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Author Topic:   Punctuated Equilibria: The Basics
PaulK
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Message 1 of 72 (816146)
07-30-2017 4:47 AM


The underlying concept of Punctuated Equilibria was to take ideas about speciation from current evolutionary theory and work what we should expect to see in the fossil record.
Mayr's ideas about allopathic speciation may be summed up as follows:
A sub-population on the edge of a species' range is cut off.
Without the stabilising effects of gene flow and with differing selective pressures this smaller population diverges quite rapidly, and becomes a new species.
Speciation, then occurs in a relatively small area over a geologically short period of time. Gould proposed that it might only take centuries, perhaps somewhere in the region of 1000 years.
If speciation occurs rapidly in a limited area we will only observe it in the fossil record if we have a very good record for that exact time and place (which is limited by our explorations, as well as by the limits of the record itself). While we have such records for some times and places they are more the exception than the rule.
It follows from this that speciation events - and the fine intergraduations of form that should have existed - should be very rare in the fossil record.
The original 1972 paper may be found here (scanned text, PDF format)

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PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.3


(2)
Message 3 of 72 (816155)
07-30-2017 12:03 PM
Reply to: Message 1 by PaulK
07-30-2017 4:47 AM


Darwin and PE
One of the controversial features of Punctuated Equilibria is that it was presented as being opposed to a Darwinian view. While it may have been opposed to a view of Darwin commonly held by Palaeontologists, it does not seem to be so different from Darwin's actual views
Quotes are from the 6th edition of On the Origin of Species which is easily found on the Internet, including Project Gutenberg.
With animals and plants that propagate rapidly and do not wander much, there is reason to suspect, as we have formerly seen, that their varieties are generally at first local; and that such local varieties do not spread widely and supplant their parent-form until they have been modified and perfected in some considerable degree. According to this view, the chance of discovering in a formation in any one country all the early stages of transition between any two forms, is small, for the successive changes are supposed to have been local or confined to some one spot.
p819
It is a more important consideration, leading to the same result, as lately insisted on by Dr. Falconer, namely, that the period during which each species underwent modification, though long as measured by years, was probably short in comparison with that during which it remained without undergoing any change.
p820
While fall short of full-blown PE these are close enough that PE can be seen as more of an extension of Darwin's views than contradicting them

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PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.3


Message 8 of 72 (816181)
07-31-2017 8:31 AM
Reply to: Message 6 by CRR
07-31-2017 8:12 AM


Re: Rapid expansion of the new species
quote:
This presents a problem since while the small population can fix mutations more rapidly it also has less resources to produce the large changes necessary to produce the saltation. Conversly the larger population is more likely to produce significant mutations.
First it is not saltation. Second the assumption that most of the change is due to mutations that occur after the populations split needs justification. There were likely local variations already present before the split and we know that selection can produce significant phenotypic variation without the assistance of mutations.
quote:
However the main problem is proposing this as the usual method of operation so that dominates gradualism in the fossil record.
Why is it a problem to suggest that the mode of speciation accepted as the most common, is the most common mode ?

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PaulK
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Posts: 17822
Joined: 01-10-2003
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Message 12 of 72 (816221)
08-01-2017 12:06 AM
Reply to: Message 10 by CRR
07-31-2017 7:20 PM


quote:
The PE model was developed to explain large morphological gaps in the fossil record, saltations
Wrong. The only gaps in the fossil record that it explains are gaps between species. And it does not explain them by saltation. As you yourself go on to explain.

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PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.3


Message 14 of 72 (816223)
08-01-2017 2:30 AM
Reply to: Message 13 by CRR
08-01-2017 2:07 AM


So, you have a definition of saltation that agrees with my point.
And as I have already shown the idea of stasis is in Darwin's writings, so hardly new to Eldridge and Gould.

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PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.3


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Message 51 of 72 (838876)
08-29-2018 1:13 PM
Reply to: Message 49 by Faith
08-29-2018 12:43 PM


quote:
There is no evidence that shows the Flood is imaginary. For that to be the case you have to ignore the abundant evidence of the fossils and the strata, which you do by redefining them to fit your "science."
The evidence of the fossils and the strata show an old Earth and evolution, not your Flood. This has been discussed many times here and repeating old falsehoods is hardly going to convince anyone.
quote:
Punctuated Equilibrium is based on the nonsensical interpretation of the fossils as showing evolution up the geologic column.
You are doubly wrong since punctuated equilibriumwas based on Mayr’s theory of speciation and evolution is by far the best explanation of the order of the fossil record.
quote:
It's nothing but a mental notion, and the Flood explains it a lot better.
As we have seen the Flood utterly fails to explain the fossil record.
quote:
Which means that PE is a magic trick just like all the other evo interpretations of the fossil record are.
Except that it does fit with the fossil record - and the Flood doesn’t.

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