A family tree is technically called a pedigree. This is because it is not really a tree. Branches do not fuse in a tree, whereas in a pedigree every individual is the fusion of two genealogical branches. That is, in sexually reproducing species, every offspring is the hybrid of two parents. A family tree is only a tree if you trace one pair of ancestors through their descendants while ignoring the spouses.
So, a pedigree is a network not a tree, and specifically it is a hybridization network. This can be seen most clearly when there is a considerable level of inbreeding going on. Under these circumstances, both spouses are likely to be offspring of the same ancestors in the not-too-distant past, and so they will both be connected by the network branches. We are all of us connected in the human pedigree network, of course, but for most of us our (shared) common ancestor is a long way back in the past.
A high degree of inbreeding is common in many human cultures, but it is particularly prevalent among royalty, even in cultures with relatively little inbreeding among the common populace. I will illustrate this phenomenon with what is often considered to be the most extreme example recorded — the inbreeding that lead to the demise of the Spanish branch of the Habsburg dynasty in 1700 (other branches of the House of Austria continued until 1780).
The Spanish branch of the Habsburgs were kings of Spain from 1516 to 1700. Under Habsburg rule, Spain reached the peak of its power in Europe (covering Spain, the Netherlands and parts of Italy), and the world-wide Spanish Empire reached its greatest extent. The last king of this dynasty was Charles II, who was the product of such serious inbreeding that he was disfigured, physically disabled and mentally retarded (see Alvarez et al. 2009 for a full description). The fact that he had no children lead to the War of the Spanish Succession, although this was mostly precipitated by the reaction of the reigning French king, Louis XIV.
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The basic issue here is that the Spanish Habsburgs tried to keep power by literally "keeping it in the family". During the last three-quarters of their time, from 1551 to 1700, no outsider married into the Spanish royal family. Indeed, if one looks at the six kings from 1497 (when Philip the Fair married Joanna I of Castile and Aragon, and thus became Philip I), then we note that there were 11 marriages, most of which were among blood relatives — two uncle-niece marriages, one double first cousin marriage, one first cousin marriage, two first cousins once removed marriages, one second cousin marriage, and two third cousin marriages. (See Wikipedia for an explanation of these relationship terms.) This gave Charles II an inbreeding coefficient of 0.254 (calculated by Alvarez et al. 2009) — for comparison, the offspring of a brother-sister union would have a value of 0.250, as would the offspring of a parent-child union. Phillip III (Charles II's grandfather) also reached a high level: 0.218. Both of these people were the offspring of uncle-niece marriages.
This first diagram (linked from Wikipedia) shows the pedigree of Charles II, the final member of the dynasty. It illustrates the above points in the usual manner for a family tree. It shows only the royal lineage, as there were many other offspring, and indeed other marriages (Philip II married four times, Philip IV twice, and Charles II also twice). However, none of the male offspring were alive at the time of the death of Charles II, and nor were most of the females. Another of the consequences of the inbreeding was a poor survival rate among the children.
My point with this blog post is that the family tree can also be drawn as a network, as shown in the second diagram (which is also called a "path diagram" by geneticists). This illustrates the same pedigree as above, but with a few additions (at the left) to illustrate the lineage to Don Carlos (crown prince Charles), another highly inbred male (coefficient 0.211), being the offspring of double first cousins. This form of the diagram makes the connection between a family tree and a hybridization network clear — they are both ways of drawing a pedigree.
Basically, the two diagrams illustrate the same point — the Habsburg's defeated their own purpose, because they ultimately lost power by refusing to share it with anyone else. Biology is about biodiversity, and conserving biodiversity applies within your own family just as much as anywhere else.
There are several follow-up posts on this topic, about other famous people:
Charles Darwin's family pedigree network
Toulouse-Lautrec: family trees and networks
Albert Einstein's consanguineous marriage
Alvarez G., Ceballos F.C., Quinteiro C. (2009) The role of inbreeding in the extinction of a European royal dynasty. PLoS ONE 4: e5147.
If you know little about the pros and cons of inbreeding, then this blog post will enlighten you:
Why inbreeding really isn’t as bad as you think it is.
Could you explain how to read the path diagram?ReplyDelete
The arrows show the flow of genetic information, from parent to offspring. So, there are two arrows leading to every person, one from their mother and one from their father (unless one or the other of their parents has not been included in the diagram). Similarly, if any of their children have been included in the diagram, then there will an arrow leading to those children.Delete
Thank you. Yes, I understood that part, but wondered if the amount of crossing between arrows means something or the length of a straight line or the number of these straight lines from one ancestor.ReplyDelete
Length of lines is irrelevant, as is any crossing of lines — they reflect the laying out of the diagram only. The number of lines simply indicates the number of children shown in the diagram (there may be others who are not included).Delete
I was looking up Henri Toulouse Lautrec on Google today, and found this page. It's good to see the family tree I drew for Charles II of Spain (11 years ago!) is still being quoted on the web. Ah, the drafts I had to do to get it to fit in that small amount of space. Poor Carlos.ReplyDelete
I have always liked the diagram, and I think that it is very effective. So, thanks very much for creating it.Delete
There has been little interest in determining just how inbred the Habsburg royal family had become, so I found the work of Alvarez, et. al. to be groundbreaking. In my own study, it was concluded that the Habsburgs were far more inbred than even the official genealogies acknowledge.ReplyDelete
The Shakespeare plays fully document the actual Habsburg genealogy. They essential employed a round-robin system of breeding in which every eligible royal female mated with every eligible male. Sister with half-brother and uncle with niece pairings were still very much in play, but disguised by the use of regional names. Little, if anything, had changed in the royal reproductive model since Ptolemaic times!
Yes, I presume that the reality is always more complex than it appears. The business of being "noble" must be tricky! Thanks for pointing out the history.Delete
When DNA results of the Amarna royals were published, the degree of inbreeding was scandalizing, and to the point that many have dismissed those results as invalid.ReplyDelete
It's not likely that access will ever be granted to collect DNA samples from the Habsburg crypt at El Escorial, but I think there is still much to be learned from studying the effects of royal inbreeding (and from a number of different disciplines and perspectives). Thanks for your courage in pursuing it!
The pedigree of the Amarna royals is discussed in the blog post on "Tutankhamun and extreme consanguinity":Delete
Thank you for pointing that out! I'll comment separately on the Amarna royals, if I may.ReplyDelete
I do find it interesting that geneticists now think that moderate incest is not particularly dangerous from a biological perspective. Ironically, if the Habsburgs had limited the incest to what the genealogies show, they would have been alright. But, to produce a Charles II required pushing it to the very limit. And, they were prepared to just that, again and again, i.e., to end every dynasty in genetic flames! They must have felt there was some reward, which justified the disturbing means. They were even proud enough to document the process! (The founding of the Stewart Dynasty is very thoroughly encoded in Shakespeare's "The Two Noble Kinsmen." Please refer to my book chapter on that play.)
The probabilities for paired recessive alleles arising from inbreeding are discussed in the post on:ReplyDelete
Consanguinity and incest can produce the same effects
This provides a guideline for the genetic problems of consanguinity.
The obvious reward for consanguinity was, and is, "keeping it in the family". Power is a powerful motive!
I'm working on a path chart for the Habsburgs, at least the portion where we have good anecdotal data for determining actual family relationships. How do I paste a chart into the reply box?Delete
What I'm finding, though, is that the royal family avoided the consanguinity trap by having each royal female mate with every royal male. That means you can't easily locate a pair of ancestors that supplied ALL of the genetic material going forward. I didn't find even one case over a period of 200 years! This seems to have also allowed them to practice aggressive incest, but then recover. Occasionally, a "John" had to be brought into the pool, but I haven't found any cases where such a male was truly a commoner. For example, John of Austria (Don Juan of Spain) was a son of Charles V of Spain by the "entertainer" Barbara Blomberg. However, in reality, she was a fully pedigreed woman on the fringe of royalty, such as Christina of Denmark (later Duchess of Milan and Florence, who was all set to become queen consort of Henry VIII of England just prior to that king's excommunication).
You can add images only if they are hosted elsewhere on the web. You do this by adding the URL between the [img] tag.Delete
The point about a breeding pool being closed, even if it is a rather large pool, is very significant. But, in the case of the royals, that pool was extremely small and they deliberately made it as small as possible as a dynasty progressed. And when they reached infertility, they only included "new blood" that was still quite closely related rather than "remote." Perhaps they were misguided into thinking this practice increased the chances of producing a genius. But, it obviously went beyond the idea of just "keeping it in the family."ReplyDelete
With regard to Charles II, there is really little point to calculating coefficients when you don't know the actual genealogy. I'll put together what his actual genealogy was and post it for you!
With regard to Cleopatra, we don't have the mummies of her dynasty, so we can't make too many judgments about their defects and mortality rates. The mummy thought to be Arsinoe IV (from Ephesus) was clearly a servant who was killed in the place of her mistress. She was emulating the first Arsinoe, who we are told had a servant that was killed as her "double."
Here's a link to a proposed "maximally inbred" Habsburg genealogy (path diagram):ReplyDelete
www.domainofman.com/A Habsburg Genealogy 2.png
Despite how "busy" it is, I've placed the two major matriarchal lines of descent right down the middle. The purple is that of Maria of Aragon and the dark red is that of her sister Catherine of Aragon, two of the daughters of the famous couple Isabella and Ferdinand (of Christopher Columbus fame).
During the 250 years covered by the chart (1430 -1680 AD), there were three attempts to inject "new blood" and all three involved a fringe prince named "John of Austria." The last of the three attempted to save the dynasty of Charles II/Carlos II, the subject of your article. The second John of Austria (Don Juan of Spain), the illegitimate son of Charles V of Spain, is the main subject of the Shakespeare plays. His male line took over with Ferdinand III of Austria, which would have been his grandson. The first John of Austria was born circa 1466 and corresponds to the "bastard" John of Gloucester in England. You know what they say: "Twice is a coincidence, three times is a habit" (lol).
I've got much more confidence in the bottom half of the chart than the top half. The Fall of Constantinople had a ripple effect upon the various courts of Europe and makes it more difficult to trace. It is interesting, though, that Spain and Portugal became an epicenter of royal activity.
In a nutshell, my research indicates that Ferdinand II of Aragon and Maximilian were full-brothers and their nominal wives were their half-sisters. So, even at the top of the chart, the Habsburgs were flirting with maximal inbreeding.ReplyDelete
The solution was to restore the status of a prince on the royal fringe. This took the form of John II of Portugal begrudgingly naming his "bastard cousin" as successor under the name of Manuel I of Portugal. This election bore immediate fruit as Manuel became father of the vigorous John III of Portugal. Back on the Austrian side of the fence, it was paralleled by Ferdinand’s adoption as the heir of Philip the Fair. Ferdinand became Holy Roman Emperor due to the infertility of Philip I, Charles V and Philip II. In my chart you can see the dramatic increase in fertility based upon the insertion of John III/Ferdinand (true son of the formerly suppressed Manuel/John of Austria). A future John of Austria (Don Juan of Spain) provided another boost in fertility, which is highlighted with black lines on my chart. Within only two or three generations his contribution also played out. Only one child of Maria Teresa (wife of Louis XIV) survived infancy. There was not a hard genetic reset by any means!
Also in my chart, there are contributions from three of the four daughters of Isabella of Castile. Margaret Tudor, older sister of Henry VIII, also made a genetic contribution as the mother of James V of Scotland. Due to her fertility she was put forward as a candidate for 4th wife of Holy Roman Emperor Maximilian. That didn't happen, however James V was quite possibly the true father of Mary Queen of Scots. That is the official relationship, but its still one that I find perplexing!
The crux of the matter is that coefficients of inbreeding may be difficult to calculate, because at no point can we find a breeding pair that were unrelated to one another!