miércoles, junio 18, 2008

Evo-Devo: The Good, the Bad, and the Ugly.

THE GOOD: Homology assesment evo-devo, and epigenetic evo-devo. Evo-Devo that works on the pretty empirical task of assessing problematic homologies, with tree-based inferences on the evolution of development, continues to greatly help the reconstruction of the evolutionary history of life on earth. Epigenetic evo-devo's, in turn, understand that developmental biology is not genetics. They have realistically confronted the role of higher level and environmental epigenetic interactions in development, and thus also in the origin of evolutionary novelties. Both of these tend to emphasize how standing developmental mechanisms, and not natural selection alone, are essential to the pathway taken by evolution.

THE BAD: Reductionist "regulatory" evo-devo. Dangerous, because it is is upheld by important figures of evo-devo, presenting itself as a triumph and empirical conclusion. Yes, mutations in cis-regulatory regions are commonplace in evolution, but these people seem to have reductionist difficulties in understanding there is anything more beyond finding such a mutation. The notion that only non-coding "regulatory" sequence changes can produce localized expression (in time or space) simply makes no good developmental sense. As Lillie pointed out, all cells have the same DNA content, including the "regulatory" elements; whether a gene is expressed or not still varies from cell type to cell type depending on something else as well. In other words, Lillie's "paradox" forces the question: "who regulates the regulators"? This question reveals that "regulation" is nothing but a sloppy, semi-nonsensical wastepaper-basket term. Both coding and non-coding sequences can be "regulatory". Even environment can "regulate" gene expression. Genes are expressed differentially in cells, NEVER because of their "regulatory" sequences alone, but ALWAYS including the higher-level and environmental interactions at the cell and tissue level, which explain "Lillies paradox". (again: This is why developmental biology is different from genetics!). Focusing only on one type of mutations (cis-regulatory) is just a re-strengthened version of the old reductionist fallacy that genotype=phenotype. This false equivalence ultimately downplays the role of understanding development, the actual mechanisms that relate genotype to phenotype. Without really introducing developmental mechanisms, no serious challenge is made to the hegemony of population genetics as a way of understanding evolution. Yes: The bad is a traitor of development, for love of genetics. Evo-Devo can now become a mere footnote: The largely uninteresting filling-in of superfluous data on "what the specific mutations were".

THE UGLY. Just plain wrong or artifactual topics, mostly born from the lack of proper integration of different fields of research. Specially silly is the "conflict" between microevolution and macroevolution. Doubtless, the study of microevolution offers many advantages. But this does not mean at all that a macroevolutionary study will not be able to derive sound conclusions: when the evidence is there, there is nothing to say about the micro or macro level in which a question is satisfactorily answered. That comparable experiments can only be tested between closely related species is a myth: gene expression experiments can produce the same phenotypic alteration despite hundreds of millions of years of separation.
This follows in an old lab-bench tradition of being purely "experimental" negating any need to know much about natural history and macroevolution. It also relates to "blind" faith in molecular phylogenies, that is, with little capacity for critically evaluating these studies (such as by morphologica implications). As a result, plain artifacts of the tree become the basis for many weird hypotheses (I have argued before this is happening right now, with new supposed clades such as "urochordates+vertebrates"). Studies continue to emerge where well-established facts of natural history are swept aside in favor of some "groundbreaking hypothesis".
Many Evo-Devos have thought that macroevolution is some kind of truly radical "body plan" change with mechanisms quite different from those observed at a microevolutionary level, appealing to some mysterious happenstance of the past for the origin of phyla or higher "grades". However, Evo-devo's are slowly wisening up to the fact that macro and micro evolutionary change proceeds pretty much in the same way, with the simple fact being that lineages diverging earlier can accumulate greater differences (as pointed out before)

6 comentarios:

Chico dijo...

Apuntas bien la falacia más grande de la malevodevo: presuponer que la variación temporal y espacial de la expresión genica depende de la variación en secuencias cis-reguladoras. Encontro que esto es un sesgo teorico imposto por la idea de que la variación con significado evolutivo hay que ser escrita en el DNA. Es raro porque ellos saben perfectamente que el desarrollo, mismo descrito reducionistamente en el nivel de la regulación de la transcripción, depende de factores trans-reguladores sobre la transcripción, que por su vez depende del contexto y de la historia celular. Además, este tipo de explicación es incompleta mismo se nos restrigisemos al nivel molecular. Ignora la regulación pós-transpripcional; ignora que la disponibilidad de un factor cis en la cromatina (competencia en molecularês) depende de la historia de célula; etc...
El problema es que los malos son muchos y producidos en serie en la industria de la ciencia. Bravos Clint Eastwood son pocos.

Sanders dijo...

afortunadamente aún hay revistas donde se puede publicar algo que no seá del estilo de los malos.

Sanders dijo...

aunque esas revistas también publican bastante "the ugly" jajaja

Chico dijo...

by the way: publicaram o genoma de anfioxo e seguem com urocordado como grupo irmão de vertebrados

Sanders dijo...

chuuuuucha 1090 genes!!
pero igual, no me convencen jejeje ya me explicaré un poco más

Sanders dijo...
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