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Author Topic:   Punctuated Equilibria: The Basics
CRR
Member (Idle past 2242 days)
Posts: 579
From: Australia
Joined: 10-19-2016


Message 6 of 72 (816179)
07-31-2017 8:12 AM
Reply to: Message 4 by RAZD
07-30-2017 2:06 PM


Re: Rapid expansion of the new species
It's not just speciation. The isolated population has to evolve to the point that when they reconnect and replace the parent population it appears as a sudden large scale change without intermediate forms.
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.
However the main problem is proposing this as the usual method of operation so that dominates gradualism in the fossil record.

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CRR
Member (Idle past 2242 days)
Posts: 579
From: Australia
Joined: 10-19-2016


Message 10 of 72 (816214)
07-31-2017 7:20 PM


JonF, PaulK, RAZD,
The PE model was developed to explain large morphological gaps in the fossil record, saltations. It proposes that most of the change occurs offstage in a small population and this new form then sweeps through the environment producing a new species with no obvious transition from a previous one. Punk Eek still uses Darwinian type evolution; it just proposed it occurred in a small isolated population that was not preserved as fossils.
If you think you can see a fossil series showing many small steps then punk eek does not apply to that example.
added ...
quote:
According to punk eek, as the theory came to be nicknamed, species evolve when small groups of organisms are separated from the main population by something as vast as an ocean or as simple as a river. Geographically and reproductively cut off, this fringe group evolves rapidly, and if it migrates back to its ancestral range, it will look dramatically different and appear as a jump in the fossil record.
Eldredge and Gould were the first to show that stasis, not continuous change, is the rule of the fossil record.
http://www.amnh.org/...esearch-posts/punk-eek-40-years-later
Saltation = an abrupt variation in the appearance of an organism, species, etc. Just a moment...
Edited by CRR, : added...

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CRR
Member (Idle past 2242 days)
Posts: 579
From: Australia
Joined: 10-19-2016


Message 13 of 72 (816222)
08-01-2017 2:07 AM


PaulK, Tanypteryx
See update to Message 10

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CRR
Member (Idle past 2242 days)
Posts: 579
From: Australia
Joined: 10-19-2016


Message 19 of 72 (816275)
08-02-2017 6:33 AM
Reply to: Message 17 by Taq
08-01-2017 11:30 AM


Terminology
More correctly I should have said "The PE model was developed to explain large morphological gaps in the fossil record, seeming saltations.

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CRR
Member (Idle past 2242 days)
Posts: 579
From: Australia
Joined: 10-19-2016


Message 22 of 72 (817019)
08-14-2017 11:54 PM
Reply to: Message 21 by Taq
08-02-2017 10:52 AM


Re: Terminology
The idea of Punk Eek is that the evolution takes place "off stage" where it isn't recorded in the fossil record so that when it later reappears there is a large change, an apparent saltation. The evolution that takes place "off stage" is assumed to follow normal Darwinian processes.
quote:
According to this idea, the changes leading to a new species don't usually occur in the mainstream population of an organism, where changes wouldn't endure because of so much interbreeding among like creatures. Rather, speciation is more likely at the edge of a population, where a small group can easily become separated geographically from the main body and undergo changes that can create a survival advantage and thus produce a new, non-interbreeding species.
This hypothesis predicts that the fossil record at any one site is unlikely to record the process of speciation. If a site records that the ancestral species lived there, the new species would probably be evolving somewhere else. The small size of the isolated population which is evolving into a new species reduces the odds that any of its members will be fossilized. The new species will only leave fossils at the same site as the old one if it becomes successful enough to move back into its ancestral range or different enough to exist alongside its relatives.
Evolution: Library: Punctuated Equilibrium
Note that evolution can potentially take place more quickly in a small population because the average time for a change to reach fixity is correspondingly smaller. On the other hand the smaller population has less chance of producing a favourable mutation.

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CRR
Member (Idle past 2242 days)
Posts: 579
From: Australia
Joined: 10-19-2016


Message 24 of 72 (817221)
08-15-2017 9:56 PM
Reply to: Message 22 by CRR
08-14-2017 11:54 PM


Re: Terminology
The idea of Punk Eek is that the evolution takes place "off stage" where it isn't recorded in the fossil record so that when it later reappears there is a large change, an apparent saltation. The evolution that takes place "off stage" is assumed to follow normal Darwinian processes.
Using Punctuated Equilibria as a reference
PE essential features are peripatric speciation in a geographically limited region and stratigraphically limited extent such that sampling of the fossil record will reveal a pattern of most species in stasis, with abrupt appearance of newly derived species being a consequence of ecological succession and dispersion.
While Eldredge and Gould acknowledge that geological processes contribute to the "gappiness" of the fossil record, they also assert that PE is by far the more important consideration in that regard.
Or in other words evolution takes place "off stage" where it isn't recorded in the fossil record so that when it later reappears there is a large change, an apparent saltation. The evolution that takes place "off stage" is assumed to follow normal Darwinian processes.

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