La evolución de los peces con mandíbulas
Humans Were Already Recycling 13,000 Years Ago, Burnt Artifacts Show
The recycling of stone tools during Prehistoric times has hardly been dealt with due to the difficulties in verifying such practices in archaeological records. Nonetheless, it is possible to find some evidence, as demonstrated in a study published in the ‘Journal of Archaeological Science’.
“In order to identify the recycling, it is necessary to differentiate the two stages of the manipulation sequence of an object: the moment before it is altered and the moment after. The two are separated by an interval in which the artefact has undergone some form of alteration. This is the first time a systematic study of this type has been performed,” as explained to SINC by Manuel Vaquero, researcher at the Universitat Rovira i Virgili.
The archaeologists found a high percentage of burnt remains in the Molí del Salt site (Tarragona), which date back to the end of the Upper Palaeolithic Age some 13,000 years ago. The expert ensures that “we chose these burnt artefacts because they can tell us in a very simple way whether they have been modified after being exposed to fire.”
The results indicate that the recycling of tools was normal during the Upper Palaeolithic Age. However, this practice is not documented in the same way as other types of artefacts. The use of recycled tools was more common for domestic activities and seems to be associated with immediate needs.
Recycling domestic tools
Recycling is linked to expedited behaviour, which means simply shaped and quickly available tools as and when the need arises. Tools used for hunting, like projectile points for instance, were almost never made from recycled artefacts. In contrast, double artefacts (those that combine two tools within the same item) were recycled more often.
“This indicates that a large part of these tools were not conceived from the outset as double artefacts but a single tool was made first and a second was added later when the artefact was recycled,” outlines the researcher. The history of the artefacts and the sequence of changes that they have undergone over time are fundamental in understanding their final morphology.
According to Vaquero, “in terms of the objects, this is mostly important from a cultural value point of view, especially in periods like the Upper Palaeolithic Age, in which it is thought that the sharper the object the sharper the mind.”
Sustainable practices with natural resources
Recycling could have been determinant in hunter-gatherer populations during the Palaeolithic Age if we consider the behaviour of current indigenous populations nowadays.“It bears economic importance too, since it would have increased the availability of lithic resources, especially during times of scarcity. In addition, it is a relevant factor for interpreting sites because they become not just places to live but also places of resource provision,” states the researcher.
Reusing resources meant that these humans did not have to move around to find raw materials to make their tools, a task that could have taken them far away from camp. “They would simply take an artefact abandoned by those groups who previously inhabited the site.”
Vaquero and the team believe that this practice needs to be borne in mind when analysing the site. “Those populating these areas could have moved objects from where they were originally located. They even could have dug up or removed sediments in search of tools,” highlights the researcher.
Source:
http://www.sciencedaily.com/releases/2012/09/120920082536.htm
Competición y Evolución
La competitividad entre especies puede ser feroz, sobre todo si dos especies compiten por la misma fuente de alimentos y el mismo espacio. Si dos especies se enfrentan bajo esas circunstancias una de las dos está condenada a la extinción. Al menos eso es lo que dice la teoría evolutiva tradicional introducida por Charles Darwin en el siglo XIX. Según Darwin, cuanto más emparentadas estén dos especies más competirán entre ellas. Después de todo, las especies más emparentadas son más propensas a depender del mismo hábitat y comida, por lo que compiten por los mismos recursos.
En un ecosistema grande hay muchos factores que nos pueden confundir y el trabajo de campo puede verse confundido por muchos factores. Dos especies pueden estar emparentadas, pero están rodeadas de muchas otras que coexisten con ellas. Así por ejemplo, un depredador puede entrar en la relación y eliminar a una de las especies de la ecuación. Así que cuanto más simple y pequeño es un ecosistema mejor es a la hora de estudiar estos aspectos.
No es fácil demostrar los distintos aspectos de las teorías que tratan de explicar el hecho evolutivo. Las generaciones se suceden demasiado lentamente y no podemos ver cómo se comporta la evolución a no se que esperemos mucho tiempo. Pero los microorganismos pueden servirnos de ayuda ya que producen una nueva generación cada poco tiempo. Basta ponerlos sobre unas placas de Petri y ver qué pasa sin que nos muramos de viejos.
Ahora, Lin Jiang, del Instituto Tecnológico de Georgia en Atlanta ha realizado un experimento de este tipo para comprobar si la hipótesis de Darwin sobre la competitividad entre especies emparentadas es cierta. Como ecosistema sencillo escogió precisamente cultivos de microorganismos sencillos, concretamente protozoos entre los que había paramecios. Estos microorganismos viven de forma natural en las aguas estancadas y se alimentan de bacterias.
Jiang y sus colaboradores escogieron 10 especies distintas de protistas, algunas estaban emparentadas entre sí estrechamente, mientras que otras eran parientes lejanos. Las emparejaron en las 45 combinaciones posibles y se les puso en sus respectivos contenedores con agua y nutrientes. A estos ecosistemas artificiales se les suele llamar microcosmos.
Después estudiaron durante 10 semanas estos cultivos, tomando muestras de cada uno de los contenedores cada semana.
En ese tiempo fueron analizando la relación entre las poblaciones de las dos especies de cada caso para ver si había un dominio de una especie sobre la otra. Resultó que al final del experimento la mitad de los microcosmos contenían sólo una especie de protista.
El análisis comparativo entre el resultado y lo predicho por la teoría evolutiva según el grado de parentesco dio como resultado un fuerte apoyo a la hipótesis de Darwin. Cuanto más emparentadas estaban las dos especies más fácil que al final sólo quedara una de ellas. Cuanto más alejadas estaban desde el punto de vista genético más fácil que se mantuvieran poblaciones estables de ambas especies.
Aunque los ecólogos se han basado durante 150 años en esta hipótesis, hasta ahora no se había comprobado experimentalmente de esta manera. El estudio de Jiang es el primero en ponerla a prueba de un modo controlado en el laboratorio.
El trabajo además puede ayudar de un modo práctico. Comprender el modo en el que las especies compiten entre sí es importante a la hora de aprender a restaurar hábitats, evitar las especies invasoras, mantener los ecosistemas naturales y aumentar la diversidad de los organismos que viven en ellos.
La pregunta es si esto se puede mantener en otros grupos de organismos distintos a los microbios. Eso es algo que habrá que comprobar, pero probablemente se mantenga la hipótesis de Darwin.
How Organisms Evolve New Functions: Evolution Is as Complicated as 1-2-3
The results, published in the current issue of Nature, are revealed through an in-depth, genomics-based analysis that decodes how E. coli bacteria figured out how to supplement a traditional diet of glucose with an extra course of citrate.
"It's pretty nifty to see a new biological function evolve," said Zachary Blount, postdoctoral researcher in MSU's BEACON Center for the Study of Evolution in Action. "The first citrate-eaters were just barely able to grow on the citrate, but they got much better over time. We wanted to understand the changes that allowed the bacteria to evolve this new ability. We were lucky to have a system that allowed us to do so."
Normal E. coli can't digest citrate when oxygen is present. In fact, it's a distinct hallmark of E. coli. They can't eat citrate because E. coli don't express the right protein to absorb citrate molecules.
To decipher the responsible mutations, Blount worked with Richard Lenski, MSU Hannah Distinguished Professor of Microbiology and Molecular Genetics. Lenski's long-term experiment, cultivating cultures of fast-growing E. coli, was launched in 1988 and has allowed him and his teammates to study more than more than 56,000 generations of bacterial evolution.
The experiment demonstrates natural selection at work. And because samples are frozen and available for later study, when something new emerges scientists can go back to earlier generations to look for the steps that happened along the way.
"We first saw the citrate-using bacteria around 33,000 generations," Lenski explained. "But Zack was able to show that some of the important mutations had already occurred before then by replaying evolution from different intermediate stages. He showed you could re-evolve the citrate-eaters, but only after some of the other pieces of the puzzle were in place."
In the Nature paper, Blount and his teammates analyzed 29 genomes from different generations to find the mutational pieces of the puzzle. They uncovered a three-step process in which the bacteria developed this new ability.
The first stage was potentiation, when the E. coli accumulated at least two mutations that set the stage for later events. The second step, actualization, is when the bacteria first began eating citrate, but only just barely nibbling at it. The final stage, refinement, involved mutations that greatly improved the initially weak function. This allowed the citrate eaters to wolf down their new food source and to become dominant in the population.
"We were particularly excited about the actualization stage," Blount said. "The actual mutation involved is quite complex. It re-arranged part of the bacteria's DNA, making a new regulatory module that had not existed before. This new module causes the production of a protein that allows the bacteria to bring citrate into the cell when oxygen is present. That is a new trick for E. coli."
The change was far from normal, Lenski said.
"It wasn't a typical mutation at all, where just one base-pair, one letter, in the genome is changed," he said. "Instead, part of the genome was copied so that two chunks of DNA were stitched together in a new way. One chunk encoded a protein to get citrate into the cell, and the other chunk caused that protein to be expressed."
Additional co-authors include Jeff Barrick, University of Texas, and Carla Davidson, University of Calgary.
The research was funded in part by the National Science Foundation.
Evolución por Carl Sagan
Explicación de Carl Sagan sobre la evolución de la vida de las especies, una explicación concreta y acertada, un video imperdible de un grán científico.
¿Cómo surgió la vida en nuestro planeta?
En este especial queda una duda... como surgió la vida en la tierra, algo de lo que la iglesia y la ciencia debaten, he aquí las respuestas científicas.
Skilled Hunters 300,000 Years Ago
Archeologists from the University of Tübingen have found eight extremely well-preserved spears -- an astonishing 300,000 years old, making them the oldest known weapons anywhere. The spears and other artifacts as well as animal remains found at the site demonstrate that their users were highly skilled craftsmen and hunters, well adapted to their environment -- with a capacity for abstract thought and complex planning comparable to our own. It is likely that they were members of the species Homo heidelbergensis, although no human remains have yet been found at the site.
The project is headed by Prof. Nicholas Conard and the excavations are supervised by Dr. Jordi Serangeli, both from the University of Tübingen's Institute of Prehistory, which has been supporting the local authority's excavation in an open-cast brown coal mine in Schöningen since 2008. They are applying skills from several disciplines at this uniquely well-preserved site find out more about how humans lived in the environment of 300,000 years ago.
The bones of large mammals -- elephants, rhinoceroses, horses and lions -- as well as the remains of amphibians, reptiles, shells and even beetles have been preserved in the brown coal. Pines, firs, and black alder trees are preserved complete with pine cones, as have the leaves, pollen and seeds of surrounding flora.
Until the mining started 30 years ago, these finds were below the water table. The archeologists say they are now carrying out "underwater archaeology without the water." Work continues almost all year round, and every day there is something new to document and recover.
Some of the most important finds of the past three years have been remains of a water buffalo in the context of human habitation, an almost completely preserved aurochs (one of the oldest in central Europe), and several concentrations of stone artifacts, bones and wood. They allow the scientists to examine an entire landscape instead of just one site. That makes Schöningen an exciting location and global reference point not just for archaeology, but also for quaternary ecology and climate research. A research center and museum, the "Paläon," is to be opened in 2013 to to provide information to the public about the work going on in Schöningen.
Source:
http://www.sciencedaily.com/releases/2012/09/120917085535.htm
