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Author
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Topic: John A. Davison: An Evolutionary Manifesto: A New Hypothesis For Organic Change
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Art
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Member # 179
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posted 11. June 2003 22:44
I'm still wondering about Davidson's take on Triticale.
More generally, I'm confused by the manifesto. It seems to me to make broad and sweeping claims about biology, yet is at odds with so much of plant and microbiology that I am inclined to view it more as some sort of statement about animal biology.
I also think that a treatise such as this would be much strengthened by reference to, and discussion of, recent (e.g., since 1990) ideas that pertain to morphological evolution. I'm not sure the term "regulatory evolution" even appears in the treatise. And it must, if it is to be considered as a serious analysis of current ideas about evolution.
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Pim van Meurs
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Member # 541
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posted 11. June 2003 23:58
Davison: I am a firm believer in Intelligent Design as I see it everywhere in the living world. I do not even regard it as debatable.
Hence the use of the term belief which shields it from any scientific inquiry. I too see by faith the handywork of my Lord in the world around us.
Thus when you make the logically falacious claim that "Darwinism, as it is based on chance, cannot accept Intelligent Design" you seem to suggest that chance and ID are irreconcilable opposites furthermore complicated by your simplistic portrayal of Darwinism as "based on chance" alone.
What is especially troublesome to me is that your 'claims' about Darwinism suggest a lack of familiarity on your part with the more recent literature on Darwinism.
Certainly it may be hard to do science ID-wise or evolution-wise if one hold the stance that ID is not debatable and that Darwinism must thus be wrong.
Charlie and others have provided you with good examples of Darwinian evolution. Feel free to address them or ignore them but one can hardly claim that there is no evidence for Darwinian evolution.
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nosivad
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Member # 767
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posted 12. June 2003 06:45
It is true that my arguements for the semi-meiotic hypothesis stem largely from animal material I am a zoologist. I have secifically indicated that it has yet to be demonstrated that creatures reproducing by obligatory sexual means are able to exceed the subspecies. As an experimental biologist I would require an experimental verification that speciation actually had a strict sexual basis. One cannot simply look at nature and assume that speciation occurred sexually. Michael J.D. White cast considerable doubt on sex as an evolutionary device as I have indicated in the Manifesto. If evolution is an experimental science then speciation should be demonstrable experimentally. The Darwinian, gradualist model has not met that criterion. The saltational semi-meiotic model has not been rigorously tested. Until it too fails, I will adhere to it. On the other hand, it is perfectly conceivable that evolution is not subject to experiment but has resulted from the expression of internal forces which may no longer be operating. Pierre Grasse suggested as much and Otto Schindewolf felt that evolution was not subject to experiment. I continue to be amazed at the certainty with which so many evolutionists regard the mechanisms which have produced the living world. I am not among them.
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nosivad
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Member # 767
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posted 12. June 2003 06:53
Pim, it is very revealing that you contrast ID with evolution. There is no basis for that whatsoever. Evolution was very real and as far as I can tell so was ID. I have simply asked the question - Has evolution been guided? I also added that the question may never be resolved. I hope that serves to clarify my position.
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charlie d.
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Member # 159
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posted 12. June 2003 07:50
quote:
It is true that my arguements for the semi-meiotic hypothesis stem largely from animal material I am a zoologist. I have secifically indicated that it has yet to be demonstrated that creatures reproducing by obligatory sexual means are able to exceed the subspecies. As an experimental biologist I would require an experimental verification that speciation actually had a strict sexual basis. One cannot simply look at nature and assume that speciation occurred sexually. Michael J.D. White cast considerable doubt on sex as an evolutionary device as I have indicated in the Manifesto. If evolution is an experimental science then speciation should be demonstrable experimentally. The Darwinian, gradualist model has not met that criterion. The saltational semi-meiotic model has not been rigorously tested. Until it too fails, I will adhere to it. On the other hand, it is perfectly conceivable that evolution is not subject to experiment but has resulted from the expression of internal forces which may no longer be operating. Pierre Grasse suggested as much and Otto Schindewolf felt that evolution was not subject to experiment. I continue to be amazed at the certainty with which so many evolutionists regard the mechanisms which have produced the living world. I am not among them.
More vague platitudes, and appeals to others' opinions. Could you please try addressing the evidence?
As for the semi-meiotic model not having been tested, I was wondering whether you did at least some of that yourself, either before publishing your 1984 paper, or at the very least in the following years, when you still were active and with a lab. Maybe you can let us know how far your experimentation has gone, what kind of results you obtained, and whether they were ever published.
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Jack Foster
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Member # 79
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posted 12. June 2003 08:23
CharlieD wrote:
quote:
More vague platitudes, and appeals to others' opinions. Could you please try addressing the evidence?
I thought this was ISCID brainstorms, and that we were discussing Dr. Davison's Evolutionary Manifesto! Nosivad might expect this reaction at Talk Origins, . . . but not here.
Dr. Davison: quote:
As an experimental biologist I would require an experimental verification that speciation actually had a strict sexual basis. One cannot simply look at nature and assume that speciation occurred sexually. Michael J.D. White cast considerable doubt on sex as an evolutionary device as I have indicated in the Manifesto. If evolution is an experimental science then speciation should be demonstrable experimentally. The Darwinian, gradualist model has not met that criterion. The saltational semi-meiotic model has not been rigorously tested. Until it too fails, I will adhere to it.
This doesn't seem particularly vague. What I find vague is the general tenor of the criticism. This is brainstorms, but nobody seems to be brainstorming on the semi-meiotic model.
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nosivad
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Member # 767
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posted 12. June 2003 09:30
In response to Charlie d. There were several factors which served to prevent me from testing the semi-meiotic hypothesis. I do not feel compelled to discuss them as they add nothing to the present discussion. As to the sources which I have cited, I am sorry that you find their perspectives unacceptable. I hope that you and others recognize that I, as a nonspecialist, have relied heavily on the conclusions of some of the most distinguished biologists of the twentieth century. Their conclusions formed the basis for my thesis and certainly cannot be considered platitudes.
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Art
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Member # 179
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posted 12. June 2003 13:18
quote:
It is true that my arguements for the semi-meiotic hypothesis stem largely from animal material I am a zoologist. I have secifically indicated that it has yet to be demonstrated that creatures reproducing by obligatory sexual means are able to exceed the subspecies.
Hi Dr. Davidson,
There's a reason I have asked about Triticale. The reason is because it is an example (not the only one, but one that my lazy ways can call upon quickly) that refutes your statement.
quote:
As an experimental biologist I would require an experimental verification that speciation actually had a strict sexual basis.
As a suggestion to imrpove your paper, I would suggest that you remove rhetorical gambits such as this strawman. For, as I alluded to in my prior post, it has no relevance to the vast scope of the biological sciences, and it is a poor representation of current views of specciation or evolution. (Heck, it's a POV that I never have seen in more than 30 years of education at many levels.)
quote:
One cannot simply look at nature and assume that speciation occurred sexually.
But we can study real-life, real-time examples of sexually-reproducing organisms that have undergone speciation. That's much better than assuming something akin to your strawman, IMO.
quote:
Michael J.D. White cast considerable doubt on sex as an evolutionary device as I have indicated in the Manifesto. If evolution is an experimental science then speciation should be demonstrable experimentally.
It's been done. Better still, in this wonderful genomics age, it's feasible to start to explore the underlying mechanisms. These are things that would, if they were to find their way into your manifesto, greatly improve the paper, and provide much for discussion. (In the context of your own hypothesis, to boot!)
quote:
....I continue to be amazed at the certainty with which so many evolutionists regard the mechanisms which have produced the living world. I am not among them.
It's not too late to learn about some of these mechanisms. (What with the internet and all, it's actually surprisingly easy to acquaint ones self at least casually with whole new fields of biology.)
Not that I am suggesting that classical works or authors be ignored. I think it's helpful to trace the history of ideas and put "the old" in a current context. This helps students to appreciate our own technical capabilities, and to think better about current issues.
As an example, I teach my students about the Meselson-Stahl experiment. I also show how pararetroelements violate the "law" that derived from this classical study. But I would not argue that this law takes precedence over observation, or that the apparent discrepancy in some way refutes M-S or the delineation of pararetroelement replication. (This is, IMO, the logical approach that most critics of Darwinism would take.) Rather, the behavior of pararetroelements lends interesting new insight into the M-S experiment, and the two issues eventually resolve themselves famously and satisfyingly.
It's the same with most of the purported difficulties that you have brought to new life from these classical works. These difficulties have faded, not because of some vast Darwinian conspiracy, but because of hard factual data that resolves things.
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nosivad
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Member # 767
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posted 12. June 2003 15:54
Art, I am sure my point of view hasn't been put out for more than the thirty years you mention. Since when does that mean anything? As for improving the Manifesto it is a little late since most of what I have presented there has already been published. When you describe my references as "strawmen" you are taking exception not with me but with them. One of my expressed purposes was to give credit where it was and still is due. To believe that chance has played any role in evolution is totally without foundation. There is also no evidence that macroevolution (the natural formation of new and discrete species) is in progress today and even if it were there is no compelling evidence proving that it might have taken place through the mediation of sexual reproduction. I still maintain for good reasons that the several independent evolutions of nonhomologous sex determining devices has served primarily to bring macroevolution to a standstill. I note that no one to date has questioned the findings from cytogenetics and developmental biology on which the semi-meiotic hypothesis securely rests. I have interpreted those facts to mean that sex is not now and was not in the past the vehicle for evolution beyond the subspecies. I am not prepared to abandon that conclusion simply because my views are not popular or those of the contemporary majority.
"When all think alike, no one thinks very much"
Walter Lippmann
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Nel
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Member # 614
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posted 12. June 2003 18:24
Charlie d writes:
quote:
Dr. Davison, what the paper shows is how reproductive isolation can be the result of relatively simple single gene changes, and how such changes may be due to selective pressures - which by the way may be entirely unrelated to the actual speciation event (so it's not like reproductive isolation is adaptive, but that adaptation can cause reproductive isolation).
Charlie, this paper is just an extension of an initial paper which demonstrates that there are 200 chromosomal regions that differ between the two fruit fly species to such an extent that they can cause death in hybrids. The Nature article you reference by Dembksi's good friend is simply the first of these regions in which they identified the gene Nup96. I guess that was pretty good timing.
As an aside, there are circumstances in which particular forms of reproductive isolation can be adaptive, but I'm writing up some replies to the EQU thread and won't be able to get into it.
[ 12. June 2003, 18:25: Message edited by: Nelson_Alonso ]
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Rex Kerr
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Member # 632
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posted 12. June 2003 18:53
The function of and differences in various genes have been shown to have major impacts on developmental morphology--look up the literature on Hox genes, Notch/Delta, pair-rule genes, and so on; or simply browse through a modern textbook on development. Thus developmental studies are consistent with changes in genes alone causing phenotypic change. There is no data I am aware of, and certainly none presented in the author's paper, that shows that the semi-meiotic hypothesis fits better with results from developmental biology.
Note: it is critical to compare recent developmental findings, since the developmentally important molecules have only been found within the last couple of decades.
As to cytogenetics, note that the difference in chromosome structure, as assayed by karyotyping, between the great apes is fairly modest. Given that, even at 99% identity, a majority of genes are different at at least one spot between any two of the species, the karyotype can hardly be regarded as showing a dramatic difference where amino acid sequence of proteins does not. (Small changes in proteins often do matter.)
Further, note that Y chromosomes have very few genes, and thus are under little selective pressure, and thus are not expected to be maintained well, and thus finding divergent Y chromosomes is not really a surprise; it's consistent with standard selection.
Also, note that, as I mentioned earlier, all sorts of chromosomal aberrations have been generated in obligate sexual reproducers, Drosophila, and listed in FlyBase. In particular, it is worth noting that inversions coupled with crossing over *can* generate dicentric and acentric chromosomes, but need not (and thus do not generate automatic lethality), and that translocations that result in various bridge structures can still (randomly) be resolved properly at low frequency. Thus, there is no experimental or theoretical reason to believe that chromosomal rearrangement requires the semi-meiotic hypothesis.
Speciation in the sense of reproductive isolation has been directly observed in Drosophila in the laboratory starting with Dobzhansky in 1972. Further, wild-type Drosophila are observed in nature at practically every level of speciation, from mild mate-selection and fertility deficits through to complete hybrid lethality (see the talk.origins FAQ, or search for "drosophila speciation" on PubMed). Thus there are counterexamples to the claim that speciation has ended, or that it doesn't happen through sexual mechanisms. Further, the diversity in MHC alleles in humans that is shared with chimpanzees apparently rules out a semi-meiotic origin to humans, as a single female could not transmit as many different alleles as are actually observed.
Now, that said, there may be certain cases where semi-meiosis has given rise to interesting evolutionary events. However, the case for it and against gradual mutational models of evolution is vastly overstated, especially in light of molecular evidence of the past couple of decades.
Given the history of the discussion, I don't really anticipate an evidence-based response to any of my points. Since I'm interested primarily in scientific evidence, this will therefore probably be my last post in this thread.
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nosivad
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posted 12. June 2003 21:03
Rex, it is clear from your comments that you have already dismissed the semi-meiotic hypothesis. The issue is the formation of the homozygote. The sexual model requires small inbreeding populations to establish homozygosity. That is precisely where Darwinism fails, witness Darwin's celebrated finches. The semi-meiotic model produces each chromosomal alteration as a homozygote in a single step, with half being a new karyotype and half retaining the original configuration. My reference to developmental biology referred to the origin of the germ cells and the equally nonhomologous modes of sex determination in the various animal taxa. If sexual reproduction were the means for macroevolution one would anticipate a universal mechanism of sex determination as well as some evidence for a homologous origin for the gametes. Such is certainly not the case. I interpret this to mean that sex was a secondary evolutionary invention. Let me put it this way. What was the reproductive mode animals prior to their aquisition of the familiar cytogenetic devices we see now. Were they all reproducing sexually? If so why did they find it necessary to change, some adopting a heterogametic male system, some a heterogametic female, some a haplo/diplo device etc etc. I think it is far more reasonable to conclude that these differences were preceded by the first meiotic division which is after all a perfectly valid form of diploid reproduction. Sexual reproduction is a remarkably conservative means of reproduction which I still maintain is incapable of any significant evolutionary change. I agree with Michael J.D. White that many chromosomal differences that have been described including those in Drosophila were not produced sexually. I do not understand why his views have been ignored by the evolutionary community. Or perhaps I do. I am sorry if you fail to regard this as a scientific response and there is little I can do if you stop posting.
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Nel
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Member # 614
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posted 12. June 2003 21:14
Rex writes:
ddd
quote:
The function of and differences in various genes have been shown to have major impacts on developmental morphology--look up the literature on Hox genes, Notch/Delta, pair-rule genes, and so on; or simply browse through a modern textbook on development. Thus developmental studies are consistent with changes in genes alone causing phenotypic change.
Simply observing that the same genotype does not cause the same phenotypes refutes that statement:
Lowe, C.J. and Wray, G.A. (1997) Radical alterations in the roles of homeobox genes during echinoderm evolution. Nature 389:718-21.
In one case the genotype changes and morphology stays the same:
Dev Biol. 2000 May 1;221(1):68-86.
, and in other cases, similar genotypes result in different phenotypes.
It seems as though the IC thread and this one might be converging. In fact, the genetic circuitry involved in development can undergo a lot rewiring, and yet the phenotype stays relatively the same.
Evolution: Developmental circuits rewired EÖRS SZATHMÁRY
Neo-Darwinism, with it's gene-centric view, can only explain variation, not origination of phenotypic traits. Even Darwin kind of warned of this when he said:
quote:
we may easily err in attributing importance to characters, and in believing that they have been developed through natural selection."
The situation today is exactly the opposite of your post, in my opinion. You can't tell me the shape of an organism simply by looking at the genes.
[ 20. February 2006, 13:40: Message edited by: Nel ]
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charlie d.
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Member # 159
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posted 12. June 2003 21:18
Jack:
sorry you think my replies feel like they could fit in Talkorigin - that's quite a low blow! ![[Wink]](wink.gif)
Personally, I don't mind brainstorming, when somewhat grounded in reality. Alas, the pattern in this thread seems to be:
A. Make an unfounded statement
B. Receive a reply asking for clarification and evidence, and/or providing counterevidence
C. Reply that someone else said so at some point (with no reference to even verify this attribution), and therefore no justification is required. Ignore counterevidence.
D. Make another unfounded statement (or the same one, again).
E. Repeat B.-E.
I personally do not think this pattern is conducive to any sane discussion, let alone "brainstorming", but hey, I guess it's a matter of taste...
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Pim van Meurs
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Member # 541
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posted 12. June 2003 22:33
Nelson references various papers which he claims support his argument although I am not really clear what his argument is
quote:
Echinoderms possess one of the most highly derived body architectures of all metazoan phyla, with radial symmetry, a calcitic endoskeleton, and a water vascular system,. How these dramatic morphological changes evolved has been the subject of extensive speculation and debate, but remains unresolved. Because echinoderms are closely related to chordates and postdate the protostome/deuterostome divergence, they must have evolved from bilaterally symmetrical ancestors. Here we report the expression domains in echinoderms of three important developmental regulatory genes ( distal-less, engrailed and orthodenticle ), all of which encode transcription factors that contain a homeodomain. Our findings show that the reorganization of body architecture involved extensive changes in the deployment and roles of homeobox genes. These changes include modifications in the symmetry of expression domains and the evolution of several new developmental roles, as well as the loss of roles conserved between arthropods and chordates. Some of these modifications seem to have evolved very early in the history of echinoderms, whereas others probably evolved during the subsequent diversification of adult and larval morphology. These results demonstrate the evolutionary lability of regulatory genes that are widely viewed as conservative.
Radical alterations in the roles of homeobox genes during echinoderm evolution
CHRISTOPHER J. LOWE AND GREGORY A. WRAY
Nature 389, 718 - 721 (1997);
The other 'reference' seems somewhat obscure "Dev Biol. 2000 May 1;221(1):68-86"
But I think I may have found the reference
Felix MA, De Ley P, Sommer RJ, Frisse L, Nadler SA, Thomas WK, Vanfleteren J, Sternberg PW.
Evolution of vulva development in the Cephalobina (Nematoda)
Perhaps Nelson could elaborate on what he is trying to communicate here?
And I would like to hear what Nelson believes the relevance of this is to Hox genes for instance.
Nelson suggests that "Simply observing that the same genotype does not cause the same phenotypes refutes that statement"
What does it exactly refute? " Thus developmental studies are consistent with changes in genes alone causing phenotypic change."
Certainly the fact that Hox genes may be coding for very different parts does not disprove the fact that differences in Hox genes and genes in general can cause genetic change?
From the same author
quote:
An interesting evolutionary puzzle has recently emerged, involving an apparent disconnection between the evolution of genes and the evolution of anatomy. Anatomically, animals are an enormously diverse group, including such disparate forms as jellyfish, hummingbirds, and lobsters. Despite their anatomical differences, these animals contain, to a first approximation, the same complement of genes. This is particularly true of the genes that encode anatomy, the developmental regulatory genes. Most famously, Hox genes are responsible for patterning developing insect and vertebrate embryos. How can the same genes encode such different anatomies? The resolution to this apparent paradox lies in evolutionary "rewiring" of interactions among genes. Although their developmental roles are sometimes conserved, regulatory genes can also evolve new roles, such that they direct quite different developmental processes in different groups of animals. Evolutionary changes in interactions among genes are likely to be responsible for many important anatomical changes in the history of animals, including the diversification of body plans and the origin of novel structures.
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