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Author Topic:   Criticizing neo-Darwinism
NosyNed
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Posts: 9007
From: Canada
Joined: 04-04-2003


Message 5 of 309 (296968)
03-20-2006 10:36 PM
Reply to: Message 3 by nwr
03-20-2006 10:08 PM


Gradualism
The neo-Darwinistic account is one of gradual change.
I was surprised to learn that Darwin, in his original publication of the Origin was not a total gradualist. He even recognized that the speed of evolution doesn't have to be constant. I'm not sure that there as ever been utter gradualism.
PE (punc eck) is simply a statement that the changes in speed may be greater than recognized explicitly before and account for some of the patterns of the fossil record. It is totally within neo-darwinism. Even the extremes suggested there are still "gradual" by everyday standards.
The arguments about irreducible complexity arise because gradual change does not plausibly lead to very complex structures. The biology shows how complex structures can arise, but the gradualism of the neo-Darwinist model seems to argue against it.
You'd have to explain why you think this is so. The problems introduced by IC have NOTHING to do with gradualism as far as pace goes. They do have to do with "step size". However, they do not deal with pathways through evolutionary space.
Biology suggests that large step sizes are unlikely to be successful. To that degree "gradualism" is presented with a problem by IC. However, gradual movement through more complex pathways than one step at a time to a final result works just fine. This is exemplified by the scaffolding approach for one. Coopting for another.
However, it seems to me that a species cannot exist unless it is already adapted. And becoming over-adapted would only result in exponential growth of a species until it destroyed its own habitat. The only way I can see a species being mal-adapted, is when some environmental change destroys the environment to which a species was previously adapted. Granted, such changes can and do occur, some caused by other evolutionary changes in the biosphere (what Dawkins refers to as an arms race). But I am skeptical that such environmental change can account for all of the adaptation that would be needed to explain the degree of biological diversity and complexity that we find.
The question is: Why are you skeptical?
Species do destroy their habitat and go extinct. However, over adaptation (what ever the heck that means) is difficult I think. You have the solution to this just a little further down. The evolutionary arms race is a "red queen's race". That is you have to run faster and faster just to stay in the same place.
You are right that everything alive now is adapted rather well to where it is. Until something changes! And, of course, something is almost always changing. Perhaps slowly but on rare occasions more rapidly.
It could be that a slightly deleterious gene occurs on the same chromosome as a slighly beneficial gene. Since they are on the same chromosome, they tend to be inherited together. The disadvantages of the one are offset by the benefits of the other, so there is no net filtering effect. Agreed, the two genes can be separated during a crossover. But if they are close together on the same chromosome, then the probability that a crossover will divide them is relatively small. To consider the filtering in this case, you have to look not at the time between generations, but at the time between crossover events that divide between the two genes. The rate of filtering would be extremely slow.
I don't know enough genetics to be sure but I think you are wrong in what you are stating here.
Sure, there might be a statistical filtering effect. But for small differences in how well adapted, this filtering is a weak effect in a sea of contingencies. Any filtering would be very slow, and in my opinion it would be too slow to account for biological diversity.
Again I am not an expert but I believe that the math of population genetics says that your opinion is wrong.

This message is a reply to:
 Message 3 by nwr, posted 03-20-2006 10:08 PM nwr has replied

Replies to this message:
 Message 11 by nwr, posted 03-21-2006 2:00 PM NosyNed has not replied

  
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