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Saturday, July 07, 2007


The basic postulate of Darwin is that natural selection selects effectively small individual differences (of generation in generation), originating in the necessary time, great evolutionary changes. I) The first critics against this theory was constructed on the basis of fossil finding that demonstrated the opposite: instead of continuous progressive changes, the common thing was the emergency of new species through steep especiatives changes (phyletic gradualism or punctuate equilibrium: evolution of species is not given of uniform form, but in periods of fast evolution, deduced by the shortage of intermediate animal forms fossils). When defending his theory, Darwin said that intermediate fossil absence was due to : a) an imperfect fossil registry -intermediate forms- would be in sediments of marine bottoms b) Some organic forms were reasonable to be preserved c) frequently dominant species widely distributed are single recovered, the same that to being found in distant places give the impression of to be created of sudden d) within multiple intermediate gradations, few had undergone the pressure of evolutionary changes. Today, epigenetic amplification (a small change during the morphogénesis: epithelial invaginación or, others, can create great phenotypic changes) and heterocronia (change in the rate of the processes of development of taxon, so that an event that happens before, does later at a different speed in comparison with that same process from development in its predecessor), can explain the macroevolutionary jumps. II) Between 1930-1950, some genetiticists studied the genetic variation, on which the natural selection acts. Unifying paleontological-genetic findings, a new evolutionary vision was forced (modern synthesis), the same one that argued that mutations of the DNA, were the true creative forces of the new adaptive genetic variants, the same ones that with time, will become in common. He was sure that natural selection did not develop, single gave form to new adaptations. For that reason, some present geneticists, have proposed that mutations and not natural selection handle the intimate aspects of the evolution or, at least the main innovatives episodes, like the origin of the greater animals groups. Observation that matters, because as mutations are produced at random (independently of the necessities of the species), they will turn irrelevant many aspects of natural selection. III) The third critic to Darwin’s postulate, come from works in ecology emphasizing the effort of many organisms to construct his own environment. Eric H. Davidson, recently discovered an interactive network of buildings genes in sea urchins and sea star organisms, during their development. The novel thing is that the center of the network was constituted by a nucleus of 5 genes -preserved during 500 million years- with essential interactions for the formation of intestines. When the other genes (environmental genetic surroundings, constructed by the network), were removed, the developing embryo found the way to replace them. However if the nucleus of 5 genes were removed it was impossible the formation of the embryo. It also happens to the termites that build their own environment with masses of earth in hundreds of years in a luck of ecological inheritance to successive generations of thermites. The First cyanobacteria that turned CO2 to O, established a revolution that completely changed the chemistry of oceans and the atmosphere. Most species modifies its environment influencing the selection, that as also affects them, again.

IV) The fourth criticism to modern synthesis (or, NeoDarwinism), happens from the fact that this primarily deals with the transmission of genes from a generation to another, but not of as how the genes produce the bodies. Recent advances in evolutionary Biology development (evo-devo: comparison of the development of different organisms in order to determine its phylogenétic relations), has shown that gene Pax-6 controls the formation of eyes in mice and humans, the gene Nkx2.5, the heart formation and a set of other genes the formation of the nervous system, providing a weapon to investigate the genetics and development mechanisms that influence the evolution of the forms. A barren problem in this area is the knowledge that different morphologic newness that we observed in clades are not always reflected in the genome. Some biologists argue that this could be explained by genetic duplication (fixation of a cellular or biochemical function in a locus, so that duplicated locus be free to perform a new function) or, by changes in genetic regulation (resulting of interaction and rate of activity of genetic networks, with properties different from the operation of individual genes of the network). Of some way, the discovery of the Homeobox genes allowed to evaluate previous things. Changes in the genetic cis-regulatory systems, would be more significant than changes in the number of genes or the function of proteins (Sean B.Carroll, 2000). The evo-devo theory, maintains that combinatory nature of the regulation of the genetic transcription provides a rich substrate for morphologic diversity, in as much the variations in these level, pattern or rate of genetic expression can provide more variation when natural selection acts on them. Ephigenétics changes include modification of genetic material due to reversible methilatión and other chemical alterations (Eva Jablonka and Marion Lamb, 1995), as well as nonprogrammed remodelling of organism by environmental causes, are due to inherent phenotypic plasticity of developing organisms (Mary Jean West-Eberhard,2003). For some authors, the origin of evo-devo as a consolidated disciplines has to do with Biology transformation undergone by developments made in molecular Biology. Also it has contributed the discovery of unexpected similarities in the genetic regulation of phylogenetically related species of which few genetic regulators are implied in the embriológic foundation of all corporal plans (M. Akam, 1989; Holland, 1992, Holland et. al, 1996).

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Blogger Israel Barrantes said...

Le he dado diez vueltas al libro de Jablonka y Lamb que supuestamente ud cita (que por cierto, es del 2005, no de 1995), y no aparece tal concepto de "modification of genetic material due to reversible methilatión" (se escribe methylation). Ni en el capitulo 4, The Epigenetic Inheritance Systems, ni en ninguna otra pagina del libro. Es mas, Jablonka y Lamb aclaran que ellas tratan en el libro solo de la herencia epigenetica y no de epigenetica en si, "which is a much broader topic" (ver pag.395 de la edicion harcover). Notoriamente ud no ha visto este libro. En fin... escribir sobre temas de lo que uno no tiene ni minima idea, hace llorar al Niño Jesús...

Por cierto, tampoco entiendo el proposito de su articulo. Ud no deja su opinion, no analiza el articulo... cual es la intencionalidad, entonces?

Saludos cordiales.

11:13 PM  
Blogger Israel Barrantes said...

Otro si digo: El concepto de "epigenetic amplification" que ud cita (creo que data de Waddington), ya no se usa desde la aparicion de la Epigenetica Moderna, alla por fines de los años 70s cuando se empezaron a describir los fenomenos de imprinting a nivel molecular. Asi que ademas de incorrecto, esta desactualizado.

La enorme cantidad de spelling faults tambien hacen llorar al Niño Jesús. Mejor no complicarse la vida y dejar de hacer el ridiculo, y escribir en castellano, una lengua muy bonita de paso.

1:11 PM  
Anonymous Anonymous said...

La idea básica de las investigaciones relacionadas con evo-devo, no tienen nada que ver con los conceptos parciales y adjetivaciones a los que Usted reiteradamente alude. La idea basica en esta renovada propuesta es lo relacionado con determinismo y/o azar. Algunos proponentes de evo-devo han dejado en claro que los cambios geneticos a nivel molecular tendrian que ver mas con el azar que con la presion de la seleccion natural (Darwin,ver equilibrio punteado). En todo caso esta ultima actuaria sobre lo determinado (primero), por los cambios geneticos. Ese es el asunto de fondo. Si hay determinismo condicionado por las circunstancias, cabe plantear la posibilidad de planes maestros o diseños inteligentes. Si por el contrario, el azar es el agente rector entonces las cosas adquieren un cariz diferente. Relea el articulo y trate de pensar holisticamente. vmm

10:40 AM  

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