April 21st, 2006

homuncul

КОСМОЛОГИЯ

Что было до Большого взрыва и откуда взялось время?

Одно время физики надеялись, что квантовая гравитация будет описана с помощью теории суперструн, но недавний кризис суперструнных теорий поколебал эту уверенность. В такой ситуации больше внимания стали привлекать иные подходы к описанию квантовогравитационных явлений, и в частности, петлевая квантовая гравитация

Абэй Аштекар, один из создателей теории петлевой квантовой гравитации, уделяет много времени как популяризации этой конкретной теории, так и квантовой гравитации вообще.
На его сайте можно найти список научно-популярных статей и лекций , адресованных широкой аудитории.


Ли Смолин "Атомы пространства и времени" (SciAm, апрель 2004)
Если удивительная теория петлевой квантовой гравитации верна, то пространство и время, воспринимаемые нами как непрерывные, на самом деле состоят из дискретных частиц.


Space.com: Skulls, Tornadoes and Insects - The Bizarre Sightings of Modern Astronomy
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homuncul

БИОЛОГИЯ

How plastic is the transcriptome? - considerably more than genomes...

Current Biology, April 2006
Evolution: The Plastic Transcriptome

Studies across a wide range of species point to a surprising degree of plasticity in the transcriptional states that organisms can adopt, suggesting that organisms often respond to environmental challenges through wholesale reprogramming of their gene expression.

How plastic is the transcriptome? This is probably not a question that many of us have thought about much; yet it is fundamental to an understanding of how organisms adjust their physiology and behavior to cope with the diverse challenges posed by the environment. The literature on the topic is as yet quite slim, but one profound insight is beginning to emerge, namely that organisms can globally switch transcriptional states. Individuals in either state display considerably more divergent expression profiles than those seen across the geographic range of the species within a given state.

. . . . . . . . . .

The combined message from these diverse studies is that transcriptomes can adopt highly differentiated states involving large percentages of the genes expressed in a particular tissue. It is no longer surprising that single transcription factors can regulate the activity of batteries of hundreds of target genes; after all, this is how development is orchestrated. However, what is important here is that the magnitude and extent of the effects have been found to be large in comparison to genetic differentiation between individuals and even populations.

The relevance to evolutionary biology is that these findings once again remind us to look beneath the surface of the phenotype if we are to understand the forces shaping genetic variation. Much of the classical literature on phenotypic plasticity deals with polyphenism, which is the adoption of qualitatively distinct traits by different individuals of a species, such as winged and wingless castes of ants or horn size in beetles. Now we have a sense that polyphenism may indeed be prevalent at the molecular level across a broad array of organisms....
Widespread plasticity would imply greater potential for the balancing of variation: just as the sexes provide alternate physiological environments, so too should conditions of stress, behavioral caste, or other responses to environmental shifts.



Physiol. Genomics, April 2003
Evolutionary changes in heat-inducible gene expression in lines of E. coli adapted to high temperature


Nature, April 2006
Repeated morphological evolution through cis-regulatory changes in a pleiotropic gene

Repeated evolution of the same morphological trait is quite common, prompting the question whether evolution is constrained to follow certain paths, or whether there are many genetic routes to a phenotype. A study of the male wing pigmentation pattern involved in Drosophila courtship display shows that similar patterns arose independently at least twice and were lost at least five times in related Drosophila species. All these events involved regulatory changes at the yellow pigmentation gene but the two independent gains of wing spots resulted from co-option of different regulatory elements. Evolution went through the gene twice, but took a different route each time.
http://www.nature.com/nature/journal/v440/n7087/edsumm/e060420-13.html
homuncul

БИОЛОГИЯ

Haeckel's drawings: re-examine biogenetic law

Science, 1997
Haeckel's Embryos: Fraud Rediscovered
Using modern techniques, a British researcher has photographed embryos like those pictured in the famous, century-old drawings by Ernst Haeckel--proving that Haeckel's images were falsified. Haeckel once admitted to his peers that he doctored the drawings, but that confession was forgotten.

/

Answers in Genesis: Data manufactured
http://www.answersingenesis.org/creation/v20/i2/fraud.asp


Download original paper (pdf):
Richardson MK Hanken J Gooneratne ML Pieau C Raynaud A Selwood L & Wright GM (1997) There is no highly conserved embryonic stage in the vertebrates: implications for current theories of evolution and development Anat. embryol. 196 91-106.


from "Developmental Biology", chapter 23
Haeckel and the Vertebrate Archetype

paper by Michael Richardson and his colleagues (1997) has corrected a major misunderstanding among developmental biologists and evolutionary biologists which can be traced back to Ernst Haeckel. Haeckel (1874) had claimed that members of all vertebrate classes pass through an identical evolutionarily conserved "phylotypic" stage. Until this new paper appeared, it was assumed that Haeckel was correct and that there was a particular stage of development that was identical in all vertebrates. Only later in development would specific differences appear....
But Haeckel's drawings are wrong. Photographing actual embryos at these stages, Richardson and colleagues show that Haeckel's drawings are oversimplified to the point of obscuring important differences between classes of vertebrates.

On-line Scott F. Gilbert "Developmental Biology"


Stephen Jay Gould:
“We do, I think, have the right to be both astonished and ashamed by the century of mindless recycling that has led to the persistence of these drawings in a large number, if not a majority, of modern textbooks.”
(Stephen Jay Gould, “Abscheulich! Atrocious!” Natural History, March, 2000, p. 45)



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а ведь всего-то надо было просто сфотографировать соответствующие эмбрионы ...Только к 1997 удосужились. И стыдно, похоже, одному только Гоулду....
homuncul

NEUROSCIENCE

is Math hardwired?


The researchers reported in the May 2006 issue of the Public Library of Science Biology that a brain region called the intraparietal sulcus (IPS) is activated when both four-year-olds and adults perceive numerical quantities.

....very little is known about how the mind of a young child becomes so sophisticated, especially for mathematics, over a relatively short period of time.
"Our study suggests that the human brain is prepared for basic mathematics at an early age, and that the same neural circuits that perform basic math at an early age continue to process mathematical information over the whole course of development, into adulthood"

Also, in behavioral studies, the researchers found that the same children could not verbally count to 64, even though they were capable of discriminating such large numbers when presented in a nonsymbolic way.
http://www.eurekalert.org/pub_releases/2006-04/du-nps040406.php



PLoS Biology, May 2006
A Neural Seat for Math?
By four years old, children's brains already selectively respond to nonsymbolic numerical values, suggesting that the neural networks for number processing are established early in life...