Cambrian explosion: Burgess Shale: punctuated equilibrium

verysincere

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Do your research first, then open your mouth. Otherwise you won't look like you know an awful lot.

Unfortunately, there's more than one person on this forum who endorses the "Research can take a hike!" mantra.

I commend you for your patience. (It certainly exceeds mine. But then I have the added embarrassment of having to explain that many of us are truly creationists -- in the original definition of the term as one who affirms that God created everything -- and we do NOT reject the scientific evidence nor the conclusions reached from that evidence.)

.
 
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Jazer

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if there were as you say other people alive before Adam and Eve where did they come from?
The Bible is a history of the last 6,000 years. IF there were other people alive before Adam and Eve you will have to look at the natural record, the DNA and talk to science. You will not find anything in the Bible about it. So you are pretty much barking up the wrong tree. Are you trying to suggest that the Hebrew people today do not have a common ancestor as the Bible says. Then your argument is with science. Because science clearly tells us that we all have a common ancestor. For the Hebrew's Brian sykes gives her the name of Jasmine. Science would assign Eve in the Bible the J2B2 Mutation. That would put Eve in the Haplogroup J2. Clearly the Bible tells us who the decendents of Eve was. Even there are stories about her decendents. You have people like Ruth, David and eventually Even Jesus is decended from Adam and Eve in the Bible.

302433_163572983721461_100002062816270_348023_4622218_n.jpg
 
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RickG

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That seems to be clear that you do not have a response. Other then to mix up and confuse what I said.

Actually he was pretty much "spot on".

You keep going on about there were not enough phyla to explain the CE. Well, here's a news flash for you, there aren't all that many phyla today either because the biological division of phyla is near the top of all those divisions. In fact, even today there are less than 3 dozen animal phyla and only a dozen of plant phyla. To get to species you still have to go through class, order, family, genus and finally species. But even species can be subdivided as well.

Just passing on info, have a nice day. :)
 
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RickG

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I asked a VERY SIMPLE QUESTION. I am still waiting for an answer. What common ancestor did the phyla evolve from in the Cambrian Explosion. Is this question to difficult for all of the evo experts out there?

Face palm.
 
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No, I would say that you managed to do that entirely on your own.
Why is it that so much of what you say is rude and crude? Didn't your mamma teach you that if you can not say nothing nice then don't say nothing at all. Or that uncultured people can talk like that but a refined person knows how to show a bit of restraint.
 
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juvenissun

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I'm not sure how often PE is observed in molecular evolution. It was intended mainly as an explanation of the fossil record.

This is where I don't like the idea of evolution the most. It seems that I am talking to two different persons but have the same identity. When one get stuck, he simply says: not me, it is him.
 
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Valkhorn

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I asked a VERY SIMPLE QUESTION. I am still waiting for an answer. What common ancestor did the phyla evolve from in the Cambrian Explosion. Is this question to difficult for all of the evo experts out there?

I posted an entire presentation from an accredited college course showing what ancestors gave rise to the CE and you ignored it.

I'll repost it:
http://www.csun.edu/~dgray/Evol322/Chapter17.pdf

If you can't follow it, why don't you email the professor yourself?
evol322.html
 
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Valkhorn

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This is where I don't like the idea of evolution the most. It seems that I am talking to two different persons but have the same identity. When one get stuck, he simply says: not me, it is him.

It's more likely that those who support Evolution are so versed in the subject that they are able to cite and reference the actual opinion of scientists - which is very convergent.

If you ask two separate people who know a few things about physics how gravity works and get the same response, it's not because they are the same people.
 
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juvenissun

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It's more likely that those who support Evolution are so versed in the subject that they are able to cite and reference the actual opinion of scientists - which is very convergent.

If you ask two separate people who know a few things about physics how gravity works and get the same response, it's not because they are the same people.

Exactly. In the former case, one person can give 10 answers. And in the latter case, 10 people give one answer.
 
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Naraoia

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I will see if I can find it. But the basic argument has to do with Convergent & Parallel evolution. These are cases where there was no common ancestor. In the case of the protein you had it evolve in at least 25 independent organisms. Again no common ancestor. Although this is considered to be a example of Convergent evolution.
Are you talking about analogous enzymes? Because the whole point of that list is that these are NOT the same protein. They have no sequence similarity beyond that expected from chance, and they have completely different structures. This is why we think they evolved independently under similar selective pressures.

You are the evo, so go ahead and explain it away as to how you can have evolution without common ancestors that you find in Convergent and Parallel evolution.
Note: parallel evolution does have a lot to do with common ancestors. The way I understand the term, it refers to cases where

(1) a feature evolved indepedently in two related lineages
(2) from a common precursor
(3) in a similar way

One example I can think of is the loss of pelvic spines in three- and nine-spine sticklebacks. Because a gene called Pitx1 is a master regulator of pelvis development in both (and, in fact, in all vertebrates with a pelvis), switching it off in the pelvic area is a straighforward way of getting rid of the bones, and in fact both stickleback species followed this route.

Convergence refers to cases where features with similar functions evolved independently, but in different ways. The wings of insects and birds are a clear-cut example - different ancestral structures, totally different wings. The wings of the three groups of vertebrate fliers are slightly less so, since the starting material is the same forelimb - but the actual details of the resulting wings are quite different. (Incidentally, this is a point worth remembering: there is not a sharp line between parallelism and convergence.)

Because like the Cambrian Explosion they like to try and hide this information away. Until Gould came along and blew the lid off of it.
Once more, no one was trying to hide information. Walcott didn't think the Burgess Shale creatures were that special, and preparing and describing tens of thousands of specimens is a hell of a lot of work. For all people knew, there wasn't much point in going into all that trouble. No one quite realised how strange some of the creatures were until a bunch of crazy grad students (again, IIRC Gould didn't actually have a major part in reexamining Walcott's fossils) decided to fiddle around with them.

But you read Wonderful Life, didn't you? Where else would you be getting these ideas from?

(I should add that Gould's view of the Burgess Shale is pretty radical. Being radical was his modus operandi.)

I thought it was clear that we were talking about the common ancestor for the animal phyla that showed up in the Cambrian explosion. There were perhaps 50 of them and around 30 were said to have survived.
Oh, right.

To the best of our knowledge, the last common ancestor of animals may have looked something like this:

Dayel_Protero_colony_100x.jpg


(Colony of Proterospongia/Salpingoeca rosetta by Mark Dayel from the King lab. Source: ChoanoWiki.)

This is a colonial choanoflagellate - choanoflagellates are the closest living relatives of animals based on molecular phylogenies, and the fact that sponges (which are animals) possess food-capturing cells very similar to these confirms the link.

The most recent common ancestor of bilaterian animals (which could be described in a very simplified way* as "anything with a head and tail end"), which most of the Cambrian explosion was about, is a tough nut. The outgroup (sponges, jellyfish, comb jellies and... Blobs) are a diverse bunch each with their own derived quirks, and there is no living bilaterian that is an obviously good proxy for the last common bilaterian ancestor (or the Urbilaterian for short). We don't have a direct fossil record of the creature either, but there are several lines of evidence we might follow to narrow the possibilities:

(1) We know that it possessed several genetic pathways that organise the body plans of distantly related modern bilaterians. Examples include Hox genes for defining regions along the head to tail axis, BMP signalling to define the back and belly sides, Pax6 and Six to organise simple eyes, and possibly, Notch/Delta signalling to generate repeated body sections or repeated structures like the "rungs" of the prototypical ladder-like bilaterian nervous system. (Here's a very nice image of an annelid embryo with its nervous system stained in yellow - you can see the repetition here very clearly. While annelids are segmented animals with pretty much everything in them repeating like that, ladder-like nervous systems also occur in animals no one would call "segmented", for example, flatworms.)

(2) We know that possessing the genetic pathways "for" something doesn't necessarily mean that you also possess a full-blown version of that something. Case in point: the gene expression pattern that defines hands and feet actually originated well before hands and feet themselves.

(3) We know that the Urbilaterian lived quite far into the Precambrian - certainly before definitive bilaterians like Kimberella (~555 Mya, mid-Ediacaran). Clearly, the last common ancestor of a group had to live before any recognisable subgroups of that group appeared, and Kimberella is generally considered to be a relative of molluscs, many branches into the bilaterian tree.

(4) We know that the Precambrian is very poor in trace fossils like trackways and burrows, which quickly become abundant in the Cambrian. This suggests that the ancestral bilaterian was likely relatively small and simple - large, complex, active bilaterians tend to leave traces.

Putting all of that together, I think this Urbilateria guy was most likely a simple soft-bodied "worm" with a head and tail end and perhaps a flatworm sort of nervous system.

*Very simplified because of the inevitable exceptions. For example, starfish and other echinoderms are undisputed bilaterians, but their adults have (more or less) radial symmetry and not much of a head.

***

... by the way, that's what you get when you bring up a subject I've actually read a lot about. Thank (mostly) a third-year essay assignment for the length of the above :D If anything went over your head, I'm happy to explain. Just ask ;)

So what? There are two theories and they can not both be true.
But both are utterly irrelevant to whether life on earth (or animals, or anything on earth) had a common ancestor. The evidence for common ancestry - nested hierarchies and fossils - is equally valid regardless of the detailed mechanisms.

Does that mean anything goes?
When you are only hypothesising, anything goes (if you're willing to risk being laughed at :p). Not once you start collecting evidence.

Do evolutionists even know what they believe in?
We're certainly far less confused about our beliefs than you are :p

You must have more confidence then I do that you can somehow blend opposites. Maybe we can get you a job as a marriage counselor if your so good to bring reconciliation between extreme viewpoints.
I don't have to blend opposites. The reason there are opposites is because the evidence isn't sufficient to decide either way.

(The determinism of evolution is not a black and white issue anyway; it's a continuum from "nothing would turn out the same" to "everything would turn out the same".)

I think the main thing overlooked in the Cambrian explosion is the basic mechanism driving it, which were significant changes in atmospheric and oceanic chemistry. Prior to that there were several significant and long snowball earth periods. Otherwise, the Cambrian explosion could have occurred a billion or so years earlier.
I'm sure that's part of it, but I'm very reluctant to believe we've already found "the" basic mechanism ^_^ As to the billion years, there isn't really good evidence that animals existed 1.5 billion years ago, is there? They sort of had to be around for them to radiate explosively.
 
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Split Rock

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I asked a VERY SIMPLE QUESTION. I am still waiting for an answer. What common ancestor did the phyla evolve from in the Cambrian Explosion. Is this question to difficult for all of the evo experts out there?

I think Naraoia, answered your question very nicely. And btw... it is NOT a "VERY SIMPLE QUESTION." We are talking about an organism that lived hundreds of millions of years ago and left no known fossil record.
 
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Split Rock

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RickG

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I'm sure that's part of it, but I'm very reluctant to believe we've already found "the" basic mechanism ^_^ As to the billion years, there isn't really good evidence that animals existed 1.5 billion years ago, is there?

Ahhh, well yeah, there is. The oldest undisputed fossils go back 3 billion years and possibly as old as 3.5 million years.

http://physwww.mcmaster.ca/~higgsp/3D03/BrasierArchaeanFossils.pdf

As for the basic mechanism, life for most of Earth's history was pretty well restricted to bacterial life due to the lack of oxygen in the atmosphere and oceans. In fact there is considerable evidence that Earth's atmosphere had less than 1% oxygen 2.4 - 2.1 billion years ago. Aside from an anaerobic atmosphere and ocean life at the oceans surface and on land was completely impossible due to the lack of an ozone layer. The rise of atmospheric oxygen has to be one of the key elements in preparing for the Cambrian explosion.

There has been considerable research into the development of Earth's early atmosphere. Here's just a few.

http://umanitoba.ca/geoscience/people/faculty/bekker/Bekker et al 2004 Nature.pdf
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http://www3.geosc.psu.edu/~jfk4/PersonalPage/Pdf/kump_et_al._G%5E3_01.pdf
http://geoclasses.tamu.edu/atmo/geos489/lecture3/science298_2341.pdf
 
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Naraoia

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This is where I don't like the idea of evolution the most. It seems that I am talking to two different persons but have the same identity. When one get stuck, he simply says: not me, it is him.
Sorry, how does that apply to anything I said?

Ahhh, well yeah, there is. The oldest undisputed fossils go back 3 billion years and possibly as old as 3.5 million years.
None of them are animals. Your argument seemed to be that were it not for the snowball glaciations, the CE could've occurred a billion years earlier. Since a significant part of the CE - and to me, an animal biologist, obviously the dearest - is the radiation of animals, and AFAIK the earliest fossil evidence of animals is well this side of 1 Ga, that logic doesn't fly.

Now, if the billion-year line was hyperbole and you actually meant to argue for an interplay of glaciations and atmospheric chemistry, that sounds better, but it's still too simple a solution to my mind.

(And I'll just leave it at that. I love the CE to pieces, but my views about its nature right now are a giant mess of half-convictions and question marks... for the moment I don't want to get into an argument about it :))
 
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J

Jazer

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the earliest fossil evidence of animals )
I thought the first animal was a slug.
That is little more then a digestive system.
Some people are little more then that now.

How long will you slumber, O sluggard?
When will you rise from your sleep?
10 A little sleep, a little slumber,
A little folding of the hands to sleep—
11 So shall your poverty come on you like a prowler,
And your need like an armed man
 
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RickG

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Now, if the billion-year line was hyperbole and you actually meant to argue for an interplay of glaciations and atmospheric chemistry, that sounds better, but it's still too simple a solution to my mind.

I thought that is what I stated. And I agree, that scenario is stated in simple loosely defined terms. I'm just saying that the cryogenic conditions along with the lack of an oxygen atmosphere and ozone layer is very restrictive with the respect of all life and its diversification.
 
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