Punctuated Equilibria: The Basics

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)

Thread copied here from the Punctuated Equilibria: The Basics thread in the Proposed New Topics forum.

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 viewsQuotes are from the 6th edition of On the Origin of Species which is easily found on the Internet, including Project Gutenberg. p819 p820While 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

The other phase of punk-eek as I understand it, is that once this new species has evolved it expands outside its "incubation" habitat, and pushes into the areas inhabited by the parent population, displacing it. In the fossil record this looks like one species being replaced by a different one, with no intermediates at this species level.Creationists like to point to this as evidence of special creation of new species.For an idea of how a small initial population could spread into other habitats see Differential Dispersal Of Introduced Species - An Aspect of Punctuated Equilibrium. This takes several species that were introduced into North America with small initial populations and looks at their survival.

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1. European House Sparrow
2. European Starling
3. English Skylark
4. Crested Myna
5. Chukar
6. Budgerigar
7. Rose-ringed Parakeets

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Conclusions

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Thus we see two extremely successful dispersions and others of limited success and finally some that succeeded only to lose out to later competition. Obviously not all introductions are successful, and just as obviously not all newly evolved species will win out in similar circumstances.

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Native species are being impacted by the "successful" introductions (Starlings and House Sparrows) but they are still viable at this time (probably most impacted is the Eastern Bluebird). There was no eco-niche vacuum for the newcomers to fill and there was competition, but they have been able to disperse across the continent.

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Any one of these would have appeared "suddenly" and "without any transitions" in the fossil record.

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(Once a new species has evolved it could disperse in much the same way, and if they evolved in isolation in a small area or an area that didn't make fossils then there would be no record of any transitions).

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While these examples are all birds and thus able to disperse widely fairly rapidly, the same process would hold for other organisms, with the rapidity of the dispersal dependent on their mobility.Enjoy

This has certainly been true for invasive weeds and insects. We see wood boring insects being moved from one part of North America to another with devastating effects for forests and orchards. Add to that transport of non-native species brought from other continents by global trade and you have disasters for agriculture simmering around the planet.

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.

The new population need not replace the parent population. AFAICT it seldom does.

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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.

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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.

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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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Why is it a problem to suggest that the mode of speciation accepted as the most common, is the most common mode ?

What is "large scale change?"When I was exploring horse evolution on the Dogs will be Dogs will be ??? I did not see any specific change I would call "large scale" ... just the variations seen in dogs ... (further discussion on this concept should probably be best done on that thread).In punk-eek the new species appears in the fossil record, but there are obvious multiple homologies with older fossils found in the same geographical location, showing a clear path of lineage, and no radical change (nothing beyond what we see in the variations of dogs).So what is "large scale change?"Enjoy

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 ...

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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.

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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

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Saltation = an abrupt variation in the appearance of an organism, species, etc. Just a moment...Edited by CRR, : added...

You speak so authoritatively I assume you can point out in the Gould and Eldredge paper where they state that they developed their hypothesis to explain large morphological gaps in the fossil record, saltations.

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The PE model was developed to explain large morphological gaps in the fossil record, saltations

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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.

PaulK, Tanypteryx
See update to Message 10

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.

What is a "large morphological gap?" So what is a "large morphological gap?"EnjoyEdited by RAZD, : .