punctuated equilibrium

[Dylab]

Can someone explain to me what it is and how strong is the evidence for it?

 

[arcticpenguin]

Punctuated equilibrium is the hypothesis that one species transforms into another rapidly, instead of via slow tranformation. So it all hinges on your definition of "rapidly".

 

[JSFolk]

Punctuated equilibrium is the theory that in some cases, rather than a whole population gradually evolving, that you get long periods of stasis followed by relatively rapid changes. This is evidenced by us seeing exactly that pattern in some fossil records.

One explanation for this is that, say, a small daughter population is separated from the mother population. The smaller population can evolve faster (smaller gene pool, more chances of gene drift, etc, etc) and if it is re-introduced into the territory of the mother population, rapidly supplant members of the old pop. In the fossil record this would look like "rapid evolution" even though it's not the mother population evolving, but rather getting replaced by the new improved model.

There is nothing in PE that says that this happens EVERY time, nor is PE "an excuse made by evolutionists that have too many gaps in the fossils".

I'd refer you to TalkOrigins for mor information.

 

[Brian]

And just as a funny aside. I've read that evolutionists that believe change occurs at slow steady pace are called "creeps" and those that believe not much happens for a long time and then suddenly some animals change drastictly in a short time are called "jerks". I have no idea how often these terms are actually used ny researchers.

 

[fishbob]

Punctuated equilibrium is a minor tweaking of evolution theory - to better explain some of the fossil data. The PE hypothesis does not conflict with or supplant or weaken evolution in any way.

 

[a_unique_person]

Just read in interesting view of this in the paper. Apparently there was a massive and incredible leap in evolution. One moment there were sponges, jellyfish and worms, and not much else . All of a sudden, there were all kinds of new species. He puts it down to the development of the eye, which makes sense.

 

[athon]

The evidence is pretty strong for the existance of punctuated equilibrium. A recent study done on rock wallabies on Queensland's coast has strengthened the theory, with recent discoveries pointing to transposons in viruses as the main culprits in creating veritable new species over several generations.

It has been all but accepted that both punctuated equilibrium (large stresses creating large genetic divides over several generations) and gradualism (accumulation of point mutations over many generations) have contributed to speciation events in the past.

Athon

 

[Dancing David]

The theory of punctuated equlibrium was proposed by SJ Gould and his partner whose name I forget.

darwin suggested that species always fill an eco system to capcity and the compete with each other, the one that gets an advatage will slowly dominate it's niche. A process referered to as 'wedging'. And this does occur during periods of relative stability.

Howevr , much evolutionary change occurs after some major enviromental change of disaster. During these times the ecosystem niches are not chock full or major chunck of biomass have been eradicated. During these times species are more likely to fill in new areas and go through 'radiations' leading to new species.

So there is the equilibriuum in which wedging occurs and genetic change occurs but not at a drastic pace, then there are the times of upheaval when huge potential for change exists.

So when Antaartic broke off from India and moved to the south pole, the climate change and the dinosaurs got wiped out. A period of euilibria (slow change) followed by a rapid shift in biomass.

But you can have radiations of new species during times of equilibrium as well. A species gets an advantage and spread even during atime of relative stability.

The basic idea is that you don't always have the steady 'progress' of evolution but that it jumps at times.

 

[arcticpenguin]

The theory of punctuated equlibrium was proposed by SJ Gould and his partner whose name I forget.

The other was Niles Eldrege.

Gould's specialty was paleontology. In paleontology, a short period of time might be 50000 years or more.

 

[Darwin]

PE could be proudly summed as evolution as it is displayed by the fossil record.It is not very wise imo to place all the weight on one extreme interpretation.Fossil record is,and will always be imperfect.
Today,we have interesting examples of directly observed,notable evolutionary change which happens in what can be considered a single step in geological time.

"So when Antaartic broke off from India and moved to the south pole, the climate change and the dinosaurs got wiped out. A period of euilibria (slow change) followed by a rapid shift in biomass."

I wonder whether you are saying that THIS is why dinosaurs "got wiped out"?


"Just read in interesting view of this in the paper. Apparently there was a massive and incredible leap in evolution. One moment there were sponges, jellyfish and worms, and not much else . All of a sudden, there were all kinds of new species. He puts it down to the development of the eye, which makes sense."

Basic plan for life to come was laid in what paleontologists call the cambrian explosion.
It is true that by this time,even considerably "complex" eyes had evolved.The eye hypothesis sounds fascinating but carries with it a load of other explanations of worth.


"And just as a funny aside. I've read that evolutionists that believe change occurs at slow steady pace are called "creeps" and those that believe not much happens for a long time and then suddenly some animals change drastictly in a short time are called "jerks". I have no idea how often these terms are actually used ny researchers."

I think the opponents of PE may refer to it as "evolution by jerks",little to do with scientific terminology of course.

 

[Supercharts]

Dawkins and Gould fought over this quite a bit. There's a book of the collected essays between Dawkin's and Gould about this entire subject. I forget the title and publisher but it's quite a lively debate.
But I could be wrong.

 

[Dragon]

Dawkins and Gould fought over this quite a bit. There's a book of the collected essays between Dawkin's and Gould about this entire subject. I forget the title and publisher but it's quite a lively debate.
But I could be wrong.

Here's a page of links and articles on the Gould/Dawkins debate (from a site dedicated to Dawkins - but it is balanced). The first link there gives an overview.
I've never really understood why this debate, between two brilliant communicators of science to the wider world, was quite so acrimonious.

 

[Hexxenhammer]

Here's a page of links and articles on the Gould/Dawkins debate (from a site dedicated to Dawkins - but it is balanced). The first link there gives an overview.
I've never really understood why this debate, between two brilliant communicators of science to the wider world, was quite so acrimonious.

Evolution debate always seems to be acrimonious even if it's between two evolutionists. Richard Leakey got into it with another anthropologist (his name escapes me)over the human family tree. They really seemed to dislike one another.

 

[JSFolk]

Some of the quotes on this page are of interest.

Gould and Eldridge became famous for popularizing PE, but "... the periods during which species have undergone modification, though long as measured by years, have probably been short in comparison with the periods during which they retained the same form. It is the dominant and widely ranging species which vary most frequently and vary most, and varieties are often at first local--both causes rendering the discovery of intermediate links in any one formation less likely. Local varieties will not spread into other and distant regions until they are considerably modified and improved; and when they have spread, and are discovered in a geological formation, they appear as if suddenly created there, and will be simply classed as new species." sure sounds like punctuated equilibrium to me.
The source? The sixth edition of "The Origin of Species" C. Darwin, 1872

 

[Dragon]

Some of the quotes on this page are of interest.

Gould and Eldridge became famous for popularizing PE, but "... the periods during which species have undergone modification, though long as measured by years, have probably been short in comparison with the periods during which they retained the same form. It is the dominant and widely ranging species which vary most frequently and vary most, and varieties are often at first local--both causes rendering the discovery of intermediate links in any one formation less likely. Local varieties will not spread into other and distant regions until they are considerably modified and improved; and when they have spread, and are discovered in a geological formation, they appear as if suddenly created there, and will be simply classed as new species." sure sounds like punctuated equilibrium to me.
The source? The sixth edition of "The Origin of Species" C. Darwin, 1872

Superb! I had some vague recollection about this but you've found the exact quote. It's amazing how Darwin got so much right even though he new nothing of genetics.

 

[arcticpenguin]

Yes, it is impressive how complete Darwin's grasp of evolution was. He developed the theory for decades before he finally published, under threat of competition.

 

[jj]

One explanation for this is that, say, a small daughter population is separated from the mother population. The smaller population can evolve faster (smaller gene pool, more chances of gene drift, etc, etc) and if it is re-introduced into the territory of the mother population, rapidly supplant members of the old pop. In the fossil record this would look like "rapid evolution" even though it's not the mother population evolving, but rather getting replaced by the new improved model.

I think another explanation that would seem to have some basis in fossil records is that when an organism evolves something new (say for instance primitive vascularization in plants), the new species have so much more viability that the rapid spread looks instantaneous.

 

[Dymanic]

Originally posted by jj

I think another explanation that would seem to have some basis in fossil records is that when an organism evolves something new (say for instance primitive vascularization in plants), the new species have so much more viability that the rapid spread looks instantaneous.

Every organism has a range in which conditions favor its survival, and populations tend to become stable within that range. The type of 'sweep' of a gene pool you suggest depends not only on a mutation producing a significant advantage, but also on it producing a relatively drastic change -- this is highly disfavored probabilistically.

Niles Eldrige explained this very well in Reinventing Darwin: The Great Debate at the High Table of Evolutionary Theory.

As you approach the outer edges of an organism's range, conditions generally become less favorable, until you reach a point at which any individuals able to survive at all are unlikely to reproduce successfully. Even if some mutation occured which would better equip offspring for survival at the edge of the range (or even beyond), that mutation would (by definition) make the offspring less suited to life nearer the middle of the range, so it can't take hold unless a sub-population becomes reproductively isolated from the main population. Evolving independently of the main population, such a daughter population might then chance on something that would be a significant advantage back in the home range.

Another way of looking at it is that the main population had reached an adaptive peak, but it wasn't the highest one around. Reaching the higher peak meant backing up so as to permit passage through a fitness valley, but backing up is an evolutionary no-no. The sub-population, though, started in a fitness valley (being under-adapted to their environment, which was outside the ancestoral range) and climbed a different peak (which turned out to be higher).

A lot of the debate around PE seems to have centered on whether it is anything all that exciting a new; such allopatric speciation is easily handled by mainstream Darwinism.

 

[hgc]

This little book sums up the Dawkins/Gould debate quite nicely. Quick read, and reasonably accessible to the layman (such as myself).

 

[hammegk]

Today, we have interesting examples of directly observed, notable evolutionary change which happens in what can be considered a single step in geological time.

Which interesting examples do you have in mind? Or better yet, an uninteresting example.

I.E. Bulls*it!