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Author
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Topic: Ontogenetic Depth and the Origin of Animals
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Argon
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Member # 276
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posted 15. September 2003 11:33
"If two organisms are not related by common descent, how would you-evolutionists know it?"
Good question. I think that has been addressed a couple pages ago. But let's generalize the question so that Paul can contribute his thoughts too:
If two organisms are not related by common descent, how would one know it?
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Paul A. Nelson
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Member # 26
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posted 15. September 2003 12:05
Argon asked:
quote:
If two organisms are not related by common descent, how would one know it?
I'll write about this in the commentary materials appended to my SDB 2003 poster pdf.
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gordon
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Member # 781
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posted 15. September 2003 12:36
Walter ReMine wrote:
quote:
The systematic absence of clear-cut lineages and ancestors.
in reference to, basically, the failure of 'Darwinism.'
I am not usre I understand why this should be expected of evolution - the very nature of Nature seems to prohibit the "clear cut" lineages and ancestors as ReMine seems to think should be in abundance.
I am curious as to whether Discontinuity Systematics does provide evidence of, or better yet, examples of, "clear cut lineages and ancestors".
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andyg
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Member # 415
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posted 15. September 2003 13:04
Paul wrote:
quote:
Sorry about being delayed in getting the pdf of the poster up here with commentary. I hope Andy Groves will join the discussion (Andy, are you reading this?)
Yes.
AndyG
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Walter ReMine
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Member # 906
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posted 15. September 2003 20:19
gordon
Darwin's Origin of Species never discussed the origin of species -- the process of cladogenesis. Instead, his book discussed the transformation of species through time -- anagenesis or LINEAGE. Also, anagenesis (not cladogenesis) is where natural selection was said to operate. Yes, the classical Darwinians expected to find identifiable lineages. I'd say the classical Darwinians themselves contradicted your notion of what evolution predicts. Their research program devoted many resources and over a hundred twenty years in the search for clear-cut ancestors and lineages -- and failed. Indeed, they went considerable distance in (unintentionally) creating, what turned out to be, an illusion that ancestors are clear and had been identified. An entire systematic methodology (Darwinian Systematics) went down with it. And the entire edifice of illusion constructed by the Darwinian Systematists (e.g. paraphyletic groups) had to be torn down by the cladists and thrown in the dumpster of history.
I have to keep it very short here, because the moderator wants us back on track. I'm looking for guidance from Paul on what he wants his thread to pursue here.
My question currently on the table: How do evolutionists explain von Baer's laws? (I don't think evolutionists ever explicitly answered that. Darwin's answer was implicit, and very incomplete. The difficulty arises when evolutionists seriously attempt to explain von Baer's laws. Try it!)
-- Walter ReMine
The Biotic Message
Discussion
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andyg
Member
Member # 415
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posted 15. September 2003 21:08
Walter wrote:
quote:
How do evolutionists explain von Baer's laws?
Von Baer's laws have been described as:
(I) The more general characters of a large group of animals appear
earlier in their embryos than the more special characters.
(II) From the most general forms the less general are developed, and
so on, until finally the most special arise.
(III) Every embryo of a given animal form instead of passing through
the other forms, becomes separate from them.
(IV) Fundamentally, therefore, the embryo of a higher form never
resembles any other form, but only its embryo.
(Raff Rudolf A., Kaufman Thomas C. 1983. Embryos, Genes and Evolution:
The Developmental-Genetic Basis of Evolutionary Change. )
Which ones are you having a problem with?
AndyG
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Walter ReMine
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Member # 906
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posted 16. September 2003 03:44
andyg
Yes, you correctly recited von Baer's laws in their classic form.
First, do leading evolutionists embrace those (in some form or other) as substantial?
Second, an evolutionary explanation please........
-- Walter ReMine
The Biotic Message
[ 16. September 2003, 03:50: Message edited by: Walter ReMine ]
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andyg
Member
Member # 415
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posted 16. September 2003 12:37
Walter wrote:
quote:
First, do leading evolutionists embrace those (in some form or other) as substantial?
Second, an evolutionary explanation please........
To your first question - I don't know. Perhaps you should write to some leading evolutionists and ask them. Von Baer's work is often cited in textbooks, usually under the section dealing with refutations of Haeckel's theory of recapitulation. It certainly isn't a cornerstone of evolutionary theory as far as I can see. For example, in Futuyma's "Evolutionary Biology" (3rd edition) , Von Baer's laws take up exactly one paragraph in a book of 763 pages.
To your second question, there appears to be a significant conservation of the molecular processes underlying the development of body forms. In chordates, for example, the signaling events that bring about neural induction and mesoderm induction are extremely well conserved. Moreover, the requirement for morphogenetic movements that constitute gastrulation seem to be highly conserved too.
In other words, the reason why the basic body plans of different chordate embryos look the same is because the molecular and morphological processes that form them are the same.
The fact that divergence of different chordate bodies occurs later in embryological development is simply a consequence of the fact that you necessarily have to make a limb (or eye or ear, or whatever) primordium before you make the limb itself. Specializations of the limb are therefore likely to occur after the assignment of the limb territory. Common sense, really.
More on this topic:
Old Brainstorms thread
and here:
Article by PZ Myers
AndyG
[ 17. September 2003, 21:10: Message edited by: andyg ]
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Walter ReMine
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Member # 906
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posted 17. September 2003 23:53
andyg wrote:
quote:
"I don't know. Perhaps you should write to some leading evolutionists and ask them."
The evolutionists' views on von Baer's laws ought be a matter of public record by now. If evolutionists privately hold views at odds with their publications, then that would be their fault.
quote:
"Von Baer's work is often cited in textbooks, usually under the section dealing with refutations of Haeckel's theory of recapitulation."
Yes. That is ironic...
My question isn't concerned with whether von Baer's laws are formally a "cornerstone of evolutionary theory." Evolutionists don't put it that strongly, (and there is a reason why, as I point out below). Evolutionists are a bit more indirect about the matter. Darwin found the embryological evidence for evolution "second to none", and von Baer's laws are frequently cited by evolutionists as our best generalizations of embryological patterns, indeed Gould recognized von Baer's laws as "probably the most important words in the history of embryology." Evolutionists (such as Gould and others) significantly embrace von Baer's laws (not recapitulation theory), and convey the impression that von Baer's laws are compatible with common descent.
I am challenging that latter point in order to bring something deeper to light: Given their commonplace presence within embryological writings, has any evolutionist given an explicit evolutionary explanation of von Baer's laws? How are those laws explained by evolution?
-- Walter ReMine
The Biotic Message
P.S. andyg: Your post discussed a special case, but contained no explanation of von Baer's laws. Sorry. The article by PZ Myers frequently misrepresented Jonathon Wells. It mentioned von Baer a view times, but gave no explanation of von Baer's laws.
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andyg
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Member # 415
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posted 18. September 2003 12:48
Walter,
I'm sorry - I thought my explanation above was what you were looking for.
I think you have to understand that the similarity of vertebrate embryo forms at some point in their development is merely compatible with common descent. It doesn't prove common descent to the exclusion of other hypotheses. It can also be compatible with a lot of other explanations too, such as special creation by God.
If you think that similarities between different types of embryo are NOT compatible with common descent, can you describe why?
As for my description of the "developmental hourglass" - I would hardly refer to it as a "special case". It's perhaps the best example of why von Baer's "Laws" don't concern developmental biologists very much. I guess that calling them "von Baer's generalizations" doesn't sound so impressive...... ![[Wink]](wink.gif)
AndyG
[ 18. September 2003, 14:58: Message edited by: andyg ]
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Walter ReMine
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Member # 906
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posted 18. September 2003 15:46
Does anyone here know any evolutionist who has given an explicit evolutionary explanation of von Baer's laws? (I'll take andyg's diversions as indicating he doesn't know of any.) Surely a pattern so commonly addressed in the literature ought have an evolutionary explanation, or at least an attempt. Do you know of any? It's a simple question, please stop trying to divert it.
I am calling evolutionists out on this.
-- Walter ReMine
The Biotic Message
P.S. andyg had previously offered a special case as though it were an explanation of von Baer's laws. It wasn't. It was merely a special case. (And no, I am not here referring to his mention of the "developmental hourglass".)
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andyg
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Member # 415
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posted 18. September 2003 17:00
**Sigh**
I thought at first that you wanted a mechanistic explanation for why embryonic development is the way it is, and I gave one. You then seemed to suggest that embryonic similarities is not compatible with common descent, and I corrected you.
Walter, the explanation for the similarity of embryonic development in different animals is that the animals derived from a common ancestor. Is that really so hard? You seem to be suggesting that there's some other deep meaningful issue here, and I can't see what it is.
AndyG
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Walter ReMine
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Member # 906
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posted 18. September 2003 19:36
Yes, there are deep meaningful issues here. And the first step toward those, which we have now established, is that evolutionists have not given an explicit explanation of von Baer's laws. Not now. Not ever.
The second step comes when you try to provide that. The explanation should sound something like this: "The following evolutionary mechanisms, operating in the following way, will produce all the patterns described in von Baer's laws ........" TRY IT! I CHALLENGE YOU! At that point the evolutionary contradictions come to light -- which is why evolutionists staunchly avoid explicit attempts at explaining von Baer's laws.
I am puncturing the illusion, long-lived since the time of Darwin, that von Baer's laws are easily 'compatible with,' 'predicted by,' or 'evidence for' evolution.
-- Walter ReMine
The Biotic Message
P.S. If andyg found my simple, direct question uninteresting, he would merely ignore it. However, I object to his repeated misrepresentations of it, and diversions from it.
P.P.S. To the moderator -- I do intend to tie all this even more directly to deeper issues of this thread.
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andyg
Member
Member # 415
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posted 18. September 2003 20:01
Walter,
I have a modest proposal, and one which (hopefully) will bring this thread back on topic again.
Forget Von Baer's laws. They aren't laws in the sense that scientists understand them. They are generalizations.
Let's deal with the observations, and stick with vertebrates for the time being. Vertebrate embryos share many similarities in the period shortly after gastrulation. The explanation for this is that the early signaling and morphogenetic events in embryogenesis are conserved. The explanation for that is common ancestry. The fact that limb buds appear in vertbrates before digits do is common sense.
What more is there to explain? What patterns have I not accounted for?
quote:
I am puncturing the illusion, long-lived since the time of Darwin, that von Baer's laws are easily 'compatible with,' 'predicted by,' or 'evidence for' evolution.
The fact that vertebrate embryos share similarities at early stages in their development is compatible with common descent. It can be used as evidence for common descent. If one came up with notion of common descent out of the blue, one would predict that embryos might share similarities early on. It's certainly a valid retrodiction.
Why are these illusions, and how are you puncturing them? At the moment all you seem to be offering is opinion masquerading as fact.
AndyG
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RBH
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Member # 380
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posted 18. September 2003 21:48
ReMine says quote:
I am puncturing the illusion, long-lived since the time of Darwin, that von Baer's laws are easily 'compatible with,' 'predicted by,' or 'evidence for' evolution.
Given no references it's difficult for someone outside this discussion to decide what the appropriate locution is, "compatible with," "predicted by," or "evidence for." So I went out looking around a little and found Stephen Jay Gould (in the March 2000 Natural History) on von Baer's law: quote:
Von Baer's law makes good sense, but nothing in Darwinian theory implies or requires its validity, while evolution itself clearly permits embryology to proceed in either direction (or in no linearized manner at all): from embryonic similarity to adult discordance (as in groups that follow von Baer's principle) or from larval discordance to adult likeness (as in several invertebrate groups, notably some closely related sea urchin species, where larvae have adapted to highly different lifestyles of planktonic floating versus development from yolk-filled eggs that remain on the seafloor. Meanwhile, the highly similar adults of both species continue to live and function like ordinary sea urchins).
The bottom line may now be simply stated: the validity and relative frequency of von Baer's law remains an open, empirical question within evolutionary theory, an issue that can be resolved only by observational evidence from a wide variety of organisms. Moreover, this issue has become quite important in the light of current excitement over recent advances in genetics that have finally allowed us to identify and trace the genes regulating early development. In this crucial and valid context, Richardson wisely chose to reevaluate our complacency about the probable validity of von Baer's law. (Emphasis added)
It leads one to believe that ReMine's rhetoric is much to-do about the wrong thing. As AndyG remarked, and as Gould's examples illustrate, von Baer's "law" is an empirical generalization over some limited number of instances, not a pillar of evolutionary theory: it is not a natural "law" as science understands "laws". Thus ReMine's request for an evolutionary explanation of von Baer's "law" is a request for the explanations for a bunch of instances - their particular causal histories and contingencies - not for a general law of nature.
RBH
(Edited to add URL)
[ 18. September 2003, 22:26: Message edited by: RBH ]
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