A endogamia acabou com os Áustrias
This topic is classified in the following rooms Genética
A endogamia acabou com os Áustrias
Cada hora dizem uma coisa. Faz poucas semanas postei aqui algo no sentido contrário, vide:
http://www.geneall.net/P/forum_msg.php?id=222637
LA GENÉTICA DE LOS HABSBURGO
La endogamia acabó con los Austrias
Los matrimonios emparentados durante generaciones provocaron alteraciones genéticas
Carlos II sufrió esa situación en forma de diversas enfermedades como la hidropesía
Actualizado miércoles 15/04/2009 02:20 (CET)
MARÍA VALERIO
MADRID.- Carlos II, el Hechizado, fue el último rey de la dinastía de los Habsburgo que gobernó en España y su muerte en 1700 dejó paso a los Borbones. Se dice de él que era impotente (murió sin descendencia tras dos matrimonios), eyaculador precoz, de constitución débil y corta estatura; padecía diarreas y vómitos frecuentes y tenía aspecto de anciano cuando murió con sólo 39 años. Investigadores gallegos acaban de demostrar que las relaciones de consanguinidad pudieron ser la causa de la extinción de la casa de Austria y de los males del monarca.
La dinastía de los Habsburgo gobernó en nuestro país entre 1516 y 1700. Precisamente su empeño en esos dos siglos por mantener el poder en el seno de la familia a base de matrimonios entre parientes directos pudo ser la causa de su desaparición; según explican en la revista 'PLoS ONE' investigadores de la Universidad de Santiago de Compostela y la Fundación Pública Gallega de Medicina Genómica.
Para su estudio, los genetistas Gonzalo Álvarez y Francisco Ceballos y la doctora Celsa Quinteiro han repasado el árbol genealógico de más de 3.000 individuos a lo largo de 16 generaciones; incluido el propio Carlos II, descendiente de tres generaciones de abuelos con siete matrimonios consanguíneos (la mayoría entre tíos y sobrinos o primos carnales). Su propio padre, Felipe IV, se casó con su sobrina carnal Mariana; hija del matrimonio compuesto por Fernando III y su prima María Ana.
Para cada individuo, los investigadores calcularon un coeficiente de endogamia; un valor matemático que indica la probabilidad de que dos genes sean idénticos por descendencia. Es decir, si una persona hereda una copia de cada gen de su padre y otra de su madre; en los hijos de parientes cercanos existe la probabilidad de que ambas copias heredadas sean iguales.
Similar a un incesto
En el árbol genealógico de los Austrias, Carlos II (seguido de cerca por su abuelo paterno, Felipe III) fue el sujeto con un peor coeficiente de endogamia. "El rey tenía un coeficiente del 25%, que equivale al que tendría un individuo fruto de un incesto entre hermanos o entre padres e hijos", explica Gonzalo Álvarez, que tuvo la idea de indagar en esta cuestión mientras preparaba una clase de genética evolutiva para sus alumnos de Santiago.
Ese 25% significa que una cuarta parte de su genoma era homocigoto; es decir, "que las secuencias en un cromosoma [el heredado del padre] y el otro [por vía materna] eran idénticos". Esta circunstancia ya se había relacionado hasta ahora con la susceptibilidad de un individuo a padecer diversas enfermedades; "pero nunca había visto ningún caso con un índice tan elevado", explica el investigador, que insiste en que su trabajo sólo confirma desde el punto de vista genético lo que los historiadores ya decían desde hace tiempo.
De hecho, Álvarez explica que aunque la endogamia es frecuente entre tribus actuales de África y Asia, como lo fue también entre los egipcios y otras realezas europeas (como los Borbones), es difícil que alcanzase un índice de consanguinidad tan elevado como Carlos II. "Porque la suya es una situación heredada tras los matrimonios familiares que se sucedieron durante generaciones y generaciones. Es lo que se llama una consanguinidad remota".
Sabiendo que esa homocigosis le hacía muy susceptible a ciertas enfermedades hereditarias, la doctora Quinteiro repasó todas las manifestaciones clínicas del débil monarca (muchos de ellos a través de los retratos que los mejores artistas de la época dejaron de él) para tratar de dar con las patologías que podrían estar detrás de sus padecimientos. "La deficiencia de hormonas pituitarias y la acidosis tubular renal, dos enfermedades causadas por genes recesivos, nos permiten explicar más del 90% de los síntomas que padecía Carlos II", explica Álvarez, "pero no deja de ser algo especulativo. Una hipótesis".
El arte, aliado de la genética en este caso, ha retratado a varios de los infantes de los Austrias (que sufrían una mortalidad infantil mayor que la media de su época) cubiertos de amuletos y símbolos de buena suerte para protegerles de los malos espíritus. "Ellos eran conscientes de que pasaba algo y por eso trataban de protegerles desde niños", concluye el profesor.
http://www.elmundo.es/elmundosalud/2009/04/14/biociencia/1239731297.html
El sexo entre primos acabó con los Austrias
Un estudio confirma que la dinastía de los Habsburgo, que rigió España hasta 1700, se extinguió por su endogamia
- PÚBLICO
MANUEL ANSEDE - Madrid - 15/04/2009 02:00
El 1 de noviembre de 1700, el rey de España, Carlos II de Habsburgo, El Hechizado, murió en Madrid sin dejar descendencia a los 39 años. Había nacido con una cabeza de tamaño desproporcionado, no aprendió a hablar hasta los 4 años y fue incapaz de andar hasta los 8. Su muerte -tras un episodio de fiebres altas, retortijones de tripas insoportables y un coma- remató una existencia marcada por el sufrimiento. Según los testimonios de la época, Carlos II, en cuyo reinado Francia invadió Catalunya, era un "enano abúlico", que pasó sus últimos años con el cuerpo hinchado por múltiples edemas y retorcido de dolor a causa de violentos vómitos y diarreas.
El monarca, hijo de Felipe IV y su sobrina, era el último fruto de la política matrimonial de la Casa de Austria, que rigió España entre 1516 y 1700. Durante años, los historiadores han supuesto que los sucesivos matrimonios entre primos, tíos y sobrinos de la misma familia, concertados para sellar alianzas, desembocaron en la extinción de la dinastía que acumuló el mayor imperio de la historia, en época de Carlos I, tatarabuelo de Carlos II.
El 25% de los genes de Carlos II, último rey de la estirpe, estaban repetidos
Ahora, un estudio genético realizado en la Universidad de Santiago de Compostela ha confirmado una hipótesis que parecía obvia, pero que nadie había ratificado. Los científicos, dirigidos por el catedrático de Genética Gonzalo Álvarez, han analizado la información disponible sobre Carlos II y 3.000 de sus parientes, trepando 16 generaciones en su árbol genealógico, para obtener el coeficiente de consanguinidad del monarca: 0,25. Esta cifra -altísima comparada con la media europea, próxima a cero- significa que el 25% de sus genes estaban repetidos, al haber recibido la misma copia de su madre y de su padre. Y esa monótona secuencia facilitó la aparición de enfermedades genéticas recesivas, aquellas que necesitan dos copias de un gen mutado para que el gen se manifieste. Como ocurre con el color claro de los ojos.
"Queremos ver al paciente"
Los infantes llevaban amuletos para ahuyentar el mal de ojo
"El coeficiente de consanguinidad de Carlos II es equiparable al resultado de un cruce entre dos hermanos", explica Álvarez, que publica hoy su estudio en PLoS ONE. Según los autores, la mayor parte de los males que afectaron al rey pudieron ser consecuencia de dos desórdenes genéticos: la deficiencia múltiple de hormonas pituitarias y una acidosis tubular renal. La coincidencia de estos trastornos explicaría el complejo cuadro clínico de El Hechizado, incluyendo su infertilidad, que desembocó en la extinción de la dinastía.
El equipo de Álvarez también ha analizado óleos de pintores como Velázquez y Tiziano para corroborar sus teorías, en colaboración con la Fundación Pública Gallega de Medicina Genómica. "Lo primero que me pidieron los médicos fue ver al paciente", bromea el genetista. Y en los cuadros de los siglos XVI y XVII, los investigadores descubrieron que los Austrias sabían que algo extraño estaba ocurriendo. La mitad de los infantes de la dinastía no llegaba a cumplir un año, frente al 80% del resto de la población española. En las pinturas, los niños de los Habsburgo aparecen con garras de tejón, cuentas de ámbar y campanillas: amuletos para ahuyentar el mal de ojo.
La médica Celsa Quinteiro ha sido la encargada de diagnosticar a Carlos II tres siglos después de su muerte. "Tenía los ojos saltones y la frente abombada, rasgos relacionados con un déficit de hormonas", señala la especialista.
Su primera esposa, apunta, se quejó de la eyaculación precoz del monarca. Y la segunda, de su impotencia. "Es un empeoramiento del cuadro compatible con las enfermedades que describimos", indica. Su nulidad con las mujeres, tatuada en sus genes, dejó el trono expedito a los Borbones.
Endogamia también en los Borbones
Los autores del trabajo sobre la endogamia de los Habsburgo, que anteriormente han realizado análisis genéticos de moscas y mejillones, han comenzado un estudio sobre los efectos de la consanguinidad en la dinastía que ocupa el trono español desde la muerte de Carlos II: la Casa de Borbón. Los matrimonios entre parientes, subraya el catedrático de Genética Gonzalo Álvarez, también eran comunes entre los Borbones, pero sin alcanzar la degeneración biológica de los Habsburgo. La tatarabuela del rey Juan Carlos, Isabel II, se casó con su primo hermano, como hicieron muchos miembros de la dinastía a lo largo de los siglos. Sin embargo, según Álvarez, los efectos de la endogamia se han diluido recientemente, como en otras monarquías europeas, gracias al matrimonio con personas ajenas a la familia. “El coeficiente de consanguinidad del rey Juan Carlos debe de ser mínimo”, conjetura.
http://www.publico.es/ciencias/218794/sexo/primos/acabo/austrias
Direct link:
RE: A endogamia acabou com os Áustrias
Monigo soy Francisco Ceballos, uno de los autores de ese paper de PLOS en donde analizamos la consanguinidad de los Austrias. Para la informacion de los presentes la genealogia que hemos utilizado en el estudio se ha podido desarrollar gracias a esta base de datos.
La consanguinidad es bastante complicada de estudiar y de entender a niveles geneticos. En Principio no hay problema que dos primos tengan hijos... o si, depende de muchas cosas. Carlos II tenia la misma consanguinidad que un individuo nacido de una relacion incestuosa (padre-hija, madre-hijo, hermano-hermana), es decir F = 0,25. Que no te confundan las noticias ni la prensa... no saben bien de lo que hablan.
Direct link:
A endogamia
Encontrei em http://io9.com/5863666/why-inbreeding-really-isnt-as-bad-as-you-think-it-is um bom artigo sobre endogamia, com alguns exemplos (por exemplo, o de Carlos II de Espanha) e considerações que me parecem interessantes aqui colocar. O texto está em inglês mas quem o quiser ler numa outra lingua poderá copiá-lo e coloca-lo no tradutor automático do google (http://translate.google.com/). Não é perfeito mas serve para uma leitura rapida. Assim transcrevo o texto abaixo:
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Why inbreeding really isn’t as bad as you think it is
Inbreeding is where cousins and other close relatives have children together. Most cultures have strong taboos against it, primarily because of the increased risk of birth defects. Here's why that risk isn't all it's cracked up to be.
Of course, there can be some very serious consequences to inbreeding, particularly when it's sustained over multiple generations. Genetic diversity is important, and inbreeding erodes that. There are some dramatic, tragic examples of the dangers of sustained inbreeding. We'll get to all that in due course.
But the fact is that two cousins with no prior history of inbreeding in the family don't have a much greater risk of birth defects in their children than an unrelated couple, and in fact slightly more distant relatives actually appear to produce healthier offspring than the general population. So let's put the taboos to one side and examine what the consequences of inbreeding really are.
A Problem Of Overlapping Genes
While the dangers of inbreeding are generally overstated, they certainly do exist, and can get quite extreme over multiple generations. At its root, the problem is all about recessive genes. While most of the genes that we carry are either beneficial or neutral in character - otherwise, we wouldn't survive - we all have a handful of genes that have the potential to have a serious negative impact on our health. These are known as autosomal recessive disorders, and they include cystic fibrosis, sickle cell anemia, Tay-Sachs disease, albinism, and a variety of other conditions.
These recessive genes, however, generally remain inactive because they are the recessive form of the gene. This means that of our parents, only one carried that gene in the first place and passed it onto us. The other half of the pair came from the other parent, and it was the dominant, harmless form of the gene. The recessive form, or allele, cannot be expressed in the presence of the dominant gene, and so we end up just being a carrier of these potentially harmful genetic conditions rather than a sufferer.
We're all carriers of these potentially harmful genes, but the recessive alleles are so rare that it's unlikely a random reproductive partner will also carry it, and there's always 50-50 chance that we won't even pass on our various dangerous recessive genes. With inbreeding, however, we're talking about family members who already share an unusual percentage of their genes. Cousins, for instance, have a relationship coefficient of about 12.5%, meaning on average an eighth of their genes are identical by descent.
So let's look at a simple hypothetical and consider the case of two cousins who carry the same dangerous recessive gene - say, the one linked to cystic fibrosis - who marry and have four children. Since both parents carry one benign, dominant allele and one dangerous, recessive allele, there are three possible outcomes. Of the four kids, we would expect one to inherit both dominant alleles, meaning she is no longer a carrier. Two of the children would inherit one dominant and one recessive allele, meaning they are still carriers. And one child would inherit both recessive alleles, meaning he would suffer from cystic fibrosis. In a single generation of inbreeding, the risk of cystic fibrosis has hypothetically jumped from 0.1% in the general US population to a whopping 25% for the children of this particular inbreeding couple.
The Real Risks Of Inbreeding
That's an alarming figure, of course, and for many that sort of increased risk is likely to confirm all the taboos about the dangers of inbreeding. And yes, it would be silly to pretend such risks don't exist. But still, while we all carry the genes for such potentially deadly conditions, not all autosomal recessive disorders are so easily activated, with many requiring multiple generations of inbreeding before becoming a serious problem. There does tend to be a gradual decrease in reproductive fitness and general health - children of inbreeding tend to have more trouble having kids and are slightly sicklier, and that gets worse over time - but those don't preclude such children from living rich, full lives.
Let's take a look at some actual figures to see what the real risks are. Perhaps the best example is the work of Professor Alan Bittles, an adjunct professor at the Centre for Comparative Genomics at Australia's Murdoch University, who has worked on the subject for over three decades and in 2008 conducted a review of forty-eight studies from eleven countries on the rate of birth defects in the children of first cousins.
He found that increased risks do exist, but not nearly to the extent that we might imagine. While there's about a 2% risk of birth defects in the general population, first-cousin children have about a 4% chance. Of course, you can phrase that in any number of ways, depending on how you want to spin it. On the one hand, that means that there's double the risk of birth defects in the children of first cousins. On the other hand, 96% of such children are born completely healthy, which is still the vast majority.
What's more, Professor Bittles found that only 1.2% suffered increased infant mortalityrates. Generally speaking, these are marginal increases we're talking about, hardly the sort of guaranteed horrific outcomes that are often associated with inbreeding. But all that shows is that inbreeding isn't as bad as we often think - a statement worth making to be sure, but probably not totally earth-shattering. To that end...
Why A Little Inbreeding Can Be Good For You
Why inbreeding really isn't as bad as you think it isYes, let's go there. Here, we need to look beyond first cousins to more distant relations, specifically third cousins, people who share a common set of great-great-grandparents. Their relationship coefficient isn't huge - just 1/128. But that still means about 200 of their 23,000 protein-coding genes are identical by descent, a level of relationship easily detected by geneticists.
As weird as it might sound, third cousin marriages actually might produce healthier offspring than the general population, at least if Iceland is anything to go by. In 2008, researchers at the deCODE Genetics company in Reykjavik conducted a study of all Icelandic couples born between 1800 and 1965, a cohort that included some 160,811 couples. The results were, to put it mildly, unexpected:
Researchers were shocked to find that for women born between 1800 and 1824, marriages between third cousins produced an average of 4.04 children and 9.17 grandchildren, while marriages between eighth cousins or more distantly related couples had averages of only 3.34 children and 7.31 grandchildren. For women born between 1925 and 1949, with mates related at the degree of third cousins, the average number of children and grandchildren were 3.27 and 6.64, compared with 2.45 and 4.86 for those with mates who were eighth cousins, or more distantly related.
Lead author Dr. Kari Stefanson called these "counterintuitive, almost dislikable results", and yet after isolating for possible socioeconomic factors - a particularly easy task in Iceland, which is one of the most homogeneous countries on the planet - he and his team were left to conclude that there is some biological basis for this apparent increase in reproductive fitness.
So Where Does This Biological Benefit Come From?
That's a very good question, and one to which nobody really knows the answer. Interviewed by ABC News, Dr. Bruce Buehler, the director of HBM Genetics at the University of Nebraska Medical Center, tried to explain these surprising results. He frankly admitted that the explanation eluded him:
"At least genetically, this information doesn't suggest that second or third cousins would be at any higher risk for passing down unfavorable traits. [I] can't think of any genetic explanation for why the third or fourth cousins would have more babies. Maybe what we're seeing here is biologic attraction. If you really look alike, feel alike and think alike, then maybe you have sex more often and have more babies. We do know that there are pheromones which cause attraction, and I wouldn't be surprised if related people have higher sexual desire for one another."
For his part, Dr. Stefansson suggested what we might call a Goldilocks Zone for inbreeding. That term, which we usually see applied to exoplanets, refers to the idea that planets need to neither too far away from nor too close to their star in order to be able to support life. In much the same way, third cousins might actually have just the right amount of genetic overlap, neither too similar nor too dissimilar, and so they enjoy a reproductive advantage. However, the underlying genetics of that explanation remain unknown.
Ultimately, Stefansson concluded that maybe our taboos against consanguinity, or the marriage of related people, haven't just overestimated existing risks - they've actually covered up potential benefits:
"The take-home message is that ...we, as a society of [the] 21st century, have basically ruled against the marriages of closely related couples, because we do not look at it as desirable that closely related people have children. But in spite of the fact that bringing together two alleles of a recessive trait may be bad, there is clearly some biological wisdom in the union of relatively closely related people."
The Tragic Case of Charles II
Lest you think I'm simply here to extol the undiscovered benefits of inbreeding, let's look at the the sad story of Charles II, the last King of Spain from the House of Habsburg, who lived from 1661 to 1700 and reigned from 1665 onwards. Through a series of cleverly organized dynastic marriages two centuries previous, the House of Habsburg had acquired massive land holdings that included the Holy Roman Empire (now Germany), the Low Countries (The Netherlands, Belgium, and Luxembourg) and, most importantly, Spain, complete with its massive overseas empire.
The branch of the family that inherited the Spanish throne was loathe to share power with outsiders, and so they hit upon the same solution that countless other monarchies did - if you don't want to share power, then keep it within the family. Cousins married cousins, uncles married nieces, and second cousins married second cousins. From 1550 onward, not a single outsider married into the Spanish royal line. The result of all this was Charles II, quite possibly the most inbred person in history.
Why inbreeding really isn't as bad as you think it isCharles's ancestry was so ridiculously intertwined that he actually had a higher relationship coefficient than the child of two siblings, and 95.3% of his genes could be traced back to just five ancestors. While the previous kings had escaped their already considerable inbreeding relatively unscathed, Charles suffered from massive mental, physical, and emotional disabilities, earning him the nickname El Hechizado, "The Hexed." In their examination of the role that inbreeding played in the fall of the House of Habsburg, three Spanish researchers offer this summary of his various maladies:
According to contemporary writings, he was often described as "big headed" and "weak breast-fed baby". He was unable to speak until the age of 4, and could not walk until the age of 8. He was short, weak and quite lean and thin. He was described as a person showing very little interest on his surroundings (abulic personality). He first marries at 18 and later at 29, leaving no descendency. His first wife talks of his premature ejaculation, while his second spouse complaints about his impotency. He suffers from sporadic hematuria and intestinal problems (frequent diarrhea and vomits). He looked like an old person when he was only 30 years old, suffering from edemas on his feet, legs, abdomen and face. During the last years of his life he barely can stand up, and suffers from hallucinations and convulsive episodes. His health worsens until his premature death when he was 39, after an episode of fever, abdominal pain, hard breathing and comma [sic].
Charles II also displayed an extreme version of what's known as the Habsburg jaw, a pronounced underbite that had grown progressively more acute over successive royal generations. Charles's great-great-grandfather, Charles I, already had a severe enough underbite that he couldn't chew properly, and as a result suffered lifelong indigestion. By Charles II's time, he was completely unable to chew, his tongue was so large that he could barely speak intelligibly, and he drooled constantly.
His inability to father an heir sparked the War of the Spanish Succession, in which half a million people fought over who should inherit his throne - a deadly outcome that might have been avoided had the Habsburgs not become so completely reliant on inbreeding to preserve control of their empire, which of course they ultimately lost anyway.
Inbreeding: Not Just For Royals
Why inbreeding really isn't as bad as you think it isCharles II represents the extremest of examples, a sort of worse case scenario for inbreeding. And yet he - or at least a hypothetical person very much like him - remains a sort of benchmark for how people imagine the results of inbred relationships, when the most likely result of even first cousins inbreeding is a more or less healthy child. This taboo hasn't always been so strong.
In fact, two of the top candidates for greatest scientist of all time married their cousins. Albert Einstein's wife, whose maiden name was in fact Elsa Einstein, was a first cousin through Albert's mother and a second cousin through his father. And, as we previously discussed, Charles Darwin married his first cousin Emma Wedgwood, and in fact their mutual grandparents, Sarah and Josiah Wedgwood, were themselves cousins. To be fair, after three of Darwin's ten children died young, he and his son George conducted studies into whether the family's long tradition of inbreeding had reduced his reproductive fitness. They ultimately decided this wasn't the case, on the rather strange grounds that "the widely different habits of life of men and women in civilized nations, especially among the upper classes, would tend to counterbalance any evil from marriages between healthy and somewhat closely related persons."
The list also includes luminaries like H.G. Wells, Igor Stravinsky, Edgar Allan Poe (though his marriage to his then 13-year-old cousin was supposedly never consummated, and more like a brother-sister relationship than anything else), film director David Lean, Morse code inventor Samuel Morse, Nazi-turned-NASA rocket scientist Wernher von Braun, and even noted criminals Jesse James and Carlo Gambino, not to mention a huge fraction of monarchs throughout history. And that's just people who married their first cousins - the list gets even longer if we consider more distant relations.
Of Pedigree Collapse and Population Bottlenecks
The fact is that, at least until the greatly increased human mobility of the last couple of centuries, inbreeding was pretty much unavoidable. Most people lived in small communities where their ancestors had lived for generations, which meant finding someone in the local area who was completely unrelated to them was next to impossible. Sometimes, that's created some pretty dramatic results - consider the Doma people of Zimbabwe, whose long isolation and extensive inbreeding has actually resulted in the widespread prevalence of ectrodactyly, in which their middle three toes are completely absent and the outer ones are turned inward.
In point of fact, we're all technically inbred, if you go back far enough, because simple math demands that we have to be. Our number of ancestors grows exponentially with each generation, from two parents to four grandparents to eight great-grandparents, and so on. In less than a thousand years, you've accumulated tens of billions of ancestors, more than the amount of humans who have ever lived on this planet. This means you have to have a bunch of overlapping ancestors, even if they're all buried so far back in your family tree than none of your later ancestors were aware they were marrying their distant cousins. This necessary duplication of ancestors is known as pedigree collapse, and Cecil Adams provides this example of how extensive it is:
Demographer Kenneth Wachtel estimates that the typical English child born in 1947 would have had around 60,000 theoretical ancestors at the time of the discovery of America. Of this number, 95 percent would have been different individuals and 5 percent duplicates. (Sounds like Invasion of the Body Snatchers, but you know what I mean.) Twenty generations back the kid would have 600,000 ancestors, one-third of which would be duplicates. At the time of the Black Death, he'd have had 3.5 million - 30 percent real, 70 percent duplicates. The maximum number of "real" ancestors occurs around 1200 AD - 2 million, some 80 percent of the population of England.
Admittedly, this sort of inbreeding is really more philosophical than genetic. Again, this is a matter of exponents. Of our 23,000 protein-coding gene base pairs, we get 11,500 from each of our parents, 5,750 from our grandparents, 2,875 from our great-grandparents, and so on. That repeated division means that by the fifteenth generation - which is only a few centuries ago - your average ancestor (assuming zero inbreeding) is contributing, on average, less than a single gene to your current genome. Go back a thousand years to the 30th generation, and the average genetic contribution is effectively zero.
While it isn't really accurate to say that we're all inbred, at least not in a genetic sense, it might actually be fair to say that we're all the descendants of inbred people. Numerous theories have been put forward about a huge decrease in the human population tens of thousands of years ago - one particularly extreme version suggests the human population in sub-Saharan Africa remained under 2,000 for as much as 100,000 years, while more moderate hypotheses suggest a population bottleneck of about 15,000 that occurred about 70,000 years ago. Either population bottleneck would most likely necessitate fairly extensive inbreeding, and that's backed up today by the relatively low level of genetic variation within humans.
So, what can we say about inbreeding, in the end? There's no way of escaping the fact that it does increase the risk of birth defects, particularly over multiple generations, and it can have some fairly horrific consequences. That said, the risks of limited inbreeding do seem to be pretty massively overstated, and inbreeding by slightly more distant relatives like third cousins might actually confer a significant benefit. And, depending on just how low our population got in our deep prehistory, it's entirely possible that without inbreeding, the human race would have long since gone extinct.
Additional Reading:
Consanguinity, human evolution, and complex diseases by A.H. Bittles and M.L. Black.
The genetics of inbreeding depression by Deborah Charlesworth and John H. Willlis.
A Background Summary of Consanguineous Marriage by A.H. Bittles.
The Role of Inbreeding in the Extinction of a European Royal Dynasty by Gonzalo Alvarez, Francisco C. Ceballos, and Celsa Quinteiro.
Was the Darwin/Wedgwood Dynasty Adversely Affected by Consanguinity? by Tim M. Berra, Gonzalo Alvarez, and Francisco C. Ceballos.
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Cumprimentos
Ricardo Charters d'Azevedo
Direct link:
Os Habsburgos objecto de estudos dos cientistas.
Ciencia / EL ADN DE LAS DINASTÍAS REALES
Los Habsburgo y sus bodas entre parientes, laboratorio de consanguinidad de la humanidad
e. mONTAÑÉSemontanes / madrid
Día 22/04/2013 - 11.05h
Investigadores compostelanos toman como muestra esta dinastía y estudian sus lazos genéticos durante 300 años para concluir que tienen un grado de parentesco superior al 10% del resto: la mitad de sus relaciones eran incestuosas
La dinastía real de los Habsburgo, convertida en el «conejillo de indias» de un experimento que analiza la consanguinidad de toda la humanidad. Éste es el apriorismo del que partió un equipo de investigadores de la Universidad de Santiago de Compostela (USC) y cuyos resultados ya han sido publicados en la revista «Heredity», al tiempo que van a encontrar mayor eco con un artículo que está preparando para dentro de unos días «Nature News». Según explican desde la Universidad gallega, los Habsburgo se alzan como una de las Casas más interesantes para estudiar estos lazos genéticos, debido a «su política matrimonial», que devino en «un caso de persistente consanguinidad durante generaciones».
Así, los científicos del Departamento de Genética de la USC resaltan las ventajas que rezuma el estudio de la endogamia característica de cualquiera de las dinastías reales de principios de la Edad Moderna para llevar a buen puerto una investigación que la utilice como modelo de endogamia humana durante siglos. Para ello, este artículo, firmado por Francisco Camiña Ceballos y Gonzalo Álvaraz Jurado, avala que en su trabajo los investigadores recabaron documentación provenitente de fuentes históricas de 300 años de genealogía (entre los años 1450 y 1750).
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Escudo de la casa de Habsburgo
Según desglosan en la revista, los investigadores calcularon los coeficientes de parentesco y consanguinidad de los Habsburgo a partir de una base de datos de más de 4.000 personas pertenecientes a 20 generaciones entre padres e hijos. En el periodo señalado, añade Francisco Camiña, analizaron un total de 73 matrimonios pactados entre emperadores del Sacro Imperio Romano y reyes de la Casa de Habsburgo española, así como sus hijos y sus nietos en ese ciclo. Coligen los científicos que el coeficiente de consanguinidad más elevado se produjo en la rama austriaca, con Maria Antoine de Habsburgo, hija de Leopoldo I y su sobrina Margarita de España (hermana de Carlos II de España) como protagonistas, ya que ostentó un coeficiente de endogamia de 0,3053, superior al que se registra en la descendencia de una unión incestuosa (relaciones sexuales entre padres e hijos o entre hermanos).
Más que bodas entre primos...
En la Casa de los Habsburgo, la mitad de los matrimonios tiene un coeficiente de parentesco por encima del que supone la unión de primos, y cerca de dos de cada diez de estos enlaces registran un parentesco superior al que correspondería a una unión entre un tío y su sobrina, de acuerdo con esta curiosa investigación.
Es muy interesante la conclusión de Camiña y Álvarez en el artículo, cuando infieren que «la comparación de estos promedios con los registros de depresión endogámica en poblaciones humanas contemporáneas pone de manifiesto el fuerte impacto de la endogamia en la supervivencia de la progenie de los Habsburgo», por lo que -completan- «las dinastías reales de la Edad Moderna son perfectos laboratorios de consanguinidad».
La política de alianzas elevó notablemente la progenie de la dinastía de los Habsburgo
En esta línea abundan en que más del 10% de la humanidad es consanguínea, así que resulta útil estudiar los efectos que tiene este porcentaje en las poblaciones humanas. En dicho artículo, del que informa la Universidad compostelana, Camiña resalta que es conveniente este estudio debido a que la información demográfica, los datos del número de hijos que tiene cada pareja o la edad de mortalidad de los niños permite estudiar con mayor eficacia los efectos de la consanguinidad tanto en la morbilidad de la especie humana, como en su fertilidad y en la propia supervivencia.
Enfermedades raras
Y ponen otro ejemplo aún más claro: estudiar esta proporción de consanguinidad resulta crucial para el abordaje por ejemplo de enfermedades raras, y también en la relación que existe entre el genotipado y el fenotipado de otras dolencias más comunes como la hipertensión, el asma, la gota, la depresión, el cáncer o la esquizofrenia, entre otras. «La consanguinidad actúa a nivel del genoma, por lo tanto toca todo e interviene en todo», finalizan los investigadores gallegos.
http://www.abc.es/ciencia/20130421/abci-dinastia-habsburgo-201304191753.html
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