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¿Cuál es la diferencia entre el incesto y la endogamia?

¿Cuál es la diferencia entre el incesto y la endogamia?



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¿Son lo mismo? Ya que ambos están relacionados con la actividad sexual entre parientes cercanos.


Incesto es un concepto humano definido por la ley y las convenciones sociales. Por ejemplo, consulte una definición de la palabra: "Relaciones sexuales entre personas tan estrechamente relacionadas que la ley les prohíbe casarse.".

Una persona que fue adoptada puede tener hermanos que sean genéticamente más diferentes a ellos que otras personas con las que legalmente podrían tener relaciones románticas. En muchos países puede casarse con su primo, pero no con su hermano o hermana adoptiva nacido en el otro lado del mundo.

El antropólogo Claude Lévi-Strauss fue pionero en el estudio de la universalidad de la noción de incesto; Las relaciones románticas con miembros de la familia están prohibidas culturalmente en casi todas las culturas del mundo. ¿Pero por qué? Una de las explicaciones está ligada a la noción de endogamia.

La endogamia (apareamiento entre individuos genéticamente estrechamente relacionados) favorece la homocigosidad y, como consecuencia, una cierta homogeneidad genética en la que a menudo no hay un alelo "funcional" para compensar el "roto" - las consecuencias en la fisiología y las capacidades cognitivas mentales son a menudo dramático (ver Roberts, BMJ, 1967 o este artículo de Stanford @ the Tech, por ejemplo); se hipotetiza que esta es la razón por la cual la evolución seleccionó comportamientos que evitan los riesgos vinculados a la endogamia.


El incesto y la endogamia son conceptos diferentes. El incesto implica el mestizaje entre parientes cercanos. La endogamia es un concepto más amplio. Puede ser una conexión entre parientes o autopolinización. UPD: Este ciertamente no es un artículo de revista, pero… https://en.wikipedia.org/wiki/Inbreeding


Los humanos antiguos sabían que el incesto era asqueroso y construyeron una red de seguridad

Dejando a un lado la negación cultural, el incesto y la consanguinidad subsiguiente no son buenos. Las relaciones incestuosas dan como resultado niños con menor diversidad genética, lo que aumenta su probabilidad de desarrollar enfermedades genéticas. En consecuencia, los primeros humanos descubrieron que un buen número de Game of Thrones los personajes aún no lo han hecho: que debes hacer todo lo posible para no tener relaciones sexuales con tus parientes inmediatos.

En un estudio publicado en Ciencias El jueves, arqueólogos y genetistas revelaron que los primeros humanos comenzaron a evitar la endogamia mucho antes de lo que pensamos. La secuenciación genómica de cuatro humanos del Paleolítico superior que fueron enterrados juntos en Rusia hace unos 34.000 años demostró que no estaban más cerca que primos segundos, lo que el coautor Eske Willerslev, Ph.D. dice "va en contra de lo que muchos hubieran predicho".

Esto probablemente significa que los primeros humanos tomaron precauciones adicionales cuando llegó el momento de elegir pareja, conectándose con una red más amplia de grupos más allá de su pequeña unidad familiar para mantener la diversidad genética. Los científicos creen que estas bandas de cazadores-recolectores deben haber desarrollado un sistema con propósito para la selección de pareja; de lo contrario, verían más evidencia de endogamia.

No se puede decir lo mismo de los neandertales, que parecían pensar que el incesto estaba bien, según una investigación sobre especímenes de 50.000 años de antigüedad. Si bien los científicos no saben exactamente por qué lo hicieron, teorizan con cautela que Homo sapiens sobrevivió como especie, mientras que los neandertales no lo hicieron porque evitamos en gran medida la endogamia.

Pero los primeros humanos pueden haber tenido otro truco que les dio una ventaja sobre los neandertales: el romance. O, al menos, algo parecido a un romance. Estos cuatro humanos fueron encontrados juntos en un sitio de enterramiento, lo cual es raro, y el sitio también contenía lo que parecen ser objetos y joyas elegidos a propósito.

Estos artefactos, dicen los autores del estudio, sugieren que se desarrollaron reglas y rituales que acompañaron el intercambio de parejas entre grupos, ceremonias que podrían haber presagiado la invención de los servicios matrimoniales modernos.

Si te gustó este artículo, mira este video sobre el incesto en Game of Thrones.


Calcular la relación

En los organismos diploides, cada niño recibe la mitad de sus genes de su madre y la mitad de su padre3. Por tanto, cada padre comparte la mitad de sus alelos con un hijo, y decimos que los padres y la descendencia están relacionados por & frac12. Dos hermanos cualesquiera también están relacionados por & frac12. Cada hermano recibe la mitad de sus genes de cada padre. Como resultado, los hermanos no podían compartir alelos (en el improbable caso de que cada hijo obtuviera la mitad de los genes de cada padre que el otro no), todos los alelos (en el improbable caso de que ambos niños obtuvieran el mismo conjunto de genes de cada uno). parent), o en cualquier lugar intermedio. Eso tiene un promedio de (0 + 1) / 2, por lo que los hermanos comparten la mitad de sus alelos en promedio y r = & frac12. Este ejemplo ilustra el punto:

Este hipotético organismo diploide tiene cuatro cromosomas, R, S, T y U. Cada padre tiene dos copias de cada cromosoma y cada gameto (óvulo o esperma) lleva solo una de esas copias. Un niño obtiene la mitad de sus cromosomas de cada gameto, por lo que padre e hijo están relacionados por & frac12. Dado que los cromosomas se segregan aleatoriamente en gametos, la proporción real de alelos compartidos por dos hermanos puede variar. En este ejemplo, A y C comparten todos los alelos, mientras que B y D no comparten ninguno. A y B comparten & frac12 sus alelos, al igual que B y C. A y D comparten solo & frac14, al igual que C y D. Considerando todas las posibles combinaciones de gametos, los hermanos comparten & frac12 de sus alelos en promedio.

Dado que los padres y los hijos están relacionados por & frac12 y los hermanos están relacionados por & frac12, podemos calcular la relación de cualquier miembro de la familia. El razonamiento sobre padres e hijos muestra que un abuelo y un nieto están relacionados por & frac14, ya que uno de los padres recibió la mitad de sus genes de ese abuelo y luego pasó la mitad de esos genes a sus hijos. También podemos seguir ese razonamiento para demostrar que está relacionado con un tío o una tía por & frac14. Su padre y su hermano comparten la mitad de sus alelos, y la mitad de esos alelos compartidos le fue transmitida por su padre.

Si rastrear genes de una generación a la siguiente parece complicado, existe una forma gráfica sencilla de lograr lo mismo mirando un árbol genealógico. Dibuja el árbol como en el siguiente ejemplo. Luego marque el camino más corto posible entre dos miembros de la familia y cuente el número de pasos entre ellos. Cada paso entre generaciones (de padres a hijos) o entre hermanos cuenta como uno. Una vez que tenga este número de pasos (n), r = & frac12 n, o & frac12 multiplicado por sí mismo n veces.

Árbol de familia: A es padre de B y C, B es padre de D y E, y así sucesivamente. Solo se muestran dos hermanos por generación si hay más, todos están relacionados entre sí por la misma cantidad. Las líneas continuas conectan a los padres y a los hijos. Las líneas discontinuas conectan a los hermanos.

Por ejemplo, ¿cómo se relacionan D y K (sobrino o sobrino con tía o tío)? Hay dos pasos, D-E y E-K, entonces r = & frac12 & times & frac12, o & frac14. ¿Cómo se relacionan H y J (primos hermanos)? Hay tres pasos, H-D, D-E y E-J, por lo que r = & frac12 & times & frac12 & times & frac12, o & # x215B. Si desea más práctica, pruebe estos ejemplos. Todos se refieren al árbol anterior.

Con esto concluye el tutorial básico de parentesco, que es suficiente para la mayoría de los propósitos.


Chicos más útiles

la genética es una cosa extraña.
Básicamente, todos tenemos un montón de información genética dentro de nosotros. Y cuanto más distante esté alguien de nosotros genéticamente, más diversos serán los genes de nuestros hijos.
Esto es bueno y malo. Más diversidad significa que pueden ingresar más genes para cosas malas. También significa más genes para cosas buenas.
La mayoría de las cosas malas provienen de genes recesivos. Esto significa que el gen de la afección debe provenir de ambos lados. también significa que deben faltar genes que de otro modo eliminarían los problemas.
Cuando ocurre el incesto, hay menos diversidad genética. No se agrega nada nuevo. Los buenos rasgos genéticos se transmiten con fuerza de esta manera, pero, lamentablemente, también lo son los malos. Y debido a que ambos padres tienen los mismos rasgos recesivos, la posibilidad de que sucedan cosas malas aumenta.
En la población general, es posible que tenga un 1% de probabilidad de tener algún defecto congénito. Porque incluso las personas no relacionadas con usted tendrán los mismos genes recesivos. Si te relacionas con un primo, puede subir del 2 al 4%, porque tienen lo mismo que tú, pero algo diferente. Conéctate con un hermano o hermana y estarás en un 10% más alto. Menos diversidad, más posibilidades de que los genes defectuosos se vuelvan pronunciados.
El incesto ocasional puede ser en su mayoría inofensivo. Si la familia tiene genes particularmente buenos, incluso puede resultar en niños muy sanos, y por lo demás bendecidos. Pero el incesto regular o constante, o incluso solo 2 o 3 generaciones, multiplica la posibilidad de problemas por mucho.

Ahora, esto NO es solo un problema humano. Varias especies animales sufren de "cuellos de botella genéticos", porque la población era tan pequeña en algún momento que todos los miembros vivos ahora están relacionados porque obtuvieron su número de un grupo pequeño. Este es el caso de los guepardos. Si alguna vez has oído hablar de perros o gatos puros que no son tan inteligentes, que viven vidas más cortas y tienen más problemas de salud, esta es la razón. Son muy endogámicos para obtener los rasgos deseados, pero los problemas de salud provienen de eso.

Entonces, ¿por qué algunos animales lo manejan mejor? Porque mueren animales débiles o enfermos. Entonces, los animales que viven para seguir reproduciéndose son los más fuertes y saludables. Como dije, no todo incesto produce descendencia enferma, y ​​si hay buenos rasgos, también se transmiten. Así que los animales que no están en peor situación por ser producto del incesto, o incluso los pocos que están mejor por ello, continúan reproduciéndose. Y los animales que sufren su reproducción mueren y no transmiten sus genes dañados.

No es solo con los humanos, pasa con cualquier animal.

El ADN es un código de letras. AATGGCAT, lo que sea

Esas letras representan información, genes. Los genes se expresan mediante ARN. Una proteína llamada ARN polimerasa aparece y lee el ADN y convierte la información genética en proteínas combinando diferentes aminoácidos. Una proteína contiene muchos aminoácidos.

Todo lo que haces en la vida, todo lo que eres, cada movimiento que haces, es una interacción proteína a proteína.

Cuando su cuerpo no puede producir una determinada proteína, es necesario que se produzcan complicaciones que conducen a una enfermedad que a menudo no se puede tratar. ¿Cómo se estropea la proteína? Por una mutación. ¿Cómo ocurre una mutación? Una mutación ocurre cuando hay un error en el material genético, el código del ADN. ¡Eso es lo que es una mutación! Puede resultar en una proteína diferente o que no funciona, lo que a su vez arruinará su vida. Ahora puede preguntar ¿dónde encaja la endogamia en la imagen?

Tenemos que hablar un poco sobre genes. Los genes tienen 2 loci. Cuando dos padres tienen relaciones sexuales y tienen un bebé, el bebé hereda 1 conjunto de genes de cada padre. 1 loci podría estar dañado, existe una probabilidad, pero al menos la mitad del material genético está sano. Cuando los parientes se reproducen, existe una alta probabilidad de que su descendencia tenga 2 genes del mismo conjunto. A esto se le llama genes homocigotos.

Cuando hay 1 gen bueno y 1 malo, aún se pueden producir proteínas y tu cuerpo puede funcionar, pero cuando obtienes 2 genes malos, tendrás algún tipo de enfermedad.


Está científicamente probado y ampliamente reconocido que, en promedio, el efecto de la endogamia / línea es:

  1. Un aumento en la prevalencia de trastornos hereditarios.
  2. Una disminución de la viabilidad.
  3. Disminución de la capacidad reproductiva y
  4. La pérdida de diversidad genética (es decir, disminución de la variación genética).

La endogamia también puede resultar en una interrupción del desarrollo, una mayor mortalidad infantil, una vida más corta y una reducción de la función del sistema inmunológico. El sistema inmunológico está estrechamente relacionado con la eliminación de células cancerosas de un cuerpo sano, por lo que la reducción de la función del sistema inmunológico aumenta el riesgo de desarrollo de tumores. La función del sistema inmunológico también es fundamental para la defensa contra las enfermedades infecciosas. Los problemas de bienestar pueden ocurrir cuando el sistema inmunológico está comprometido.

En conjunto, estos efectos de la consanguinidad / línea se denominan depresión endogámica. Es importante destacar que la depresión por consanguinidad aumenta a medida que aumenta la extensión de la consanguinidad / línea.


¿Por qué la endogamia no es tan mala como crees?

La endogamia es cuando los primos y otros parientes cercanos tienen hijos juntos. La mayoría de las culturas tienen fuertes tabúes en su contra, principalmente debido al mayor riesgo de malformaciones congénitas. Aquí se explica por qué ese riesgo no es todo lo que parece.

Por supuesto, la endogamia puede tener consecuencias muy graves, especialmente cuando se mantiene durante varias generaciones. Diversidad genetica es importante, y la endogamia erosiona eso. Hay algunos ejemplos dramáticos y trágicos de los peligros de la endogamia sostenida. Llegaremos a todo eso a su debido tiempo.

Pero el hecho es que dos primos sin antecedentes de endogamia en la familia no tienen un riesgo mucho mayor de defectos de nacimiento en sus hijos que una pareja sin parentesco y, de hecho, los parientes un poco más distantes en realidad parecen producir defectos de nacimiento. mas saludable descendencia que la población general. Así que dejemos & # x27s los tabúes a un lado y examinemos cuáles son las consecuencias de la endogamia. De Verdad están.

Imagen superior de Arrested Development.

Un problema de superposición de genes

Si bien los peligros de la endogamia generalmente se exageran, ciertamente existen y pueden volverse bastante extremos a lo largo de varias generaciones. En el fondo, el problema tiene que ver con los genes recesivos. Si bien la mayoría de los genes que portamos son benéficos o de carácter neutral, de lo contrario, no sobreviviríamos, todos tenemos un puñado de genes que tienen el potencial de tener un impacto negativo grave en nuestra salud. Estos se conocen como trastornos autosómicos recesivos e incluyen fibrosis quística, anemia de células falciformes, enfermedad de Tay-Sachs, albinismo y una variedad de otras afecciones.

Sin embargo, estos genes recesivos generalmente permanecen inactivos porque son la forma recesiva del gen. Esto significa que de nuestros padres, solo uno portaba ese gen en primer lugar y nos lo transmitió. La otra mitad del par provenía del otro padre, y era la forma dominante e inofensiva del gen. La forma recesiva, o alelo, no se puede expresar en presencia del gen dominante, por lo que terminamos siendo simplemente portadores de estas condiciones genéticas potencialmente dañinas en lugar de sufrirlas.

Todos somos portadores de estos genes potencialmente dañinos, pero los alelos recesivos son tan raros que es improbable que una pareja reproductora aleatoria también los lleve, y siempre hay 50-50 posibilidades de que no podamos transmitir nuestra información. varios genes recesivos peligrosos. Sin embargo, con la endogamia, estamos hablando de miembros de la familia que ya comparten un porcentaje inusual de sus genes. Los primos, por ejemplo, tienen un coeficiente de relación de aproximadamente el 12,5%, lo que significa que, en promedio, una octava parte de sus genes son idénticos por descendencia.

Así que miremos una hipótesis simple y consideremos el caso de dos primos que portan el mismo gen recesivo peligroso, por ejemplo, el relacionado con la fibrosis quística, que se casan y tienen cuatro hijos. Dado que ambos padres son portadores de un alelo dominante benigno y un alelo recesivo peligroso, existen tres posibles resultados. De los cuatro niños, esperaríamos que uno heredara ambos alelos dominantes, lo que significa que ya no es portadora. Dos de los niños heredarían un alelo dominante y otro recesivo, lo que significa que todavía son portadores. Y un niño heredaría ambos alelos recesivos, lo que significa que sufriría fibrosis quística. En una sola generación de endogamia, el riesgo de fibrosis quística ha aumentado hipotéticamente del 0,1% en la población general de EE. UU. A un enorme 25% para los hijos de esta pareja endogámica en particular.

Los verdaderos riesgos de la endogamia

Esa es una cifra alarmante, por supuesto, y es probable que para muchos ese tipo de aumento del riesgo confirme todos los tabúes sobre los peligros de la endogamia. Y sí, sería una tontería pretender que tales riesgos no existen. Pero aún así, aunque todos portamos los genes de estas afecciones potencialmente mortales, no todos los trastornos autosómicos recesivos se activan tan fácilmente, y muchos requieren múltiples generaciones de endogamia antes de convertirse en un problema grave. Suele haber una disminución gradual en la aptitud reproductiva y la salud en general (los niños de endogamia tienden a tener más problemas para tener hijos y están un poco más enfermos, y eso empeora con el tiempo), pero esos no impiden que esos niños vivan ricos, plenos. vidas.

Echemos un vistazo a algunas cifras reales para ver cuáles son los riesgos reales. Quizás el mejor ejemplo es el trabajo del profesor Alan Bittles, profesor adjunto en el Centro de Genómica Comparada en Australia & # x27s Murdoch University, quien ha trabajado en el tema durante más de tres décadas y en 2008 realizó una revisión de cuarenta y ocho estudios de once países sobre la tasa de defectos de nacimiento en los hijos de primos hermanos.

Descubrió que existen mayores riesgos, pero no tanto como podríamos imaginar. Si bien existe un riesgo de alrededor del 2% de defectos congénitos en la población general, los niños primos hermanos tienen alrededor del 4% de probabilidades. Por supuesto, puede expresarlo de varias maneras, dependiendo de cómo quiera girarlo. Por un lado, eso significa que existe & # x27s el doble de riesgo de defectos de nacimiento en los hijos de primos hermanos. Por otro lado, el 96% de estos niños nacen completamente sanos, que sigue siendo la gran mayoría.

Lo que es más, el profesor Bittles descubrió que solo el 1,2% sufría un aumento de las tasas de mortalidad infantil. En términos generales, estos son aumentos marginales de los que estamos hablando, difícilmente el tipo de resultados horribles garantizados que a menudo se asocian con la endogamia. Pero todo lo que muestra es que la endogamia no es tan mala como a menudo pensamos, una afirmación que vale la pena hacer, pero probablemente no sea del todo trascendental. Con ese fin.

Por qué un poco de endogamia puede ser bueno para usted

Sí, vamos a & # x27s. Aquí, tenemos que mirar más allá de los primos hermanos hacia las relaciones más distantes, específicamente los primos terceros, personas que comparten un grupo común de tatarabuelos. Su coeficiente de relación no es enorme, solo 1/128. Pero eso todavía significa que unos 200 de sus 23.000 genes codificadores de proteínas son idénticos por descendencia, un nivel de relación que los genetistas detectan fácilmente.

Por extraño que parezca, los matrimonios de primos terceros en realidad podrían producir una descendencia más saludable que la población en general, al menos si Islandia es algo por lo que pasar. En 2008, los investigadores de la empresa deCODE Genetics en Reykjavik llevaron a cabo un estudio de todas las parejas islandesas nacidas entre 1800 y 1965, una cohorte que incluía a unas 160,811 parejas. Los resultados fueron, por decirlo suavemente, inesperados:

Los investigadores se sorprendieron al descubrir que para las mujeres nacidas entre 1800 y 1824, los matrimonios entre primos terceros produjeron un promedio de 4.04 hijos y 9.17 nietos, mientras que los matrimonios entre primos octavos o parejas más lejanas tenían promedios de solo 3.34 hijos y 7.31 nietos. Para las mujeres nacidas entre 1925 y 1949, con parejas emparentadas con el grado de primos terceros, el número promedio de hijos y nietos fue de 3,27 y 6,64, en comparación con 2,45 y 4,86 ​​para aquellas con parejas que eran primos octavos o parientes más lejanos.

El autor principal, el Dr. Kari Stefanson, los llamó "resultados contraintuitivos, casi desagradables" y, sin embargo, después de aislar los posibles factores socioeconómicos, una tarea particularmente fácil en Islandia, que es uno de los países más homogéneos del planeta, él y su equipo se quedaron para concluir. que hay alguna base biológica para este aparente aumento de la capacidad reproductiva.

Entonces, ¿de dónde proviene este beneficio biológico?

Esa es una muy buena pregunta, y nadie sabe realmente la respuesta. Entrevistado por ABC News, el Dr. Bruce Buehler, director de Genética de HBM en el Centro Médico de la Universidad de Nebraska, trató de explicar estos sorprendentes resultados. Francamente admitió que la explicación se le escapó:

"Al menos genéticamente, esta información no sugiere que los primos segundos o terceros tengan un mayor riesgo de transmitir rasgos desfavorables". [No] puedo pensar en ninguna explicación genética de por qué los primos tercero o cuarto tendrían más bebés. Quizás lo que estamos viendo aquí es atracción biológica. Si realmente te pareces, te sientes igual y piensas igual, entonces tal vez tengas relaciones sexuales con más frecuencia y tengas más bebés. Sabemos que hay feromonas que causan atracción, y no me sorprendería que las personas emparentadas tuvieran un mayor deseo sexual el uno por el otro.

Por su parte, el Dr. Stefansson sugirió lo que podríamos llamar una Zona de Ricitos de Oro para la endogamia. Ese término, que solemos ver aplicado a los exoplanetas, se refiere a la idea de que los planetas no necesitan ni estar ni demasiado lejos ni demasiado cerca de su estrella para poder sustentar la vida. De la misma manera, los primos terceros podrían tener la cantidad justa de superposición genética, ni demasiado similar ni demasiado diferente, por lo que disfrutan de una ventaja reproductiva. Sin embargo, la genética subyacente de esa explicación sigue siendo desconocida.

En última instancia, Stefansson concluyó que tal vez nuestros tabúes contra la consanguinidad, o el matrimonio de personas relacionadas, no han sobrestimado los riesgos existentes; en realidad, han encubierto el potencial. beneficios:

& quot; El mensaje para llevar a casa es ese. nosotros, como sociedad del siglo XXI, básicamente nos hemos pronunciado en contra de los matrimonios de parejas estrechamente relacionadas, porque no consideramos deseable que personas estrechamente relacionadas tengan hijos. Pero a pesar del hecho de que juntar dos alelos de un rasgo recesivo puede ser malo, es evidente que hay algo de sabiduría biológica en la unión de personas relativamente cercanas ".

El trágico caso de Carlos II

Para que no crean que estoy aquí simplemente para ensalzar los beneficios no descubiertos de la endogamia, miremos la triste historia de Carlos II, el último rey de España de la Casa de los Habsburgo, que vivió de 1661 a 1700 y reinó desde 1665. adelante. A través de una serie de matrimonios dinásticos hábilmente organizados dos siglos antes, la Casa de Habsburgo había adquirido grandes posesiones de tierras que incluían el Sacro Imperio Romano Germánico (ahora Alemania), los Países Bajos (Países Bajos, Bélgica y Luxemburgo) y, lo más importante, España. , completo con su imperio masivo en el extranjero.

La rama de la familia que heredó el trono español detestaba compartir el poder con los forasteros, por lo que encontraron la misma solución que hicieron muchas otras monarquías: si no quieres compartir el poder, mantenlo dentro de la familia. Los primos se casaron con primos, los tíos se casaron con sobrinas y los primos segundos se casaron con primos segundos. Desde 1550 en adelante, ni un solo forastero se casó con la línea real española. El resultado de todo esto fue Carlos II, posiblemente la persona más consanguínea de la historia.

La ascendencia de Charles estaba tan ridículamente entrelazada que en realidad tenía un coeficiente de relación más alto que el hijo de dos hermanos, y el 95,3% de sus genes se remonta a solo cinco antepasados. Mientras que los reyes anteriores habían escapado relativamente ilesos de su ya considerable endogamia, Charles sufría de discapacidades mentales, físicas y emocionales masivas, lo que le valió el apodo El Hechizado, `` The Hexed ''. En su examen del papel que jugó la endogamia en la caída de la Casa de los Habsburgo, tres investigadores españoles ofrecen este resumen de sus diversas enfermedades:

Según los escritos contemporáneos, a menudo se lo describía como "de cabeza grande" y "bebé amamantado débil". No pudo hablar hasta los 4 años y no pudo caminar hasta los 8 años. Era bajo, débil y bastante delgado y delgado. Fue descrito como una persona que mostraba muy poco interés por su entorno (personalidad abúlica). Se casa por primera vez a los 18 años y luego a los 29, sin dejar descendencia. Su primera esposa habla de su eyaculación precoz, mientras que su segunda esposa se queja de su impotencia. Padece hematuria esporádica y problemas intestinales (diarreas frecuentes y vómitos). Parecía un anciano cuando solo tenía 30 años, sufría de edemas en los pies, piernas, abdomen y rostro. Durante los últimos años de su vida apenas puede ponerse de pie y sufre alucinaciones y episodios convulsivos. Su salud empeora hasta su muerte prematura cuando tenía 39 años, tras un episodio de fiebre, dolor abdominal, dificultad para respirar y coma. [sic].

Carlos II también mostró una versión extrema de lo que se conoce como la mandíbula de los Habsburgo, una mordida pronunciada que se había vuelto progresivamente más aguda a lo largo de las sucesivas generaciones reales. El tatarabuelo de Carlos, Carlos I, ya tenía una mordida lo suficientemente grave que no podía masticar correctamente y, como resultado, sufría una indigestión de por vida. Para la época de Carlos II, era completamente incapaz de masticar, su lengua era tan grande que apenas podía hablar de manera inteligible y babeaba constantemente.

Su incapacidad para engendrar un heredero desató la Guerra de Sucesión española, en la que medio millón de personas pelearon por quién heredaría su trono, un resultado mortal que podría haberse evitado si los Habsburgo no se hubieran vuelto tan completamente dependientes de la endogamia para preservar el control de su imperio, que por supuesto finalmente perdieron de todos modos.


Entonces, ¿la familia Addams practica la endogamia o qué?

Con una nueva encarnación de La familia Addams Llegando a los cines a finales de este mes, es hora de abordar esa molesta pregunta que seguramente está en el fondo de la mente de todos.

La familia Addams ... hay algunas cosas horribles y extrañas de endogamia que están sucediendo allí, ¿verdad?

Más La familia Addams

¿No? ¿Eso no está en el fondo de la mente de todos? ¿Sólo soy yo? Pero aun así… ¿verdad? ¿Derecha?

La unidad familiar nuclear que constituye el centro de La familia Addams - en sus diversos programas de televisión y películas, así como en el original de Charles Addams Neoyorquino cómics: son más o menos objetivos de relaciones, objetivos familiares, objetivos de diseño de interiores, todo objetivos. Gomez y Morticia son una pareja casada que en realidad parecen disfrutan estar juntos y disfrutar teniendo sexo, ambas cosas están muy lejos del estereotipo "estar casado apesta, mi esposa es una vieja bola y cadena, tee hee"idea de la heteronormatividad que surgió - y sigue apareciendo - en tantas comedias de situación de mediados de siglo. Co-crían y lo hacen bien, apoyando a sus hijos incluso cuando sus intereses se inclinan hacia los moralmente degenerados, como disfrutar El gato en el sombrero (bebé pubertad en Valores de la familia Addams) o querer unirse a los Boy Scouts (Pugsley en "Morticia and the Psychiatrist", el segundo episodio de la comedia de situación de los años 60). Gómez y su hermano Fester se respetan y admiran claramente. Demonios, Gomez se lleva bien con su suegra.

Pero echemos un vistazo al universo más amplio aquí. Aunque los miembros del mundo exterior los miran en gran medida con miedo y disgusto, los Addams existen aparentemente en el centro de un pequeño grupo de inadaptados y bichos raros que se congregan en la mansión Addams para eventos especiales. Una de las primeras escenas de la nueva película animada muestra a este grupo en la boda de Gomez y Morticia. ¿Cuál es el lado de la novia? ¿Cuál es el del novio? ¿Quién sabe? Es todo el mismo grupo de personas. La familia Addams es el eje de un culto nu-gótico que se ha estado casando a lo largo de los siglos.

Inclina la cabeza y entrecierra los ojos y todo comienza a tener sentido. En siglos anteriores, la endogamia prevalecía entre las familias reales de Europa, lo que provocaba todo tipo de problemas de salud física y mental. A medida que la importancia de la monarquía ha disminuido y la comprensión de la genética ha aumentado, ya no se acepta en la mayoría de los rincones del mundo casarse con un primo hermano. Entonces, no podemos decir si, dadas unas cuantas generaciones más de mejoramiento de primos, la mandíbula de los Habsburgo se habría convertido, por ejemplo, en una capacidad para conducir la iluminación colocando una bombilla en la boca. ¡Simplemente no lo sabemos!

Hablando del tío Fester calvo y socialmente torpe, varias veces en la tradición de la familia Addams se le cita como deseable, encantador, guapo, básicamente un Chris Evans en el universo. "¡Eras tan apuesto que podías tener a cualquier mujer que quisieras, viva o muerta!" exclama Gómez en La familia Addams. O tomemos a Morticia en el estreno de la comedia de situación de los 60, cuando Fester argumenta que él nunca fue a la escuela, por lo que su sobrino y su sobrina tampoco deberían tener que hacerlo. "La apariencia, el encanto y la personalidad no lo son todo. ¡Existe el aprendizaje y los logros!" ¿Qué explica esta marcada diferencia en los estándares de belleza masculina entre nuestro mundo y la mudanza de los Addams? ¿Escritores de guiones en busca de una broma? Quizás. Probablemente. Definitivamente no. Es la cuestión de la endogamia.

Aunque varias versiones de La familia Addams Muy a menudo muestran al clan Addams interactuando con personas fuera de su grupo social relativamente pequeño, rara vez es de una manera que sugiera que es posible una eventual ampliación del acervo genético. De hecho, cuando los forasteros hacer entrar en la esfera de Addams en un contexto romántico, tienden a morir. En Valores de la familia AddamsEl miércoles (está implícito) mata a su amante Joel Glicker, y la esposa de Fester, Debbie Jellinsky, una persona perfecta literalmente en todos los aspectos, muere electrocutada en el proceso de intentar robar el dinero de Addams. La única persona que se une con éxito a la familia desde el exterior es la esposa del malvado abogado Tully Alford, Margaret, quien se casa con el primo Itt después de la muerte de su esposo.

Cousin It, por supuesto, es notable por su cabeza llena (y cuerpo) de cabello y el hecho de que habla en un galimatías agudo. Lo que ella diciendo cuando conoce y seduce a Margaret en una de esas elaboradas fiestas familiares de la película de 1991? "Oye niña, ¿tu trasero se ve tan redondo como tu cabello?" Quizás. Eso definitivamente funcionaría en mí, de todos modos.

"Ayuda, estoy atrapado en una pesadilla genética. Mi laringe no funciona y apenas puedo respirar debido a siglos de matrimonios mixtos de un grupo de, como máximo, 200 personas".


¿Cuál es la diferencia entre el incesto y la endogamia? - biología

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Genetic sexual attraction

At first, Ivor Lytton's emotional predicament seems unremarkable, no different from the woes that make up any agony aunt's weekly column. On Sunday October 4 1998, Lytton, an Edinburgh public relations consultant, met the love of his life. The meeting took place at a dinner party at a fashionable country inn. Rita Meadows, who lives in South Africa, was on holiday in Scotland. Describing their meeting, Lytton's words overflow with sentiment. "From the moment we met, I was smitten, and continued to be drawn to her like a magnet. As I got to know her, I felt she had given me a life transmission. She put a smile in my heart and a spring in my step." Each October for the past four years, he has sent her a card to commemorate the date of their meeting.

What Lytton didn't know was that the consequences of that love would plunge him into the most devastating crisis of his life. "To say that I have been to hell and back wouldn't be accurate. The situation is far worse than that." On the surface, his ordeal seems a classic case of unrequited love. Despite forming a warm friendship with Lytton, and meeting him several times a year either abroad or in Britain, Meadows, a divorcee, has never shared his feelings. Irritated and, at times, angry with his outpourings of affection, she recently emailed him curtly to think of her as "just a casual friend". Unable to reconcile himself to her indifference, Lytton's subsequent depression and sense of rejection, and the continuing compulsion to declare his feelings, are no different from the irrational fixation and emotions that mark any young adult's first major infatuation. But that is as far as the Mills & Boon scenario goes.

In the circumstances, Lytton's new-found love was doomed to be a nonstarter. He is a married man of 66, semi-retired, with grown-up children and grandchildren. The story might be relatively straightforward, and there may even have been a happy ending of sorts had he merely fallen for a woman half his age or abandoned his family to start a new life in another country. Instead, his love for Meadows represents society's most abhorrent taboo. She is his younger sister, adopted as a baby shortly after the death of their mother from an illness contracted after the birth, when Lytton was two. Although Meadows had no idea she had a brother, Lytton, who was raised by his stepmother after his father's death during the second world war, had always known of her existence, but waited until 1995 to begin searching for her. The 1998 party at which they met had been organised by Lytton, with the help of his wife and children, as a celebratory reunion after he had tracked down his 60-year-old sister in Durban.

"I knew Rita was my sister," he says now. "I didn't choose to fall in love with her, or expect to feel sexual desire. It just happened. Even in front of my wife, I made no attempt to hide my adoration, I just buzzed whenever she was around. It was as if no one else existed. The two biggest mistakes I made were deluding myself that I could become all-important in her life, a brother and a surrogate lover, even though she didn't desire me, and then believing I could control and resolve the problem by myself."

When we met, Lytton brought with him several large files bulging with four years' correspondence, mainly email printouts, to and from Rita. A tall, white-haired and articulate man, he has recorded every emotion, thought and incident involving his sister since their reunion. Photographs taken on his trips to South Africa, and on her visits to Scotland, show a vivacious and elegant redhead, seemingly little older than 40. From the sharp intake of breath as he begins reading aloud from his correspondence, it is clear that his feelings are still raw. Letters written shortly after their reunion begin with such endearments as "my special girl", "goddess", "darling miracle", "my princess". Declaring that she "walks on water", Lytton confesses how much he misses and thinks of her, miserable at the distance between Edinburgh and Durban. The places they have visited together are described as "sacred shrines".

But a persistent undercurrent of uncertainty and despair runs through almost every message, as he urges her to write more frequently and to reveal her own feelings. "I have found it easy to love you since we met, and am totally committed to our relationship. You illuminate my life. let this be our secret. But how important am I to you? Do you feel affection for me?" Breaking off, Lytton's voice cracks. Far worse than the pain, he says, are the shame and guilt. "You see how besotted I was? Every line oozing with obsession. I mean, what normal brother ever spoke to a sister in this way? How can a man approaching 70 experience emotions usually attributed to a screwed-up adolescent? It's sick."

He then produces a diary, one of several in his briefcase, labelled The Journal Of An Emotional Junkie, and offers to lend it to me. He started to keep the journal eight months ago, after discovering that his sister had begun a relationship with a 40-year-old South African banker. He became intensely jealous - an emotion, he stresses, that is virtually alien, and therefore deeply shameful, to him. In one revealing passage he fantasises about his sister having sex with her new lover. "On a visit, she'd shown me some sexy underwear she'd bought in London, including a thong. Once she left England, I visualised her gyrating around a pole, in a G-string, her boyfriend watching lustfully on the bed."

Although this is the first time Lytton has told any of this to a stranger, he feels that, by doing so, he is beginning to control and resolve the situation. "I'm letting you inside my head. Perhaps my experiences can help anyone else in a similar predicament, let them realise they are not alone, that they aren't going mad and haven't turned into some sick, perverted individual - all of which I thought until very recently."

In the past year, Lytton says, he came close to wrecking his marriage, having a complete nervous collapse, even committing suicide. What saved him was his sister's emotional detachment, his wife's extraordinary patience and understanding - and, most crucially, learning about a little-known phenomenon called genetic sexual attraction (GSA), increasingly acknowledged by post-adoption agencies to be a common feature of reunions between blood relatives who have never before met. "I seem to have contracted this condition, GSA, in its severest form," he declares, as if describing a virus. "Now that I know there is a condition, and why it occurs, I feel I have reached a turning point and will be able to work towards building a normal, balanced relationship with my sister." If, as seems possible, he comes through the crisis with his marriage, mental stability and relationship with his sister intact, Lytton will be in a fortunate minority.

The term GSA was first coined in the US in the late 1980s by Barbara Gonyo, the founder of Truth Seekers In Adoption, a Chicago-based support group for adoptees and their new-found relatives. The emergence of GSA both in the US and the UK coincided with the relaxation of adoption laws in the mid-1970s, which gave adopted children easier access to their records and led to an increase in the number of reunions between adoptees and their blood relatives.

The unexpectedly high number of reported cases of men and women struggling with sudden and terrifying emotions after a reunion has surprised and perplexed most post-adoption agencies. So far, because of the taboos surrounding GSA and its variable and complex nature, the frequency of these cases is almost impossible to quantify, although some agencies estimate that elements of GSA occur in 50% of reunions. Growing awareness of its potentially devastating implications, especially in cases where relatives embark on a sexual relationship, has prompted some organisations to warn all clients attempting to trace a relative about the phenomenon, while also training counsellors to recognise the warning signs and to help adoptees and their families cope with the damage.

These may sound like important and timely advances but they don't, in fact, add up to much. Because of the revulsion aroused by incest, and the stigma attached to anyone who admits experiencing GSA - let alone those who embark on sexual relations with a parent or sibling - the condition remains obscured by myth, tainted by smutty innuendo, under-reported by sufferers and, worse, virtually ignored in academic circles. Although, occasionally, a story involving GSA is given predictably lurid tabloid coverage, ignorance prevails. Why GSA occurs only in some reunions, whether certain people are more predisposed to GSA than others, or whether it manifests itself differently between parents and children or siblings, is simply unknown. Above all, GSA raises serious questions about what factors influence sexual attraction: are the origins of GSA social, environmental or biological?

The lack of any serious scientific research is especially disturbing in view of the growing number of reunions between adoptees and their birth parents, and the prospect of many future reunions between children born through IVF involving sperm and egg donors. In the view of Sue Cowling, deputy director of the Post-Adoption Centre, "Genetic sexual attraction associated with IVF births is a time bomb waiting to go off." Cowling, like many professionals, suspects that the subject has remained a no-go area, even for psychologists, because even in a society wide awake to the spectre of paedophilia and sexual abuse in families, GSA - which falls into neither category - threatens to explode too many cosy assumptions about "normal" and aberrant sexual instincts.

Gonyo, the non-academic who originally "outed" GSA in the 1980s, has written the only book on the subject. In it, she suggests that romantic love and erotic arousal may be the delayed by-product of "missed bonding" that would have normally taken place between a mother and her newborn infant, or between siblings had they not been separated by adoption. "Many such people, as adults, need to go through that early missed closeness. It may become sexual, or it may not."

Gonyo's reputation as the world's leading GSA "expert" came about largely as a result of her own experience of strong sexual attraction, when, in 1979 and aged 42, she was reunited with her adult son 26 years after she had given him up for adoption. Now a 65-year-old grandmother, she admits, like Lytton (whom she has been counselling by email since he contacted her via the Truth Seekers website), that what saved her marriage and allowed her eventually to build a healthy relationship with her birth son Mitch was that she did not have sex with him, due to his unresponsiveness.

An energetic, cheery and straight-talking woman, Gonyo estimates that it took her a dozen years to overcome the desire to sleep with Mitch. "Believe me, the state of arousal, which grew as I got to know him, was as erotic as anything I felt for my husband. I wanted to get naked with Mitch, feel his flesh against mine. The first time I hugged him, it beat any feeling I've experienced in my life. If he had felt the same way, I don't know if I could have stopped myself. But Mitch was very afraid of my feelings, and wouldn't ever talk about any of this, or how he felt."

At that time, Mitch, an art teacher, had various girlfriends. "Despite this, my behaviour around him was atrocious. I was flirtatious, coquettish and playful. When getting ready to see him, I primped and primed, becoming like a 16-year-old in mind and body. I was trying to win him over, like someone I wanted to date or marry." Gonyo recalls feeling ashamed and dirty. "At the beginning, the urge was less erotic, more like bonding with a newborn child. As with all my subsequent children, I wanted to smell him, stroke and run my fingers through his hair. I saw so much of myself in him, and he also reminded me strongly of his father, my first teenage love." But having experienced that primary stage of "delayed bonding", Gonyo wanted more. "I was no longer looking for the baby, I wanted a relationship with the adult - the man." What frightened her was that these emotions did not fit into any appropriate context. "I wasn't Mitch's lover or girlfriend, and I couldn't be his mother, because he had one, although he never allowed me to meet her. I felt like an intruder, unimportant and humiliated."

When Mitch got married 12 years ago, Gonyo finally established a relaxed friendship with him. "It's as if I've turned him over to his wife, so now we can be friends. It took me until then to be able to say honestly that I don't have those sexual feelings any more. What meeting Mitch taught me was self-control." It also led to her passionate "mission" to encourage widespread understanding of GSA.

Twenty-five years ago, that would have seemed an absurdly unrealistic goal given that this realm of human desire was guaranteed to repel most people, including Gonyo's clients. Since then, not much has changed. "GSA becomes an incest issue, whether or not it is carried out in a sexual act," she says, pinpointing the most likely explanation for the paucity of research. "Most people will only reveal their own situation once someone else breaks the ice." Gonyon recalls that, when she told a support group for adoptees and birth mothers about her own feelings on meeting Mitch, her disclosure was met with repugnance. "Some openly dismissed such feelings as 'sick'." But, a few days later, she was phoned by the wife of one of the group's male participants, telling her that she was convinced her husband was similarly infatuated with his birth mother, whom he had recently met, and asking Gonyo if she could help him.

It wasn't until almost a decade later, when Gonyo became the director of Truth Seekers In Adoption and raised the issue of GSA, that others began plucking up the courage to confess their own "forbidden" attraction to a parent, adult child or sibling with whom they had been reunited. She vividly remembers the first time someone raised their hand in one workshop. A man in his 30s, he was the first person she saw stand up in a room full of people and speak the unspeakable. "He simply said, 'I slept with my mother. I was 21 when I found her. We were very much in love. After several years, it stopped.' His mother had ended the relationship because it was too painful for her she felt guilty and was afraid of being discovered. That was more than 10 years ago, and he said he'd not only lost his lover but what was even more important: his mother. He said he had never regretted having sex with his mother, only that losing her was a high price to pay."

Many clients consult Gonyo privately, even anonymously, by phone or email. "Often, the attraction isn't sexual, but it's still frightening and alien, and therefore perceived as abnormal and sinful. One woman told me that she and her birth mother, soon after they met, slept together in the nude: there was no sex, only a strong need to be close as parent and child. Grown men tell me they've sat in their mother's lap, just being rocked and held. One man talked about his need to be sexual with his newly found brother, but not being homosexual they shared a woman instead."

Sometimes, she warns, there may be an underlying element of revenge: "One man admitted openly, 'My real mother fucked me over. Now I'm going to fuck her.'" In contrast, many others experience an almost primordial sense of having "belonged" to the other person all their life. For Gonyo, the recognition that she shared her son's sarcastic humour and artistic talents, and saw the "male side" of herself in him, were especially powerful. (This sudden "shock of familiarity" is often also commented on by twins separated at birth.)

Gonyo is not surprised that attraction between fathers and daughters should be the least reported variant of GSA. "That group tends to stay very silent. It's still regarded as dangerously close to abuse, even though it is no different from other forms of GSA." But it does happen: a woman who recently traced her non-identical twin daughters, and included the birth father at the reunion, was horrified when one of the daughters and the father became instantly attracted to one another. As is common in cases of parent-child GSA, the attraction involved the girl who most resembled her father. "It's like my meeting Mitch: for a woman, meeting your father is to meet the male aspects of yourself for the first time."

Sometimes, that recognition may act as a powerful aphrodisiac. A young woman in one of Gonyo's workshops confessed that she had been in love with her father, and he with her, since their reunion. Only after they both suffered mental breakdowns did they have sex. "Sadly, although they imagined it would be cathartic, after sleeping together they felt no happier."

Almost invariably, the outcome of sexual relations between reunited relatives is that any subsequent lasting relationship, platonic or otherwise, is doomed - a dilemma illustrated in Kathryn Harrison's 1997 memoir The Kiss, a frank, sometimes shocking, account of her affair with her father.

That awareness has led New York psychotherapist Joe Soll to adopt the term "genetic attraction", believing the word "sexual" is in many cases inaccurate and also responsible for the underlying shame and fear that make the condition so distressing. He has noticed that the "romance" that develops, especially when mothers meet their adult children, mirrors the sensuous bonding between a new mother and her baby. "These people regress to a very early stage of development. The relationship is sensual, but we don't call it 'romance' or being 'in love' when it's breastfeeding, cradling and stroking, or when it's a mother and baby gazing into one another's eyes. Often, people tell me all they want to do is snuggle up together. A woman reunited with her adult son felt an overwhelming urge to suckle. There's an urge for intimacy, which they were previously denied."

Where that urge leads to sex, which appears to be more common between brothers and sisters, Soll and Gonyo encounter the greatest desperation and refusal to exert self-control. "I'll get calls from clients asking me in which of the American states they would be allowed to set up home together, or even get married," says Gonyo. "It doesn't matter what age they are - when your hormones are raging, you don't think about the consequences."

GSA rarely features at conferences on adoption, however, because the big US institutions, such as the National Council For Adoption, are reluctant to recognise the phenomenon. On the rare occasions that workshops do take place, they are usually packed. Unlike the UK, most US states are opposed to "open" adoption, so adoptees' records are sealed, which presents a formidable obstacle to family research. Gonyo, meanwhile, is convinced that the more an adopted child is told about their original family, and sees photographs of parents and siblings indicating shared characteristics, the less likely this will come as an intense shock if they meet. "Although it is better to play in the sandbox as kids than in bed as adults," she says, "the authorities prefer to ignore GSA, so it remains confused with real incest, rape and child abuse."

But in the light of the confessions and desperate actions of some "victims" of GSA, isn't it understandable that such confusion exists? Understandable, perhaps, but not inevitable. In contrast to America's squeamishness in addressing the issue, by the early 1990s British post-adoption agencies such as Norcap, the Child Migrants Trust and the Post-Adoption Centre were already admitting that, far from being either unique or bizarre, or a sign of deviance or emotional disorder, GSA was an all too normal reaction to an extreme emotional situation - and more commonplace than supposed.

Not that this makes it any easier to understand. Today, the Post-Adoption Centre, which offers practical information and counselling at any stage before, during and after adoptee reunions, and sees 3,000 new clients a year, estimates that up to half of reunions are accompanied by anything from temporary attraction to obsessive sexual obsession - and, very occasionally, even to the birth of a child.

At their most extreme, such relationships can have dangerous and potentially tragic consequences for families, especially spouses. In a recent, well-publicised case, a mother of two, Jennifer Grant, and her adopted half-brother, John Shannon, a former mayor of Pickering, North Yorkshire, left their respective spouses and children and set up home together after being united for the first time in 46 years. Interviewed by a Sunday newspaper in 2001, Jennifer's husband Graham, whose physical resemblance to John is striking, talked about his ordeal, typical of casualties floundering in the riptide of such obsessions. "I asked her if she had gone to bed with him and she said they had. I just left the house, got in my van and drove. I wanted to do myself in. Then I thought of the boys and what it would do to them. When I got back, she had gone."

Graham Grant reportedly cannot come to terms with what has happened: "It fills me with shock and dread," he said. "Members of our family have found it hard to discuss the matter with me. There's a sense of shame and disgust. It's left me feeling like a leper." Although, reportedly, there was a police inquiry into his wife's relationship with Shannon, with which they co-operated fully, the investigation ended due to lack of evidence that any crime had been committed.

Under the Sexual Offences Act of 1956, sexual intercourse between a brother or even a half-brother and sister is an offence that carries a maximum prison sentence of seven years. Although he escaped imprisonment, Scarborough police officer Tony Smedley's nine-month affair with his half-sister Janet Paveling tore apart his life. When Smedley's colleagues accidentally came across love letters that clearly referred to their sexual relationship, he and Paveling were arrested and committed for trial on charges of incest. He pleaded guilty when the case came to York crown court last month, and received a conditional discharge the charges against Paveling were not pursued. Even so, Smedley lost his job, and must now try to rebuild a future with his wife and children, and with his sister's family. Another British brother and sister, Kim Straker and Terri O'Neill, who lived together as a couple and eventually had a child, were taken to court in the early 1990s. They were given suspended sentences and allowed to keep their daughter they have since parted.

Even where such relationships do not end in turmoil and trauma, the effects of the taboo itself remain inescapably powerful. One of the strangest cases in recent years is that of Gary Klahr and Micka Zeman, who met in 1979 in their Connecticut hometown and enjoyed a casual six-month affair. In 1998, by which time both were in their 50s and married, Micka, knowing she was adopted, had traced her biological parents and found that she was one of 13 children born to the same couple, nine of whom were given up for adoption to couples in the area - one of them was Gary Klahr. On realising that she had had sex with her brother, Micka was physically sick. "Although it was brief and we were not that involved or serious, it was a shocking revelation and I was filled with tremendous guilt and sadness. I have since forgiven myself and realise it was foolish to feel guilty: after all, we did not know we were brother and sister, and when we re-met in 1998 the chemistry had long disappeared."

Although the news also shocked Gary, he maintains that someone less emotionally well-adjusted might have suffered greater damage. "A person with a different personality might have jumped out of the window, or at least had profound long-term feelings of guilt. But if you understand that nine out of 13 children from the biological family were adopted out to different families, with different names and different religions, within a 15-mile radius of the hospital where we were born, then something like this was bound to happen. I never had an idea, until 1998, that I was adopted: how could we have known that we were brother and sister?"

Cowling says that neither the threat of prosecution nor the suffering of families are a deterrent to those caught up in and determined to pursue such relationships. "I've heard women, including mothers sleeping with their sons, tell me, 'It's the most amazing sex I've ever had. Don't ask me to give it up - I can't.'"

When the relationship becomes obsessive and violent, especially between mothers and sons, the danger seems only to heighten the sexual chemistry and magnetic bond. "I've worked with cases where the violence has been terrifying because one person becomes fixated, phoning their relative 10, 12 times a day, demanding to know their movements, stalking them like a jealous lover," says Cowling. "But the other person still can't pull away. It's like an addiction." She cites a man who was imprisoned for violence against his mother: "The woman went into hiding, but he found her. We were getting panic-stricken calls from her at all hours, saying, 'He's coming for me, what shall I do?' Yet she, too, was obsessed with him. In another instance, a woman referred to her son as 'my lover' and talked of her body 'aching' for him. Unfortunately, for some men, the sex and violence is a way of punishing the birth mother for abandoning them, and for mothers the sex is a guilt trip: they feel they owe it to their son after giving him up for adoption."

The dilemma originally faced by professionals such as Cowling was that everyone wanted to help, but no one knew how. In 1992, Dr Maurice Greenberg, a consultant psychiatrist, head of student counselling services at University College London and former adviser to the Post-Adoption Centre, conducted what, incredibly, remains the only academic study into GSA. He interviewed eight male and female adoptees and analysed another 40 cases, including birth parents, reported by the Post-Adoption Centre the objective was largely to gather information to help guide counsellors. Greenberg, who has the gentle, amiably absent-minded manner that instantly makes you want to tell him your troubles, admits he knew he was entering an unusual and special area and asked the Post-Adoption Centre why it did not simply acknowledge that these people were having incestuous relationships, rather than use the euphemism genetic sexual attraction. But was it really such a euphemism? What Greenberg couldn't foresee was how promptly he would do a u-turn, concluding that the consummation of GSA was "incest" only in the strictest biological sense. Today, he insists that it is essential to distinguish GSA from incest, and especially from child abuse. "There is no force, coercion, usually no betrayal of trust. And no victim. If sex occurs, it involves consenting adults."

He stresses that none of the interviewees who were sexually aroused by or had sex with a parent or sibling considered this incestuous, or that their behaviour was wrong, "But when I asked them if they might ever have similar feelings about members of their adoptive family, they shuddered at the suggestion".

Most interviewees described the period before a reunion as already exceptionally emotionally charged, filled with excitement and fantasies about meeting their relative. Reunions were characterised by so-called "mirroring" - the shock of familiarity and self-recognition on first meeting. Even where there is little physical resemblance, the emergence of shared interests, similar traits, mannerisms and instincts, often subtly transmitted through sense rather than verbal communication, tended to have a profound impact on one or both relatives. Greenberg says that many used the terms "finding a soulmate" and "like looking in the mirror for the first time".

Body odour, too, held an especially powerful attraction: there was, says Greenberg, frequent fascination with a relative's characteristic smell - acknowledged to be a potent factor in both human and animal attraction - as well as the feel of their skin and the sound of their voice. "The sudden, overwhelming sense of falling in love, a profound need for unusual closeness and intimacy, was almost universal. As adults, we have very limited abilities for communicating such intense feelings, and sometimes sex becomes the only familiar means."

The intriguing paradox that Greenberg appears to have uncovered is that, no matter how shocking it appears, GSA is a largely normal response to an extremely unusual situation: blood relatives meeting as strangers. More crucially, the existence of GSA, as distinct from habitual incest and child abuse within families, raises fundamental issues concerning sexual attraction, as well as with the origins of the "incest taboo" - areas that have only recently been the subject of serious research.

No analysis of incest and sexual desire is possible without the shadow of Freud looming over the debate. A new study by psychologists at the University of St Andrews shows that men and women are more likely to choose a spouse whose eye, skin and hair colour resembles that of their opposite-sex parent. Last year, a study by the same team revealed that women with older fathers, and men with older mothers, are usually attracted to older-looking partners. The same principle applies to racial characteristics, and to the smell of an opposite-sex parent. Although the reasons are unclear, one theory is that we are "imprinted" from birth with certain familiar characteristics with which we feel comfortable and to which we are eventually attracted.

However, Freud would have had an altogether different take on it, believing that the Oedipus complex was paramount in determining all sexual behaviour. Freud's theory, propounded in 1897, that every male infant has an overwhelming sexual desire for his mother, and every female for her father, is the cornerstone of psychoanalytic theory. He maintained that these incestuous drives were so powerful that they had to be suppressed. Our transition, between the ages of two and five, from the incestuous Oedipal phase to the post-Oedipal phase, resolves these impulses and, according to Freudian theory, is crucial to healthy human development. By the time we reach the post-Oedipal stage, the incest taboo, Freud reasoned, is indelibly imprinted on the psyche, governing future sexual behaviour.

But how persuasive is this Oedipal theory nowadays? Because Freudian ideas dominated much of the 20th century, what is less well known is that, at the turn of the 19th century, a contemporary of Freud's, the Finnish social anthropologist Edward Westermarck, put forward the opposite view, based not on the theory of natural attraction but of natural aversion. According to Westermarck, children growing up in close proximity are not sexually attracted to each other as adults. Quite the contrary: the "Westermarck effect" meant that overfamiliarity and boredom automatically caused siblings and other close relatives raised together to go out of their way to avoid sexual contact. Westermarck also reasoned that, since we find the idea of sex with our relatives so distasteful, we developed moral codes and laws to ensure that society conformed to this "norm" to avoid any social disruption, shame or discrimination.

Although these ideas were rubbished by Freud for their lack of supportive evidence - despite his own inability to provide a scientific rationale for the Oedipus complex - in recent years evidence confirming the Westermarck effect among humans and other species continues to grow. By revealing more about what lies behind our choice of sexual partners, these findings may hold clues to the "mystery" of GSA.

In one ongoing study of children raised on Kiryat Yedidim, an Israeli kibbutz, between the 1950s and late 1960s, US and Israeli anthropologists were amazed to discover that the sabras - boys and girls of almost identical ages from different families - did not, as their parents hoped and anticipated, marry each other. As one of the first researchers, Melford Spiro, observed in 1958, the intimacy between these children, especially between the ages of seven and 12, could not have been greater. Not only did they shower, sleep and run around naked together and explore each other's bodies, as they approached puberty they began openly to play sex games, including intimate kissing, fondling and simulated, or attempted, sexual intercourse. Despite this climate of sexual freedom, by their mid-teens the girls, especially, displayed signs of shame and became hostile towards the boys, to the point of insisting on having unisex showers. At around 15, the girls became attracted to older students and young unmarried men in the kibbutz, admitting that they saw their peers as "brothers".

In a second phase of the study, when these children had grown up, it emerged that not only had no marriages taken place between any of the sabras from Kiryat Yedidim, and three other kibbutzim, but neither was there a single reported incident of sexual intercourse. Eventually, another team of sociologists analysed the records of almost all known kibbutz marriages, totalling nearly 3,000: in only 16 cases did members of the same peer group marry - and in these cases the couple had met only after the age of six.

In the 1960s, about the same time as the kibbutz studies were being concluded, Professor Arthur Wolf, an American anthropologist from Stanford University in California, travelled to Taiwan to study the effects of child-training methods on child behaviour. He ended up living for long periods in Chinese communities after discovering, by chance, that these had a high incidence of a certain type of arranged marriage - known as the sim-pua, or "minor form" - in which the bride was sent away as a young child by her parents to be brought up alongside her future husband as an adopted "daughter-in-law" of the family.

Wolf, now 70, has spent the past four decades examining the effects of this now almost extinct practice, and revealing its previously unforeseen consequences. "Although the age at which the girl went to the future husband's family was between three and five, in some areas of Taiwan they were under two. Many who entered these marriages were, in fact, nursed by their future mothers-in-law." When Wolf asked some of these surviving mothers-in-law why they did this, he was taken aback by their candour. "They explained that the children weren't treated as daughters: they were referred to as 'little daughter-in-law'. They'd say, 'It's better to raise your son's wife, because she will listen to what you tell her and won't always be talking about your son behind your back.' It was the classic mother-in-law strategy!"

A shortage of suitable brides in these developing communities in the late 19th and early 20th century made this "trade" in girl children an attractive proposition. Wolf discovered that the mothers of infant boys whose next child was a girl preferred to give her away and then adopt someone else's infant daughter as a future daughter-in-law. As in the kibbutzim, the future couple, very close in age, were effectively raised as siblings. Unlike the children from the kibbutz, however, they had to marry - and, as grown-ups, many refused to go through with the marriage, or did so only under threat of severe punishment. Some women, says Wolf, became prostitutes rather than marry their fiancée. And in marriage adultery was rife: "One man promised he would marry any other woman as long as it wasn't his fiancée, although she was very attractive. This was more than lack of sexual interest - it was a complete sexual indifference towards their intended partner, which, as Westermarck claimed, led to disgust and aversion when the act was merely thought of or became a possibility."

Wolf's studies of government records of marriages, divorces and births of everyone in Taiwan prove that, compared with other arranged marriages in which couples were introduced as adolescents, such "minor marriages" were a disaster. His analysis of 25,000 minor marriages found that many ended in divorce and few offspring. Most significant of all is Wolf's discovery that these marriages were spectacularly unsuccessful if the girl had been adopted into her husband's family when aged five or younger. "If she came at three or younger, the sexual aversion and rate of marriage breakdown was very high. After five or six, there wasn't much difference between married couples who met at 16. There is some factor in developmental psychology during the first three years of life that seems critical in determining sexual attraction, but we don't know yet what this factor is."

It may be a long time, if ever, before we can identify the complex interplay of nature and nurture behind the dramas of love and loathing played out in the kibbutz and in Taiwan. Or know precisely at what stage in the sweaty rough and tumble of shared childhood that the potential for mutual sexual desire is switched off. But one thing seems clear: GSA is neither a horror, an illness, nor a perversion. Indeed, given what we already know, might it eventually prove to be not that much of a mystery?


A genetic interpretation of the variation in inbreeding depression

Inbreeding depression is expected to play an important but complicated role in evolution. If we are to understand the evolution of inbreeding depression (i.e., purging), we need quantitative genetic interpretations of its variation. We introduce an experimental design in which sires are mated to multiple dams, some of which are unrelated to the sire but others are genetically related owing to an arbitrary number of prior generations of selfing or sib-mating. In this way we introduce the concept of "inbreeding depression effect variance," a parameter more relevant to selection and the purging of inbreeding depression than previous measures. We develop an approach for interpreting the genetic basis of the variation in inbreeding depression by: (1) predicting the variation in inbreeding depression given arbitrary initial genetic variance and (2) estimating genetic variance components given half-sib covariances estimated by our experimental design. As quantitative predictions of selection depend upon understanding genetic variation, our approach reveals the important difference between how inbreeding depression is measured experimentally and how it is viewed by selection.

Cifras

Lineage-specific inbreeding depression with selfing…

Lineage-specific inbreeding depression with selfing and sib-mating. (A) Each selfing line begins with…

Important genetic components that contribute…

Important genetic components that contribute to the variation in inbreeding depression effects (assuming…

Important genetic components that contribute…

Important genetic components that contribute to the variation in inbreeding depression effects (assuming…