Punctuated equilibrium

[juvenissun]

No, I am saying that it isn't always aplicable.

If so, then it is un-necessary.

 

[juvenissun]

Sorry if I sounded confusing, we kind of got sidetracked from the basic idea with all the discussion of environmental catastrophes... You could try this for a breakdown of the PE model. It's got pictures and all

The only way to understand the fossil record is to use what we know of living things and ecosystems today. That, in this case, includes some basic facts about population genetics.

If so, it also says that PE is not needed.

 

[NailsII]

If so, it also says that PE is not needed.

So, are you saying that we don't need a working theory to explain the observations found in the fossil record?

 

[variant]

If so, then it is un-necessary.

It would be "unessisary" like red would be unessisary in the case that the entire world presents in shades of blue.

It's not the case though, the world is both red and blue.

Evolutionary history has examples that fit both models.

This isn't physics that describes forces consistantly, evolutionary history is describeing events among millions upon millions of species over the history of the earth. The rate of evolution depends on the exact circumbstances of those species and their enviroments.

Darwin did his work before we were even aware of genetics. He proposed a gradual change because he did not observe quicker ones. Gould, knowing that the rate of evolution is mutable, and having more examples from evolutonary history proposed a differn't picture of how species evolved and the rates that it happened.

Sometimes the change is gradual and sometimes it is not.

 

[RickG]

If so, it also says that PE is not needed.

It is not needed, but it (abrupt environmental changes) hurry's things along and insures diversity. Without PE life would probably resemble that of the Devonian or Silurian Periods.

I'm not asking you to accept the concept, just understand what it says. Fair enough?

 

[juvenissun]

So, are you saying that we don't need a working theory to explain the observations found in the fossil record?

No. But it seems we already have a better one. Don't we?
Why do we still need it if all it gave are some conditional uncertainties?

 

[juvenissun]

It is not needed, but it (abrupt environmental changes) hurry's things along and insures diversity. Without PE life would probably resemble that of the Devonian or Silurian Periods.

I'm not asking you to accept the concept, just understand what it says. Fair enough?

Fine. I don't study paleontology very well. PE to me is put to a even lower level. I am just curious and hope to get some ideas from you people.

The process of PE should also be applied to Proterozoic, right? Can we apply it to those creatures found in the Burgess Shale? I think the simpler the life form, the more applicable the PE. Is that right?

 

[juvenissun]

It would be "unessisary" like red would be unessisary in the case that the entire world presents in shades of blue.

It's not the case though, the world is both red and blue.

Evolutionary history has examples that fit both models.

This isn't physics that describes forces consistantly, evolutionary history is describeing events among millions upon millions of species over the history of the earth. The rate of evolution depends on the exact circumbstances of those species and their enviroments.

Darwin did his work before we were even aware of genetics. He proposed a gradual change because he did not observe quicker ones. Gould, knowing that the rate of evolution is mutable, and having more examples from evolutonary history proposed a differn't picture of how species evolved and the rates that it happened.

Sometimes the change is gradual and sometimes it is not.

I think there must be something which bothered the gradualism too much so that the idea of PE emerged. Could you explain what is that serious problem of gradualism? (I promise that I won't say: AHA, creationism!)

 

[RickG]

The process of PE should also be applied to Proterozoic, right?

Yes, but only where PE events take place.

Can we apply it to those creatures found in the Burgess Shale? I think the simpler the life form, the more applicable the PE. Is that right?

No, I disagree with that. First of all, I don't see an PE event associated with the Burgess Shale, just an exceptionally well persevered cache of middle Cambrian fossils. Remember, with PE extinction events are at the forefront. This usually causes a reshuffling of the predatory hierarchy allowing other species to flourish where they previously could not. Also adaptation to those new environments is essential.

 

[NailsII]

I think there must be something which bothered the gradualism too much so that the idea of PE emerged. Could you explain what is that serious problem of gradualism? (I promise that I won't say: AHA, creationism!)

The evidence caused a problem for gradualism, as it explains much but not all of the fossil finds.
There are specific periods in pre-history where evolution has flourished in the geological blink of an eye, which gave rise to punctuated equilibrium.

 

[variant]

I think there must be something which bothered the gradualism too much so that the idea of PE emerged. Could you explain what is that serious problem of gradualism? (I promise that I won't say: AHA, creationism!)

The problem that Gould was addressing were examples where fossils that changed very little over very lengthy periods of time, achieving a homeostasis between their genetic makeup and the relatively stable environment and then suddenly changed or were replaced with many new (but very similar) species over a relatively short period of time.

The problem of gradualism is the problem of stasis and the genetic stability of large centralized populations.

The issue here is the speed at which speciation does occur at, where it occurs, and what happens afterward which are all open areas of biological study.

What exactly is happening in the fossil record is still up for debate because gradual changes piling up (somewhere else and migrating in) looks a lot like the sudden appearance of a new species.

 

[Naraoia]

If so, it also says that PE is not needed.

How does that follow?

It is not needed, but it (abrupt environmental changes) hurry's things along and insures diversity. Without PE life would probably resemble that of the Devonian or Silurian Periods.

Or more likely Proterozoic.

The process of PE should also be applied to Proterozoic, right? Can we apply it to those creatures found in the Burgess Shale?

PE is primarily an explanation of why we rarely observe smooth transitions between closely related (ancestor/descendant) species. If you mean applying it to the Cambrian explosion, no, I don't think it's very applicable - we're not talking just about speciation there, but large-scale morphological change. There are gaps and (relatively) sudden appearances there, of course. However, it's not at all obvious that the incompleteness or suddenness of phylum-level transitions is caused by the same mechanisms as the incompleteness of species to species transitions.

I think the simpler the life form, the more applicable the PE. Is that right?

Why would it be?

I think there must be something which bothered the gradualism too much so that the idea of PE emerged. Could you explain what is that serious problem of gradualism? (I promise that I won't say: AHA, creationism!)

I think you should read the original proposal of PE. There's a bit of a philosophical statement in there, but it's probably the best place to go for the answer to your question.

In short: the problem is that examples of smooth species to species transitions in the fossil record are extremely rare (if they exist at all; Eldredge and Gould didn't seem convinced). Traditionally, this had been explained by the incompleteness of the fossil record - but what if the gaps are biologically meaningful, and not just random data deficiencies?

Remember, with PE extinction events are at the forefront.

Wait, what?

 

[Jro]

The problem that Gould was addressing were examples where fossils that changed very little over very lengthy periods of time, achieving a homeostasis between their genetic makeup and the relatively stable environment and then suddenly changed or were replaced with many new (but very similar) species over a relatively short period of time.

I think it's worth pointing out that you can't tell if a fossil population has achieved homeostasis between its genetic makeup and environment, but only between its morphology and its environment.

 

[variant]

I think it's worth pointing out that you can't tell if a fossil population has achieved homeostasis between its genetic makeup and environment, but only between its morphology and its environment.

True enough.

 

[Guy1]

For most of the nearly 4 billion years that life has existed on Earth, evolution produced little beyond bacteria, plankton, and multi-celled algae. Then all of a sudden all the basic body plans found in nature today are here: bodies with heads, tails, and appendages, all specialized segments performing specialized functions. All animal evolution for the last half billion years has come from tinkering with these Cambrian body plans.

This is more consistant with creationism rather then evolutionary theory.

By definition, this is evolution; not creationism.

 

[variant]

This is more consistant with creationism rather then evolutionary theory.

Why did you quote me on this one? What you said had nothing to do with what I said.

Creationism explains nothing because it explains everything and can explain anything.

Also why would that be consistant with a creator? What was the creator doing for those first couple billion years?

 

[NailsII]

For most of the nearly 4 billion years that life has existed on Earth, evolution produced little beyond bacteria, plankton, and multi-celled algae. Then all of a sudden all the basic body plans found in nature today are here: bodies with heads, tails, and appendages, all specialized segments performing specialized functions. All animal evolution for the last half billion years has come from tinkering with these Cambrian body plans.

Plenty of body plans not seen today also evolved in the 'cambrian explosion'.
Note with interest, this 'all of a sudden' you are referring to was a period of at least 15 million years.

This is more consistant with creationism rather then evolutionary theory.

How so?
Creation states, unequivocally, that god made the cosmos in 6 days (or ages). The bible does not claim that complexity of living systems increased over time - hundreds of millions of years in fact.
Evolution doesn't happen in the same order, or in neat and tidy little timescales, and creation says nothing of extinctions for a start.

 

[Wiccan_Child]

For most of the nearly 4 billion years that life has existed on Earth, evolution produced little beyond bacteria, plankton, and multi-celled algae.

First billion years: no life
Second and third billion years: simple life
Fourth and fifth billion years: complex life

1 billion years of no life, 2 billion years of simple life, 1.5 billion years of complex life. In the time that evolution has been working, 42% has been complex life. Pretty good.

Then all of a sudden all the basic body plans found in nature today are here: bodies with heads, tails, and appendages, all specialized segments performing specialized functions. All animal evolution for the last half billion years has come from tinkering with these Cambrian body plans.

"All of a sudden"? No. "Over hundreds of millions of years"? That's more like it.

This is more consistant with creationism rather then evolutionary theory.

Genetic variation in environmental attrition manipulated by natural selection to create radiative adaptation - specifically, the adaptation over time of phenotypes from genetic mutation and natural selection?

Yes, sounds just like creationism...

 

[juvenissun]

I think it's worth pointing out that you can't tell if a fossil population has achieved homeostasis between its genetic makeup and environment, but only between its morphology and its environment.

The environment (physical and biological) keep changing all the time. Are humans in the state of homeostasis? We passed through several (?) ice ages since our appearance. If we are not, then what species could?

 

[juvenissun]

How does that follow?

Or more likely Proterozoic.

PE is primarily an explanation of why we rarely observe smooth transitions between closely related (ancestor/descendant) species. If you mean applying it to the Cambrian explosion, no, I don't think it's very applicable - we're not talking just about speciation there, but large-scale morphological change. There are gaps and (relatively) sudden appearances there, of course. However, it's not at all obvious that the incompleteness or suddenness of phylum-level transitions is caused by the same mechanisms as the incompleteness of species to species transitions.

Why would it be?

I think you should read the original proposal of PE. There's a bit of a philosophical statement in there, but it's probably the best place to go for the answer to your question.

In short: the problem is that examples of smooth species to species transitions in the fossil record are extremely rare (if they exist at all; Eldredge and Gould didn't seem convinced). Traditionally, this had been explained by the incompleteness of the fossil record - but what if the gaps are biologically meaningful, and not just random data deficiencies?

Wait, what?

What do you mean by "smooth" transition? Are you referring to the argument of transitional fossils? So, we like to see morphological change on fossils like 1 3 5 7 9 ... But instead, we see 1 4 5 11 20 ... ? So, PE got in and suggested: there must be some dramatic environmental changes happened which lead to the "fast" change between the 11 and the 20. Is that right?