O desenvolvimento põe um fim à evolução das formas infinitas?

domingo, outubro 26, 2008

Interessante artigo para ser lido cum granum salis considerando-se o presente status epistêmico da atual teoria geral da evolução: transição paradigmática. PDF gratuito. Sorry, periferia, mas está em inglês.

An End to Endless Forms: Epistasis, Phenotype Distribution Bias, and Nonuniform Evolution

Elhanan Borenstein1,2*, David C. Krakauer2

1 Department of Biological Sciences, Stanford University, Stanford, California, United States of America, 2 Santa Fe Institute, Santa Fe, New Mexico, United States of America


Studies of the evolution of development characterize the way in which gene regulatory dynamics during ontogeny constructs and channels phenotypic variation. These studies have identified a number of evolutionary regularities: (1) phenotypes occupy only a small subspace of possible phenotypes, (2) the influence of mutation is not uniform and is often canalized, and (3) a great deal of morphological variation evolved early in the history of multicellular life. An important implication of these studies is that diversity is largely the outcome of the evolution of gene regulation rather than the emergence of new, structural genes. Using a simple model that considers a generic property of developmental maps—the interaction between multiple genetic elements and the nonlinearity of gene interaction in shaping phenotypic traits—we are able to recover many of these empirical regularities. We show that visible phenotypes represent only a small fraction of possibilities. Epistasis ensures that phenotypes are highly clustered in morphospace and that the most frequent phenotypes are the most similar. We perform phylogenetic analyses on an evolving, developmental model and find that species become more alike through time, whereas higher-level grades have a tendency to diverge. Ancestral phenotypes, produced by early developmental programs with a low level of gene interaction, are found to span a significantly greater volume of the total phenotypic space than derived taxa. We suggest that early and late evolution have a different character that we classify into micro- and macroevolutionary configurations. These findings complement the view of development as a key component in the production of endless forms and highlight the crucial role of development in constraining biotic diversity and evolutionary trajectories.

Author summary

At the very end of his On the Origin of Species, Charles Darwin wrote, “from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” Nature truly displays a bewildering variety of shapes and forms. Yet, with all its magnificence, this diversity still represents only a tiny fraction of the endless “space” of possibilities; research on the evolution of development has revealed that observed common morphologies and body plans (or, more generally, phenotypes) occupy only small, dense patches in the abstract phenotypic space. In this paper, we introduce a simple model of evolving gene regulation and show that these empirically identified patterns can be attributed, at least in part, to interaction between genes (epistasis) in the developmental network. Our model further predicts that early developmental programs with low levels of interaction would span most of the variation found in extant species. The theory presented in our paper complements the view of development as a key component in the production of endless forms and highlights the crucial role of development in constraining (as well as generating) biotic diversity.