A seleção natural cada vez mais enfraquecida como mecanismo evolutivo

quarta-feira, janeiro 28, 2009

Eu não sei o que o Daniel Dennett vai fazer com a declaração dele de louvaminhice, beija-mão e beija-pé de Darwin que ele foi "o homem que teve a maior idéia que toda a humanidade já teve" - a evolução através da seleção natural. Não é isso que os cientistas encontram em suas pesquisas.

Eis aqui mais uma que enfraquece cada vez mais a seleção natural como mecanismo evolutivo.

Alô MEC/SEMTEC/PNLEM: Como é que vai ficar a abordagem nos livros didáticos de Biologia do ensino médio sobre o papel da seleção natural na evolução? Vai ficar como está? Se ficar, é desonestidade acadêmica e descompasso com a verdade das evidências que as pesquisas estão revelando, e flagrante violação da cidadania dos alunos terem acesso à informação científica objetiva e atualizada.

Olha que o neodarwinismo é uma teoria morta desde 1980 (segundo Stephen Jay Gould), mas os autores desses livros teimam manter este morto-vivo teórico favorecendo um naturalismo filosófico em detrimento da educação científica.

Fui, tchê, nem sei por que pensando que é melhor o Dennett enfiar a viola dele no saco...


Natural Selection Not The Only Process That Drives Evolution?

ScienceDaily (Jan. 28, 2009) — Why have some of our genes evolved rapidly? It is widely believed that Darwinian natural selection is responsible, but research led by a group at Uppsala University, suggests that a separate neutral (nonadaptive) process has made a significant contribution to human evolution.

Their results have been published January 27 in the journal PLoS Biology.
The researchers identified fast evolving human genes by comparing our genome with those of other primates. However, surprisingly, the patterns of molecular evolution in many of the genes they found did not contain signals of natural selection.

Instead, their evidence suggests that a separate process known as BGC (biased gene conversion) has speeded up the rate of evolution in certain genes. This process increases the rate at which certain mutations spread through a population, regardless of whether they are beneficial or harmful.

"The research not only increases our understanding of human evolution, but also suggests that many techniques used by evolutionary biologists to detect selection may be flawed," says Matthew Webster of the Department of Medical Biochemistry and Microbiology at Uppsala University.

BGC is thought to be strongest in regions of high recombination, and can cause harmful mutations can spread through populations. The results lead to the provocative hypothesis that, rather than being the result of Darwinian selection for new adaptations, many of the genetic changes leading to human-specific characters may be the result of the fixation of harmful mutations. This contrasts the traditional Darwinistic view that they are the result of natural selection in favour of adaptive mutations.


Hotspots of Biased Nucleotide Substitutions in Human Genes

Jonas Berglund1, Katherine S. Pollard2, Matthew T. Webster1*

1 Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden, 2 Gladstone Institutes, University of California, San Francisco, California, United States of America.

Genes that have experienced accelerated evolutionary rates on the human lineage during recent evolution are candidates for involvement in human-specific adaptations.
To determine the forces that cause increased evolutionary rates in certain genes, we analyzed alignments of 10,238 human genes to their orthologues in chimpanzee and macaque. Using a likelihood ratio test, we identified protein-coding sequences with an accelerated rate of base substitutions along the human lineage. Exons evolving at a fast rate in humans have a significant tendency to contain clusters of AT-to-GC (weak-to-strong) biased substitutions. This pattern is also observed in noncoding sequence flanking rapidly evolving exons. Accelerated exons occur in regions with elevated male recombination rates and exhibit an excess of nonsynonymous substitutions relative to the genomic average. We next analyzed genes with significantly elevated ratios of nonsynonymous to synonymous rates of base substitution (dN/dS) along the human lineage, and those with an excess of amino acid replacement substitutions relative to human polymorphism. These genes also show evidence of clusters of weak-to-strong biased substitutions. These findings indicate that a recombination-associated process, such as biased gene conversion (BGC), is driving fixation of GC alleles in the human genome. This process can lead to accelerated evolution in coding sequences and excess amino acid replacement substitutions, thereby generating significant results for tests of positive selection.

Funding. JB and MTW were funded by The Swedish Research Council and Erik-Philip Sörensens Stiftelse. KSP was supported by National Institutes of Health (NIGMS) grant #GM82901-01A1. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests. The authors have declared that no competing interests exist.
Academic Editor: Laurence D. Hurst, University of Bath, United Kingdom.

Citation: Berglund J, Pollard KS, Webster MT (2009) Hotspots of Biased Nucleotide Substitutions in Human Genes. PLoS Biol 7(1): e1000026 doi:10.1371/journal.pbio.1000026

Received: June 18, 2008; Accepted: December 11, 2008; Published: January 27, 2009

Copyright: © 2009 Berglund et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Abbreviations: BGC, biased gene conversion; FET, Fisher's exact test; GO, gene ontology; HAR, human-accelerated region; LRT, likelihood ratio test; MK test, McDonald-Kreitman test; ML, maximum likelihood; PAR, pseudoautosomal region; W→S, weak-to-strong

* To whom correspondence should be addressed. E-mail: matthew.webster@imbim.uu.se
Journal reference:

1. Berglund J, Pollard KS, Webster MT. Hotspots of Biased Nucleotide Substitutions in Human Genes. PLoS Biology, 2009; 7 (1) PDF gratuito aqui.