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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 canít 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?


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PaulK
Member
Posts: 10709
Joined: 01-10-2003
Member Rating: 1.9


Message 2 of 40 (96226)
03-31-2004 2:06 AM
Reply to: Message 1 by Parsimonious_Razor
03-30-2004 8:50 PM


Gould's idea that practically all morphological change happened during the punctuations of PE is the really controversial part of Punctuated Equilibria. It's also been rejected as an absolute because of contrary evidence. For instance the oldest remains of Homo sapiens have smaller braincases and are referred to as "archaic Homo sapiens" - and in that feature at least they are intermediate between modern Homo sapiens and Homo erectus.

The generally accepted view is that speciation is important but that morphological changes can occur in a more gradualistic way.


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Denesha
Inactive Member


Message 3 of 40 (96255)
03-31-2004 6:24 AM
Reply to: Message 1 by Parsimonious_Razor
03-30-2004 8:50 PM


Dear Parsi,

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.
Eldredge and Gould's theory explain some things.
It's a theory.

Denesha


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Brad McFall
Member (Idle past 1411 days)
Posts: 3428
From: Ithaca,NY, USA
Joined: 12-20-2001


Message 4 of 40 (96305)
03-31-2004 10:25 AM
Reply to: Message 1 by Parsimonious_Razor
03-30-2004 8:50 PM


Can you supply a "geometrical" vision of your termed 'relative stasis' please?

As to "base rate", in terms of a any sequence of data collection and analysis, I know by experience there is a exploratory tendency, which admitted IS subjective, that tends to extrapolate from a local knowledge to larger regions but it seems to me that Mayr's insistence that Croizat "accept" the standard rates (or perhaps 'base rate' as you had it) was a wrong way to grow"" biological thought or simply an ad hominomen on how Croizat reasoned reverse wise from a global or pantropical distributions to local "endemisms" or Cain centers of origin. There could be a better logical rework of Croizat's corpus if one were to get beyond the mass matrix defintions of NZ panbiogeographers per track width which so far I assoicate univocally with two-way velocities FROM empty space for any local endemism but this is less biological than even physical chemists think so it is not quite delimited even if it is logical. I almost think that it is possible to consider stasis in terms of the geography of different chrophyll stacks(intraorganically) but that is quite an extreme kind of thought on the subject.


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RAZD
Member
Posts: 15743
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.1


Message 5 of 40 (96355)
03-31-2004 1:31 PM
Reply to: Message 1 by Parsimonious_Razor
03-30-2004 8:50 PM


evolved rate?
Interesting post and good question.

I do not think there can be a standard or steady rate of change. Certainly some sections of DNA are more susceptible to mutations so the randomness of mutations would affect the rates as they are realized. But I also think that the susceptibility to mutation has evolved to be in rough equilibrium with the need to change, to adapt to changes that occur to climate and ecology (elephants converting forest to savannah?). Thus those parts that are more likely to lead to viable mutations (live long enough to reproduce) become more mutation able and those parts that lead to non-viable mutations (spontaneous abortion deformed fetus) become less mutation able. Over long time periods this explains the evolved "hotspots" noted and the current rate of {mutation \ change} in a Nash equilibrium with the need to change.

Hope that helps.


we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}


This message is a reply to:
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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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Loudmouth
Inactive Member


Message 10 of 40 (96388)
03-31-2004 3:13 PM


I think people are missing another important part of PE theory. This has to do with population size. As theorized, small populations are able to build up beneficial mutations faster, especially at the periphery of the larger population where selection may be stronger. That is, a beneficial mutation will spread through a small population in fewer generations than in a larger population. These changes then sweep through the larger populations, or the larger population is overtaken by the new species/sub-species. My own understanding is that population size is just as important within PE theory as mutation rates, and that if the larger population is kept as a cohesive unit, gradualism may play a role.
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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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PaulK
Member
Posts: 10709
Joined: 01-10-2003
Member Rating: 1.9


Message 12 of 40 (96437)
03-31-2004 5:27 PM
Reply to: Message 6 by Parsimonious_Razor
03-31-2004 2:41 PM


I'm not sure what the consensus is - or if there is a consensus - on which is most important. I would tend to the view that speciation is more important because the same forces that cause speciation promote evolutionary change. Gradual change still happens but there don't seem to be that many definite examples.

Of course in human timescales even the fastest evolutionary change is not that quick. The highest recorded rates of physical change through evolution come from laboratory experiments.


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Loudmouth
Inactive Member


Message 13 of 40 (96439)
03-31-2004 5:34 PM
Reply to: Message 12 by PaulK
03-31-2004 5:27 PM


quote:
I'm not sure what the consensus is - or if there is a consensus - on which is most important. I would tend to the view that speciation is more important because the same forces that cause speciation promote evolutionary change.

Not only that, but speciation isolates genetic populations which will eventually lead to divergent body plans over time. Stasis could be argued after speciation, but I think we can also agree that speciation is the first step towards large differences in morphology. To me, speciation is more important than gradualism in describing the mechanisms for biological diversity. 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.


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RAZD
Member
Posts: 15743
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.1


Message 14 of 40 (96443)
03-31-2004 5:51 PM
Reply to: Message 8 by Parsimonious_Razor
03-31-2004 2:53 PM


Re: evolved rate?
The only way to benchmark it that I can think of is to correlate it with the fossil record. We have the experimental information from the mitochondrial "eve" and the y-gene "adam" and the earliest known modern humans (160,000 years old Ethiopian skulls) and I believe both genetic data point closer to 200,000 years -- close but not on target, on the right side of the target ...

This needs to be done for as many instances as can be found. That can then give you a plot of predicted vs actual age on a graph and see if it correlates good enough to use.

Find the correlation before making too many predictions.

The assumption that the rate is steady-state is just that, an assumption. The concept that genetic trees can be built from the age data so derived is a theory that needs to be validated, imho.

I suspect the line will vary from a 45į straight line.


we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}


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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 donít 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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