Excremento prehistórico permite rastrear la evolución del ser humano

Científicos de la Universidad de Massachusetts utilizan residuos de heces fecales para estudiar los movimientos de los ancestros del ser humano, por ejemplo de poblaciones de hace 7300 años, en latitudes tan altas como el círculo Ártico de Noruega, en las islas Lofoten.

Antes, los marcadores para rastrear la actividad humana habían sido los restos de carbón de las primeras fogatas, o el polen de las plantas que cultivaban. Afortunadamente, encontraron que los componentes del excremento emiten una señal muy fuerte.

Descubrieron que el coprostanol, un producto de la digestión del colesterol en el sistema humano, es un marcador increíblemente certero. Por ejemplo, encontraron una relación con los cambios climáticos de esas épocas, entre los años 2,040 y 1,900  a.C, y después alrededor del año 1705 a.C, cuando hubo un declive en la actividad humana y en su población.

“Esta área se encuentra en el límite norte de posibilidades de agricultura. Las más ligeras variaciones en las temperaturas de las estaciones afectarían enormemente a las poblaciones”, dice el investigador Robert D’Anjou.

Por otro lado, cuando hubo tiempos de prosperidad, “encontramos un punto alto de residuos fecales, justo cuando hubo un aumento dramático de fuegos en el área, asociados con la agricultura de tala y quema”, afirma D’Anjou

Se espera que éste método se utilice para complementar la información que no se tiene segura sobre la actividad humana. “Es sólo otra cosa que deja huella en el medio ambiente”, dice D’Anjou, “y las cosas buenas pueden venir de los lugares más inesperados”.

[BBC]

Scientists Discover Children’s Cells Living in Mothers’ Brains The connection between mother and child is ever deeper than thought

By Robert Martone

The link between a mother and child is profound, and new research suggests a physical connection even deeper than anyone thought. The profound psychological and physical bonds shared by the mother and her child begin during gestation when the mother is everything for the developing fetus, supplying warmth and sustenance, while her heartbeat provides a soothing constant rhythm.
The physical connection between mother and fetus is provided by the placenta, an organ, built of cells from both the mother and fetus, which serves as a conduit for the exchange of nutrients, gasses, and wastes. Cells may migrate through the placenta between the mother and the fetus, taking up residence in many organs of the body including the lung, thyroid muscle, liver, heart, kidney and skin. These may have a broad range of impacts, from tissue repair and cancer prevention to sparking immune disorders.
It is remarkable that it is so common for cells from one individual to integrate into the tissues of another distinct person. We are accustomed to thinking of ourselves as singular autonomous individuals, and these foreign cells seem to belie that notion, and suggest that most people carry remnants of other individuals. As remarkable as this may be, stunning results from a new study show that cells from other individuals are also found in the brain. In this study, male cells were found in the brains of women and had been living there, in some cases, for several decades. What impact they may have had is now only a guess, but this study revealed that these cells were less common in the brains of women who had Alzheimer’s disease, suggesting they may be related to the health of the brain.
We all consider our bodies to be our own unique being, so the notion that we may harbor cells from other people in our bodies seems strange. Even stranger is the thought that, although we certainly consider our actions and decisions as originating in the activity of our own individual brains, cells from other individuals are living and functioning in that complex structure. However, the mixing of cells from genetically distinct individuals is not at all uncommon. This condition is called chimerism after the fire-breathing Chimera from Greek mythology, a creature that was part serpent part lion and part goat. Naturally occurring chimeras are far less ominous though, and include such creatures as the slime mold and corals.
 Microchimerism is the persistent presence of a few genetically distinct cells in an organism. This was first noticed in humans many years ago when cells containing the male “Y” chromosome were found circulating in the blood of women after pregnancy. Since these cells are genetically male, they could not have been the women’s own, but most likely came from their babies during gestation.
In this new study, scientists observed that microchimeric cells are not only found circulating in the blood, they are also embedded in the brain. They examined the brains of deceased women for the presence of cells containing the male “Y” chromosome. They found such cells in more than 60 percent of the brains and in multiple brain regions. Since Alzheimer’s disease is more common in women who have had multiple pregnancies, they suspected that the number of fetal cells would be greater in women with AD compared to those who had no evidence for neurological disease. The results were precisely the opposite: there were fewer fetal-derived cells in women with Alzheimer’s. The reasons are unclear.
Microchimerism most commonly results from the exchange of cells across the placenta during pregnancy, however there is also evidence that cells may be transferred from mother to infant through nursing. In addition to exchange between mother and fetus, there may be exchange of cells between twins in utero, and there is also the possibility that cells from an older sibling residing in the mother may find their way back across the placenta to a younger sibling during the latter’s gestation. Women may have microchimeric cells both from their mother as well as from their own pregnancies, and there is even evidence for competition between cells from grandmother and infant within the mother.

Why Is it Impossible to Stop Thinking, to Render the Mind a Complete Blank?

Barry Gordon, professor of neurology and cognitive science at the Johns Hopkins University School of Medicine, replies:
Forgive your mind this minor annoyance because it has worked to save your life—or more accurately, the lives of your ancestors. Most likely you have not needed to worry whether the rustling in the underbrush is a rabbit or a leopard, or had to identify the best escape route on a walk by the lake, or to wonder whether the funny pattern in the grass is a snake or dead branch. Yet these were life-or-death decisions to our ancestors. Optimal moment-to-moment readiness requires a brain that is working constantly, an effort that takes a great deal of energy. (To put this in context, the modern human brain is only 2 percent of our body weight, but it uses 20 percent of our resting energy.) Such an energy-hungry brain, one that is constantly seeking clues, connections and mechanisms, is only possible with a mammalian metabolism tuned to a constant high rate.
Constant thinking is what propelled us from being a favorite food on the savanna—and a species that nearly went extinct—to becoming the most accomplished life-form on this planet. Even in the modern world, our mind always churns to find hazards and opportunities in the data we derive from our surroundings, somewhat like a search engine server. Our brain goes one step further, however, by also thinking proactively, a task that takes even more mental processing.
So even though most of us no longer worry about leopards in the grass, we do encounter new dangers and opportunities: employment, interest rates, “70 percent off” sales and swindlers offering $20 million for just a small investment on our part. Our primate heritage brought us another benefit: the ability to navigate a social system. As social animals, we must keep track of who's on top and who's not and who might help us and who might hurt us. To learn and understand this information, our mind is constantly calculating “what if?” scenarios. What do I have to do to advance in the workplace or social or financial hierarchy? What is the danger here? The opportunity?
For these reasons, we benefit from having a brain that works around the clock, even if it means dealing with intrusive thoughts from time to time.

This article was originally published with the title Ask the Brains.

El uso de metáforas por parte de niños avala el carácter “relativamente cultural” del conocimiento humano

Que los niños de edades más tempranas construyan y entiendan en general metáforas denominadas “universales” o “casi universales” (utilizadas en todas o casi todas las culturas) y luego desarrollen las “específicamente culturales” (propias de algunas sociedades) indica que el conocimiento humano se construye de forma universal, pero también está condicionado culturalmente. Ésta es la conclusión de Marisol Velasco, filóloga de la Universidad de Valladolid.

Actualmente persiste el debate científico sobre si las metáforas son exclusivamente universales o culturales, es decir, si se construyen e interpretan del mismo modo por todas las personas, o si su producción e interpretación está condicionada culturalmente. Existe una “tercera alternativa” que propone la existencia de “una base universal sobre la que actúa la cultura”, y la forma en que los niños utilizan las metáforas la avala, explica a SINC la científica, que ha participado en el I Encuentro Internacional sobre investigación en adquisición del lenguaje de la Universidad de Valladolid.
Hasta los cuatro años, los niños describen los objetos con metáforas basadas en las percepciones sensoriales como el color, el tamaño o la forma, con metáforas basadas en el movimiento, mediante metáforas sinestésicas (utilizando un sentido por otro), o caracterizando las cosas como personas (metáforas fisionómicas), según certifican múltiples estudios. En ellos, los niños dicen que una piruleta de cereza es una sartén (similitud de forma) o sangre (similitud de color), que el movimiento de un tapón al desenroscarse es como el de una bailarina, afirman con los ojos tapados que una lija, áspera para un adulto, es clara u oscura o se refieren a la foto de una galleta salada como una sonrisa humana (similitud de forma).
Una metáfora perceptual como es asociar el cariño al calor puede ser una metáfora extendida por todo el planeta porque “un niño, cuando lo abrazan, siente calor y al principio no diferencia ambos conceptos”, ejemplifica la investigadora.
Desde los cuatro años, los niños desarrollan años, los niños desarrollan metáforas más abstractas y de carácter más cultural (metáforas de tipo físico-psicológico y taxonómicas), construidas sobre las universales pero que varían según la cultura, como asociar el enfado a sentir presión dentro del propio cuerpo (“explotar”), una unión típica de la población norteamericana pero que se ha extendido a niños de otros países a través de los cómics, o al modo en que la energía fluye a través del cuerpo (China) o al propósito de ocultar o no la verdadera intención (Japón).
Sería interesante investigar cómo los niños bilingües adquieren los conceptos metafóricos (verbales y no verbales), aspectos muy difíciles para el aprendizaje de idiomas, y cómo cruzan las metáforas culturales a partir de los cuatro o cinco años, cuando se empieza a distinguir que diferentes conceptos y la forma en que se expresan “pertenecen a un idioma y cultura determinados”, propone la investigadora.

Referencias bibliográficas:
J.A. Seitz, “The neural, evolutionary, developmental, and bodily basis of metaphor”, New Ideas in Psychology, 23, 74-95 (2005).
Z. Kövecses, Metaphor in culture. Universality and variation. Cambridge: Cambridge University Press (2005).
J.A. Seitz, “The biological and bodily basis of metaphor: a twostage theory of metaphor development”, Journal of Genetic Psychology. Disponible en http://www.york.cuny.edu/~seitz/bio.html (2002).