Did Inbreeding Royals Evolve?

A new study suggests that in the Spanish Habsburg royal family, natural selection may have diminished the most harmful effects of inbreeding.

By | April 22, 2013

Charles II of Spain (1661-1700), who was infertileSCHLOSS ROHRAUThe Habsburg royal family of Spain, which favored inbred marriages to keep titles in the family and forge alliances, may have evolved from 1450–1800 to blunt the worst effects of inbreeding, according to a study published this month in Heredity. But some geneticists are not convinced, reported Nature.

Evolutionary theory predicts that over time, there will be a purging of the harmful mutations that result from inbreeding. But while the effect has been observed in animals and plants, there is little evidence for this phenomenon in human populations. Researchers from the University of Santiago de Compostela in Spain decided to look for that evidence by analyzing 350 years of genealogical records of the Spanish Hapsburgs, a family with a long history of inbreeding.

Inbreeding increases the probability that offspring will inherit two copies of a recessive disease-causing mutation, but infertility—which may be a  consequence of inbreeding—can block such mutations from being passed down. Assuming that early deaths—in infancy, excluding miscarriages and stillbirths, and early childhood, up to the age of 10—were a result of inbreeding, the researchers hypothesized that if natural selection had purged the harmful mutations, the number of early deaths would go down over time.

Sure enough, their analysis of deaths in the written records of the Habsburg royal family revealed significantly fewer early deaths in children between 1600 and 1800 than between 1450 and 1600.

The number of infant deaths went up over the same period, however, which the authors said might be because deaths in infancy and early childhood were caused by different mutations—so the infants might have died as a result of mutations that only cause disease some of the time, and were thus purged more slowly than those that almost always cause disease and might have caused the deaths in early childhood.

But Princeton University geneticist Leonid Kruglyak told Nature that the observed changes in mortality may not be due to natural selection, and are more likely to be a statistical fluke caused by the small size of the sample.

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Avatar of: McEB


Posts: 2

June 17, 2013

This is a brief discription of the study, I'm sure all the information is not here from the study...but....There could many differences that could affect survival. I'm thinking of things like evironmental, disease and knowledge base. Was the overall population observed in the surrounding area and what was happening at the time to that population. Looking at the 19th and 20th century there is an increase survival rate in children in many areas of the world that is not due to evolution, but to knowledge base. We are actually more able to keep people a live with various genetic problems that would have died in the past. Increase knowledge and experience with infant births or changes in cultural practices over time could have led to increase survival. How is that eliminated from a possible cause.

Avatar of: McEB


Posts: 2

June 17, 2013

Something that always bugs me in scientific writing....sentence from above:

"But while the effect has been observed in animals and plants, there is little evidence for this phenomenon in human populations."

It would be accurate to say the affect has been observed in other animals and plants, but not in humans. Scientific writers especially should be aware that we are a specific animal species and not something other than that. We are not a virus,fungi, bacteria, protista....we belong to the animal kingdom. We are an animal.  I'm sure science writers  know we are animals, but there's a bias I often see in the writing of information that I think affects thinking. Thinking of humans as non animals has always slowed scientific thought and I continue to see that occuring.

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