Darwin Still Rules, but Some Biologists Dream of a Paradigm Shift
By DOUGLAS H. ERWIN
Published: June 26, 2007
Corrections Appended
Is Darwin due for an upgrade? There are growing calls among some evolutionary biologists for just such a revision, although they differ about what form this might take. But those calls could also be exaggerated. There is nothing scientists enjoy more than the prospect of a good paradigm shift.
Paradigm shifts are the stuff of scientific revolutions. They change how we view the world, the sorts of questions that scientists consider worth asking, and even how we do science. The discovery of DNA marked one such shift, the theory of plate tectonics another.
Many scientists suffer from a kind of split personality. We believe that this is the most exciting time to be working while yearning for the excitement of a revolution. What ambitious scientist would not want to be part of a paradigm shift? Not surprisingly, this yearning occasionally manifests itself in proclamations that a revolution is at hand.
To understand the current tumult it helps to understand how our evolutionary framework developed. It was constructed from the 1930s to 1950s by early geneticists, paleontologists and others, who disagreed about the efficacy of natural selection in driving evolutionary change (Darwin’s big idea) and about the nature of the underlying genetic variation upon which natural selection could act. What they came to agree on was called the modern synthesis, and it established an intellectual zeitgeist that continues today, and has been continually adapted, in the best evolutionary fashion, to encompass new discoveries.
That synthesis holds that mutations to DNA create new variants of existing genes within a species. Natural selection, driven by competition for resources, allows the best-adapted individuals to produce the most surviving offspring. So adaptive variants of genes become more common. Although selection is often seen, even by biologists who should know better, as primarily negative, removing poorly adapted individuals, Charles Darwin understood that it was a powerful creative tool.
It is the primary agent in shaping new adaptations. Analytical studies have shown how selection can produce a complex eye from a simple eyespot in just a few hundred thousand years.
In the past few years every element of this paradigm has been attacked. Concerns about the sources of evolutionary innovation and discoveries about how DNA evolves have led some to propose that mutations, not selection, drive much of evolution, or at least the main episodes of innovation, like the origin of major animal groups, including vertebrates.
Comparative studies of development have illuminated how genes operate, and evolve, and this places less emphasis on the gradual accumulation of small genetic changes emphasized by the modern synthesis. Work in ecology has emphasized the role organisms play in building their own environments, and studies of the fossil record raise questions about the role of competition. The last major challenge to the modern synthesis came in the 1970s and 1980s as my paleontological colleagues, including the late Stephen Jay Gould, argued for a hierarchical view of evolution, with selection occurring at many levels, including between species.
Transitions between species documented by the fossil record seemed to be abrupt, perhaps too abrupt to be explained by the modern synthesis. If this were generally true, it could render irrelevant much of natural selection occurring within species, because just as mutations are produced randomly with respect to the needs of a species, with selection shaping these into new adaptations, new species might evolve randomly with species selection shaping them into evolutionary trends. This challenge was greeted with less than fulsome praise by evolutionary biologists studying changes within species. The resulting hubbub has yet to fully die down. But the newer work cuts closer to the core of the modern synthesis, and is potentially more revolutionary, because it addresses the fundamental question of how really new things happen in the history of life. What brought about the origin of animals, or the invasion of land?
The Achilles’ heel of the modern synthesis, as noted by the philosopher Ron Amundson, is that it deals primarily with the transmission of genes from one generation to the next, but not how genes produce bodies. The recent discoveries in the new field of evolutionary developmental biology, or evo-devo, that the gene Pax-6 controls the formation of eyes in mice and humans, Nkx2.5 heart formation, and a suite of other genes the formation of the nervous system, has provided a means to investigate the genetic and developmental mechanisms influencing how the form of organisms has evolved, not just their genes. Perhaps the most exciting area in evolution is in exploring how rewiring the circuitry of genes produces different arthropod appendages, or wingspots on butterflies.
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Douglas H. Erwin is a senior scientist at the National Museum of Natural History at the Smithsonian Institution and a research professor at the Santa Fe Institute
Read more here/Leia mais aqui:
http://www.nytimes.com/2007/06/26/science/26essay.html?_r=0
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NOTA CAUSTICANTE DESTE BLOGGER
Erwin começa perguntando, "Is Darwin due for an upgrade?" [Está na hora de um upgrade em Darwin?] e destaca:
"Há crescente alertas entre alguns biólogos evolucionários por tal revisão, embora eles divirjam sobre qual forma isso deva ter." Ele explica então o que é fundamental na Síntese Moderna Neodarwinista da evolução:
"Aquela síntese defende que [o processo] das mutações ao DNA novas variantes de genes existentes são criadas dentro de uma espécie. A seleção natural, impulsionada pela competição de recursos, permite que os indivíduos melhor adaptados produzam descendência que mais sobrevive. Assim, as variantes adaptarias de genes se tornam mais comuns. Embora a seleção seja frequentemente observada, até por biólogos que deveriam saber melhor, como principalmente negativa, removendo os indivíduos pobremente adaptados, Charles Darwin entendeu que ela era uma poderosa ferramenta criativa."
(Douglas H. Erwin, "Darwin Still Rules, but Some Biologists Dream of a Paradigm Shift," New York Times (June 26, 2007).)
OK, nenhuma novidade aqui. Mas Erwin joga a bomba que a Nomenklatura científica não quer ver debatida nas universidades:
"Nós últimos anos cada elemento deste paradigma tem sido atacado. Preocupações sobre as fontes de inovação evolucionária e descobertas sobre como evolui o DNA tem levado alguns cientistas a propor que as mutações, e não a seleção, é que conduzem o grosso da evolução, ou pelo menos os principais episódios da inovação, como a origem dos principais grupos de animais, inclusive os vertebrados."
Como é que é mesmo, Prof. Dr. Leandro R. Tessler (Unicamp)? "Cada elemento" do paradigma neodarwinista "tem sido atacado"? Erwin, um cientista evolucionista honesto, não está falando de "criacionistas" e nem da turma perversa do Design Inteligente (aprenda Tessler, é assim que se fala e escreve sobre nossa teoria) que o New York Times e a Grande Mídia gosta de abusar, mas está falando claramente de cientistas evolucionistas academicamente honestos e que se encontram na nata da Academia.
Contrariando a Nomenklatura científica, Erwin explica como as falhas fundamentais na Síntese Evolutiva Moderna começaram a aparecer no contexto de justificação teórica:
"As transições entre as espécies documentadas pelo registro fóssil pareciam ser abruptas, talvez abruptas demais para serem explicadas pela Síntese Moderna. Se sido fosse geralmente verdade, isso poderia tornar irrelevante muito da seleção natural ocorrendo dentro das espécies, porque assim como as mutações são produzidas aleatoriamente no que diz respeito às necessidades de uma espécie, com a seleção moldando isso em novas adaptações, novas espécies podem evoluir aleatoriamente com a seleção de espécies moldando-as em tendências evolutivas. Este desafio foi saudado com menos do que louvor pelos biólogos evolucionistas estudando mudanças dentro de uma espécie. A confusão resultante ainda está por desaparecer. Mas, o trabalho mais recente corta bem próximo do fundamento da Síntese Moderna, e é mais potencialmente revolucionário, porque aborda a questão fundamental de como realmente novas coisas acontecem na história da vida. O que provocou a origem dos animais, ou a invasão terrestre."
Traduzindo em miúdos, Tessler, aqui nós temos o exemplo de um evolucionista academicamente honesto reconhecendo que Darwin está de volta à estaca zero quanto a explicação da origem e evolução das espécies.
Sinuca de bico da Nomenklatura científica sobre a falência heurística da teoria da evolução de Darwin: ficar em silêncio, demonizar e perseguir os críticos, ou empurrar com a barriga até 2020...
Pobre ciência!!!
