries available to the common man now, the majority of humans spend their life anchored to one place for an extended period of time. There is bound to be inbreeding.

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  6. 6. EvolvingApe 8:11 pm 05/3/2010

    Iahmad, the irony that Scientific American is part of this "Western corporate media" obviously escapes you.

    While much of the mainstream media certainly exhibits pack mentality and can get things wrong sometimes, it still does a reasonably good job in most cases.

    But wacky conspiracy claims about something called "Western corporate media" are just…, well, wacky.

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  7. 7. abyssalmystery 8:19 pm 05/3/2010

    There may be some validity to this study, however, how can you project the causes of mortality into a period of time when hygeine, sanitation, and medicine were non existant?

    I have done extensive research into my won family tree well back into the 1600′s. There are very few cases of close relatives marrying. Despite this, child mortality was always very high.

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  8. 8. greg14701 5:33 pm 05/4/2010

    Typical creationist, Highlite. You devalue a scientific theory because of its originators personal life. Should we also stop seeing doctors because Hypocrates (the founder of modern medicine) was accused of theft? People, evolution is a scientific FACT….it is no longer Darwin’s theory…literally millions of scientifists around the world have validated and added knowledge to the process of evolution. According to the bible, god advocated stoning rape victims to death, so if i were you, i’d worry more about the validity of your religion than of a scientific fact. Guys, its the year 2010, we need to get over superstition based centuries old tradition. Evolution is as much a fact as antibiotics and astrophysics. 1000 years from now, when our descendants look back at us, they will laugh at the religious and consider our scientists pioneers. Its your choice what you want to be viewed as.

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