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Author Topic:   Rate changes for evolution
Parsimonious_Razor
Inactive Member


Message 1 of 40 (96142)
03-30-2004 8:50 PM


I have seen some archives of interesting discussions on here about punctuated equilibrium and gradualism but thought maybe I could reintroduce the topic with some specific questions, I am still becoming familiar with the board guide lines and could not come up with an existing thread for this, but if there is one let me know.
From what I can tell most evolutionary biologist do not deny that there can be great changes in the frequency at which evolution takes place, and that perhaps the view of gradualism put up as the antithesis to PE is a straw man. But on average how much weight is put on this change in frequency? For example is speciation and large-scale morphological changes in a population viewed as being fueled primarily during spats of increased change, or can these types of changes occur during periods of relative stasis?
Are there really significant gaps in transitional fossils such that it can’t be explained in terms of the low probability of fossilization? I have seen some pretty amazing trees of transitional forms and there corresponding fossils that seem to suggest that at least at some level morphological changes are occurring over vast time spans or are these change fueled by burst and stops as well?
Is the process for these burst of fast evolutionary change easily reducible into classic ideas of natural and sexual selection and mutation? Along this same vain is one speed of evolution more the base rate than the other, are the periods of stasis due to selection pressures that are slowing down evolutionary change, or are the burst periods due to selection pressures that are speeding up evolutionary change, or is the concept of a base rate a totally meaningless idea?

Replies to this message:
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 Message 3 by Denesha, posted 03-31-2004 6:24 AM Parsimonious_Razor has replied
 Message 4 by Brad McFall, posted 03-31-2004 10:25 AM Parsimonious_Razor has replied
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 Message 20 by mark24, posted 04-01-2004 4:00 AM Parsimonious_Razor has not replied

  
Parsimonious_Razor
Inactive Member


Message 6 of 40 (96370)
03-31-2004 2:41 PM
Reply to: Message 3 by Denesha
03-31-2004 6:24 AM


Paulk writes:
The generally accepted view is that speciation is important but that morphological changes can occur in a more gradualistic way.
Denesha writes:
Sudden environmental changes are related to speciation bursts. From Cretaceous and Paleogene fossils, more species appear after transgressive events and flooding. It's quite stable between.
So what I am getting here is that speciation burst are more common than gradual changes? I suppose this is somewhat statistically an obvious point but what I am curious about is the difference significant enough to declare burst of speciation as more important than gradual changes. I assume the null hypothesis lies some what like this: that gradual changes and speciation burst are equally important and equally likely to occur but due to the time step gradual changes will result in less total speciation events than burst.

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Parsimonious_Razor
Inactive Member


Message 7 of 40 (96373)
03-31-2004 2:47 PM
Reply to: Message 4 by Brad McFall
03-31-2004 10:25 AM


What do you mean by a geometrical vision? Are we talking about a geometrical distribution or do you want some sort of state space to describe what I mean by stasis?
Are you talking about Leoan Croizat (sp??)? I assume so with your reference to panbiogeographers.

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Parsimonious_Razor
Inactive Member


Message 8 of 40 (96376)
03-31-2004 2:53 PM
Reply to: Message 5 by RAZD
03-31-2004 1:31 PM


Re: evolved rate?
So how does all this relate with say the idea of the molecular clock that supposedly can measure phylogenetic splitting based on a known rate of mutation? Is there a way to quantify the difference between just the general rate of mutation and the rate that expressed mutations occur, and then I guess to quantify further you would need to figure out adaptive benefits/costs for the expressed mutation. Probably outside the realm of molecular probabilistic theory???
I guess if you could describe the rate at which we would see beneficial mutations arising in a population under normal stress you could define a base rate of evolution and then decide if punctuated bursts occur at a higher frequency than you would expect. Sort of a weird hardy-weinberg type approach.

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Parsimonious_Razor
Inactive Member


Message 9 of 40 (96377)
03-31-2004 2:54 PM
Reply to: Message 5 by RAZD
03-31-2004 1:31 PM


Re: evolved rate?
Double post
[This message has been edited by Parsimonious_Razor, 03-31-2004]

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Parsimonious_Razor
Inactive Member


Message 11 of 40 (96393)
03-31-2004 3:24 PM
Reply to: Message 10 by Loudmouth
03-31-2004 3:13 PM


I agree with the importance of population size certainly and I think there are many other factors that could contribute to burst rates of speciation. All this reminds me way to much of my undergraduate courses on hardy-weinberg and the use of these horrible red and white beans. The beans are beside the point, but the hardy-weinberg stuff may not be.
If they can establish a basic probability that defines a population in stasis as far as alleles go and can then establish under what conditions this stasis is violated I would think you could do something with the rate of speciation or morphological changes. If you could define the rate of change under normal stress environments with no inhibitory or excitatory processes you could see maybe whether punctuated change or gradual change is closest to this statistical rate and then look for what factors might cause a speed up or down of the processes.

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Parsimonious_Razor
Inactive Member


Message 15 of 40 (96444)
03-31-2004 5:54 PM
Reply to: Message 13 by Loudmouth
03-31-2004 5:34 PM


loudmouth writes:
PE doesn't argue with the mechanisms (random mutations and natural selection) but rather about what we would expect to see in the progression from one niche strategy and the next and the consequences both in morphology and in the fossil record. I'll stop here, this is too much like preaching to the choir.
Sometimes preaching to the choir is nice, less stress on the cardiovascular system than trying to argue about spiritual universes separating 6200 years ago.
So if you pull in the idea of a non-evolving population you have to have a certain theoretical setup if I remember correctly:
1. no mutation or no expressed mutation
2. no natural selection
3. very large populations (technically infinite I suppose)
4. Everyone breeds, and breeds at random.
5. everyone produces the same number of offspring
6. there is no migration in or out of the population
This would produce a truly static population right? So is the rate of evolution simply defined by how far removed the population is from these traits? Does anyone know if there are mathematical models that show the relationships of these variables to how fast the population evolves? I can't imagine that it would be too difficult to write of the model especially if you are defining the initial conditions and don’t have to immediately justify that they correspond to a specific reality.
I think you could make some impressive predictions from such a model, and I have a feeling this is probably been done extensively somewhere. I am going to go dig through the literature.

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