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Cambrian Explosion and Evolution

DC

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DC
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Mar 20, 2008
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I wondered what is the current state of Science regarding Cambrian Explosion and Punctuated Equilibrium?

Some YTuber just pretty much confused me with quote-mining Gould.
He has like brought up 10 different quites from Gould regarding no intermediates, species stay species etc.

And honestly i don't have much of deep knowledge when it comes to such details.

Is Punctuated Equilibrium a theory or a hypothesis?
what are the alternatives? Scientific one, not dogmatic ones.
 
Stephen Jay Gould proposed punctuated equilibrium. It has some useful points, but doesn't stand alone as an explanation of evolution.

As for the Cambrian Explosion, that's pretty much "old news" with the discovery that it may have taken much longer for the "explosion" to happen than originally thought. No surprise there, of course, the initial shock of finding so many new species so quickly kind of stunned the paleos. Now that they've had time to look the evidence over they're sorting it out.
 
Punctuated equilibrium is a hypothesis[1][2] in evolutionary biology which proposes that most sexually reproducing species will experience little net evolutionary change for most of their geological history, remaining in an extended state called stasis. Punctuated equilibrium also proposes that stasis is broken by rare events of large net change, characterised by rapid events of branching speciation called cladogenesis. Cladogenesis is the process by which species split into two distinct species, rather than one species gradually transforming into another. Thus, "punctuated equilibria is a model for discontinuous tempos of change (in) the process of speciation and the deployment of species in geological time."[3]

Punctuated equilibrium is commonly contrasted against the theory of phyletic gradualism, which states that evolution generally occurs uniformly and by the steady and gradual transformation of whole lineages (anagenesis). In this view, evolution is seen as generally smooth and continuous.
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http://en.wikipedia.org/wiki/Punctuated_equilibrium
 
Gawdzilla said:
Stephen Jay Gould proposed punctuated equilibrium. It has some useful points, but doesn't stand alone as an explanation of evolution.

As for the Cambrian Explosion, that's pretty much "old news" with the discovery that it may have taken much longer for the "explosion" to happen than originally thought. No surprise there, of course, the initial shock of finding so many new species so quickly kind of stunned the paleos. Now that they've had time to look the evidence over they're sorting it out.
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yeah Explosion is so misleading, it lasted 80 million years. that a lot time.

Luckely he stoped the debate after i quote a few of Gould's anti creatards statements.

But i was very weak in that area of punctuated equilibrium and Camrbian time.
 
Things are never as clear cut as a Creationist would like. They have certainty because their source at the end of the day is the Bible. Unfortunatley Science has to deal with the real world and it's a messy place.
 
To be honest, I don't think the Cambrian explosion is that unexpected.

Before Cambrian most organisms were actually quite simple things, lacking in the way of vision or mobility or generally complexity. You were quite the high-tech thing if you were a cup on a small organic pole, filtering plankton as it went by, or some frond like thing filtering food as it went by, or, if I remember the age for that one right, a star shaped microbial film filled with jelly and filtered food as it went by. And spent your life either anchored to the floor, or lying on the floor, except when currents moved you somewhere else.

Then leading to the Cambrian, they get eyes and mobility, not to mention a genetic code that allowed such cell differentiation and control over which cell does what.

And suddenly there are a lot more viable configurations for an organism with those. You can burrow, you can swim, you can dodge other predators who are also making good use of those, you start to need body armor to defend against those new predators, etc. As well as an "arms race" for who gets a better configuration for that.

I'd think that such an accelerated diversification to fully fill a new niche (except this time the "niche" was the whole old ecosystem and then some) is actually quite expectable.

The Ordovician following it also saw some rapid diversification, to fill the niches freed by the Cambrian-Ordovician extinction. Not as fast as in the Cambrian, but then it also wasn't such a radical new design or filling as big a suddenly available "niche".

Though probably a better comparison would be the land parts of the Devonian. Plants, animals _and_ arthropods have quite the rapid evolution and diversification, once one goes on land and starts evolving to fill all those newly available niches.
 
DC said:
But science has no single answer, it might be that or that. when i understand correctly, what made the debate rather hard for me :(
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That, that, that, or any combination thereof.

Unfortunatley, creationists tend to recurse to binary thinking. I once had one triumphantly that evolution was proved false by phenotype flexibility. He simply couldn't wrap his mind around the idea that both could be true.

Hans
 
HansMustermann said:
To be honest, I don't think the Cambrian explosion is that unexpected.

Before Cambrian most organisms were actually quite simple things, lacking in the way of vision or mobility or generally complexity. You were quite the high-tech thing if you were a cup on a small organic pole, filtering plankton as it went by, or some frond like thing filtering food as it went by, or, if I remember the age for that one right, a star shaped microbial film filled with jelly and filtered food as it went by. And spent your life either anchored to the floor, or lying on the floor, except when currents moved you somewhere else.

Then leading to the Cambrian, they get eyes and mobility, not to mention a genetic code that allowed such cell differentiation and control over which cell does what.

And suddenly there are a lot more viable configurations for an organism with those. You can burrow, you can swim, you can dodge other predators who are also making good use of those, you start to need body armor to defend against those new predators, etc. As well as an "arms race" for who gets a better configuration for that.

I'd think that such an accelerated diversification to fully fill a new niche (except this time the "niche" was the whole old ecosystem and then some) is actually quite expectable.

The Ordovician following it also saw some rapid diversification, to fill the niches freed by the Cambrian-Ordovician extinction. Not as fast as in the Cambrian, but then it also wasn't such a radical new design or filling as big a suddenly available "niche".

Though probably a better comparison would be the land parts of the Devonian. Plants, animals _and_ arthropods have quite the rapid evolution and diversification, once one goes on land and starts evolving to fill all those newly available niches.
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Thanks, that is indeed a good explanation.
 
As I understand it, the current views are complex. See, the problem is the Cambrian Explosion (CE) A) wasn't an explosion, B) happened well after the rise of complex animals, and C) isn't that well understood.

A) It happened over a few million years. It's a remarkable amount of diversification, but it's also a remarkable amount of time. It was called an explosion back when we had one locality for it. I know of four off hand, one of which is a long weekend trip for me (San Bernardino County, California). We have a much better view of how long the event took now, and it's only an explosion in geological terms.

B) This one confuses people. Most people know about the CE. What they don't know about is the Ediacara Fauna, which consisted of animals prior to the Cambrian which were complex, relatively large (some were as long as my forearm), and...well, frankly weird. We're still debating what the bloody things ARE--we know they're animals, but after that it's mostly anyone's guess. Some say they're primative forms of modern animals, but those arguments are about as rediculous as an argument can get before the editor of the journal literally dies laughing. My take? They're something completely new, something we have no modern analogs for. Then there's the Small Shelly Fauna, which is exactly what it states--it's a bunch of small shells that we know came from animals, but we can't pinpoint WHICH animals. And sadly we have no conservat lagerstattens to aid us.

Oh, and keep in mind that most of the more famous CE sites are Middle Cambrian in age. And there are a number of Precambrian trace fossils, which may or may not have been fromed by complex animals.

C) We have maybe a half dozen sites for the CE. The fauna from the first site is still being hotly debated. Things back then were WEIRD. It's increadibly difficult to figure out what the environment was like, let alone the selective pressures. This isn't like the dinosaurs, where we've got the basics and are filling in details (let's face it, all vertebrates follow more or less the same body plan); this fauna throws our assumptions of what's normal out the window, which makes it very challanging to figure out. Which is most of the fun.

And we don't know what caused it. The theory I hold with (very tentatively) is that there was a chemistry change in the oceans, which allowed for the preservation of hard parts. Remember, paleontologists don't deal with organisms, we deal with fossils--prior to the rise of hard parts it's VERY unlikely that we'll see anything. I always put it this way: If every worm went extinct today, the ecosystem would collaps. Paleontology would never see it. Meaning that, thanks to the vagerancies of taphonomy, soft parts only rarely make it into the fossil record. And there aren't a whole lot of people looking for conservat lagerstattens in Pre-Ediacara rock.

As for Punctuated Equilibrium, it's one of several viable tempos of evolution. Marine plankton tend to follow the "Cone of Increasing Diversity" model until they reach some equilibrium state, from what I've heard (never got into micropaleontology that much). Large animals tend towards punk. eq. The thing to keep in mind, though, is how long "fast" is--Gould speculated that speciation would happen in 10,000 generations once it got started. For humans, that's 10 millenia. For bacterial, that's 200,000 minutes. And this is a speculative average--it could be a lot longer/shorter. Punc. eq. is a good thing to keep in mind, but not something earth-shattering.

The real question with the CE is why only one or two phyla evolved after it. We should have expected something similar when animals invaded land, and we didn't see it (though to be fair, Arthropoda is polyphyletic). Chordates are still chordates. Mollusks are still mollusks. Why the dirth of novel body plans?
 
DC said:
But science has no single answer, it might be that or that. when i understand correctly, what made the debate rather hard for me :(
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.
Why would there need to be a "single answer"?
P.E. makes sense to me, explaining -some- of what we see. It need not explain all.
It is a subset of "all".
Like Newton's gravity is a subset of Einsteinian thought.
It explains a feature, but does not take on the whole subject.
 
HansMustermann said:
To be honest, I don't think the Cambrian explosion is that unexpected.

Before Cambrian most organisms were actually quite simple things, lacking in the way of vision or mobility or generally complexity. You were quite the high-tech thing if you were a cup on a small organic pole, filtering plankton as it went by, or some frond like thing filtering food as it went by, or, if I remember the age for that one right, a star shaped microbial film filled with jelly and filtered food as it went by. And spent your life either anchored to the floor, or lying on the floor, except when currents moved you somewhere else.

Then leading to the Cambrian, they get eyes and mobility, not to mention a genetic code that allowed such cell differentiation and control over which cell does what.

And suddenly there are a lot more viable configurations for an organism with those. You can burrow, you can swim, you can dodge other predators who are also making good use of those, you start to need body armor to defend against those new predators, etc. As well as an "arms race" for who gets a better configuration for that.

I'd think that such an accelerated diversification to fully fill a new niche (except this time the "niche" was the whole old ecosystem and then some) is actually quite expectable.

The Ordovician following it also saw some rapid diversification, to fill the niches freed by the Cambrian-Ordovician extinction. Not as fast as in the Cambrian, but then it also wasn't such a radical new design or filling as big a suddenly available "niche".

Though probably a better comparison would be the land parts of the Devonian. Plants, animals _and_ arthropods have quite the rapid evolution and diversification, once one goes on land and starts evolving to fill all those newly available niches.
Click to expand...
.
Prior to the Cambrian stuff, there were living things which left few if any descendants.

http://en.wikipedia.org/wiki/Ediacaran_biota
 
I Ratant said:
.
Why would there need to be a "single answer"?
P.E. makes sense to me, explaining -some- of what we see. It need not explain all.
It is a subset of "all".
Like Newton's gravity is a subset of Einsteinian thought.
It explains a feature, but does not take on the whole subject.
Click to expand...

it would be easier if there was one :D
 
I Ratant said:
Why would there need to be a "single answer"?
Click to expand...
Yeah, that's the problem when you throw biology into the mix--different organisms react differently. There's no single right answer, there's only the possible range of answers, and the parts of that range the organisms fill. P.E. is a great mode of evolution, and explains what we see in many fauna remarkably well, but to take it as The One True Mode is just as wrong as to say it never happens.

A better way to look at it is as one of several working hypotheses for how any individual taxon evolved. There are several potential correct answers, and all we need to do is figure out which actually happened.

it would be easier if there was one :D
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But a lot less fun. ;)
 
Thanks for the good answers :)
Seems i have fallen for his strawmen that Punctuated Equilibrium and phyletic gradualism are mutual exclusive, while it seems they more go hand in hand.
 
I Ratant said:
.
Prior to the Cambrian stuff, there were living things which left few if any descendants.

http://en.wikipedia.org/wiki/Ediacaran_biota
Click to expand...

Yes, I know about those, but those seem to be

A) exactly the kinds of things I'm talking about. They were much simpler things with apparently not much mobility and most of which just lied on the ocean floor. There just isn't as much of a pressure to evolve in radically different ways when you're still a tube or frond lying on the ocean floor filtering whatever comes by, and any other creatures that can chase you around also didn't exist.

B) the more complex ones are actually right before Cambrian.
 
No one's denying that complex animals radiated fairly close to the Cambrian. However, the Ediacara has a rich fossil record (well, relatively) of complex animals well before the Cambrian. Also, as I stated before, the issue is one of preservation. Until organisms evolved hard parts there isn't much chance of being fossilized; it's been argued quite effectively that the C.E. is really the diversification of shell forms. And as I said earlier, we just don't know what kinds of soft-bodied organisms there were prior to the Cambrian. There could have been all sorts of nectic soft-bodied things that we either haven't found or which never fossilizied in the first place.

Characterizing Precambrian animals as simple tube-things lying on the ground is a mischaracterization of the fauna. The only thing we can really say is "We don't know what animals were like". And you still haven't addressed the trace fossils of the Precambrian, which argue for complex, mobile organisms relatively early.
 
Well, no paleontologist does. And that statement holds true for a paleontological definition of "close to". ;)
 
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