The Cambrian Explosion

[achilles12604]

Besides the apologist answer that God was responsible for this phenomina by some method, does secular science have a theory as to the cause of this sudden explosion of new life all at once? (Remember I do not fall for that God of Gaps theory)

I am looking for science answer to this mystery. Anyone care to enlighten me?

[Goat]

The fossil record of the last 3.5 billion years thus shows not a gradual accumulation of biological form, but a relatively abrupt transition from body plans of single cells to those of a rich diversity of animal phyla. (emphasis mine)

[/quote]

Yes, that is a partial quote of the lead into the article. What you are seeing is the technique that is used to 1 ) describe the problem, 2) analyse the problem and 3) propose a solution.

You haven't even done the full paragraph.

The full paragraph is

The fossil record of the last 3.5 billion years thus shows not a gradual accumulation of biological form, but a relatively abrupt transition from body plans of single cells to those of a rich diversity of animal phyla. In geological terms, an explosion indeed. Was this explosion real, or is it an artifact of a strangely biased fossil record?

It goes on , and then proceeds to answer the question.

For example, you didn't include the next paragraph either.

that is

Over the past few years new fossil discoveries have greatly clarified the sequence of events up to and during the Cambrian explosion. This in turn has set the stage for integrating information from several fields that had once operated in near isolation. Modern techniques for extracting and analyzing molecular data have shed new light on the evolutionary relationships among the living animal groups whose roots extend back to, or even precede, the beginning of Cambrian time. Perhaps most extraordinary have been the discoveries in developmental biology. Molecular techniques have shown that the developmental systems that control patterns from eggs through embryos to adults, and thus determine animal architectures, are remarkably similar across a wide range of phyla. In spite of their similarities, which have persisted despite the long separation of the phyla, the systems produce very disparate body plans. Evolutionary biologists can now reconstruct basic aspects of the developmental control systems of long-extinct animals, and can attempt to track not only the diversification of animal form but also the establishment and evolution of the genetic controls that regulate it. Taken together, all these advances are permitting a new, multidisciplinary look at the early history of animals and into the mysteries of the Cambrian explosion.

It seems sort of odd to just quote part of the description of the problem, then assume there isn't any solution to the problem. That is missing the whole point of the article, being able to answer the question being asked.

[Cathar1950]

Fine Rob if you are going to go thru the effort of making changes I guess I can drop it.
I think it is interesting when I think of the millions of years of plant life to clean the water of all that iron with rust so o2 could fill the air
and organisms could take advantage of it. Maybe even more then one line of decent came from that new resource.
I guess it just bothered me that you assumed ignorance because of some book was quoted. There are many obscure studies that have ideas and information that are being wrestled with and it seemed like you were preaching to the choir about some other preachers sermon.

But I was thinking about the idea of common decent thanks to otseng.
The idea of many lines of decent seems interesting.
This would not invalidate evolutionary theory just expand it.
It is possible more then one line of decent may have evolved. I guess everything is of the same line of decent if you start with Atoms or particles.

[Cathar1950]

I got a weird question.
Let look at the most simple life form or even quasi-life form. Say virus single celled organism or less, or maybe bacteria.
I am sure we could find millions or maybe billions of year old creatures or their leftovers fossils, minerals, and such.
Have they evolved from then to their modern day equivalent?
I mean the other way around.
Are today's quasi-life forms, virus, single celled organism or less, and bacteria new creations or are they evolved from those early ones?
What are the changes. Did they have them back then?
Are new ones evolving somewhere? I don't mean from a ameba to a fish either I mean change.

[Rob]

Humans and other Anthropoids share very similar chromosome structure and genomic sequences as seen in the 98.5% homology at the DNA level between us and Great Apes. However, anatomical and behavioral traits distinguish Homo sapiens from his closest relatives. I review here serveral recent studies that address the issue by using different approaches: large-scale sequence comparison (first release) between human and chimpanzee, characterization of recent segmental duplications in the human genome and analysis of exemplary gene families. As a major breakthrough in the field, the heretical concept of 'human-specific' genes has recently received some supporting data. In addition, specific chromosomal regions have been mapped that display all the features of 'gene nurseries' and could have played a major role in the gene innovation and speciation during primate evolution. A model is proposed that intergrates all known molecular mechanisms that can create new genes in the human lineage. (Nahon 2003: 193)

(....) Evolution is neither inherently gradualistic nor punctuated but progresses from one extreme to the other. (Nahon 2003: 204)

-- Nahon, Jean-Louis (2003) "Birth of 'human-specific' genes during primate evolution." In Origin and Evolution of New Gene Functions. Contemporary Issues in Genetics and Evolution (Vol. 10), Reprinted from Genetica, Volume 118 (issues 2-3).

Hi Otseng,

My statement regarding "old quotes" was not meant to refer to your post or use of the article. That was why I said specifically, "You are missing the point it seems goat" that generally speaking the age of quote is not relevant to the question of whether or not it is useful or true. Rather, and more importantly in my view, is the quote taken in full context, and is it true based both upon what was known then and what is known now. After all, that which is old and also true will abide, while likewise, that which is new but false will be rejected. But that which is new and also true, we should have the faith and courage to accept. Is it not written, "Forsake not an old friend, for the new is not comparable to him. As new wine, so is a new friend; if it becomes old, you shall drink it with gladness."

In reference to your post I stated:

What in my view Otseng overlooks or fails to understand is that whether or not the mechanism of how new forms appear is "suddenly" in what has traditionally been called saltations or gradually in small accumulations of changes in gene frequencies makes no difference to the fact that organic evolution has occurred. With the discovery of the Regulatory Genome scientists are now proposing mechanisms by which changes in form can happen "suddenly", pointing out that small mutations effecting the Regulatory Genome can result in large, sudden changes in morphology. In other words, saltations, once pooh poohed, may be real data in the fossil record rather than artifacts of interpretation. But the ultimate forensic record that organic evolution is a fact is found in the same discoveries of the ancient Regulatory Genome that now open up an understanding of the possible mechanisms of sudden changes in form leading to new phyla. And it may well turn out to be a combination of both mechanisms, gradual in some respects and sudden in others. And not one iota of this debate going on within the scientific community challenges the fact that organic evolution occurred.

With all due respect my friend, your logic is flawed in my view in that the rate at which changes in morphology take place makes no difference to the fact of organic evolution. Like many other time-worn creationist arguments, you are setting up a straw man argument, i.e., the definition that evolution must be 'gradualistic' when in fact the fact of evolution is not dependent upon such an assumption or claim, which is really part of one among many theories about the mechanisms of evolution. This is an idea, which has long ago been dealt with in evolutionary theory both within traditional neo-Darwinian theory and in newer versions which are based on new evidence forthcoming from Evo Devo. Whether we see these sudden radiations as periods of increased rates of traditional neo-Darwinian allopatric evolution, or due to ancient master genes and genetic switches (genetic modules) that through combinatorial shuffling evolve diverse body plans, it makes no difference with regards to the fact that organic evolution has taken place.

This new information regarding the arrays of Hox genes and their role in the evolution of body plans (and they show how it could happen suddenly) does challenge some assumptions contained within traditional neo-Darwinian theory, and many scientists are debating this issue right now, and some argue that we are witnessing a re-synthesis of evolutionary theory which will take into consideration this new information, but one thing is perfectly clear -- this new information is the smoking gun that organic evolution has indeed taken place. And the discovery of those master genes and their associated genetic switches that show that the genes that built a fin also built a limb also explains the Cambrian Explosion and confirms the fact of organic evolution.

The coming decade is sure to bring a much deeper understanding of the evolutionary interplay between developmental control genes and the morphologies they help to construct. A partnership of paleontology, developmental biology and molecular systematics has enormous potential to reveal the evolution of the fundamental body plans that characterize all animals.

Otseng,

I have a question for you. I believe one day, ten, twenty, or perhaps fifty years from now, scientists are going to understand the regulatory genome enough to enable them to actually flip the genetic switches they have already discovered in such a manner that they will cause those changes in form that we now recognize as characterizing different phyla. If this actually should happen, then scientists would in real time be bringing about those changes in morphology that we now recognize as those changes brought about through the process of evolution.

If scientists were to be able to do this, what would then say? Upon the basis of what logic and reason would you then argue that evolution never happened? We already have the ancient genetic architectures of the master genes and their associated genetic switches, and should we one day learn to manipulate this regulatory genome to create in the labrotory changes in morphology would this not be strong evidence that what can be done in the labrotory has occurred naturally in the process of evolution?

[Rob]

The idea of many lines of decent seems interesting. This would not invalidate evolutionary theory just expand it.

Hi Cathar,

That is an interesting idea, and coincidently I was just reading about that idea a few hours ago. I am reading a book by a scientist named Leo S. Berg called Nomogenesis, in which he proposes this very and idea. And that was in 1926. And Darwin himself entertained this very idea. So, it would not be so much an expansion, as a returning to older ideas that were forgotten about How we would ever really confirm it on the scientific level I am not sure, as the earliest forms of life did not leave any fossil records. Our only hope would be via molecular biology and molecular phylogenetics.

You ask:

Are today's quasi-life forms, virus, single celled organism or less, and bacteria new creations or are they evolved from those early ones? What are the changes. Did they have them back then?

I really think you would enjoy Carroll's books Cather, as they address these very questions and show how much science has hard evidence shedding light upon them. Here is my best shot at remembering what he said. Virus and Bacteria are evolved from those early forms of life. The most simple single celled organisms, such as bacteria, we have discovered share ancient conserved common genetic modules with worms, mice, and men. Since we don't have access to the DNA of the earliest life forms, we cannot compare the DNA of modern bacteria with the first ancient life forms, but scientists can see that there has been some evolutionary change, yet nevertheless, much to their surprise is conserved.

[achilles12604]

Regardless of if evolution includes or excludes fast development, doesn't the fact the record exists the way it does lend credibility to the bible?

Genesis documents several steps.

waters and lands appearing.

Vegetation and plant life.

animals in the water

Animals in the air.

Animals on the land.

Then finally man.



How does it strike you that this account matches what scientists have discovered to be what happened? And how does it strike you that the people who wrote it had ZERO knowledge of science?

Considering man was the most important thing (in their minds) shouldn't the account have read Man was made and needed these things so God created a place for man and gave him food to eat. Wouldn't this account which is similar to other ancient religions be what we would expect rather than the account that is provided in the beginning of Genesis?


This ties into the explosion in that the stages could be found in the record. This is assuming that genesis was read litterally as quickly developing stages. This idea is an assumption by those who read genesis as a textbook which is not necessarily true.

Really you could read it either way, but no matter which way you read it, science does not contradict the series of events including the advancement of animal species, be it gradually or very quickly. Quickly fits if you want to read genesis as a series of pointed events. Gradually fits if you read genesis as a general overview. In either case, science has supported the writings of the bible, rather than refuting them. And once again the bible was written way before anyone had an scientific knowledge at all.

[jwu]

Animals in the air are in the wrong place though...terrestrial ones came first. The rest has a pretty good chance to get right by guessing or deduction. Herbivores depend on vegetation, hence vegetation had to come before them. Vegetation depends on water and land...

[Jose]

But, what I am challenging is common descent in which all life evolved from a single cell. I know most people see them as one and the same, but for me, they are separate (though related).

I acknowledge that evolution exists, but it occurs in a limited scope. In the diagram above, it would be within each separate "tree" (phylum). What we see in the fossil record is that basically all the phyla arise simultaneously in the Cambrian strata. Only one other phylum, Bryozoa, is first found in a different different strata. So, why did practically all the extant (and extinct) phyla only first appear in the Cambrian? Why did not others arise in the half billion years afterwards (except the lowly Bryozoa)?

It might help to consider some of the things that did appear earlier. Take this guy, for instance, Nimbia occlusa.

These are from the 610 to 600 Ma Twitya Formation in the Mackenzie Mountains, north-western Canada.

Oldest occurrences, such as those from the Twitya and Drook Formations, are taxonomically impoverished. The assemblage becomes rich around 565 Ma (e.g. at the Mistaken Point locality) but does not achieve full diversity until about 555 Ma. From then it continues in full bloom until the Vendian-Cambrian boundary after which, although some taxa linger on, the characteristic assemblage as a whole abruptly disappears.
http://www.palaeos.com/Ecology/Biota/Ediacara.html

Two relevant things here: first, the Cambrian starts at 542 Ma, as defined by, among other things, trace fossils that look like worm burrows or tracks. The age of these first Vendian fossils, Nimbia occlusa is some 60 Ma older. It is no longer correct to refer to the Cambrian Explosion as the first appearance of all the phyla; we now have to go back another 60 Ma and fill in this period.

Second, the Twitya assemblage is, as noted above, "taxonomically impoverished" at the lowest geological levels. There are very few different types of fossils. For all I know, Nimbia is all there is at the beginning. Maybe Nimbia is the common ancestor of current animals; maybe not. At a minimum, though, we have to extend your figure downward a long ways, with only one known critter at the bottom.

By the time we get to the Edicaran, there's lots more diversity. There are these kinds of guys:

Are these diversified descendents of Nimbia? Could be. We don't have DNA to test, so we can't tell for sure. Are they fore-runners of the phyla we know today, that supposedly appeared full-blown in the Cambrian? Doesn't look like it when we view them through our normal lens of "what animals look like now." But do they have characteristics that exist in the phyla we know today?

Let's look at what Rob has been telling us. There's the "regulatory genome," meaning that portion of the genome involved in regulating gene expression, and thereby regulating developmental form. One of the hallmarks for many animals is a repeating pattern of segments, or "meres." The guys above have repeating patterns of segments--even the little frisbee at the bottom, Tribrachidium, whose three "arms" are wrapped around in a little triskelion. Look at those obvious segmental units on each "arm." I'll guess that we're seeing the results of the Master Switch genes that Rob has told us about, and that we're seeing diversity of form because of the way the Regulatory Genome has produced different patterns of expression of those Master Switch genes.

It's not so easy, though, to tell which of the Ediacaran animals is the progenitor of Arthropods, and which is the progenitor of Chordates. Maybe that's because this split had not yet occurred. I'll offer an oversimplification that illustrates part of the problem: without hard parts, it's hard to tell whether the skeleton is on the outside (arthropods) or on the inside (chordates). There are other issues besides this, of course, but the point is: we can't tell which is which. In the Ediacaran, say at 555 Ma, a "short" 10 Ma before the Cambrian "Explosion," there are things that could be precursors to the critters of the Cambrian.

Therefore, the drawing you gave us above, otseng, may be a reasonable representation of a part of history well after the Cambrian. But, to be an accurate representation of the fossils god gave us, we must extend it downward. That extension goes from the 10 lineages shown in your drawing to a smaller number, and eventually to one.

So, from the fossil evidence, starting 3.4 billion years ago, we see very little activity for several billions years. Then half a billion years ago, practically all the phyla is found. And it all came about within 50 million years (some even estimate 10 million years). Then for half a billion years afterwards, practically no new phyla is found.

For the first couple of billion years, we are limited to looking at fossil dots. Even today, if we were stuck with looking, we'd have to classify bacteria as a few types of dots. Bacterial taxonomy relied for years on biochemical and nutritional characteristics; we can now add DNA sequence to get a sharper picture. But none of these tools are available for fossils. Biochemically and genetically, there may have been lots of activity. There probably was--but our tools for "seeing" that activity are rather limited.

There's another way to look at it, as well. Suppose we count the numbers of species. Suppose we quantify the diversity of species. Suppose we look at the total mass of species. By any measure, plants and animals are a tiny fraction of life on earth. At best, we can say that some "interesting event" occurred 50-100 Ma before the Cambrian (or earlier) that enabled some cells to make multicellular things. Those multicellular things then diversified and filled in some niches that single-celled things couldn't use. This wasn't a big deal for the "real" life composed of single-celled things, because these newcomers also created new opportunities for the single-celled guys, as pathogens or symbionts or decomposers. In this view, the bacteria started the show, and remain the major players in it.

But to your question of why no new phyla appeared after the original few. Again, look at what Rob has been telling us. There are constraints. Once you've got a Hox gene family, and once you're using it in a particular way, you can't make big changes to how you use these genes without screwing up development so much that you're dead. Tiny changes can be tolerated, but not big ones.

Add to this an ecological perspective. Barring catastrophes, life fills all of the niches that are available to it at any particular time. A new variation of life, whether phylum or species, cannot easily out-compete the guys who are already established in any particular niche. Instead, the newcomers are out-competed. To get diversification into previously-occupied niches, it seems to take a mass extinction to clear the niches first. As an example, think of mammals not doing much as long as dinosaurs were around. Wipe out the dinosaurs with a meteor, though, and now the mammals can diversify because there's nobody to eat them, and nobody to out-compete them. Then, we get a new equilibrium as the "age of mammals."

So, the normal rules of ecology, and the normal constraints of genetics and development, conspire to place limits on what can be achieved evolutionarily.

The main point I'm trying to get across is that there is a lack of gradualism to be found in the fossil record. I believe this fact is undisputable, even if I quote old quotes or take them "out of context".

Actually, there are a great many well-documented examples of gradual change. Many of them were unknown at the time the old quotes were freshly spoken. So, while it may be true that at one time gradualism was not documented in the fossil record, that is no longer true. BUT it is important to understand the context of this statement. On "short" time-scales of a few million years, in some lineages, enough fossils have been collected to see the pattern expected of gradual change. On longer time scales, and in less well-sampled lineages, we don't have as much data. Nor do we know precisely where and when the "interesting things" occurred--the things Rob refers to when he speaks of changes in regulation of the Master Switch genes, when distinct changes in form occurred (and survived).

In the case of the Cambrian Explosion, it is no longer justifiable to hang onto the old model, that all of the phyla just sort of suddenly appeared. We may not know the precise route that evolution followed, but we certainly know that there wasn't a *pop* and there everything was. There was a very long time beforehand during which lots and lots of gradual events could occur at their leisure.

But to quote a recent full length article:
http://www.americanscientist.org/templa ... &print=yes

About 565 million years ago, the larger, multicellular animals of the Neoproterozoic appear in the fossil record, with their striking variety of form, only to be overshadowed about 35 million years later by the explosion of body plans recorded in early Cambrian rocks: Nearly all known kinds of shelled invertebrates appear then, including clams, snails and arthropods (the group including crabs and trilobites), soon joined by echinoderms and soon thereafter by chordates, the lineage that gave rise to humans and all other vertebrates. All of the basic architectures of animals were apparently established by the close of the Cambrian explosion; subsequent evolutionary changes, even those that allowed animals to move out of the sea onto land, involved only modifications of those basic body plans. About 37 distinct body architectures are recognized among present-day animals and form the basis of the taxonomic classification level of phyla.

The fossil record of the last 3.5 billion years thus shows not a gradual accumulation of biological form, but a relatively abrupt transition from body plans of single cells to those of a rich diversity of animal phyla. (emphasis mine)

So life tootles along for a long time, without having the occurrence of an unplanned, and unplannable, fortuitous event. Then, for whatever reason, a fortuitous event occurs. Whether it's a type of mutation, or a cell-fusion, or what isn't critical right now. The point is, a fortuitous event occurred. After that event occurred, some new possibilities were made available. It may have taken 60 million years to get from a simple multicellular form to a bunch of different forms, but that is, strictly speaking, "relatively short" compared to 3.5 billion years. How long it took to get to that first-known simple multicellular form, we don't know. We could add another 50 million years, or even a billion years (1.2 billion was the last I heard for the prokaryote/eukaryote split). Even with the "relatively short" 50 million years added in, we're still talking about a very long time.

In the end, I think this is a time-scale problem. "Deep time" is too hard for people to grasp. All I can do is compare the sizes of the numbers, or maybe create "model representations" as clock-faces, or maybe road trips. Even so, the times are just too immense. It's easier to turn it around and think of it in terms of "human lifetimes," and recognize that the 60 Ma between Nimbia and the first recognizable trilobite is immensely long.

[Goat]

This news article just was printerd about complex life. Some fossils from China show that multicelluar life started 10 million years before the Cambrian Explosian, so the 'seeds' of the increased diversity happened a lot sooner than originally though.

http://www.physorg.com/news79884109.html

Embryo Fossils Reveal Animal Complexity 10 Million Years Before Cambrian Explosion

Fossilized embryos predating the Cambrian Explosion by 10 million years provide evidence that early animals had already begun to adopt some of the structures and processes seen in today's embryos, say researchers from Indiana University Bloomington and nine other institutions in this week's Science. James Hagadorn of Amherst College led the multi-disciplinary international collaborative project.

[Cathar1950]

It sounds to me like you are saying jwu;
Just because they got a couple of things in the right order, with no details, but not al of them, that it does not prove the whole bible is right and perfect.

I can agree with that.