As I understand it....Darwin himself proposed the following make or break test for his theory:
"If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find out no such case.”
ID reads “complex multi-protein genetically defined structure with a novel function” for “complex organ” and proposes that the bacterial flagellum motor function is one such case. Not that it could not occur by numerous successive slight modifications BUT that the pathway to the final working structure is too improbable to allow us to accept chance mutation and natural selection as reasonable causes of the structure.
ID suggests that the pathway to a useful motor function does not have sufficient selectively advantageous “stopping places” along the way to allow an unintelligent process to reach it in the amount of time available.
Thus Darwin proposes that the “golf course” where the “hole” is the working motor performing a useful function is more like a cone with the hole at the tip….gradually the “golf ball” will move under the weight of selective advantage to the “hole” of molecular motor function.
ID proposes that the “golf course” is more like a real golfcourse where blind and deaf golfers are at a distinct disadvantage!
If ID is true then one would hope to find:
(a) there would be very few functional selectively advantageous structures as intermediate stopping places along the way to the motor function. (the golf course is not designed to make a 'hole in one' likely for any rolling golf ball)
(b) The number of possible structures with a motor function will be relatively few (the hole is small)
If Darwin’s theory were the true explanation of the origin of the motor function of the bacterial flagellum then one would hope to find:
(a) there would be many functional selectively advantageous structures as intermediate “stopping places” along the way to motor function. (the golf course slopes down to the hole)
(b) The number of possible structures with a selectively advantageous motor function will be relatively large (the hole is large.)
...have I grasped the issue?
11 comments:
Yup. Pretty good summary, I'd say. Mind if I borrow your analogy in future?
No, I think you've missed the point that there are billions of "golfers." The course doesn't need to be sloped to allow one ball to roll into the hole; there are a billion, or five billion, balls being shot -- it's almost statistically impossible that less than a handful would be in on the first stroke; another several dozen would make it on the second stroke; etc.
Don't ignore the role that variation plays in evolution, and don't ignore the role that sheer population size, and reproduction, play.
Your gut has six billion or so e. coli. Next week, a diffeerent six billion. What are the odds that you could avoid having a new species arise after living a hundred weeks or so?
Ed,
You said "It's almost statistically impossible that less than a handful would be in the hole on the first round."
If it is so straightforward as to happen pretty much inevitably why hasn't someone from "your side" actually made a motor by random mutation and selection? Why object that ID is setting an impossible standard of proof if it is so easy?
As I understand it at best the number of mutations in a single bacteria is going to be about 4 in each generation.
My point is that we are going to be looking for a particular set of mutations occuring independently in several proteins
Ed,
The "slope" is the selectively advantageous "stopping places" along the way to motor function. Your side suggests that there will be lots of these ie a sloped golf course.
Ed's right that the golf course model isn't a fundamentally accurate representation of what's going on. For it to be true to life, we'd drop the concept of rolling. We'd decree that each golf ball split into ten or so new golf balls when it hit the ground, each one of these bouncing a Poisson-distributed distance in a random direction. We'd then kill off most of the golf balls that landed higher up and proceed to calculate what happened when the survivors threw out their ten or so new golf balls.
However, as we discussed when talking about the Nilsson and Pelger experiments*, a mathematical approximation is a fairly decent approach to a stochastic model. And as a metaphor I'd say it's great, as long as you allow the ball to bounce a little.
Why hasn't a flagellum developed?
What are you talking about? There are several different species of bacteria that have flagella, as well as semen in thousands of animals, and other critters.
How you can look at something that exists and say it's impossible for it to have happened is a mystery. If you're saying it's impossible for it to have evolved, you have a difficult time explaining why we observe evolution today.
If you're wondering why we don't observe such evolution occurring today, I'd say you need to look again. It's not possible to draw such a conclusion on the basis of the data we have.
And there is always the evolutionary reality that, if it exists already, it's difficult for something else to come along cold turkey and create a better model to bump the old one out of the way.
Can you demonstrate that flagella do not evolve today? You'd need to make that demonstration before we could even start discussing why we don't see new replacements.
If there's a golf ball in the hole already, it's difficult to get another in.
Is it safe to assume you don't golf, as well as you don't garden, or raise animals?
The "evolved" golf course would only look that way if there was some reproductive advantage gained by looking that way.
If the golf course does not reproduce, then why are you using it as some sort of analogy?
beer,
Of course the analogy is not perfect...but I think the analogy is helpful in distinguishing the predictions of the two models.
RMNS needs lots of functional selectable intermediates to make the chance mutation pathway reasonable. I don't think that there is any controversy there. Each one has to be on the pathway to the "hole" and they have to happen in the right order.
I guess I don't even follow what you just said, but I'll try.
I think the analogy is helpful in distinguishing the predictions of the two models.
Predictions of what models? What exactly is the prediction that the ID "model" would make? That an intelligent designer would design a golf course that was difficult to play? Natural selection would produce a golf course that is easy to play?
Each one has to be on the pathway to the "hole" and they have to happen in the right order.
I don't know if I'm deciphering this correctly.
If there were a small population of golf courses and
1. they reproduced to make more and more golf courses with slight differences
2. Golf courses reproduce more often the more people play on them.
3. People like to play on challenging golf courses and play on those more often
Then, after many many generations, you find a population of golf courses that are challenging to play.
Beervolcano,
I obviously have not made this very clear....
I have had another go on the main blog posting...
Does that help?
Way to go beervolcano!
Andrew Rowell, maybe you need to explain why that a "fitness landscape" is like a map of where evolution could go, and that golf-courses dont breed.
I think the blind-peoples golf course is a pretty good analogy. Will use it. It should be easy to estimate what population of blind-people would be needed, but an estimate of the size of blind-family-units would also be important (clustering due to species). A host of other effects would come in to play, and we have no reason to think that they would be helpful to evolution (unless you already believe firmly in evolution). But by the time you have tested them and found the opposite to be the case you will have forgotten that it was evo-mentalism (sorry :> ) that led you in the wrong direction.
Does anyone still believe in "junk DNA"?
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