Este es el poder del conocimiento contra los Illuminatis

Kenderr

#180
Pero se estaba hablando de la teoria de Darwin no de otras. Esta claro. Y esta claro que hay otras teorias. Pero como te contraargumente la teoria de darwin y el tema del craneo de Piltdown. Te me fuiste por otra banda y hablaste de otras teorias para desviar. Como haces siempre.

Te respondí dos veces a lo de piltdown, tú te has centrado en descontextualizar mis palabras. Seguro que tú eras ese niño que se reía cada vez que alguien decía peonza e histérico gritaba "Ha dicho peo, ha dicho peo"

Lo cierto es que la teoria de Darwin es la mas extendida y aceptada por la sociedad occidental pasando por toda la educacion. Es por ello que el video lo hace titular y unico ya que somos nosotros los que le hemos dado veracidad.

No, esto es mentira ,es más, seguramente la de Lamarck tenga mucho más éxito entre los que desconocen el tema, porque es la más sencilla de todas.

Claro que hay mas teorias, o pensabas que eras la unica persona que lo sabia? O wait y dice que discute con un medio cerebro xd

Claro que muchísima gente las conoce, pero tú no las conocías hasta que te las mencione, solo alguien que desconoce las teorías sigue hablando de la de Darwin y tú aun sigues haciendolo xD

Porque lo pones en negrita?No te alteres, mantente firme. El video para nada es obsoleto y falso. La teoria de Darwin esta a la orden del dia, pero por lo visto vives en el mundo de yupi

En ningún sitio esta a la orden del día salvo entre los ignorantes y entre los que intenta atacar la evolución. En el mundo académico la más aceptada es la teoría sintética, aunque la biología del desarrollo esta pegando muy fuerte.

Solo un necio cree que esa teoría esta vigente y si se estudia, es por su importancia histórica y porque la figura de Darwin es muy relevante para la ciencia. Al igual que se estudian siempre las cosas desde la primera teoría hasta la ultima para conocer el recorrido.

Para cuando te paseas tambien en el hilo de Obama? Es que entre este thread contigo y en el de aquel de Siria disfruto.

¿De que mierdas me hablas? ¿Crees que te sigo? Eres tu el que visita mi perfil y me da la brasa. Es más, hace poco dijiste que me ibas a ignorar, ahora quieres que postee en tus hilos. Dios mio, ve al medico que tu trastorno bipolar empeora.

Pd: Sigo sin ver ningún argumento de esos que has dicho que pusiste en el hilo.

1 1 respuesta
E

#181 Pero como voy a descontextualizar si es lo que has puesto. A mi no me metas en tus fregados

El cráneo de Piltdown es una demostración de la evolución

Yo no he dicho que el cráneo de Piltdown sea una demostración de la evolución

Esa muestra de pensar que eres la unica persona que sabe de otras teorias es equivalente al comportamiento de un niño.

Si que esta a la orden del dia. La teoria de Darwin esta puesta en todos los libros escolares de ciencias naturales y es la mas aceptada, cuando la ciencia lo ha destripado y no lo ve valido.Y tambien un sinfin de concursos universitarios etc

Pues entonces eres ignorante ya que en el video solo se hablaba de Darwin y tu te ponias a defenderla poniendo lo del maiz. Pero espera, vas a decir que hablabas de otras teorias. Que estamos hablando de Darwin como bien dicta el video. No te escondas.

Pero por favor paseate en el hilo de Obama, paseate anda y deleitanos como en la primera pagina. Yo me divierto. Visitarte el perfil? Y porque deberia visitarte el perfil. Me gustan las mujeres.

Pero ahora tengo trastorno bipolar cuando sufres persecucion paranoica? Si ya te dije que deliras. No te exaltes.

Si no lo ves, es que es necesario a que te graduen unas gafas.

1 respuesta
jackvendetta

Buen artículo como siempre los tuyos, fundamentado, con bases contrastadas. Además siempre estás abierto al diálogo y reconoces tus errores. Sigue así!!!

1
Kenderr

#182 No sabes leer.

Yo digo: Claro que muchísima gente las conoce, pero tú no las conocías hasta que te las mencione, solo alguien que desconoce las teorías sigue hablando de la de Darwin y tú aun sigues haciendolo xD

Tú respuesta a lo que yo digo:

Esa muestra de pensar que eres la unica persona que sabe de otras teorias es equivalente al comportamiento de un niño.

xDDDD penoso, es que no tiene ni sentido tu frase.

Pues entonces eres ignorante ya que en el video solo se hablaba de Darwin y tu te ponias a defenderla poniendo lo del maiz. Pero espera, vas a decir que hablabas de otras teorias. Que estamos hablando de Darwin como bien dicta el video. No te escondas.

Nop, si hubieras leído, hubieras visto que yo menciono el maíz como ejemplo de EVOLUCIÓN contrastable. Y no, el vídeo habla de la evolución, te recuerdo que el vídeo dice que DESMONTA LA EVOLUCIÓN cosa que es mentira.

Si que esta a la orden del dia. La teoria de Darwin esta puesta en todos los libros escolares de ciencias naturales y es la mas aceptada, cuando la ciencia lo ha destripado y no lo ve valido.Y tambien un sinfin de concursos universitarios etc

¿Pero tu te lees? ¿O sueltas tus estupideces sin pensar? ¿En que libros esta? No me pongas libros de hace 40 años. Si la ciencia la ha destripado ¿Por que la enseñan en los colegios? ¿Por que son públicos todos los descubrimientos? ¿Por que el gobierno recomienda libros actuales sobre evolución?

Pero venga, ponme un libro de texto donde digan que la teoría de Darwin es la verdadera y aceptada.

Te voy a poner yo lo que he encontrado buscando un poco, sacado de un libro de 1º de la ESO.

¿Se menciona a Darwin? No, yo solo veo una versión extremadamente sencilla de la teoría sintética. Evidentemente a niños de 1º de la ESO no puedes meterles en cosas complicadas.

Tú y tu vídeo AFIRMAIS que la evolución es falsa y que es un conocimiento secreto en poder de los illuminati, ahora dices que la ciencia y las universidades son las que destripan a Darwin ¿Donde esta el conocimiento secreto?

Pero por favor paseate en el hilo de Obama, paseate anda y deleitanos como en la primera pagina. Yo me divierto. Visitarte el perfil? Y porque deberia visitarte el perfil. Me gustan las mujeres.

Sigo sin saber de que hilo me hablas. xD Y repito, hace nada me ignorabas y no querías que te hablara, ahora quieres que vaya a tus hilos me visitas el perfil.. Lo tuyo es para medicarse.

1 1 respuesta
B

Iba, por una vez, a darle una oportunidad, pero en los 10 primeros segundos del vide he escuchado tal gilipollez que he dado un salto de la cama para quitarlo rápidamente antes de que me sangraran las orejas.

Zerokkk

Emotional, eso de que la teoría de la evolución no es válida es una ida de olla, digas lo que digas. Y eso que yo estoy muy a favor de muchos de tus temas y lo sabes, pero eso es tirarse mucho a la piscina.

Si bien es cierto que el darwinismo no es la teoría más aceptada, sino el neodarwinismo (corregidme si me equivoco), eso no significa que puedas cargarte la evolución con tanta facilidad. Si no, estaríamos hablando de creacionismo, y eso no tiene ni pies ni cabeza.

2 respuestas
E

#184 Ahora no se leer? joder xddd.

Ya pero tu pones la evolucion del maiz para darle apoyo a Darwin. Porque el video habla de Darwin, no de otras teorias de evolucion. Y te has postulado a ello.

Dices que no se leer? Cuando en el video desmonta la teoria de Darwin, no la evolucion en general. Sabes leer.

Pues claro que esta en los libros actuales de la educacion en este pais.

Que me pongas una imagen de la biodiversidad no quita lo otro. Ademas tiendes a juntar evolucion con teorias de evolucion.

Primero, debemos clarificar lo que significa la " evolución ". Como tan muchas otras palabras, tiene más de uno su significado. Su definición biológica terminante es " un cambio en frecuencias del alelo en un cierto plazo." Por esa definición, la evolución es un hecho incuestionable. La mayoría de la gente se parece asociar la palabra " evolución " principalmente a la pendiente común, la teoría que toda la vida se presentó a partir de un antepasado común. Mucha gente cree que hay bastante evidencia para llamar esto un hecho, también. Sin embargo, la pendiente común todavía es no la teoría de la evolución, sino apenas una fracción de ella (y una parte de varias teorías absolutamente diversas también). La teoría de la evolución dice que la vida no solamente se desarrolló, también incluye mecanismos, como las mutaciones, la selección natural, y la deriva genética, que van una manera larga hacia explicar cómo la vida se desarrolló.

Llamar la teoría de la evolución " solamente una teoría " es, en sentido estricto, verdad, pero la idea que intenta transportar es totalmente incorrecta. El argumento se basa sobre una confusión entre lo que significa la " teoría " en uso informal y en un contexto científico. Una teoría, en el sentido científico, es " un grupo coherente de asuntos generales usados como principios de la explicación para una clase de fenómenos " [Diccionario Americano]. El término no implica tentativas o la carencia de la certeza. Generalmente hablando, las teorías científicas diferencian de las leyes científicos solamente en que las leyes se pueden expresar más concisamente. El ser una teoría implica uno mismo un estado coherente, el acuerdo con observaciones, y la utilidad. (Los creacionistas no pueden ser una teoría principalmente debido al pasado; hace pocas o ningunas demandas de lo específico sobre lo que esperábamos encontrar, así que no puede ser utilizada para cualquier cosa. Cuando hace predicciones falsificables, demuestran ser falsas.)

La carencia de la prueba no es una debilidad, tampoco. En el infalibilidad contraria, que demanda para sus conclusiones está una muestra de carencia. No se ha probado, ni estará siempre nada en el mundo verdadero siempre riguroso. Impermeabilice, en el sentido matemático, es posible solamente si usted tiene el lujo de definir el universo si usted está funcionando adentro de es universo. En el mundo verdadero, debemos ocuparnos de los niveles de la certeza basados en evidencia observada. Más y la evidencia mejor que tenemos para algo, más la certeza le asignamos; cuando hay bastante evidencia, etiquetamos un hecho, aunque todavía no es el 100% seguro.

Lo qué evolución tiene es lo que tiene cualquier buena demanda científica -- evidencia, y las porciones de ella. La evolución es utilizada por una amplia gama de observaciones a través de los campos de genéticas, de la anatomía, de la ecología, del comportamiento animal, de la paleontología, y de otras. Si usted desea desafiar la teoría de la evolución, usted debe tratar esa evidencia. Usted debe mostrar que la evidencia es incorrecta o inaplicable o que cabe otra teoría mejor. Por supuesto, para hacer esto, usted debe saber la teoría y la evidencia.

Es algo que juntan siempre los ignorantes y que vuelves hacer el honor.

Pero porque cortas la pagina? Y habra mas paginas.

Te repito que eso no quita lo otro igualmente.

Es un intento de seguir defendiendo la teoria de darwin y esto

El cráneo de Piltdown es una demostración de la evolución

Yo no he dicho que el cráneo de Piltdown sea una demostración de la evolución

Llamar el craneo de Piltdown una demotracion evolutiva lo rompe xddddddd

A que no sabes que hilo, aqui tienes no te hagas el longui eh http://www.mediavida.com/foro/off-topic/obama-apoya-abiertamente-qaeda-484802

Postea por favor, me gusta cuando lo haces.

#186 Pero si el darwinismo y su corriente estan mas que desmentidas por la ciencia y la tecnologia moderna.

No junteis esto

Si la evolución es un hecho, el evolucionismo es su interpretación. Por tanto, no significan lo mismo. Entre todas las interpretaciones de la evolución, la darwinista es –con mucho– la más aceptada, hasta el punto de que evolucionismo y darwinismo suelen confundirse en el lenguaje corriente. Pero no debería ser así. Como atestigua la Historia Natural, de Buffon, el hecho de la evolución era conocido y debatido en el ámbito científico desde finales del siglo xviii, con un importante núcleo en la Academia de las Ciencias de París. Sin embargo, todavía a mediados del xix, Darwin y la mayoría de los naturalistas europeos pensaban que cada especie había sido creada por Dios de forma independiente.

2 respuestas
Zerokkk

#187 Como ya dije, creo que la aceptada ahora mismo es el neodarwinismo, que es una interpretación distinta, mejorada y revisada del darwinismo. Que yo sepa, eh.

#189 Es la teoría más aceptada por la ciencia así que déjame dudarlo xD.

1 respuesta
E

#188 Pero por quien? Si la ciencia ha desechado por completo el darwinismo y el neodarwinismo.

#188 Por supuesto eso en el siglo XIX. Ahora no. Ahora gracias a la genetica, bioquimica y biologia molecular han demostrado que no tienen fundamento.

Hay que saber diferenciar evolucion con teorias de evolucion. Que todo evoluciona esta clarisimo, nadie lo pone en duda en este planeta.

2 respuestas
Kenderr

#187 Eres un mentiroso, no hay más.

Pues claro que esta en los libros actuales de la educacion en este pais.

Enseñamelo, dime donde. Yo te he puesto uno de primero de la ESO, tú no pones nada.

Que me pongas una imagen de la biodiversidad no quita lo otro. Ademas tiendes a juntar evolucion con teorias de evolucion.

Esto te lo inventas, te lo inventas como el mentiroso que eres.

Es más, mis palabras son "La gente no cuestiona la evolución, es un hecho probado, hasta el ser humano la puede realizar, lo que se discute es sobre como se produce de forma natural, por eso hay distintas TEORÍAS. en #112

Y me hace gracia que copies un texto y no pongas la fuente, tienes la poca desverguenza de hacerlo pasar como tuyo.

Si la evolución es un hecho, el evolucionismo es su interpretación. Por tanto, no significan lo mismo. Entre todas las interpretaciones de la evolución, la darwinista es –con mucho– la más aceptada, hasta el punto de que evolucionismo y darwinismo suelen confundirse en el lenguaje corriente. Pero no debería ser así. Como atestigua la Historia Natural, de Buffon, el hecho de la evolución era conocido y debatido en el ámbito científico desde finales del siglo xviii, con un importante núcleo en la Academia de las Ciencias de París. Sin embargo, todavía a mediados del xix, Darwin y la mayoría de los naturalistas europeos pensaban que cada especie había sido creada por Dios de forma independiente.

Otro texto copiado sin ninguna fuente. Ademas, el texto es incorrecto. Buffon no dio una teoría de la evolución, más bien de degeneración y justamente la refuto el mismo.

#186 Si, es la más extendido, aunque se le llama de muchas formas, neodarwinismo porque es la heredera directa.

#189 Pero por quien? Si la ciencia ha desechado por completo el darwinismo y el neodarwinismo.

Mentira pura y dura. ¿Donde se ha rechazado el neodarwinismo? Tu forma de utiliza el termino ciencia es insultante.

Ahora no. Ahora gracias a la genetica, bioquimica y biologia molecular han demostrado que no tienen fundamento.

Dame un solo dato que refute el neodarwinismo.

Pd: Y respecto a tu hilo, ya te respondí, ya demostré que no tenias pruebas. ¿Para que volver? Quédate en tus mentiras.

1 respuesta
B

360º....

si empiezas a los 18 y te jubilas a los 60... son como a mes por grado ¿no?

Los iluminati se deben pasar la vida de fiesta, con que en la ceremonia o fiesta no se que haran haya 20 personas, ya tienes que ir a 20 fiestas/ceremonias al mes de media, ¿como gobiernan el mundo con 10 dias libres al mes? y de resaca....

E

#190 Pero si el unico mentiroso aqui eres tu xd

El cráneo de Piltdown es una demostración de la evolución

Yo no he dicho que el cráneo de Piltdown sea una demostración de la evolución

Pues en los libros de educacion tanto en ciencias sociales como en naturales aparece el Darwinismo.

Que tu quieras negarlo y pedirme donde esta significa que eres un completo inepto.

Pero claro diciendo que el craneo de Pitdown es una demostracion evolutiva ya me lo dices todo

La explicacion me lo he inventado no? Vale xdd

hahahahahaahahahahahhahahaahahahahahaaha me estas diciendo que no hay nada que refute el neodarwinismo?

Hijo mio lo tuyo si es insultante con la ciencia diciendo estas paridas, incluyendo la aceptacion del craneo de Pitdown como evolucion.

Como ya he dicho la biologia moderna refuta en rotundidad el neodarwinismo. Ignorante.

Sobre tu ultima frase. Yo quiero esa droga para volverme ignorante y evadirme de la realidad.

Comenta en ese hilo, estoy esperando con muchas ganas.

1 respuesta
Kenderr

#192 Pues en los libros de educacion tanto en ciencias sociales como en naturales aparece el Darwinismo.

Una cosa es que aparezca el darwinismo y otra que digan que es la unica teoria o la teoria más aceptada, que es lo que tú dices mintiendo. Yo en la universidad he estudiado el darwinismo y eso no significa que se considerara como cierta o como la más aceptada.

ERES UN MENTIROSO.

Pero claro diciendo que el craneo de Pitdown es una demostracion evolutiva ya me lo dices todo

Te lo he explicado dos veces y ninguna de las dos veces te has molestado en leer lo que he dicho.

El cráneo de Piltdown es una demostración de la evolución, porque aunque se acepto, muchisimagente lo criticaba, pues no encajaba con la teoría de la evolución, se ignoro los descubrimientos de Raymond Dart sobre australophitecus. También estamos en la época de mayor apogeo de Gran Bretaña y no podian aceptar que no hubiera restos prehistoricos en Inglaterra, por eso también fue muy aceptado.

Como seguias dale moreno con tus estupideces te tuve que puntualizar a que me referia.

Aparte, no sabes leer, eres un inepto ignorante. Yo no he dicho que el cráneo de Piltdown sea una demostración de la evolución, sino que el fraude lo es, puesto que se vio que no encajaba con la teoría de la evolución, no tenia sentido, no cumplía ninguna norma.

Ni regurgitandote los conocimientos como si fueras un polluelo te entrarían.

Como ya he dicho la biologia moderna refuta en rotundidad el neodarwinismo. Ignorante.

¿Donde sale eso? Eres un mentiroso. Dame un articulo, algo minimamente científico para saber de donde inventas. Dime autores, dime biólogos, dime algo, pero no inventes mentiroso.

Sobre tu ultima frase. Yo quiero esa droga para volverme ignorante y evadirme de la realidad.

¿Más? Si te pasas el día fuera de la realidad.

2 2 respuestas
Korth

#193 Creo que estás discutiendo con un tío que no entiende cómo funciona el método científico.

En casos así, la única estrategia ganadora es no jugar.

1 respuesta
Kenderr

#194 No me preocupa el, me preocupa la gente que pueda llegar, ver sus hilos y creerse sus mentiras.

Esta claro que no le voy a cambiar de idea, es demasiado zopenco para entender nada y tiene nulos conocimientos sobre el tema. Va tirando de textos que encuentra y poco más, no veras una sola idea redactada por el.

Esto es como con los testigos de jehova, la mejor forma de que te dejen en paz es dejar sus argumentos por el suelo.

1 respuesta
E

#193 Pues es lo que estaba diciendo el darwinismo sale en todos los libros escolares. Es que no te enteras Kender. Luego dije que el darwinismo es aceptado generalmente por la educacion occidental.

Zerock ya me ha dado la razon diciendo antes que es la teoria mas aceptada.

Vamos a ver que no te exaltes, tranquilizate. No te pongas nervioso, ya sabes que el unico mentiroso aqui eres tu.

Lo del craneo de Pitdown no intentes arreglarlo xd

El cráneo de Piltdown es una demostración de la evolución

Yo no he dicho que el cráneo de Piltdown sea una demostración de la evolución

Si has quedado como mentiroso e ignorante.

Me pides articulos cientificos cuando el neodarwinismo no aporta nada cientifico y solo se actualizado a los tiempos actuales.

Me muero de risa.

Como eres ignorante desconoceras la figura de William Ford Doolite. Por supuesto para ti es un don nadie xd

La teoría “oficial” que sigue figurando en los libros de texto, a pesar de estar totalmente descalificada por los datos recientes es la llamada “Teoría sintética moderna”. El término “moderna” hace referencia a la época en que fue elaborada, desde los años veinte a los cincuenta, fundamentalmente por matemáticos (Wrigth, Fisher y Haldane) que tenían muy pocos conocimientos de genética cuando incluso los genetistas tenían muy pocos conocimientos de genética. La idea de evolución (de cambio en la organización morfológica, fisiológica y genética) se resume así de sencillamente: La visión de Darwin sobre la selección natural se puede incorporar fácilmente a la visión genética de que la evolución se produce típicamente a partir de cambios en las frecuencias génicas. (Boyd y Silk, 2001).

La “visión genética” a la que se refieren es la simplificación mendeliana que explica (solo en ciertas ocasiones) la transmisión de características superficiales (en su mayor parte “defectos”), como las famosas características de la piel de los guisantes, o el pelo de los ratones, que no afectan en absoluto a la condición de guisantes o ratones, pero que, sobre todo, ha conducido a la concepción de que existe “un gen” responsable directo de cada carácter, ya sea fisiológico, anatómico o, incluso, de comportamiento, y que todavía subyace en las interpretaciones de muchos teóricos de la evolución. Lo cierto es que, después de medio siglo desde que se formuló (difusamente) la Teoría Sintética Moderna, los dos ejemplos clásicos que figuran en los libros de texto como explicación de la evolución según sus criterios ( es decir, mediante la selección natural) son la resistencia a la malaria de los heterocigotos para “el gen” de la anemia falciforme y el cambio de coloración de las famosas “polillas del abedul”. El hecho de que los individuos resistentes a la malaria, y las polillas oscuras, teóricamente supervivientes a los pájaros gracias a su ocultación en el hollín contaminante, sigan siendo los mismos hombres y las mismas polillas existentes antes de la “actuación” da la selección natural, no les invalida como ejemplo de evolución. La idea de evolución implícita (es más, firmemente asumida) en estos argumentos es que las mutaciones (errores de copia del ADN en su replicación) producen, al azar, variantes de un gen (alelos diferentes) que producen pequeñas variaciones como las anteriormente mencionadas que, “con el tiempo” llegarían a convertirse en los grandes cambios de organización genómica, fenotípica y anatómica que se han producido en los seres vivos. Según F. J. Ayala (1999), la evolución se produce mediante cambios en la composición genética de una especie, como si los genes fueran unas entidades individuales, cada una responsable de un carácter que se situarían, a modo de cuentas de un collar, en los cromosomas.

Sin embargo, hace tiempo que esta visión de los genomas está totalmente invalidada. Hoy sabemos que lo que llamamos “genes” (donde se localiza la información sobre cómo se hace y cómo funciona un organismo vivo), es algo mucho más complejo que un segmento concreto de ADN, pues puede haber genes repetidos en trozos dispersos por el genoma, hay genes con otros genes dentro, los hay enormes, formados por millones de pares de bases, y muy pequeños, formados por unos pocos miles (ver Sandín 2001). Pero, sobre todo, lo que más ha cambiado de la visión extremadamente simple y, especialmente, determinista, de la teoría sintética y que, desgraciadamente, ha pasado a formar parte de los tópicos populares es la idea de que “un gen” tiene un significado único y concreto. En la época en que se elaboró la Teoría Sintética se hablaba de “un gen - un carácter”. Posteriormente, se pasó a asociar un gen con una proteína y, finalmente se ha comprobado que la información genética es algo de una complejidad difícil de abarcar. En primer lugar, el ADN en sí mismo no es ni autorreplicable ni de único significado. Es algo así como un diccionario, que necesita de una gramática, incluso de un idioma que dé sentido (y contexto) a la información que contiene. En el primer aspecto, para la replicación del ADN son necesarias un buen número de complejísimas y muy específicas proteínas que separan la doble cadena, inducen la replicación, revisan, corrigen los errores, los reparan y unen los trozos reparados. En cuanto a los mensajes codificados en el ADN, el “significado” de una secuencia concreta de bases, varía según su situación en el genoma, de la regulación por parte de otros genes y del tipo de organismo en el que esté. Por ejemplo, el gen llamado GAI codifica en plantas una proteína que frena su crecimiento, excepto en presencia del ácido giberélico (una especie de hormona vegetal). Se ha visto (Peng, et al., 1999; Boss y Thomas, 2002), que una mutación de este gen tiene distintas consecuencias en plantas diferentes: en Arabidopsis (una planta silvestre muy común) este gen o su mutante pueden producir hojas o flores; en vides, uvas o zarcillos, y en trigo, tallo largo o corto.

Pero la plasticidad del ADN puede ir aún más lejos. Muchos genes tienen la capacidad de lo que se conoce como “splicing” (empalme o ligamiento) alternativo (Herbert y Rich, 1999), es decir, de producir diferentes mensajes (diferentes proteínas) en función de las condiciones del ambiente celular (que, a su vez, depende del ambiente externo), lo que en definitiva significa que el ADN posee la capacidad de respuesta al ambiente. Y esta capacidad de respuesta va aún más lejos si tenemos en cuenta los descubrimientos derivados de la secuenciación (parcial) del genoma humano (The Genome Sequencing Consortium, 2001). El 95% de nuestro genoma está constituido a partir de elementos móviles y virus endógenos (Sandín, 2002). Los primeros pueden estar de dos formas: transposones, que son “trozos” de ADN que pueden saltar de unas partes a otras de los cromosoma, y retrotransposones, que pueden realizan (mediante las proteínas correspondientes) copias de sí mismos que se insertan en otra zona del genoma, produciéndose duplicaciones de sus secuencias. Ambos se activan como reacción a agresiones ambientales (Whitelaw y Martin, 2001, ). En cuanto a los virus endógenos, que constituyen, por el momento, el 10% del genoma, se considera que su presencia obedece a que, en algún momento de la historia evolutiva “infectaron” al “hospedador” y se insertaron en el genoma, donde permanecen como “parásitos”. Lo cierto es que sus secuencias participan activamente en procesos celulares normales de distintos órganos, como: cerebro, pulmón, corazón… (Genome directory, 2001). Y también tienen capacidad de respuesta al ambiente, “malignizándose” ante agresiones ambientales (Gaunt y Tracy, 1995) e incluso reconstruyendo su cápsida y recuperando su capacidad infectiva (Ter-Grigorov et al., 1997).

Por si todos estos datos sobre la enorme complejidad del material genético no fueran suficientes para mostrarnos lo mucho que todavía nos queda por conocer, los estudios sobre el proteoma (el conjunto de proteínas celulares que participan en todos sus procesos) están poniendo de manifiesto fenómenos que, según sus investigadores (Gavin, et al., 2002; Ho et al., 2002) desafían la imaginación: los miles de complejas proteínas que interactúan en las células se asocian en grupos de, al menos, 96 proteínas. Cada combinación determina, al parecer, sus estructuras y funciones características. Según los autores La célula está organizada en una forma para la que no estamos preparados.

En suma, los procesos biológicos, incluso al nivel más básico, están resultando tan diferentes de la visión reduccionista del darwinismo que todavía figura en los libros de texto, que la conclusión lógica es la que planteó Phillip Ball (2001), uno de los editorialistas de la revista Nature, ante el informe de la secuenciación del genoma humano: Nos encontramos sin base teórica para explicar esta complejidad. En otras palabras, la que tenemos es inútil. Porque, desde luego, todo esto implica que la evolución de la vida, no ha podido ser, según la narración darwinista, mediante mutaciones, es decir, “errores” o desorganizaciones al azar, productoras de variantes de un mismo gen, con pequeñas consecuencias en el fenotipo, que serían “fijadas” por la selección natural en el caso de ser “mejores” que sus otras variantes, produciendo como consecuencia una evolución gradual.

Y, efectivamente, los datos nos informan de que la historia no ha sido así. Desde el origen de las células que constituyen los seres vivos que, como ha sido comprobado por W.F. Doolittle (2000), Lynn Margulis (1995) y R. Gupta (2000), se ha producido por agregaciones de bacterias, hasta las bruscas remodelaciones de fauna y flora que inician los grandes periodos geológicos ( Moreno, 2002) y que coinciden con grandes catástrofes ambientales perfectamente documentadas en la actualidad, (Kemp, 1999), pasando por la todavía, misteriosa para los científicos, “explosión del Cámbrico” (Morris, 2000), en la que aparecieron, de un modo repentino, todos los tipos generales de organización animal (ver Sandín 2002), constituyen un relato más acorde con las características reales de los fenómenos naturales. Desde la naturaleza de la información genética hasta el todavía indescifrable funcionamiento celular, desde las sofisticadas e interdependientes actividades de los procesos fisiológicos, hasta la coordinación en la formación de un organismo, o la complejidad de los ecosistemas, la Naturaleza nos habla, fundamentalmente, de cooperación. De sistemas biológicos de una enorme complejidad en los que no hay sitio para los “errores”, pero, sobre todo, de una gran interacción con el ambiente y una gran capacidad de respuesta, con poco de aleatorio, a las condiciones o agresiones ambientales. Una realidad totalmente opuesta a la visión de las características genéticas rígidamente determinadas y herméticamente aisladas del ambiente, en las que los supuestos cambios aleatorios serían seleccionados por medio de una implacable competencia.

Sin embargo, los términos y los conceptos, incluso el modo de razonar darwinista, aparentemente “grabados a fuego” en el cerebro durante nuestra formación como biólogos, impiden dar a estos hechos el significado que tienen. Sólo a modo de ejemplo de los sistemáticos y tópicos argumentos, a veces realmente peregrinos, que se utilizan para embutir los nuevos datos en el paradigma darwinista, vamos a hacer referencia a algunas interpretaciones sobre los fenómenos fundamentales de los procesos evolutivos que se producen continuamente en las revistas especializadas en referencia a cualquier fenómeno investigado, incluido el nivel molecular.

Radhey Gupta, de la Universidad Macmaster de Canadá, ha conseguido identificar de qué tipo de bacterias proviene el material genético (ADN y proteínas) de nuestras células: los genes y las proteínas que controlan la replicación del ADN provienen de arqueobacterias; los que controlan el metabolismo celular, de eubacterias. Sin embargo, para él, este hecho fundamental en la evolución de la vida y que indica hasta qué punto son importantes en ella los fenómenos de cooperación y de integración de sistemas, en sí mismos complejos, de “cómo tienen que ser” para conseguir los increíbles niveles de complejidad e interconexión que se encuentran en los más mínimos procesos biológicos, es el resultado de un fenómeno ocasional aleatorio y único ( a pesar de la increíble eficacia de su resultado) y considera que “los siguientes” fenómenos evolutivos tuvieron lugar por medio de la selección natural (Gupta, 2001).

Pero los “siguientes procesos evolutivos” también resultan, para los especialistas que los estudian, fenómenos excepcionales. La llamada “explosión del Cámbrico” en la que aparecieron, en un período máximo de cinco millones de años ( Gª Bellido, 1999) todos los grandes tipos de organización animal existentes en la actualidad (anélidos, artrópodos, moluscos,... e incluso vertebrados), tuvo lugar en un medio marino muy estable y a partir de antecesores muy sencillos. Antonio García Bellido, sin duda, el científico español de mayor prestigio internacional, ha denominado “sintagma” al conjunto de genes/proteínas responsable de la regulación embrionaria de la diferenciación de distintos tejidos y órganos (que constituyen los llamados homeoboxes) y que, forzosamente, tuvieron que aparecer en aquel período. Se ha podido comprobar, por ejemplo, que los homeoboxes que coordinan la aparición de las alas de los mamíferos, aves e insectos están formados por las mismas secuencias de ADN. Sólo se diferencian en el número de duplicaciones. Y lo mismo ocurre para los ojos, extremidades, tubo digestivo... También se ha podido comprobar (Morata, 2000) que “transplantando”los genes que controlan el ojo de ratón, y "activándolos" en diversos puntos del embrión de la mosca del vinagre, se formaban ojos de mosca (que para colmo, son ojos compuestos, muy diferentes a los de mamífero). Una vez más, la misma secuencia genética en un medio celular diferente, se expresa de modo distinto. Según García Bellido sintagmas completos, en un número creciente de casos, están conservados desde el origen. Es decir, que la evolución de los organismos y las estructuras biológicas no ha sido, ni mucho menos, mediante “mutaciones” aleatorias fijadas por la selección natural. De hecho, García Bellido lo expresa claramente: Las mutaciones clásicas en los genes que codifican para proteínas han debido ser de escasa relevancia para la evolución morfológica ( García Bellido, 1999). Sin embargo, no podemos olvidarnos de la reverencia al darwinismo: Así se inició una competición morfológica y de comportamiento entre organismos, elaboraciones que han continuado y diversificado (sic) desde entonces.

Como se puede ver, aunque los descubrimientos “reales”, los datos, nos indican que la competencia y la selección no han podido tener nada que ver en la formación de estos sistemas “conservados desde el origen” tiene que existir, forzosamente, una competencia que suponemos que fue “después”.

Y la competencia se busca donde haga falta. En la sutil proliferación embrionaria de las células que forman las alas de la mosca Drosophyla existe, al parecer, un proceso llamado “competición celular”, que “elimina” las células que proliferan lentamente (Moreno et al., 2002) (y se supone que las alas son consecuencia de esta competición). Incluso el centrómero, un orgánulo celular que contiene ADN formado por “secuencias repetidas en tándem” y que es el responsable de la separación exacta de las dos hebras de los cromosomas en la división celular no es, en realidad, una muestra más de eficacia y coordinación de los procesos celulares, sino “ADN egoísta” (Menikoff y Malik, 2002) y “la competición darwiniana entre centrómeros oponentes aporta un mecanismo molecular general para la evolución del centrómero...”.

En suma, visto desde una “mentalidad biológica exterior al paradigma” resulta una desalentadora sensación de que el “adiestramiento” (Feyerhabend,1989) en el modo de ver darwinista, impide la compresión de lo que tenemos delante de los ojos. Y no parece que este problema tenga fácil solución. No sólo es una visión reforzada por el modelo social del “libre mercado” y la “libre competencia” que se ha impuesto en todos los ámbitos de la vida en la llamada “civilización occidental”, sino que ya ha sido “científicamente demostrado” nada menos que mediante programas de ordenador. Leamos: Los organismos digitales, esencialmente programas de ordenador que obedecen las leyes de mutación y selección natural, pueden ser usados para investigar las relaciones entre los procesos básicos de evolución (Wilkie et al., 2001). Es decir, si se programa una secuencia para que “obedezca” las “leyes” de la mutación y la selección natural, las obedecerá. Pero difícilmente se podrá programar el funcionamiento de una simple célula con sus cientos de miles de moléculas interactuando y contribuyendo a su funcionamiento. Sencillamente, porque actualmente, lo desconocemos.

La consecuencia de todo esto es una Biología con una gran cantidad de informaciones inconexas sin una base teórica capaz de unificarlas y dar sentido científico a estos conocimientos. Simplemente, se mantienen las interpretaciones basadas en la competición. Y mientras en las universidades se enseña la evolución como “un cambio gradual en las frecuencias génicas”, en sus propios laboratorios se observa que los procesos implicados en la evolución morfológica nos dicen exactamente lo contrario. Pero el darwinismo subsiste, en forma de auténtica creencia, en muchos casos con carácter integrista, en la que el azar y la competencia son los dogmas intocables. Pero además, son “conceptos científicos”: Entre la ordalía de opiniones personales en que se ha convertido la base teórica de la Biología, se pueden leer sentencias como esta, aportada por Lynn Margulis, una de los principales contribuyentes a la teoría del “origen endosimbionte” de las células eucariotas: La variación en la evolución no viene de la selección natural / .../ Estamos de acuerdo con Darwin en casi todo, excepto en de donde vienen las variaciones; pero no estamos de acuerdo con sus seguidores, que han corrompido la teoría (?) / ... / la cooperación y la colaboración (derivación lógica de sus descubrimientos) son términos sociales (El País, 12-5-2002). Es decir, son inutilizables y desechables frente a los términos “competencia” y “más apto” (más adecuado) que son conceptos realmente “científicos”. Porque éste es el más grave daño que ha provocado el darwinismo: el convertir unos prejuicios culturales en conceptos científicos. Y el daño de esta visión deformada de la realidad no se ha limitado al ámbito científico.

Pasate por el thread de Obama. Te has vuelto un magufo en toda regla. Y luego dice que no defiende el darwinismo. Pero el neodarwinismo si xddddd que son practicamente lo mismo aplicandose los tiempos de ahora. Es que vaya tela.

2 respuestas
Korth

#195 Yo me hago el católico intransigente y les pregunto si veneran a la virgen María.

Mira, ahora está recurriendo a la estrategia del calamar. Copiando y pegando muros de texto que no se ha leído ni él con la esperanza de que te canses de hablar con una pared y abandones el hilo. La discusión dejó de importar hace mucho, lo único que quiere es tener la última palabra.

E

O vaya ya se estan comiendo lo duro visto que su aliado pierde fuel en la batalla.

Respeto.

Kenderr

#196 Sigues copiando textos sin poner ni fuente ni nada. Lo peor es que algo que ni te has leído.

Me pides articulos cientificos cuando el neodarwinismo no aporta nada cientifico y solo se actualizado a los tiempos actuales.

OMG, con eso demuestra que no sabes absolutamente nada del tema. Te podría dar artículos y artículos sobre el tema, libros, manuales.

No te vas a leer nada.

Zerock ya me ha dado la razon diciendo antes que es la teoria mas aceptada.

Nope, zerock ha dicho el neowdarwinismo, no el darwinismo. Se que no entiendes la diferencia, eres tonto, no hay mucho más que hacer aquí.

Pero mira, voy a hacer lo mismo que tú y con esto acabo.

Evolution is a change in the gene pool of a population over time. A gene is a hereditary unit that can be passed on unaltered for many generations. The gene pool is the set of all genes in a species or population.

The English moth, Biston betularia, is a frequently cited example of observed evolution. [evolution: a change in the gene pool] In this moth there are two color morphs, light and dark. H. B. D. Kettlewell found that dark moths constituted less than 2% of the population prior to 1848. The frequency of the dark morph increased in the years following. By 1898, the 95% of the moths in Manchester and other highly industrialized areas were of the dark type. Their frequency was less in rural areas. The moth population changed from mostly light colored moths to mostly dark colored moths. The moths' color was primarily determined by a single gene. [gene: a hereditary unit] So, the change in frequency of dark colored moths represented a change in the gene pool. [gene pool: the set all of genes in a population] This change was, by definition, evolution.

The increase in relative abundance of the dark type was due to natural selection. The late eighteen hundreds was the time of England's industrial revolution. Soot from factories darkened the birch trees the moths landed on. Against a sooty background, birds could see the lighter colored moths better and ate more of them. As a result, more dark moths survived until reproductive age and left offspring. The greater number of offspring left by dark moths is what caused their increase in frequency. This is an example of natural selection.

Populations evolve. [evolution: a change in the gene pool] In order to understand evolution, it is necessary to view populations as a collection of individuals, each harboring a different set of traits. A single organism is never typical of an entire population unless there is no variation within that population. Individual organisms do not evolve, they retain the same genes throughout their life. When a population is evolving, the ratio of different genetic types is changing -- each individual organism within a population does not change. For example, in the previous example, the frequency of black moths increased; the moths did not turn from light to gray to dark in concert. The process of evolution can be summarized in three sentences: Genes mutate. [gene: a hereditary unit] Individuals are selected. Populations evolve.

Evolution can be divided into microevolution and macroevolution. The kind of evolution documented above is microevolution. Larger changes, such as when a new species is formed, are called macroevolution. Some biologists feel the mechanisms of macroevolution are different from those of microevolutionary change. Others think the distinction between the two is arbitrary -- macroevolution is cumulative microevolution.

The word evolution has a variety of meanings. The fact that all organisms are linked via descent to a common ancestor is often called evolution. The theory of how the first living organisms appeared is often called evolution. This should be called abiogenesis. And frequently, people use the word evolution when they really mean natural selection -- one of the many mechanisms of evolution.

Common Misconceptions about Evolution

Evolution can occur without morphological change; and morphological change can occur without evolution. Humans are larger now than in the recent past, a result of better diet and medicine. Phenotypic changes, like this, induced solely by changes in environment do not count as evolution because they are not heritable; in other words the change is not passed on to the organism's offspring. Phenotype is the morphological, physiological, biochemical, behavioral and other properties exhibited by a living organism. An organism's phenotype is determined by its genes and its environment. Most changes due to environment are fairly subtle, for example size differences. Large scale phenotypic changes are obviously due to genetic changes, and therefore are evolution.

Evolution is not progress. Populations simply adapt to their current surroundings. They do not necessarily become better in any absolute sense over time. A trait or strategy that is successful at one time may be unsuccessful at another. Paquin and Adams demonstrated this experimentally. They founded a yeast culture and maintained it for many generations. Occasionally, a mutation would arise that allowed its bearer to reproduce better than its contemporaries. These mutant strains would crowd out the formerly dominant strains. Samples of the most successful strains from the culture were taken at a variety of times. In later competition experiments, each strain would outcompete the immediately previously dominant type in a culture. However, some earlier isolates could outcompete strains that arose late in the experiment. Competitive ability of a strain was always better than its previous type, but competitiveness in a general sense was not increasing. Any organism's success depends on the behavior of its contemporaries. For most traits or behaviors there is likely no optimal design or strategy, only contingent ones. Evolution can be like a game of paper/scissors/rock.

Organisms are not passive targets of their environment. Each species modifies its own environment. At the least, organisms remove nutrients from and add waste to their surroundings. Often, waste products benefit other species. Animal dung is fertilizer for plants. Conversely, the oxygen we breathe is a waste product of plants. Species do not simply change to fit their environment; they modify their environment to suit them as well. Beavers build a dam to create a pond suitable to sustain them and raise young. Alternately, when the environment changes, species can migrate to suitable climes or seek out microenvironments to which they are adapted.

Genetic Variation

Evolution requires genetic variation. If there were no dark moths, the population could not have evolved from mostly light to mostly dark. In order for continuing evolution there must be mechanisms to increase or create genetic variation and mechanisms to decrease it. Mutation is a change in a gene. These changes are the source of new genetic variation. Natural selection operates on this variation.

Genetic variation has two components: allelic diversity and non- random associations of alleles. Alleles are different versions of the same gene. For example, humans can have A, B or O alleles that determine one aspect of their blood type. Most animals, including humans, are diploid -- they contain two alleles for every gene at every locus, one inherited from their mother and one inherited from their father. Locus is the location of a gene on a chromosome. Humans can be AA, AB, AO, BB, BO or OO at the blood group locus. If the two alleles at a locus are the same type (for instance two A alleles) the individual would be called homozygous. An individual with two different alleles at a locus (for example, an AB individual) is called heterozygous. At any locus there can be many different alleles in a population, more alleles than any single organism can possess. For example, no single human can have an A, B and an O allele.

Considerable variation is present in natural populations. At 45 percent of loci in plants there is more than one allele in the gene pool. [allele: alternate version of a gene (created by mutation)] Any given plant is likely to be heterozygous at about 15 percent of its loci. Levels of genetic variation in animals range from roughly 15% of loci having more than one allele (polymorphic) in birds, to over 50% of loci being polymorphic in insects. Mammals and reptiles are polymorphic at about 20% of their loci - - amphibians and fish are polymorphic at around 30% of their loci. In most populations, there are enough loci and enough different alleles that every individual, identical twins excepted, has a unique combination of alleles.

Linkage disequilibrium is a measure of association between alleles of two different genes. [allele: alternate version of a gene] If two alleles were found together in organisms more often than would be expected, the alleles are in linkage disequilibrium. If there two loci in an organism (A and B) and two alleles at each of these loci (A1, A2, B1 and B2) linkage disequilibrium (D) is calculated as D = f(A1B1) * f(A2B2) - f(A1B2) * f(A2B1) (where f(X) is the frequency of X in the population). [Loci (plural of locus): location of a gene on a chromosome] D varies between -1/4 and 1/4; the greater the deviation from zero, the greater the linkage. The sign is simply a consequence of how the alleles are numbered. Linkage disequilibrium can be the result of physical proximity of the genes. Or, it can be maintained by natural selection if some combinations of alleles work better as a team.

Natural selection maintains the linkage disequilibrium between color and pattern alleles in Papilio memnon. [linkage disequilibrium: association between alleles at different loci] In this moth species, there is a gene that determines wing morphology. One allele at this locus leads to a moth that has a tail; the other allele codes for a untailed moth. There is another gene that determines if the wing is brightly or darkly colored. There are thus four possible types of moths: brightly colored moths with and without tails, and dark moths with and without tails. All four can be produced when moths are brought into the lab and bred. However, only two of these types of moths are found in the wild: brightly colored moths with tails and darkly colored moths without tails. The non-random association is maintained by natural selection. Bright, tailed moths mimic the pattern of an unpalatable species. The dark morph is cryptic. The other two combinations are neither mimetic nor cryptic and are quickly eaten by birds.

Assortative mating causes a non-random distribution of alleles at a single locus. [locus: location of a gene on a chromosome] If there are two alleles (A and a) at a locus with frequencies p and q, the frequency of the three possible genotypes (AA, Aa and aa) will be p2, 2pq and q2, respectively. For example, if the frequency of A is 0.9 and the frequency of a is 0.1, the frequencies of AA, Aa and aa individuals are: 0.81, 0.18 and 0.01. This distribution is called the Hardy-Weinberg equilibrium.

Non-random mating results in a deviation from the Hardy-Weinberg distribution. Humans mate assortatively according to race; we are more likely to mate with someone of own race than another. In populations that mate this way, fewer heterozygotes are found than would be predicted under random mating. [heterozygote: an organism that has two different alleles at a locus] A decrease in heterozygotes can be the result of mate choice, or simply the result of population subdivision. Most organisms have a limited dispersal capability, so their mate will be chosen from the local population.

Evolution within a Lineage

In order for continuing evolution there must be mechanisms to increase or create genetic variation and mechanisms to decrease it. The mechanisms of evolution are mutation, natural selection, genetic drift, recombination and gene flow. I have grouped them into two classes -- those that decrease genetic variation and those that increase it.

Mechanisms that Decrease Genetic Variation

Natural Selection

Some types of organisms within a population leave more offspring than others. Over time, the frequency of the more prolific type will increase. The difference in reproductive capability is called natural selection. Natural selection is the only mechanism of adaptive evolution; it is defined as differential reproductive success of pre- existing classes of genetic variants in the gene pool.

The most common action of natural selection is to remove unfit variants as they arise via mutation. [natural selection: differential reproductive success of genotypes] In other words, natural selection usually prevents new alleles from increasing in frequency. This led a famous evolutionist, George Williams, to say "Evolution proceeds in spite of natural selection."

Natural selection can maintain or deplete genetic variation depending on how it acts. When selection acts to weed out deleterious alleles, or causes an allele to sweep to fixation, it depletes genetic variation. When heterozygotes are more fit than either of the homozygotes, however, selection causes genetic variation to be maintained. [heterozygote: an organism that has two different alleles at a locus. | homozygote: an organism that has two identical alleles at a locus] This is called balancing selection. An example of this is the maintenance of sickle-cell alleles in human populations subject to malaria. Variation at a single locus determines whether red blood cells are shaped normally or sickled. If a human has two alleles for sickle-cell, he/she develops anemia -- the shape of sickle-cells precludes them carrying normal levels of oxygen. However, heterozygotes who have one copy of the sickle-cell allele, coupled with one normal allele enjoy some resistance to malaria -- the shape of sickled cells make it harder for the plasmodia (malaria causing agents) to enter the cell. Thus, individuals homozygous for the normal allele suffer more malaria than heterozygotes. Individuals homozygous for the sickle- cell are anemic. Heterozygotes have the highest fitness of these three types. Heterozygotes pass on both sickle-cell and normal alleles to the next generation. Thus, neither allele can be eliminated from the gene pool. The sickle-cell allele is at its highest frequency in regions of Africa where malaria is most pervasive.

Balancing selection is rare in natural populations. [balancing selection: selection favoring heterozygotes] Only a handful of other cases beside the sickle-cell example have been found. At one time population geneticists thought balancing selection could be a general explanation for the levels of genetic variation found in natural populations. That is no longer the case. Balancing selection is only rarely found in natural populations. And, there are theoretical reasons why natural selection cannot maintain polymorphisms at several loci via balancing selection.

Individuals are selected. The example I gave earlier was an example of evolution via natural selection. [natural selection: differential reproductive success of genotypes] Dark colored moths had a higher reproductive success because light colored moths suffered a higher predation rate. The decline of light colored alleles was caused by light colored individuals being removed from the gene pool (selected against). Individual organisms either reproduce or fail to reproduce and are hence the unit of selection. One way alleles can change in frequency is to be housed in organisms with different reproductive rates. Genes are not the unit of selection (because their success depends on the organism's other genes as well); neither are groups of organisms a unit of selection. There are some exceptions to this "rule," but it is a good generalization.

Organisms do not perform any behaviors that are for the good of their species. An individual organism competes primarily with others of it own species for its reproductive success. Natural selection favors selfish behavior because any truly altruistic act increases the recipient's reproductive success while lowering the donors. Altruists would disappear from a population as the non- altruists would reap the benefits, but not pay the costs, of altruistic acts. Many behaviors appear altruistic. Biologists, however, can demonstrate that these behaviors are only apparently altruistic. Cooperating with or helping other organisms is often the most selfish strategy for an animal. This is called reciprocal altruism. A good example of this is blood sharing in vampire bats. In these bats, those lucky enough to find a meal will often share part of it with an unsuccessful bat by regurgitating some blood into the other's mouth. Biologists have found that these bats form bonds with partners and help each other out when the other is needy. If a bat is found to be a "cheater," (he accepts blood when starving, but does not donate when his partner is) his partner will abandon him. The bats are thus not helping each other altruistically; they form pacts that are mutually beneficial.

Helping closely related organisms can appear altruistic; but this is also a selfish behavior. Reproductive success (fitness) has two components; direct fitness and indirect fitness. Direct fitness is a measure of how many alleles, on average, a genotype contributes to the subsequent generation's gene pool by reproducing. Indirect fitness is a measure of how many alleles identical to its own it helps to enter the gene pool. Direct fitness plus indirect fitness is inclusive fitness. J. B. S. Haldane once remarked he would gladly drown, if by doing so he saved two siblings or eight cousins. Each of his siblings would share one half his alleles; his cousins, one eighth. They could potentially add as many of his alleles to the gene pool as he could.

Natural selection favors traits or behaviors that increase a genotype's inclusive fitness. Closely related organisms share many of the same alleles. In diploid species, siblings share on average at least 50% of their alleles. The percentage is higher if the parents are related. So, helping close relatives to reproduce gets an organism's own alleles better represented in the gene pool. The benefit of helping relatives increases dramatically in highly inbred species. In some cases, organisms will completely forgo reproducing and only help their relatives reproduce. Ants, and other eusocial insects, have sterile castes that only serve the queen and assist her reproductive efforts. The sterile workers are reproducing by proxy.

The words selfish and altruistic have connotations in everyday use that biologists do not intend. Selfish simply means behaving in such a way that one's own inclusive fitness is maximized; altruistic means behaving in such a way that another's fitness is increased at the expense of ones' own. Use of the words selfish and altruistic is not meant to imply that organisms consciously understand their motives.

The opportunity for natural selection to operate does not induce genetic variation to appear -- selection only distinguishes between existing variants. Variation is not possible along every imaginable axis, so all possible adaptive solutions are not open to populations. To pick a somewhat ridiculous example, a steel shelled turtle might be an improvement over regular turtles. Turtles are killed quite a bit by cars these days because when confronted with danger, they retreat into their shells -- this is not a great strategy against a two ton automobile. However, there is no variation in metal content of shells, so it would not be possible to select for a steel shelled turtle.

Here is a second example of natural selection. Geospiza fortis lives on the Galapagos islands along with fourteen other finch species. It feeds on the seeds of the plant Tribulus cistoides, specializing on the smaller seeds. Another species, G. Magnirostris, has a larger beak and specializes on the larger seeds. The health of these bird populations depends on seed production. Seed production, in turn, depends on the arrival of wet season. In 1977, there was a drought. Rainfall was well below normal and fewer seeds were produced. As the season progressed, the G. fortis population depleted the supply of small seeds. Eventually, only larger seeds remained. Most of the finches starved; the population plummeted from about twelve hundred birds to less than two hundred. Peter Grant, who had been studying these finches, noted that larger beaked birds fared better than smaller beaked ones. These larger birds had offspring with correspondingly large beaks. Thus, there was an increase in the proportion of large beaked birds in the population the next generation. To prove that the change in bill size in Geospiza fortis was an evolutionary change, Grant had to show that differences in bill size were at least partially genetically based. He did so by crossing finches of various beak sizes and showing that a finch's beak size was influenced by its parent's genes. Large beaked birds had large beaked offspring; beak size was not due to environmental differences (in parental care, for example).

Natural selection may not lead a population to have the optimal set of traits. In any population, there would be a certain combination of possible alleles that would produce the optimal set of traits (the global optimum); but there are other sets of alleles that would yield a population almost as adapted (local optima). Transition from a local optimum to the global optimum may be hindered or forbidden because the population would have to pass through less adaptive states to make the transition. Natural selection only works to bring populations to the nearest optimal point. This idea is Sewall Wright's adaptive landscape. This is one of the most influential models that shape how evolutionary biologists view evolution.

Natural selection does not have any foresight. It only allows organisms to adapt to their current environment. Structures or behaviors do not evolve for future utility. An organism adapts to its environment at each stage of its evolution. As the environment changes, new traits may be selected for. Large changes in populations are the result of cumulative natural selection. Changes are introduced into the population by mutation; the small minority of these changes that result in a greater reproductive output of their bearers are amplified in frequency by selection.

Complex traits must evolve through viable intermediates. For many traits, it initially seems unlikely that intermediates would be viable. What good is half a wing? Half a wing may be no good for flying, but it may be useful in other ways. Feathers are thought to have evolved as insulation (ever worn a down jacket?) and/or as a way to trap insects. Later, proto-birds may have learned to glide when leaping from tree to tree. Eventually, the feathers that originally served as insulation now became co-opted for use in flight. A trait's current utility is not always indicative of its past utility. It can evolve for one purpose, and be used later for another. A trait evolved for its current utility is an adaptation; one that evolved for another utility is an exaptation. An example of an exaptation is a penguin's wing. Penguins evolved from flying ancestors; now they are flightless and use their wings for swimming.

Common Misconceptions about Selection

Selection is not a force in the sense that gravity or the strong nuclear force is. However, for the sake of brevity, biologists sometimes refer to it that way. This often leads to some confusion when biologists speak of selection "pressures." This implies that the environment "pushes" a population to more adapted state. This is not the case. Selection merely favors beneficial genetic changes when they occur by chance -- it does not contribute to their appearance. The potential for selection to act may long precede the appearance of selectable genetic variation. When selection is spoken of as a force, it often seems that it is has a mind of its own; or as if it was nature personified. This most often occurs when biologists are waxing poetic about selection. This has no place in scientific discussions of evolution. Selection is not a guided or cognizant entity; it is simply an effect.

A related pitfall in discussing selection is anthropomorphizing on behalf of living things. Often conscious motives are seemingly imputed to organisms, or even genes, when discussing evolution. This happens most frequently when discussing animal behavior. Animals are often said to perform some behavior because selection will favor it. This could more accurately worded as "animals that, due to their genetic composition, perform this behavior tend to be favored by natural selection relative to those who, due to their genetic composition, don't." Such wording is cumbersome. To avoid this, biologists often anthropomorphize. This is unfortunate because it often makes evolutionary arguments sound silly. Keep in mind this is only for convenience of expression.

The phrase "survival of the fittest" is often used synonymously with natural selection. The phrase is both incomplete and misleading. For one thing, survival is only one component of selection -- and perhaps one of the less important ones in many populations. For example, in polygynous species, a number of males survive to reproductive age, but only a few ever mate. Males may differ little in their ability to survive, but greatly in their ability to attract mates -- the difference in reproductive success stems mainly from the latter consideration. Also, the word fit is often confused with physically fit. Fitness, in an evolutionary sense, is the average reproductive output of a class of genetic variants in a gene pool. Fit does not necessarily mean biggest, fastest or strongest.

Sexual Selection

In many species, males develop prominent secondary sexual characteristics. A few oft cited examples are the peacock's tail, coloring and patterns in male birds in general, voice calls in frogs and flashes in fireflies. Many of these traits are a liability from the standpoint of survival. Any ostentatious trait or noisy, attention getting behavior will alert predators as well as potential mates. How then could natural selection favor these traits?

Natural selection can be broken down into many components, of which survival is only one. Sexual attractiveness is a very important component of selection, so much so that biologists use the term sexual selection when they talk about this subset of natural selection.

Sexual selection is natural selection operating on factors that contribute to an organism's mating success. Traits that are a liability to survival can evolve when the sexual attractiveness of a trait outweighs the liability incurred for survival. A male who lives a short time, but produces many offspring is much more successful than a long lived one that produces few. The former's genes will eventually dominate the gene pool of his species. In many species, especially polygynous species where only a few males monopolize all the females, sexual selection has caused pronounced sexual dimorphism. In these species males compete against other males for mates. The competition can be either direct or mediated by female choice. In species where females choose, males compete by displaying striking phenotypic characteristics and/or performing elaborate courtship behaviors. The females then mate with the males that most interest them, usually the ones with the most outlandish displays. There are many competing theories as to why females are attracted to these displays.

The good genes model states that the display indicates some component of male fitness. A good genes advocate would say that bright coloring in male birds indicates a lack of parasites. The females are cueing on some signal that is correlated with some other component of viability.

Selection for good genes can be seen in sticklebacks. In these fish, males have red coloration on their sides. Milinski and Bakker showed that intensity of color was correlated to both parasite load and sexual attractiveness. Females preferred redder males. The redness indicated that he was carrying fewer parasites.

Evolution can get stuck in a positive feedback loop. Another model to explain secondary sexual characteristics is called the runaway sexual selection model. R. A. Fisher proposed that females may have an innate preference for some male trait before it appears in a population. Females would then mate with male carriers when the trait appears. The offspring of these matings have the genes for both the trait and the preference for the trait. As a result, the process snowballs until natural selection brings it into check. Suppose that female birds prefer males with longer than average tail feathers. Mutant males with longer than average feathers will produce more offspring than the short feathered males. In the next generation, average tail length will increase. As the generations progress, feather length will increase because females do not prefer a specific length tail, but a longer than average tail. Eventually tail length will increase to the point were the liability to survival is matched by the sexual attractiveness of the trait and an equilibrium will be established. Note that in many exotic birds male plumage is often very showy and many species do in fact have males with greatly elongated feathers. In some cases these feathers are shed after the breeding season.

None of the above models are mutually exclusive. There are millions of sexually dimorphic species on this planet and the forms of sexual selection probably vary amongst them.

Genetic Drift

Allele frequencies can change due to chance alone. This is called genetic drift. Drift is a binomial sampling error of the gene pool. What this means is, the alleles that form the next generation's gene pool are a sample of the alleles from the current generation. When sampled from a population, the frequency of alleles differs slightly due to chance alone.

Alleles can increase or decrease in frequency due to drift. The average expected change in allele frequency is zero, since increasing or decreasing in frequency is equally probable. A small percentage of alleles may continually change frequency in a single direction for several generations just as flipping a fair coin may, on occasion, result in a string of heads or tails. A very few new mutant alleles can drift to fixation in this manner.

In small populations, the variance in the rate of change of allele frequencies is greater than in large populations. However, the overall rate of genetic drift (measured in substitutions per generation) is independent of population size. [genetic drift: a random change in allele frequencies] If the mutation rate is constant, large and small populations lose alleles to drift at the same rate. This is because large populations will have more alleles in the gene pool, but they will lose them more slowly. Smaller populations will have fewer alleles, but these will quickly cycle through. This assumes that mutation is constantly adding new alleles to the gene pool and selection is not operating on any of these alleles.

Sharp drops in population size can change allele frequencies substantially. When a population crashes, the alleles in the surviving sample may not be representative of the precrash gene pool. This change in the gene pool is called the founder effect, because small populations of organisms that invade a new territory (founders) are subject to this. Many biologists feel the genetic changes brought about by founder effects may contribute to isolated populations developing reproductive isolation from their parent populations. In sufficiently small populations, genetic drift can counteract selection. [genetic drift: a random change in allele frequencies] Mildly deleterious alleles may drift to fixation.

Wright and Fisher disagreed on the importance of drift. Fisher thought populations were sufficiently large that drift could be neglected. Wright argued that populations were often divided into smaller subpopulations. Drift could cause allele frequency differences between subpopulations if gene flow was small enough. If a subpopulation was small enough, the population could even drift through fitness valleys in the adaptive landscape. Then, the subpopulation could climb a larger fitness hill. Gene flow out of this subpopulation could contribute to the population as a whole adapting. This is Wright's Shifting Balance theory of evolution.

Both natural selection and genetic drift decrease genetic variation. If they were the only mechanisms of evolution, populations would eventually become homogeneous and further evolution would be impossible. There are, however, mechanisms that replace variation depleted by selection and drift. These are discussed below.

Mechanisms that Increase Genetic Variation

Mutation

The cellular machinery that copies DNA sometimes makes mistakes. These mistakes alter the sequence of a gene. This is called a mutation. There are many kinds of mutations. A point mutation is a mutation in which one "letter" of the genetic code is changed to another. Lengths of DNA can also be deleted or inserted in a gene; these are also mutations. Finally, genes or parts of genes can become inverted or duplicated. Typical rates of mutation are between 10-10 and 10-12 mutations per base pair of DNA per generation.

Most mutations are thought to be neutral with regards to fitness. (Kimura defines neutral as |s| < 1/2Ne, where s is the selective coefficient and Ne is the effective population size.) Only a small portion of the genome of eukaryotes contains coding segments. And, although some non-coding DNA is involved in gene regulation or other cellular functions, it is probable that most base changes would have no fitness consequence.

Most mutations that have any phenotypic effect are deleterious. Mutations that result in amino acid substitutions can change the shape of a protein, potentially changing or eliminating its function. This can lead to inadequacies in biochemical pathways or interfere with the process of development. Organisms are sufficiently integrated that most random changes will not produce a fitness benefit. Only a very small percentage of mutations are beneficial. The ratio of neutral to deleterious to beneficial mutations is unknown and probably varies with respect to details of the locus in question and environment.

Mutation limits the rate of evolution. The rate of evolution can be expressed in terms of nucleotide substitutions in a lineage per generation. Substitution is the replacement of an allele by another in a population. This is a two step process: First a mutation occurs in an individual, creating a new allele. This allele subsequently increases in frequency to fixation in the population. The rate of evolution is k = 2Nvu (in diploids) where k is nucleotide substitutions, N is the effective population size, v is the rate of mutation and u is the proportion of mutants that eventually fix in the population.

Mutation need not be limiting over short time spans. The rate of evolution expressed above is given as a steady state equation; it assumes the system is at equilibrium. Given the time frames for a single mutant to fix, it is unclear if populations are ever at equilibrium. A change in environment can cause previously neutral alleles to have selective values; in the short term evolution can run on "stored" variation and thus is independent of mutation rate. Other mechanisms can also contribute selectable variation. Recombination creates new combinations of alleles (or new alleles) by joining sequences with separate microevolutionary histories within a population. Gene flow can also supply the gene pool with variants. Of course, the ultimate source of these variants is mutation.

The Fate of Mutant Alleles

Mutation creates new alleles. Each new allele enters the gene pool as a single copy amongst many. Most are lost from the gene pool, the organism carrying them fails to reproduce, or reproduces but does not pass on that particular allele. A mutant's fate is shared with the genetic background it appears in. A new allele will initially be linked to other loci in its genetic background, even loci on other chromosomes. If the allele increases in frequency in the population, initially it will be paired with other alleles at that locus -- the new allele will primarily be carried in individuals heterozygous for that locus. The chance of it being paired with itself is low until it reaches intermediate frequency. If the allele is recessive, its effect won't be seen in any individual until a homozygote is formed. The eventual fate of the allele depends on whether it is neutral, deleterious or beneficial.

Neutral alleles

Most neutral alleles are lost soon after they appear. The average time (in generations) until loss of a neutral allele is 2(Ne/N) ln(2N) where N is the effective population size (the number of individuals contributing to the next generation's gene pool) and N is the total population size. Only a small percentage of alleles fix. Fixation is the process of an allele increasing to a frequency at or near one. The probability of a neutral allele fixing in a population is equal to its frequency. For a new mutant in a diploid population, this frequency is 1/2N.

If mutations are neutral with respect to fitness, the rate of substitution (k) is equal to the rate of mutation(v). This does not mean every new mutant eventually reaches fixation. Alleles are added to the gene pool by mutation at the same rate they are lost to drift. For neutral alleles that do fix, it takes an average of 4N generations to do so. However, at equilibrium there are multiple alleles segregating in the population. In small populations, few mutations appear each generation. The ones that fix do so quickly relative to large populations. In large populations, more mutants appear over the generations. But, the ones that fix take much longer to do so. Thus, the rate of neutral evolution (in substitutions per generation) is independent of population size.

The rate of mutation determines the level of heterozygosity at a locus according to the neutral theory. Heterozygosity is simply the proportion of the population that is heterozygous. Equilibrium heterozygosity is given as H = 4Nv/[4Nv+1] (for diploid populations). H can vary from a very small number to almost one. In small populations, H is small (because the equation is approximately a very small number divided by one). In (biologically unrealistically) large populations, heterozygosity approaches one (because the equation is approximately a large number divided by itself). Directly testing this model is difficult because N and v can only be estimated for most natural populations. But, heterozygosities are believed to be too low to be described by a strictly neutral model. Solutions offered by neutralists for this discrepancy include hypothesizing that natural populations may not be at equilibrium.

At equilibrium there should be a few alleles at intermediate frequency and many at very low frequencies. This is the Ewens- Watterson distribution. New alleles enter a population every generation, most remain at low frequency until they are lost. A few drift to intermediate frequencies, a very few drift all the way to fixation. In Drosophila pseudoobscura, the protein Xanthine dehydrogenase (Xdh) has many variants. In a single population, Keith, et. al., found that 59 of 96 proteins were of one type, two others were represented ten and nine times and nine other types were present singly or in low numbers.

Deleterious alleles

Deleterious mutants are selected against but remain at low frequency in the gene pool. In diploids, a deleterious recessive mutant may increase in frequency due to drift. Selection cannot see it when it is masked by a dominant allele. Many disease causing alleles remain at low frequency for this reason. People who are carriers do not suffer the negative effect of the allele. Unless they mate with another carrier, the allele may simply continue to be passed on. Deleterious alleles also remain in populations at a low frequency due to a balance between recurrent mutation and selection. This is called the mutation load.

Beneficial alleles

Most new mutants are lost, even beneficial ones. Wright calculated that the probability of fixation of a beneficial allele is 2s. (This assumes a large population size, a small fitness benefit, and that heterozygotes have an intermediate fitness. A benefit of 2s yields an overall rate of evolution: k=4Nvs where v is the mutation rate to beneficial alleles) An allele that conferred a one percent increase in fitness only has a two percent chance of fixing. The probability of fixation of beneficial type of mutant is boosted by recurrent mutation. The beneficial mutant may be lost several times, but eventually it will arise and stick in a population. (Recall that even deleterious mutants recur in a population.)

Directional selection depletes genetic variation at the selected locus as the fitter allele sweeps to fixation. Sequences linked to the selected allele also increase in frequency due to hitchhiking. The lower the rate of recombination, the larger the window of sequence that hitchhikes. Begun and Aquadro compared the level of nucleotide polymorphism within and between species with the rate of recombination at a locus. Low levels of nucleotide polymorphism within species coincided with low rates of recombination. This could be explained by molecular mechanisms if recombination itself was mutagenic. In this case, recombination with also be correlated with nucleotide divergence between species. But, the level of sequence divergence did not correlate with the rate of recombination. Thus, they inferred that selection was the cause. The correlation between recombination and nucleotide polymorphism leaves the conclusion that selective sweeps occur often enough to leave an imprint on the level of genetic variation in natural populations.

One example of a beneficial mutation comes from the mosquito Culex pipiens. In this organism, a gene that was involved with breaking down organophosphates - common insecticide ingredients -became duplicated. Progeny of the organism with this mutation quickly swept across the worldwide mosquito population. There are numerous examples of insects developing resistance to chemicals, especially DDT which was once heavily used in this country. And, most importantly, even though "good" mutations happen much less frequently than "bad" ones, organisms with "good" mutations thrive while organisms with "bad" ones die out.

If beneficial mutants arise infrequently, the only fitness differences in a population will be due to new deleterious mutants and the deleterious recessives. Selection will simply be weeding out unfit variants. Only occasionally will a beneficial allele be sweeping through a population. The general lack of large fitness differences segregating in natural populations argues that beneficial mutants do indeed arise infrequently. However, the impact of a beneficial mutant on the level of variation at a locus can be large and lasting. It takes many generations for a locus to regain appreciable levels of heterozygosity following a selective sweep.

Recombination

Each chromosome in our sperm or egg cells is a mixture of genes from our mother and our father. Recombination can be thought of as gene shuffling. Most organisms have linear chromosomes and their genes lie at specific location (loci) along them. Bacteria have circular chromosomes. In most sexually reproducing organisms, there are two of each chromosome type in every cell. For instance in humans, every chromosome is paired, one inherited from the mother, the other inherited from the father. When an organism produces gametes, the gametes end up with only one of each chromosome per cell. Haploid gametes are produced from diploid cells by a process called meiosis.

In meiosis, homologous chromosomes line up. The DNA of the chromosome is broken on both chromosomes in several places and rejoined with the other strand. Later, the two homologous chromosomes are split into two separate cells that divide and become gametes. But, because of recombination, both of the chromosomes are a mix of alleles from the mother and father.

Recombination creates new combinations of alleles. Alleles that arose at different times and different places can be brought together. Recombination can occur not only between genes, but within genes as well. Recombination within a gene can form a new allele. Recombination is a mechanism of evolution because it adds new alleles and combinations of alleles to the gene pool.

Gene Flow

New organisms may enter a population by migration from another population. If they mate within the population, they can bring new alleles to the local gene pool. This is called gene flow. In some closely related species, fertile hybrids can result from interspecific matings. These hybrids can vector genes from species to species.

Gene flow between more distantly related species occurs infrequently. This is called horizontal transfer. One interesting case of this involves genetic elements called P elements. Margaret Kidwell found that P elements were transferred from some species in the Drosophila willistoni group to Drosophila melanogaster. These two species of fruit flies are distantly related and hybrids do not form. Their ranges do, however, overlap. The P elements were vectored into D. melanogaster via a parasitic mite that targets both these species. This mite punctures the exoskeleton of the flies and feeds on the "juices". Material, including DNA, from one fly can be transferred to another when the mite feeds. Since P elements actively move in the genome (they are themselves parasites of DNA), one incorporated itself into the genome of a melanogaster fly and subsequently spread through the species. Laboratory stocks of melanogaster caught prior to the 1940's lack of P elements. All natural populations today harbor them.

Overview of Evolution within a Lineage

Evolution is a change in the gene pool of a population over time; it can occur due to several factors. Three mechanisms add new alleles to the gene pool: mutation, recombination and gene flow. Two mechanisms remove alleles, genetic drift and natural selection. Drift removes alleles randomly from the gene pool. Selection removes deleterious alleles from the gene pool. The amount of genetic variation found in a population is the balance between the actions of these mechanisms.

Natural selection can also increase the frequency of an allele. Selection that weeds out harmful alleles is called negative selection. Selection that increases the frequency of helpful alleles is called positive, or sometimes positive Darwinian, selection. A new allele can also drift to high frequency. But, since the change in frequency of an allele each generation is random, nobody speaks of positive or negative drift.

Except in rare cases of high gene flow, new alleles enter the gene pool as a single copy. Most new alleles added to the gene pool are lost almost immediately due to drift or selection; only a small percent ever reach a high frequency in the population. Even most moderately beneficial alleles are lost due to drift when they appear. But, a mutation can reappear numerous times.

The fate of any new allele depends a great deal on the organism it appears in. This allele will be linked to the other alleles near it for many generations. A mutant allele can increase in frequency simply because it is linked to a beneficial allele at a nearby locus. This can occur even if the mutant allele is deleterious, although it must not be so deleterious as to offset the benefit of the other allele. Likewise a potentially beneficial new allele can be eliminated from the gene pool because it was linked to deleterious alleles when it first arose. An allele "riding on the coat tails" of a beneficial allele is called a hitchhiker. Eventually, recombination will bring the two loci to linkage equilibrium. But, the more closely linked two alleles are, the longer the hitchhiking will last.

The effects of selection and drift are coupled. Drift is intensified as selection pressures increase. This is because increased selection (i.e. a greater difference in reproductive success among organisms in a population) reduces the effective population size, the number of individuals contributing alleles to the next generation.

Adaptation is brought about by cumulative natural selection, the repeated sifting of mutations by natural selection. Small changes, favored by selection, can be the stepping-stone to further changes. The summation of large numbers of these changes is macroevolution.

The Development of Evolutionary Theory

Biology came of age as a science when Charles Darwin published "On the Origin of Species." But, the idea of evolution wasn't new to Darwin. Lamarck published a theory of evolution in 1809. Lamarck thought that species arose continually from nonliving sources. These species were initially very primitive, but increased in complexity over time due to some inherent tendency. This type of evolution is called orthogenesis. Lamarck proposed that an organism's acclimation to the environment could be passed on to its offspring. For example, he thought proto-giraffes stretched their necks to reach higher twigs. This caused their offspring to be born with longer necks. This proposed mechanism of evolution is called the inheritance of acquired characteristics. Lamarck also believed species never went extinct, although they may change into newer forms. All three of these ideas are now known to be wrong.

Darwin's contributions include hypothesizing the pattern of common descent and proposing a mechanism for evolution -- natural selection. In Darwin's theory of natural selection, new variants arise continually within populations. A small percentage of these variants cause their bearers to produce more offspring than others. These variants thrive and supplant their less productive competitors. The effect of numerous instances of selection would lead to a species being modified over time.

Darwin's theory did not accord with older theories of genetics. In Darwin's time, biologists held to the theory of blending inheritance -- an offspring was an average of its parents. If an individual had one short parent and one tall parent, it would be of medium height. And, the offspring would pass on genes for medium sized offspring. If this was the case, new genetic variations would quickly be diluted out of a population. They could not accumulate as the theory of evolution required. We now know that the idea of blending inheritance is wrong.

Darwin didn't know that the true mode of inheritance was discovered in his lifetime. Gregor Mendel, in his experiments on hybrid peas, showed that genes from a mother and father do not blend. An offspring from a short and a tall parent may be medium sized; but it carries genes for shortness and tallness. The genes remain distinct and can be passed on to subsequent generations. Mendel mailed his paper to Darwin, but Darwin never opened it.

It was a long time until Mendel's ideas were accepted. One group of biologists, called biometricians, thought Mendel's laws only held for a few traits. Most traits, they claimed, were governed by blending inheritance. Mendel studied discrete traits. Two of the traits in his famous experiments were smooth versus wrinkled coat on peas. This trait did not vary continuously. In other words, peas are either wrinkled or smooth -- intermediates are not found. Biometricians considered these traits aberrations. They studied continuously varying traits like size and believed most traits showed blending inheritance.

Incorporating Genetics into Evolutionary Theory

The discrete genes Mendel discovered would exist at some frequency in natural populations. Biologists wondered how and if these frequencies would change. Many thought that the more common versions of genes would increase in frequency simply because they were already at high frequency.

Hardy and Weinberg independently showed that the frequency of an allele would not change over time simply due to its being rare or common. Their model had several assumptions -- that all alleles reproduced at the same rate, that the population size was very large and that alleles did not change in form. Later, R. A. Fisher showed that Mendel's laws could explain continuous traits if the expression of these traits were due to the action of many genes. After this, geneticists accepted Mendel's Laws as the basic rules of genetics. From this basis, Fisher, Sewall Wright and J. B. S.. Haldane founded the field of population genetics. Population genetics is a field of biology that attempts to measure and explain the levels of genetic variation in populations.

R. A. Fisher studied the effect of natural selection on large populations. He demonstrated that even very small selective differences amongst alleles could cause appreciable changes in allele frequencies over time. He also showed that the rate of adaptive change in a population is proportional to the amount of genetic variation present. This is called Fisher's Fundamental Theorem of Natural Selection. Although it is called the fundamental theorem, it does not hold in all cases. The rate at which natural selection brings about adaptation depends on the details of how selection is working. In some rare cases, natural selection can actually cause a decline in the mean relative fitness of a population.

Sewall Wright was more concerned with drift. He stressed that large populations are often subdivided into many subpopulations. In his theory, genetic drift played a more important role compared to selection. Differentiation between subpopulations, followed by migration among them, could contribute to adaptations amongst populations. Wright also came up with the idea of the adaptive landscape -- an idea that remains influential to this day. Its influence remains even though P. A. P. Moran has shown that, mathematically, adaptive landscapes don't exist as Wright envisioned them. Wright extended his results of one-locus models to a two-locus case in proposing the adaptive landscape. But, unbeknownst to him, the general conclusions of the one-locus model don't extend to the two-locus case.

J. B. S. Haldane developed many of the mathematical models of natural and artificial selection. He showed that selection and mutation could oppose each other, that deleterious mutations could remain in a population due to recurrent mutation. He also demonstrated that there was a cost to natural selection, placing a limit on the amount of adaptive substitutions a population could undergo in a given time frame.

For a long time, population genetics developed as a theoretical field. But, gathering the data needed to test the theories was nearly impossible. Prior to the advent of molecular biology, estimates of genetic variability could only be inferred from levels of morphological differences in populations. Lewontin and Hubby were the first to get a good estimate of genetic variation in a population. Using the then new technique of protein electrophoresis, they showed that 30% of the loci in a population of Drosophila pseudoobscura were polymorphic. They also showed that it was likely that they could not detect all the variation that was present. Upon finding this level of variation, the question became -- was this maintained by natural selection, or simply the result of genetic drift? This level of variation was too high to be explained by balancing selection.

Motoo Kimura theorized that most variation found in populations was selectively equivalent (neutral). Multiple alleles at a locus differed in sequence, but their fitnesses were the same. Kimura's neutral theory described rates of evolution and levels of polymorphism solely in terms of mutation and genetic drift. The neutral theory did not deny that natural selection acted on natural populations; but it claimed that the majority of natural variation was transient polymorphisms of neutral alleles. Selection did not act frequently or strongly enough to influence rates of evolution or levels of polymorphism.

Initially, a wide variety of observations seemed to be consistent with the neutral theory. Eventually, however, several lines of evidence toppled it. There is less variation in natural populations than the neutral theory predicts. Also, there is too much variance in rates of substitutions in different lineages to be explained by mutation and drift alone. Finally, selection itself has been shown to have an impact on levels of nucleotide variation. Currently, there is no comprehensive mathematical theory of evolution that accurately predicts rates of evolution and levels of heterozygosity in natural populations.

Evolution Among Lineages

The Pattern of Macroevolution

Evolution is not progress. The popular notion that evolution can be represented as a series of improvements from simple cells, through more complex life forms, to humans (the pinnacle of evolution), can be traced to the concept of the scale of nature. This view is incorrect.

All species have descended from a common ancestor. As time went on, different lineages of organisms were modified with descent to adapt to their environments. Thus, evolution is best viewed as a branching tree or bush, with the tips of each branch representing currently living species. No living organisms today are our ancestors. Every living species is as fully modern as we are with its own unique evolutionary history. No extant species are "lower life forms," atavistic stepping stones paving the road to humanity.

A related, and common, fallacy about evolution is that humans evolved from some living species of ape. This is not the case -- humans and apes share a common ancestor. Both humans and living apes are fully modern species; the ancestor we evolved from was an ape, but it is now extinct and was not the same as present day apes (or humans for that matter). If it were not for the vanity of human beings, we would be classified as an ape. Our closest relatives are, collectively, the chimpanzee and the pygmy chimp. Our next nearest relative is the gorilla.

Evidence for Common Descent and Macroevolution

Microevolution can be studied directly. Macroevolution cannot. Macroevolution is studied by examining patterns in biological populations and groups of related organisms and inferring process from pattern. Given the observation of microevolution and the knowledge that the earth is billions of years old -- macroevolution could be postulated. But this extrapolation, in and of itself, does not provide a compelling explanation of the patterns of biological diversity we see today. Evidence for macroevolution, or common ancestry and modification with descent, comes from several other fields of study. These include: comparative biochemical and genetic studies, comparative developmental biology, patterns of biogeography, comparative morphology and anatomy and the fossil record.

Closely related species (as determined by morphologists) have similar gene sequences. Overall sequence similarity is not the whole story, however. The pattern of differences we see in closely related genomes is worth examining.

All living organisms use DNA as their genetic material, although some viruses use RNA. DNA is composed of strings of nucleotides. There are four different kinds of nucleotides: adenine (A), guanine (G), cytosine (C) and thymine (T). Genes are sequences of nucleotides that code for proteins. Within a gene, each block of three nucleotides is called a codon. Each codon designates an amino acid (the subunits of proteins).

The three letter code is the same for all organisms (with a few exceptions). There are 64 codons, but only 20 amino acids to code for; so, most amino acids are coded for by several codons. In many cases the first two nucleotides in the codon designate the amino acid. The third position can have any of the four nucleotides and not effect how the code is translated.

A gene, when in use, is transcribed into RNA -- a nucleic acid similar to DNA. (RNA, like DNA, is made up of nucleotides although t he nucleotide uracil (U) is used in place of thymine (T).) The RNA transcribed from a gene is called messenger RNA. Messenger RNA is then translated via cellular machinery called ribosomes into a string of amino acids -- a protein. Some proteins function as enzymes, catalysts that speed the chemical reactions in cells. Others are structural or involved in regulating development.

Gene sequences in closely related species are very similar. Often, the same codon specifies a given amino acid in two related species, even though alternate codons could serve functionally as well. But, some differences do exist in gene sequences. Most often, differences are in third codon positions, where changes in the DNA sequence would not disrupt the sequence of the protein.

There are other sites in the genome where nucleotide differences do not effect protein sequences. The genome of eukaryotes is loaded with 'dead genes' called pseudogenes. Pseudogenes are copies of working genes that have been inactivated by mutation. Most pseudogenes do not produce full proteins. They may be transcribed, but not translated. Or, they may be translated, but only a truncated protein is produced. Pseudogenes evolve much faster than their working counterparts. Mutations in them do not get incorporated into proteins, so they have no effect on the fitness of an organism.

Introns are sequences of DNA that interrupt a gene, but do not code for anything. The coding portions of a gene are called exons. Introns are spliced out of the messenger RNA prior to translation, so they do not contribute information needed to make the protein. They are sometimes, however, involved in regulation of the gene. Like pseudogenes, introns (in general) evolve faster than coding portions of a gene.

Nucleotide positions that can be changed without changing the sequence of a protein are called silent sites. Sites where changes result in an amino acid substitution are called replacement sites. Silent sites are expected to be more polymorphic within a population and show more differences between populations. Although both silent and replacement sites receive the same amount of mutations, natural selection only infrequently allows changes at replacement sites. Silent sites, however, are not as constrained.

Kreitman was the first demonstrate that silent sites were more variable than coding sites. Shortly after the methods of DNA sequencing were discovered, he sequenced 11 alleles of the enzyme alcohol dehydrogenase (AdH). Of the 43 polymorphic nucleotide sites he found, only one resulted in a change in the amino acid sequence of the protein.

Silent sites may not be entirely selectively neutral. Some DNA sequences are involved with regulation of genes, changes in these sites may be deleterious. Likewise, although several codons code for a single amino acid, an organism may have a preferred codon for each amino acid. This is called codon bias.

If two species shared a recent common ancestor one would expect genetic information, even information such as redundant nucleotides and the position of introns or pseudogenes, to be similar. Both species would have inherited this information from their common ancestor.

The degree of similarity in nucleotide sequence is a function of divergence time. If two populations had recently separated, few differences would have built up between them. If they separated long ago, each population would have evolved numerous differences from their common ancestor (and each other). The degree of similarity would also be a function of silent versus replacement sites. Li and Graur, in their molecular evolution text, give the rates of evolution for silent vs. replacement rates. The rates were estimated from sequence comparisons of 30 genes from humans and rodents, which diverged about 80 million years ago. Silent sites evolved at an average rate of 4.61 nucleotide substitution per site per 109 years. Replacement sites evolved much slower at an average rate of 0.85 nucleotide substitutions per site per 109 years.

Groups of related organisms are 'variations on a theme' -- the same set of bones are used to construct all vertebrates. The bones of the human

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E

#199 hahahahaahahahahaahahhahaahahaahaahahahahaahahahahahaahahahahaahah

Copyright © 1996-1997 by Chris Colby
[Last Update: January 7, 1996]

No tengo nada mas que decir.

1 respuesta
Kenderr

#200 ¿y? ¿Hay algo erróneo?

Mira voy a poner artículos sobre neodarwinismo, ya que según el genio de emotional no son cientificos los que han teorizado sobre el la sintesis evolutiva moderna.

Nothing in Biology Makes Sense
Except in the Light of Evolution

http://biologie-lernprogramme.de/daten/programme/js/homologer/daten/lit/Dobzhansky.pdf

Evolution in the Tropics

http://www.uic.edu/labs/igic/courses/BIOS532/Dobzhansky1950.html

Animal species and evolution

http://www.cabdirect.org/abstracts/19640100703.html;jsessionid=28B4051AD60B0F0993133C029157FF94

El gen egoísta

http://bahiapsicosocial.com.ar/biblioteca/Dawkins%20%20Richard%20-%20El%20gen%20egoista.pdf

Disciplining evolutionary biology: Ernst Mayr and the founding of the Society for the Study of Evolution and Evolution (1939-1950)

http://www.jstor.org/discover/10.2307/2409996?uid=3737952&uid=2&uid=4&sid=21102561098807

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E

#201 Si hay algo erroneo?

Que no vivimos en los años 50.

Buenas noches.

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Korth

#202 http://es.wikipedia.org/wiki/Argumento_ad_novitatem

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Kenderr

#203 xDDD esos son sus poderosos argumentos. Algo es falso porque tiene 15 años de antigüedad xD

Resumen final del hilo:

Los vídeos son mierda pura, un vídeo que supuestamente desmonta la evolución no desmonta nada y solo intenta atacar mal una teoría obsoleta de hace 150 años.

E

Mi resumen final

15 y 60 años no es mucho tiempo. La tecnologia en ese intervalo se estanca y no progresa. Eso dicen algunos iluminados.

Y ademas no defiendo el darwinismo, pero si el neodarwinismo!!! Uy cuidado que van a ser diferentes y todo cuando este ultimo solo añade cosas, no las cambia.

Ahora deberan de llamarse ultraneodarwinismo dadas las nuevas tecnologias y el trabajo de muchos cientificos en bioquimica.

Tienen que actualizarse y agarrarse, que ya han quedado obsoletos.

Y quien es el magufo ahora?

hahaahahahahahaha

1 1 respuesta
TH3B1GB0SS

Emotional una curiosidad ¿ nunca han ido a por ti los sionistas por desmontarles el chiringuito diciendo la verdad?

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LzO

antes de entrar al hilo ya sabia quien era el autor, macho que enfermedad.

opino que los illuminatis son los padres.

E

#206 En un foro de videojuegos es dificil.

Kenderr

#205 Evidentemente tú eres el magufo, tú eres el que primero dice que hay secretos ocultos por los illuminati y ahora ya rectificas y pones información de dominio publico.

Dime que esta mal de lo expuesto, si tanto dices que ha avanzado ¿Que ha cambiado? ¿Qué esta obsoleto?

Siguiendo tú lógica, el teorema de Pitagoras es erróneo puesto que tiene 2500 años y en ese tiempo la tecnología ha avanzado muchísimo.

Para poder decir que esta obsoleta, tendrás que decir que tiene de obsoleto.

Desconoces tanto de ciencia que es imposible intentar explicarte nada, una teoría se va desarrollando, no es algo inmutable. La teoría sintética va desarrollandose y cada investigador aporta algo, por eso es multidisciplinar y por eso tiene tanto exito. No es algo que dijo un fulano y listo, son decenas de investigadores dando su opinión.

¿Qué hay científicos en contra? Claro, hay varias teorías más. Es más, ni a mi me gusta, prefiero la evo devo+equilibrio puntuado.

Lo más claro del hilo es que confundes la teoría de Darwin con la teoría sintética (Neodarwinismo)

Coges un muro de texto y lo pegas sin siquiera leer lo que has puesto.

Desconoces todo sobre la teoría sintética.

No sabes como funciona el método científico o que es la ciencia.

1 respuesta
E

#209 No te voy a dar otra oportunidad. Lo siento.

Para todo lo demas #196 epoca actual.

Comparar el teorema de Pitagoras con el neodarwinismo. Hasta donde ha llegado el magufo xd

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