When you set a ratchet to tighten a bolt, each turn in the clockwise direction tightens the bolt, but the ratchet will not loosen a bolt when turned counter-clockwise. This concept is often used to describe other processes that only go in one direction and can not be reversed.
It would seem that Behe thinks evolution is like a ratchet. You can degrade genes, but once you lose that function you can’t get it back. This is echoed in his latest essay:
So is this true? I don’t think it is.
Let’s look at tetrapod evolution as an example at the macroscopic level. Fish evolved lungs and limbs, moved onto land, and then lost the adaptations they once had for the aquatic environment their ancestors lived in. So does this mean that tetapods were forever limited to living on land and could never adapt to an aquatic environment after that? Obviously not. Multiple lineages of tetrapods have moved back into aquatic environments, such as whales, crocodiles, and turtles.
We could also look at examples at the molecular level. In one experiment, scientists knocked out the beta-galactosidase gene in E. coli. It forever lost that gene, and according to Behe it could never go back to breaking down lactose. So is that what happened? No. When scientists allowed these E. coli to compete for lactose a new beta-galactosidase gene emerged.
As Behe states, genes can be lost if they aren’t needed. What Behe ignores is the emergence of new genes. There isn’t a ratchet. The process goes in both directions.
These mammals didn’t loose their lungs and evolve gills…
It’s because of this assumed irreversibility (atleast in some cases) that you get “nested” heirarchies in evolutionary trees…
I think you have missed Behe’s point. I understood it as a continuous reduction in the ammount of novelty in the variation that becomes available for selection. Thus curtailing the ability of species to adapt to new environments as they become more and more adapted to a particular environment… that’s how I understood the loss of flexibility comment.
Now obviously this pattern is not seen in the history of life…so I guess Behe is pointing out that variation + selection as a paradigm is insufficient to explain the patterns observed in the history of life.
Let’s assume that @T_aquaticus is getting a little “over general” with his views. I think Behe’s description is enough true that I can agree with this position: as populations adapt to new environments, they tend to lose the genetic traits that made them well adapted to the earlier environment.
We see this happen ALL. THE. TIME. in the fossil record. It’s how evolution works.
So is Behe saying that when it happens… it is because God is not paying attention, or not interested in helping to avoid that?
That’s the real question to be directed at Behe.
And frankly, I’m astounded that I haven’t read of anyone asking Behe this most important of questions!
The point is that they didn’t lose their ability to adapt to aquatic environments. Again, from Behe:
Were tetrapods forever limited to life on land? No.
That’s why I gave the example of the evolved beta-galactosidase gene. We can see right in the lab that evolution increases variation and is the source of flexibility.
You are misrepresenting his view… he explicitly says he is not talking about phenotypic effects of mutations…
. In both my Quarterly Review of Biology paper and Darwin Devolves I counted the sickle cell mutation (a single amino-acid change) of hemoglobin as gain-of-FCT (FCT stands for “Functional-Coded-elemenT), because it resulted in a new protein-protein binding site. As I explained at length in both places, I classified mutations according to their molecular effects — not their phenotypic effects — according to whether they resulted in the gain or loss of such functional coded elements as:
promoters; enhancers; insulators; Shine-Dalgarno sequences; tRNA genes; miRNA genes; protein coding sequences; organellar targeting- or localization signals; intron/extron splice sites; codons specifying the binding site of a protein for another molecule (such as its substrate, another protein, or a small allosteric regulator); codons specifying a processing site of a protein (such as a cleavage, myristoylation, or phosphorylation site); polyadenylation signals; and transcription and translation termination signals
And here he is quite wrong. I think you would do well to show how he is wrong about these positions…
… rather than to spend any more time trying to argue that Behe is wrong about “one-way ratchets”. While you and I may differ from Behe in the fine points … to the average person, the “one-way ratchet” is TRUE ENOUGH.
Tetrapods are fish who have lost their gills while on land.
Whales are mammals who have gained new fins while in the oceans.
What’s the point of disagreeing when these statements, no doubt gross simplifications, are TRUE ENOUGH?
Changes in phenotypes are at least partly a result of changes in genotypes.
@T_aquaticus got a little too bored there… and tried to “make hay” about the Behe ratchet (one way).
I agree with Behe about this ratchet aspect. The problem is not the ratchet. The problem is When does God USE the ratchet? And when does God choose NOT to use the ratchet?
What do you think of the new evolved beta-galactosidase gene that emerged in E. coli after they lost their original beta-galactosidase gene? At least to me, it shows that the ratchet doesn’t exist. New function evolves.
The ratchet refers to being able to adapt, not to specific adaptations.
If we destroy a gene in E. coli that digests lactose, does this mean E. coli can never adapt to an environment containing lactose? According to Behe’s Ratchet, E. coli lost flexibility and can no longer adapt to lactose. According to reality, E. coli can and has adapted to lactose again by evolving a new enzyme.
I don’t see a difference between the Tetrapod example and the E. coli example - - except that one fits your assessment… and one doesn’t.
This tells me you are actually just cherry picking… rather than uncovering some nuanced difficulty with Behe’s discussion. His discussions are already TOO nuanced for anyone to possibly keep it all straight… and now you are adding to the problem.
The ratchet is, for the most part, True Enough.
Forget the ratchet or non-ratchet.
Focus on the God topic. When does Behe permit God to assist with Evolution? This is the key problem.
And now you are playing with words. You say they didn’t “lose the flexibility”. No. Of course they didn’t. Evolution is eternal flexibility.
But they did lose their gills… and fins. We see that seals, walruses and such, they have re-gained their fins… but no tetrapod has regained their gills.
It’s just not an important enough point, @T_aquaticus.
Choose your battles… which, so far today, you are clearly not attempting to do.