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Author Topic:   Does Neo-Darwinian evolution require change ?
AZPaul3
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Posts: 8513
From: Phoenix
Joined: 11-06-2006
Member Rating: 5.3


Message 36 of 114 (601028)
01-18-2011 11:27 AM
Reply to: Message 26 by slevesque
01-17-2011 7:42 PM


The Dance of the Population Curves
Which is that given the high mutation rates, how can it stay at that optimal peak when every single offspring will have inherited so many mutation (the majority deleterious, most only very slightly). Whichever one natural selection ''chooses'', it will still be less fit then it's parents were.
Let me try to answer this with a visualization in the mind.
First this optimal peak is an idealization which few, if any, individuals possess. It is the distillation of many thousands of optimals for all the various attributes that lead to evolutionary fitness (reproductive success). Think visual acuity, number of olfactory sensors, leg muscle strength, hemoglobin efficiency, and literally thousands of other attributes all combined in one ideal value.
Imagine a graph. Do not be concerned with the axes values, just see the graph. On this graph you draw this optimal vertical line. This is the line that represents the optimal value of all the attributes combined and is the maximum for reproductive success. Now impose the population bell curve for any specific attribute. Populations being what they are, the apex of the curve will be just off the optimum. Some of the population will have visual acuity less then others, some more and the average (apex) value of the curve will not be on the optimal line. The energy costs of better acuity may make it sub-optimal for this specific species in this environment so better acuity may not translate directly to increased fitness. Remember that fitness does not mean bigger, meaner, stronger. It means having more babies.
Now draw the thousands of other bell curves on the graph for all the other attributes necessary for reproductive fitness.
For each succeeding generation you must redraw each attribute's bell curve since population values at each point on the curve change. My son will have visual acuity up or down slope from me and my daughter may be on the opposite slope altogether. This is due to the different alleles present, mutations and any other mechanism of genetic change. This new curve for visual acuity will shift slightly from the past generation curve. All the curves will shift with each generation.
In aggregate, those individuals closer to the optimum for each attribute will have greater reproductive success which will keep the graphs of succeeding generations from straying too far off the optimal reproductive values.
What you end up with is, over many generations, these bell curves dance and wobble around this optimal line.
The optimal line will also shift in response to changes in the environment. If this optimal line around which all these attribute curves are dancing shifts slowly enough because the environment is relatively stable over geologic timescales then this is a population in stasis.
Stasis is not a period of no change either in the individual attributes' population curves or the central optimal line, but change slow enough to appear somewhat stable over geologic time frames.
The punctuated part of PE is when there is a radical shift in the environment which forces a radical shift in the central reproductive optimal line. And a radical shift in the environment also establishes new separate optimal lines on the chart (opens up new ecological niches).
Leave catastrophism out as a separate issue altogether.
The ancestor population will split with new sets of bell curves dancing and wobbling around each of the various optimal lines established for the changed environment and the opening of new niches. Speciation events have occurred.
What we see in the fossil record is an instantaneous arising of new species. The fossil record is dictated by geologic timescales when in fact the new species were established by the usual slow gradual evolutionary processes over thousands of generations over hundreds of thousands of years. Remember that 50,000 generations taking a million years to happen is instantaneous in geologic terms and the fossil record.
Punctuated Equilibrium embraces evolutionary gradualism at it's core. What was new and radical about it was the recognition of long periods (geologic time) of populations in stasis versus the view of constant gradualism that came before it.
As long as the environment remains somewhat stable, the reproductive optimal line will not move too far too fast. It may slowly shift slightly one way or the other for a few hundred generations then slowly shift back for a few hundred more all in response to minor changes in the environment. On geologic timescales, in the fossil record, it appears to not move at all. No speciation events can be noted.
Mutation rates will affect the movement of the population curves around the reproductive optimal line and natural selection, in affecting reproductive success, will keep the curves from getting too far off the reproductive optimal center.
Edited by AZPaul3, : No reason given.
Edited by AZPaul3, : No reason given.

This message is a reply to:
 Message 26 by slevesque, posted 01-17-2011 7:42 PM slevesque has replied

Replies to this message:
 Message 46 by slevesque, posted 01-18-2011 4:26 PM AZPaul3 has replied

  
AZPaul3
Member
Posts: 8513
From: Phoenix
Joined: 11-06-2006
Member Rating: 5.3


(1)
Message 54 of 114 (601099)
01-18-2011 5:55 PM
Reply to: Message 46 by slevesque
01-18-2011 4:26 PM


Re: The Dance of the Population Curves
But can change be slowed down that much ?
Doesn't have to be. Remember what Natural Selection actually is.
Yes, in the most egregious cases it kills the individual. But in the majority of instances Natural Selection simply means reduced or enhanced reproductive success.
In the case of the dancing population curves any changes or group of changes that move the apex of the curve away from the optimum (which is set by the present environment) will correct itself by those in the population closer to that optimum having more babies and moving the curve over time back toward that optimum. And this is done for each of the thousands of attributes. It is a self-correcting mechanism.
Remember, also, that this is based upon the fossil record which can only preserve the most gross phenotypic structures. Most mutations in a population affect the soft(er) parts (since there are so many more of them) and the type of gross morphological structure changes you may be thinking of are rare to begin with in stable populations. In the case of PE, which involves sexual species, sexual selection in the base population would tend to preclude the type of "hopeful monster" you may envision from becoming a part of the population.
Major changes by mutation may indeed enter the population and become fixed for a specific attribute. It may even re-mix this idealistic optimum. But the designation of "species" from the fossil record is based on the gross phenotype which, as the evidence shows, can vary little to none at all over geologic timescales. By definition this is stasis.
{abe} And just to be pointed about it... Nothing can ever overwhelm Natural Selection (selection pressures) regardless of perceived cost. It is a nonsensical notion. Any change, rate of change, high or low that has any effect on reproductive success is part of the Natural Selection phenomenon. If the changes enhance reproductive success then these are said to be "selected for" while any that reduce reproductive success are deemed "selected against" regardless of how many there may be or how fast the come.
Edited by AZPaul3, : No reason given.

This message is a reply to:
 Message 46 by slevesque, posted 01-18-2011 4:26 PM slevesque has replied

Replies to this message:
 Message 68 by slevesque, posted 01-19-2011 3:34 PM AZPaul3 has replied

  
AZPaul3
Member
Posts: 8513
From: Phoenix
Joined: 11-06-2006
Member Rating: 5.3


Message 79 of 114 (601318)
01-19-2011 8:02 PM
Reply to: Message 68 by slevesque
01-19-2011 3:34 PM


Re: The Dance of the Population Curves
Yes, but even taking those in the population closer, their babies will be farther then there parents because of the high mutation rates.
The mutations will always force a population to drift away from the optimal peak ...
Really? Based on what?
First, why do you assume mutation moves the individual away from the optimum? Why do you assume mutation moves the offspring further away than is the parent?
Is it possible for the offspring to have a mix of beneficial mutations for some attributes, mildly dilitarious for others, neutral for most and have the kid wind up at the same point or better then the parent.
Second, those with dilitarious mutations have the least effect on the population, especially larger populations. Do you understand why?
And those closer to the optimum have a better chance of having offspring with beneficial mutations. Do you understand why?

This message is a reply to:
 Message 68 by slevesque, posted 01-19-2011 3:34 PM slevesque has replied

Replies to this message:
 Message 84 by slevesque, posted 01-20-2011 1:27 AM AZPaul3 has replied

  
AZPaul3
Member
Posts: 8513
From: Phoenix
Joined: 11-06-2006
Member Rating: 5.3


Message 88 of 114 (601371)
01-20-2011 3:19 AM
Reply to: Message 84 by slevesque
01-20-2011 1:27 AM


Re: The Dance of the Population Curves
Look
Look
Look
The most conservative estimate of the deleterious-to-beneficial ratio of mutations was 50 to 1. I've seen some suggest perhaps as high as a million to 1.
But even with the 50-1 ratio, it's still pretty obvious that the high mutations rates will push the next generation farther away from the peak then their parents from the optimal peak.
BS. Your numbers are either very wrong or very purposefully skewed.
[ABE] No, I do not mean by you, but by your sources. Which are where, btw?
Edited by AZPaul3, : No reason given.

This message is a reply to:
 Message 84 by slevesque, posted 01-20-2011 1:27 AM slevesque has not replied

  
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