segunda-feira, 8 de dezembro de 2014

Mais sobre evolução de proteínas (e, claro, sobre as parvoíces do DI)

Atentem na versão do argumento evolutivo formulado pelo bioquímico Laurence Moran:

Sandwalk: Ann Gauger keeps digging: «Ann Gauger and her creationist collaborator, Doug Axe, have been swapping amino acid residues in one kind of protein hoping to show that they cannot change into another.
I don't ASSUME that evolution occurs, I state that it is a proven fact. It has been shown repeatedly that the frequencies of alleles in a population change over time and that natural selection and random genetic drift are responsible for those changes.
I then go on to say that there is overwhelming evidence to support the idea that genes have evolved in the past over a period of billions of years. This is not an assumption. It is supported by scientific evidence.
Given that evolution occurs, I then go on to outline a scenario for the evolution of two related enzymes with different specificities. In several case those predictions have been proven by reconstructing the ancestral enzyme and showing that it can catalyze a broad range of reactions. I've posted one example of duplicated genes caught in the act of diverging [Evolution of a New Enzyme]. In another case, you have the related enzymes lactate dehydrogenase and malate dehydrogenase that catalyze different reactions but you can convert lactate dehydrogenase to malate dehydrogenase by changing only one amino acid [The Evolution of Enzymes from Promiscuous Precursors].»

Agora, atentem no argumento-espantalho que a criacionista do DI, Ann Gauger apresentou:

«1. Evolution is true. That is, enzymes have evolved new functions by a process of random mutation and natural selection.
2. Modern enzymes can't evolve genuinely new functions by random mutation and natural selection but can only tinker with existing functions.
3. Therefore, ancient enzymes must have been different, capable of carrying out a broad range of enzyme activities.
4. Those enzymes underwent duplication and diverged from one another, becoming specialized.
5. How do we know this happened? Because we now see a broad array of specialized enzymes. Evolution is the explanation.

Ann Gauger thinks this is a flawed argument because it assumes the very thing that one is attempting to prove; namely, evolution.

This begs the question of whether evolution is true. It is a circular argument unsubstantiated by the evidence and unfalsifiable. No one can know what ancient enzymes actually looked like, and whether they really had such broad catalytic specificities.»

Pois... Lá se vai qualquer potencial para credibilidade aos olhos dos medianamente esclarecidos. 

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