sábado, 23 de noviembre de 2013
viernes, 15 de noviembre de 2013
La selección natural darwiniana y su explicación genética actual
Trabajo realizado por:
Nerea R.
Lidia G.
Inmaculada G.
miércoles, 13 de noviembre de 2013
Órganos vestigiales
Un órgano vestigial es un órgano cuya función original se ha perdido durante la evolución. En 1893, Robert Wiedersheim publicó una lista de 86 órganos humanos de los que se desconocía su función. Teorizando que eran vestigios de la evolución, los llamó "vestigiales".
Algunos ejemplos son:
El Coxis
El coxis está situado debajo del hueso sacro, al final de la columna vertebral. Se cree que podría ser un vestigio de un órgano anterior similar a una cola. Quizás hace miles de años tuviera su función en mamíferos cuadrúpedos (se movían a cuatro patas), pero al ser bípedos (a dos patas) este órgano se fue atrofiando, y acabó como órgano vestigial.
Los pezones masculinos
En el hombre los pezones no tienen utilidad práctica, se forman en el feto por la acción de la hormona testosterona, antes de que se produzca la diferenciación de sexos. Cuando comienza la evolución fetal existe un periodo de unas siete semanas contando desde la última menstruación, donde no se puede determinar aún por la anatomía cual será el sexo del feto. Esta etapa es la etapa indiferenciada del desarrollo fetal. Sin embargo, hay ejemplos de machos de la especie humana que han dado el pecho a sus hijos, como Alexander Von Humboldt que refiere de varios casos en Sudamérica, pero la realidad es que los expertos no se ponen de acuerdo. Solo un macho es conocido por, espontáneamente, tener la capacidad de darle el pecho a sus crías: se trata de un murciélago de la fruta, el Dyacopterus spadiceus.
Tercer párpado o membrana nictitante
Es un nexo en común con las aves. Es posible que los primeros mamíferos contaran con esta membrana porque les era útil para lubricar y limpiar el ojo sin perder la visión. Con el tiempo el ser humano fue perdiendo este órgano ya que no le era útil; pero aún queda un pequeño repliegue localizado en la esquina interna del ojo (lagrimal). En la actualidad no se le conoce función alguna y es por esto que se le considera un órgano vestigial.
En la imagen se observa el tercer párpado de un avefría militar (Vanellus miles).
Senos Nasales
Los senos paranasales son, básicamente, bolsas de aire en la cabeza. Según algunos científicos actúan como cámara de resonancia para darle a la voz un tono único o hacen más liviana la estructura ósea del cráneo. Pero estas ventajas, según otros, no compensan por los dolores que provocan y aseguran que en ciertos dinosaurios podría haber sido útil para determinar la estructura de la cabeza.
Fuentes utilizadas:
martes, 12 de noviembre de 2013
Del fijismo al evolucionismo.
Del fijismo al evolucionismo from Nachi-Tocino
Video de lamarkismo:
Hemos encontrado esta animación en el libro de cmc Canarias.
Realizado por: Nazaret Tocino
Ingrid Ramos
Daniela Gómez
Gabriela Honorio
Ingrid Ramos
Daniela Gómez
Gabriela Honorio
lunes, 11 de noviembre de 2013
El origen de la vida en la Tierra
Trabajo realizado por:
Julieta G.
Ana B.
David G.
Salma L.
Este vídeo sacado de YouTube explica brevemente el posible origen de la vida en la Tierra:
domingo, 10 de noviembre de 2013
La formación de la Tierra y la diferenciación en capas.
La formación de la Tierra y diferenciación en capas.
Está basado en la variación de la composición química de los materiales de la Tierra a distintas profundidades. De acuerdo con este criterio se han establecido las siguientes capas: corteza, manto y núcleo.
Realizado por:
Kimberley M.
Carlos M.
Juan Antonio G.
Borja L.
Está basado en la variación de la composición química de los materiales de la Tierra a distintas profundidades. De acuerdo con este criterio se han establecido las siguientes capas: corteza, manto y núcleo.
Se basa en las propiedades físicas de los materiales que constituyen el interior de la Tierra, tales como el comportamiento mecánico y el estado físico. Según este modelo se diferencian las siguientes capas: litosfera, astenosfera, mesosfera y endosfera (núcleo externo y núcleo interno).
Realizado por:
Kimberley M.
Carlos M.
Juan Antonio G.
Borja L.
Carl Sagan
Tomado de Itsfullofstars en Tumblr
Happy Birthday Carl Sagan.
Carl Edward Sagan (November 9, 1934 – December 20, 1996) was an American astronomer, astrophysicist, cosmologist, author, science popularizer and science communicator in astronomy and natural sciences. He spent most of his career as a professor of astronomy at Cornell University where he directed the Laboratory for Planetary Studies. He published more than 600 scientific papers and articles and was author, co-author or editor of more than 20 books. He advocated scientific skeptical inquiry and the scientific method, pioneered exobiology and promoted the Search for Extra-Terrestrial Intelligence (SETI).
We embarked on our journey to the stars with a question first framed in the childhood of our species and in each generation asked anew with undiminished wonder: What are the stars? Exploration is in our nature. We began as wanderers, and we are wanderers still. We have lingered long enough on the shores of the cosmic ocean. We are ready at last to set sail for the stars. -Cosmos
Those worlds in space are as countless as all the grains of sand on all the beaches of the earth. Each of those worlds is as real as ours and every one of them is a succession of incidents, events, occurrences which influence its future. Countless worlds, numberless moments, an immensity of space and time. And our small planet at this moment, here we face a critical branch point in history, what we do with our world, right now, will propagate down through the centuries and powerfully affect the destiny of our descendants, it is well within our power to destroy our civilization and perhaps our species as well. If we capitulate to superstition or greed or stupidity we could plunge our world into a time of darkness deeper than the time between the collapse of classical civilization and the Italian Renaissance. But we are also capable of using our compassion and our intelligence, our technology and our wealth to make an abundant and meaningful life for every inhabitant of this planet. -Journeys in Space and Time, Cosmos
We live in a society exquisitely dependent on science and technology, in which hardly anyone knows anything about science and technology. -“Why We Need To Understand Science” in The Skeptical Inquirer Vol. 14, Issue 3, (Spring 1990)
Every kid starts out as a natural-born scientist, and then we beat it out of them. A few trickle through the system with their wonder and enthusiasm for science intact. -Psychology Today, (01 January 1996)
What an astonishing thing a book is. It’s a flat object made from a tree with flexible parts on which are imprinted lots of funny dark squiggles. But one glance at it and you’re inside the mind of another person, maybe somebody dead for thousands of years. Across the millennia, an author is speaking clearly and silently inside your head, directly to you. Writing is perhaps the greatest of human inventions, binding together people who never knew each other, citizens of distant epochs. Books break the shackles of time. A book is proof that humans are capable of working magic. -The Persistence of Memory, Cosmos
Happy Birthday Carl Sagan.
Carl Edward Sagan (November 9, 1934 – December 20, 1996) was an American astronomer, astrophysicist, cosmologist, author, science popularizer and science communicator in astronomy and natural sciences. He spent most of his career as a professor of astronomy at Cornell University where he directed the Laboratory for Planetary Studies. He published more than 600 scientific papers and articles and was author, co-author or editor of more than 20 books. He advocated scientific skeptical inquiry and the scientific method, pioneered exobiology and promoted the Search for Extra-Terrestrial Intelligence (SETI).
We embarked on our journey to the stars with a question first framed in the childhood of our species and in each generation asked anew with undiminished wonder: What are the stars? Exploration is in our nature. We began as wanderers, and we are wanderers still. We have lingered long enough on the shores of the cosmic ocean. We are ready at last to set sail for the stars. -Cosmos
Those worlds in space are as countless as all the grains of sand on all the beaches of the earth. Each of those worlds is as real as ours and every one of them is a succession of incidents, events, occurrences which influence its future. Countless worlds, numberless moments, an immensity of space and time. And our small planet at this moment, here we face a critical branch point in history, what we do with our world, right now, will propagate down through the centuries and powerfully affect the destiny of our descendants, it is well within our power to destroy our civilization and perhaps our species as well. If we capitulate to superstition or greed or stupidity we could plunge our world into a time of darkness deeper than the time between the collapse of classical civilization and the Italian Renaissance. But we are also capable of using our compassion and our intelligence, our technology and our wealth to make an abundant and meaningful life for every inhabitant of this planet. -Journeys in Space and Time, Cosmos
We live in a society exquisitely dependent on science and technology, in which hardly anyone knows anything about science and technology. -“Why We Need To Understand Science” in The Skeptical Inquirer Vol. 14, Issue 3, (Spring 1990)
Every kid starts out as a natural-born scientist, and then we beat it out of them. A few trickle through the system with their wonder and enthusiasm for science intact. -Psychology Today, (01 January 1996)
What an astonishing thing a book is. It’s a flat object made from a tree with flexible parts on which are imprinted lots of funny dark squiggles. But one glance at it and you’re inside the mind of another person, maybe somebody dead for thousands of years. Across the millennia, an author is speaking clearly and silently inside your head, directly to you. Writing is perhaps the greatest of human inventions, binding together people who never knew each other, citizens of distant epochs. Books break the shackles of time. A book is proof that humans are capable of working magic. -The Persistence of Memory, Cosmos
Suscribirse a:
Entradas (Atom)