Molecular Evolution Proven

reposted from bay of fundie

Molecular Evolution Proven

August 29th, 2007

Michael Behe is an especially dangerous creationist, because he isn’t the strident, shrill looney that you typically see on that side of the fence. His arguments actually sound plausible to many people, even those who reject other creationist claims as downright absurd.

I’m currently reading Darwin’s Black Box (I’ll eventually post a review). In there, he points out that there is ample evidence for the evolution of large structures, such as legs and ribs.

However, he claims there is no evidence for evolution on the molecular scale. He has a point here. Molecules typically don’t leave fossils. He especially wants to know how the more complex structures—such a his favorite “whipping boy”, the bacterial flagellum—evolved.

Behe believes in “irreducible complexity”, which is his claim that some molecular machines are so complex that they could not have evolved. He claims that if you remove one piece, the whole thing breaks. Evolution occurs piece by piece; the necessary intermediate structures would not have evolved, since they would not have provided any function.

From there he jumps to the ridiculous conclusion that God must have done it.

Wrong! You Lose!

Well, now Behe has been proven wrong. We now know how molecular evolution occurred in one case, and it works just fine without God.

Science Daily reports:

Scientists have determined for the first time the atomic structure of an ancient protein, revealing in unprecedented detail how genes evolved their functions.

“Never before have we seen so clearly, so far back in time,” said project leader Joe Thornton, an evolutionary biologist at the University of Oregon. “We were able to see the precise mechanisms by which evolution molded a tiny molecular machine at the atomic level, and to reconstruct the order of events by which history unfolded.” [Emphasis added. Flagellate that, Behe!]

What Thornton and his assistant Jamie Bridgham wanted to do was determine how a particular protein, the glucocorticoid receptor (GR), evolved its ability to interact with cortisol (a stress hormone).

They used computational techniques and a large database of modern receptor sequences to determine the ancient GR’s gene sequence from a time just before and just after its specific relationship with cortisol evolved.

So what they’re doing, if I’m interpreting the article correctly, is determining what this protein looked like right before it evolved one particular behavior. In order to conduct the new behavior, what would have to be added or changed to this protein?

Michael Behe would probably allege (if more than one mutation was necessary) that you can’t get there from here.

Now that Thornton and Bridgham have the DNA sequence, they still needed to get a sample of the protein. Remember that DNA is just the blueprint that tells how a protein is to be made. If you want to study the protein, you need to get some of it.

The ancient genes — which existed more than 400 million years ago — were then synthesized, expressed, and their structures determined using X-ray crystallography, a state-of-the art technique that allows scientists to see the atomic architecture of a molecule. The project represents the first time the technique has been applied to an ancient protein.

What that means is that they synthesized the genes, injected it into the DNA of bacteria (I’m guessing on this point, but that’s the usual method), and then let the bacteria produce the protein.

The important thing to know about this step is that proteins get their functionality from their three-dimensional shape. That’s where the X-ray crystallography came in.

The structures allowed the scientists to identify exactly how the new function evolved. They found that just seven historical mutations, when introduced into the ancestral receptor gene in the lab, recapitulated the evolution of GR’s present-day response to cortisol.

This is the part that Michael Behe would find interesting. Note how this new functionality requires seven mutations. Behe would claim that this is irreducibly complex. You need all seven. Take one away, and you’ve got nothing. Or do you?

They were even able to deduce the order in which these changes occurred, because some mutations caused the protein to lose its function entirely if other “permissive” changes, which otherwise had a negligible effect on the protein, were not in place first.

This is important. They were able to deduce the order in which these changes occurred! That’s watching evolution in action. Even though we don’t have a fossil record of this occurring, we now know how this structure had to evolve.

Ah, but what are those “permissive changes” and how did they happen? The permissive changes were random, benign mutations! This is how evolution works. Mutations happen all the time:

1. Some mutations are useful and convey an immediate benefit to the organism, which allows it to better fit its environment. This gives it a survival advantage, so it’s more likely to live long enough to reproduce and pass along the beneficial mutation. Bingo! One small step along the evolutionary path.
2. Some mutations are harmful and either kill the organism outright or reduce its fitfulness in its environment. This mutation is therefore selected against by the environment. This is evolution’s self-correcting mechanism.
3. Many mutations are benign. They have no effect on an organism’s ability to survive. Therefore, they just sit there in the population. As that organism and its descendents reproduce, that benign mutation spreads throughout a subset of the population. Any population is full of countless benign mutations like this. Now if the environment were to change, some of these mutations would, by chance, convey an advantage in this new environment. That’s another way species evolve. But failing that, the mutation just sits there in some members of the population.

The atomic structure revealed exactly how these mutations allowed the new function to evolve. The most radical one remodeled a whole section of the protein, bringing a group of atoms close to the hormone. A second mutation in this repositioned region then created a tight new interaction with cortisol. Other earlier mutations buttressed particular parts of the protein so they could tolerate this eventual remodeling.

One of the collaborators, Eric Ortlund, said:

“We were able to walk through the evolutionary process from the distant past to the present day. Until now, we’ve always had to look at modern proteins and just guess how they evolved.”

It’s that guessing that gave Michael Behe the hook he needed to claim that God did it. Well now we no longer need to guess.

Scientists have shown how one molecular structure evolved. With a lot of hard work, we can probably show how the other structures evolved.

The theory of evolution is yet again triumphant. God, and Michael Behe, need not apply.