Ernst Haeckel's embryological diagrams and biology textbooks

[A'isha]

How is it that there would be such wide differences early in development if common ancestry explains some similarities later in development?

Because there is little cell diversification in the early stages of embryo development, and little need for conserved developmental stages when nothing has really developed yet. They start to differentiate isologously, but even though the way these particular differentiated groups are consistent from species to species, the specific pattern of cell specialization and grouping does not come from the transcriptome (it seems to be epigenetic), and therefore the phylogenetic similarities of related organisms don't necessarily result in developmental similarities in the early embryonic stages.

However, in the middle stages of development, larger-scale organization of specialized cells that will develop into the later morphological features of the organism are created. At this point, similar large and intermediate scale structures will need to be established in the organism, even if the specific final form of those structures will later be converted into something else in the adult animal - in vertebrates, for instance, this is an overt head, trunk with segmented vertebrae and pharyngeal arches. During this stage, the phylotypic stage, there's more transcriptome similarity among related species (like vertebrates): whereas it didn't matter to the final organism how the building blocks were gathered together, it matters now that they're being arranged into a specific pattern, which is now regulated directly by the genome rather than epigenetically, resulting in similar gene expression and (often) morphological arrangement, since the genes doing that regulation are very similar in those species.

Once that's done, the need for conserved developmental stages is over - once you get pharyngeal arches, that structure can then be modified by later stages in development into things like the pharynx in humans and gills in fish. That's why developmental similarity thus tapers off after the middle stage.

Didn't the divergence early in development, according to evos, indicate an evolutionary break?

You're mistaking divergence in development with divergence in the genome. The phylotypic stage is an effect of conserved gene expression.

 

[A'isha]

Here's a little help for you ANT. Since you will undoubtedly refuse to deal with any analysis you fear hurts your case unless evos acknowledge it elsewhere and even then, you may still avoid it, here is an example of one of the researchers you cited mentioning the same data driven analysis I came up with, but you chose to pretend has no merit, etc, etc,....



http://www.physorg.com/news/2011-06-evolutions-waistline.html

Posting this may yet produce an emotional backlash from you, however, as if you accept the researcher's stated problem here, which is the same thing I mentioned, you would have to admit I actually knew what I was talking about and your railing against me was unfounded and just flat out unconscionable.

But on the other hand, if you do not admit the problem exists, everyone can see you are ignoring the scientists you trumpeted that agree with me on the point that they have a hard time explaining divergence within the earlier stages.

It will be interesting to see how you respond.

Will you apologize for falsely claiming I knew nothing, etc,.....? And so man up so to speak?

Or continue to dodge?

Been there, done that, read the actual paper.

 

[randman]

ANT, if you want to present tentative ideas at the beginning stages to try to solve this issue, fine, but don't pretend as you are here, that the problem does not exist, nor that it has been solved. The authors of the paper cite some possible research to try to explain the problem but unlike you, they acknowledge it as a real problem that has not yet been solved, and they say the exact same thing I have.

Did you not read the paper before you cited it?

If you had, then how could you miss I brought up a point, on my own I might add, that your cited paper also brings up. I had not read the paper but was delighted to see they recognized the issue and specifically cited it in the paper.

You claim:

Because there is little cell diversification in the early stages of embryo development, and little need for conserved developmental stages when nothing has really developed yet.

But that's totally incorrect, especially for molecular analysis such as this paper. Superficially, it doesn't seem much has developed compared to how much more will develop but on a molecular level, the encoding for specific parts and pathways has already occurred.

Note the author's comment below, btw, and think about it a little.

“It’s obvious that later developmental stages will not exist if earlier stages fail to develop successfully.”

 

[randman]

So ANT, since you understand perfectly well why earlier stages are more divergent, perhaps you'd like to write and explain your findings to the authors of the paper you cited?

They appear confused. Otherwise, why did one make this comment?

These findings offer new fuel for the evo-devo debate, but also raise complicated questions. “It is puzzling for me how vertebrate embryos established differences in early developmental stages while conserving the mid-embryonic stages,” says Irie. “It’s obvious that later developmental stages will not exist if earlier stages fail to develop successfully.”

How could it be puzzling to him but not to you?

 

[A'isha]

Wow, it really didn't take you long to go from "Evos are wrong because they thought there was a phylotypic stage, but it doesn't exist!" to "Evos are wrong because the phylotypic stage exists!"

We've always been at war with Eastasia, haven't we, randman?

How could it be puzzling to him but not to you?

Because I read the Discussion section of their paper, where the authors raise questions about the phylotypic stage data they have uncovered and discuss the various thoughts on both their results and the results of others, and make several "reasonable deductions", including the fact that their results match a prediction made by Kaneko and Yomo's 1997 isologous theory of cell differentiation based on dynamic interaction:

Regardless of the mechanism of the conservation of mid-embryonic stages, a certain characteristic of embryogenesis seems to be required to explain the waist of the hourglass model. In other words, how did vertebrate embryos allow the early developmental stages to diverge while keeping the following stage essentially unchanged? For example, in spite of considerable phylogenetic divergence in the mechanisms of vertebrate germ layer formation and gastrulation32 among the four species we analysed, all these embryos pass through the conserved pharyngula stage. How did vertebrates establish divergence of early embryogenesis while keeping pharyngular stages conserved? One reasonable deduction from this observation is that early vertebrate embryogenesis reduces the developmental fluctuations, which tend to occur around these stages, much like earthquake-resistant buildings that are built with the 'flexible structure'33. This stabilizing role of early-to-mid developmental process is consistent with a prediction of the theory called 'isologous diversification for cell differentiation' in complex systems biology34. In addition, it is important to note that developmental stages might be more or less uncoupled from each other, which would allow evolutionary changes to be introduced rather independently; indeed, adults and larvae are said to evolve and diverge independently35.

This is why science isn't done via interviews by journalists, randman.

At any rate, Irie himself, unlike you, doesn't seem all that concerned that his discoveries threaten the very foundations of evolutionary theory:

Irie now hopes to obtain further support for the hourglass model by expanding his approach to include well-characterized invertebrate species, such as the fruit fly. He also intends to dig deeper into the nuts and bolts of development. “We would like to go down to the level of tissues and primordial organs to find which structures have been conserved during evolution,” he says.

 

[randman]

Wow, it really didn't take you long to go from "Evos are wrong because they thought there was a phylotypic stage, but it doesn't exist!" to "Evos are wrong because the phylotypic stage exists!"

No, I've been clear all along I do not and still do not believe the evidence shows a phylotypic stage, and that evos fail to realize that even if true, it would be evidence against them, not for it.

Evos often have one set of confusion piled on top of another.

Oh and ANT, once again tentative proposed solutions are different than having it all figured out as you claimed.

Why not address the substance of the issue here honestly?

 

[dasmiller]

No, I've been clear all along I do not and still do not believe the evidence shows a phylotypic stage, and that evos fail to realize that even if true, it would be evidence against them, not for it.

So you believe that there's no phylotypic stage, and that the absence actually provides support for evolution, and that most developmental biologists don't understand the data and issues as well as you do?

 

[randman]

So you believe that there's no phylotypic stage, and that the absence actually provides support for evolution, and that most developmental biologists don't understand the data and issues as well as you do?

It's not just me. The existence of the phylotypic stage is hardly universally held. Taking the hourglass model molecular may seem convincing to some like ANT but it's not a concept universally accepted, which the link she cited says as well.

But a larger point is if it were true, it would not be evidence for common ancestry but rather design since the earliest stages diverge more than the middle stage(s) according to the hourglass model.

I think I've explained this at least 5-6 times now. Should be clear enough by now.

 

[Reality Check]

But a larger point is if it were true, it would not be evidence for common ancestry but rather design since the earliest stages diverge more than the middle stage(s) according to the hourglass model.

The larger point is that there is current evidence that the phylotypic stage exists and that it can be explained in detail by evolution.

The best explanation that I have found is on the Panda's Thumb blog which goes through some of the latest (2010) papers:
It’s just a stage. A phylotypic stage. Part I.
It’s just a stage. A phylotypic stage. Part II: The flies
It’s just a stage. A phylotypic stage. Part III: Fish and more

Specifically, the authors took their phylostratigraphic data and merged it with expression data at various stages of zebrafish development; they called the resulting parameter the transcriptome age index (TAI). Basically, they calculated a relative age of the genes that are turned on at each stage of development, corrected for the extent to which particular genes are being used at those stages. Then they mapped the TAI onto the timeline of zebrafish development. And this is what they saw
(figure)
Does that look familiar? Like, say, half an hourglass? In the earliest stages of development, active genes are young-ish, as they are in the juvenile and the adult. In between, the genes that are active are older – a lot older. And the low point, where genes are oldest? It’s the end of segmentation and the beginning of the pharyngula stage.

This science is in stark contrast to the IDiots and creationists who can only hand wave about the phylotypic stage because they have no actual mechanism to explain it (other than undefined or mythical beings).

 

[randman]

So how do you explain the earliest stages being so divergent?

Isn't that signaling an evolutionary break assuming common descent for sake of argument?

 

[pakeha]

Here's a little help for you ANT. Since you will undoubtedly refuse to deal with any analysis you fear hurts your case unless evos acknowledge it elsewhere and even then, you may still avoid it, here is an example of one of the researchers you cited mentioning the same data driven analysis I came up with, but you chose to pretend has no merit, etc, etc,....



http://www.physorg.com/news/2011-06-evolutions-waistline.html

Posting this may yet produce an emotional backlash from you, however, as if you accept the researcher's stated problem here, which is the same thing I mentioned, you would have to admit I actually knew what I was talking about and your railing against me was unfounded and just flat out unconscionable.

But on the other hand, if you do not admit the problem exists, everyone can see you are ignoring the scientists you trumpeted that agree with me on the point that they have a hard time explaining divergence within the earlier stages.

It will be interesting to see how you respond.

Will you apologize for falsely claiming I knew nothing, etc,.....? And so man up so to speak?

Or continue to dodge?

As usual, randman spends time and effort in useless vulgarity.
And I went around to the link.
That was it?

Anyone even going to try to answer the data and analysis here?
Let me break it down further. Many evos say the hourglass model aka the phylotypic stage is evidence for common ancestry. The evidence indicates the hourglass model is incorrect but some try to argue for it.

However, evos miss the point that the hourglass model is actually evidence against common descent and ancestry. The reason is they admit embryos start out very different; hence the wide brim of the top of the hourglass, but say they converge into a more similar stage...

Now evos can shout this is akin to being a Holocaust denier but it's actually just data-driven analysis, something evos ought to try sometimes.

randman, it's a model, and intellectual construct.
Where are you coming from?

...Is it because you are incapable of following the reasoning or what?

More bad manners

Are you even going to try to deal with the data driven analysis I gave you showing how the hourglass model would not be evidence for common ancestry?

Or are you going to keep dodging the issue?

What is the point of this exercise, randman?

Been there, done that, read the actual paper.

Thanks for the link! That was quite interesting to see for myself.

...This is why science isn't done via interviews by journalists, randman.

At any rate, Irie himself, unlike you, doesn't seem all that concerned that his discoveries threaten the very foundations of evolutionary theory:

Thanks and thanks again. I hadn't read the discussion section and it seems clear randman has simply indulged in misrepresentative quote-mining.
Again.

 

[A'isha]

So how do you explain the earliest stages being so divergent?

Isn't that signaling an evolutionary break assuming common descent for sake of argument?

No. Read the third of Reality Check's links. The genes corresponding to the conserved phylotypic stage are among the oldest genes in the lineage. In other words, those genes arose first, and the genes for early and late development evolved later. If this were a case of an evolutionary break leading to convergent evolution, the genes for the phylotypic stage would be either just as new or newer than those for the other stages. Instead, what we see is those genes have stayed the same for the longest period, and it's the genes for the other stages that have evolved and diverged.

 

[Dinwar]

So how do you explain the earliest stages being so divergent?

Evolution does not require conservative embryology, any more than it requires conservative adult morphology. Things can change, sometimes even wildly, through evolutionary processes.

Seems simple enough. It's really only Creationists/ID advocates who think embryos need to be identical. Differences in morphological development should probably even be expected under the evolutionary paradigm--a more efficient way to build a baby would lead to decreased gestation periods, which would certainly benefit the kind of species that have huge numbers of offspring of which only a few survive. (There's an important bit here that I'd like to point out: my idea is emminantly testable. ID isn't, and cannot be until they define what the Designer is.)

 

[RandFan]

Oh and ANT, once again tentative proposed solutions are different than having it all figured out as you claimed.

Because:

• Not having it all figured out means "god did it".
• "God did it" is having it all figured out.

 

[Cainkane1]

Goddidits the bottom line among IDers apparently.

 

[Reality Check]

So how do you explain the earliest stages being so divergent?

Explained in the thrid link.

How do IDiots explain the earliest stages being so divergent?
How do creationists explain the earliest stages being so divergent?
List the actual scientific explanations from them, e.g. the published papers.

 

[randman]

No. Read the third of Reality Check's links. The genes corresponding to the conserved phylotypic stage are among the oldest genes in the lineage. In other words, those genes arose first, and the genes for early and late development evolved later. If this were a case of an evolutionary break leading to convergent evolution, the genes for the phylotypic stage would be either just as new or newer than those for the other stages. Instead, what we see is those genes have stayed the same for the longest period, and it's the genes for the other stages that have evolved and diverged.

How do you know which genes are older?

The truth is all present gene types existed before plants and animals arose according to the most up to date evo molecular studies (assuming common descent) and so claiming any present gene is older than another is silly.

 

[randman]

The larger point is that there is current evidence that the phylotypic stage exists and that it can be explained in detail by evolution.

The best explanation that I have found is on the Panda's Thumb blog which goes through some of the latest (2010) papers:
It’s just a stage. A phylotypic stage. Part I.
It’s just a stage. A phylotypic stage. Part II: The flies
It’s just a stage. A phylotypic stage. Part III: Fish and more


This science is in stark contrast to the IDiots and creationists who can only hand wave about the phylotypic stage because they have no actual mechanism to explain it (other than undefined or mythical beings).

The problem is all basic gene types predated fish, plants and animals according to the latest evo molecular studies (assuming common descent) and so trying to say some genes are older than others is rather silly.

 

[Reality Check]

The problem is all basic gene types predated fish, plants and animals according to the latest evo molecular studies (assuming common descent) and so trying to say some genes are older than others is rather silly.

The problem is that you are doubly wrong.

• There are no 'gene types'.
• The fact of evolution means that the theory of evolution can use that fact to state that some genes are older than others.

This is really simple. For example, some major genes arose at specific points in time

• Before there were land dwelling animals there were no genes for hair.
• Before there were birds there were no genes for feathers.

 

[randman]

The fact of evolution means that the theory of evolution can use that fact to state that some genes are older than others.

This would be funny if it wasn't so sad you cannot see the problems with it. First, it's circular reasoning. Secondly, you are wrong on genes. Genes are in types or families, and the latest science is shown by this comment:

“The cells which gave rise to plants and animals had more types of genes available to them than are presently found in either plants or animals,” explains William Loomis, a professor of biology at UCSD and one of the key members of the international sequencing effort.

http://ucsdnews.ucsd.edu/newsrel/science/mcamoeba.asp

So considering all these genes predated animals and plants, it's a bit silly on your part to say some are older for fish than they are for mammals.