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Human Embryo Gill Slits
The White Paper and Gill Slits

     White Paper URL: http://www.rci.rutgers.edu/~ecolevol/fulldoc.html  

     Posted by Kevin Kamberg on September 14, 1998 at 20:59:20:

     Since none of y'all seem to be able to explain the White Paper's outdated misunderstanding of human anatomy, re: the appendix. I thought I'd give another example of the same type of miscomprehension of form and function.
     White Paper, section III, subsection B. Perspectives from Evolutionary Biology, first paragraph:

     That a human embryo has gill slits can be understood only by inheritance from early vertebrate ancestors..."

     That sounds remarkably like Haeckel's nonsense about Recapitulation. What the esteemed evolutionists writing the White Paper are calling *gill slits* are, in fact, Pharyngeal "pouches". What to them appears to superficially resemble fish gills, does not in fact have anything to do with any form of respiration! Yet this nonsensical line of reasoning is still being presented as an evidence that the TOE's macroevolution is science.
     Rather than having anything to do with vestigial apparatus for breathing or respiration, the pharyngeal "pouches" develop into parts of the face, neck, and important glands! "In man and other mammals, these arches and pouches develop into part of the face, muscles of mastication and facial expression, bones of the middle ear, and endocrine glands" - Dr. David Menton.
     MEANWHILE, the embryo's lungs develop quite independantly of these "gill slits."
     It appears that the White Paper is a fairy tale for adults.
     Is the Human Embryo Essentially a Fish with Gills? http://www.gennet.org/Metro06.htm [note: this article is short enough to be posted at the bottom of this thread]

First Response

     Posted by Paul Rothberg on September 14, 1998 at 22:40:36:

     As we have been discussing you give more examples of not understanding evolution. You are quite right that the embryological structures sometimes referred to as gill arches have nothing to do with respiration in humans, but develop into facial features. Similarly, our lungs do develop from our gastrointestinal tract (in one of the most celebrated examples of poor design). In fact there are other examples of structures be co-opted into new functions in evolution. The examples you gave are based on a misunderstanding of exactly what is being proposed by the TOE.
     The basis of these claims are the similarity in structures in the embryo and in how they develop. Now, Kevin, you should know that the genes that direct the formation of particular structures in the embryo are being discovered. The functions of the encoded proteins are being worked out, in addition to their patterns of expression and regulation. Evolution predicts that the genes that direct the formation of these similar structures will be the same.

     Posted by Mockingbird1 on September 14, 1998 at 22:56:58:

     PK: Paul, I don't doubt that you are tops in your field, however, you may be out of touch (?) with the errors and misconceptions common to mainstream evolutionary biology. Kevin's quotes wasn't from Haeckel, or some Creationist Journal, trumpeting Haeckels errors. The error is another 'aw, poop' for the professor's white paper. Good job, Kevin.

     "Thus, while much of biology addresses proximate causation of observed phenomena, evolutionary biology addresses ultimate causation. Answers to questions regarding ultimate causation might include "because this species inherited the feature from distant ancestors" or "because a history of natural selection favored this feature over others in the recent past." That a human embryo has gill slits can be understood only by inheritance from early vertebrate ancestors; that we walk upright can be understood as an adaptation, a trait favored by natural selection in our more recent ancestors. In emphasizing history, we must, at the same time, recognize that evolution is an active, ongoing process."

     PK: This comes as no surprise to me, that they recap Haeckel. I think they got the theory of evolution right, and CARM's evolutinists have completely different ideas. There attempts to credit the theory of evolution with all they heaped upon it indicated a depth of knowledge of accomplishments and a gross ignorance of history, causality, or presumption of gullibility on the reader's part.

     Posted by MEYER on September 14, 1998 at 23:02:23:

     You know, I come across the same thing all the time. It does seem that CARM "evolves" a different species than the universolutionus.

     Yupper (nt) Mockingbird1 23:11:25 9/14/98 (0)

Response to Mockingbird1

     Posted by Paul Rothberg on September 14, 1998 at 23:10:05:

     Although "ontogeny recapitulates phylogeny" is an outdated concept, the embryo does contain structures that give us a great deal of information about evolution. This area is becoming even more interesting as more details are discovered. Kevin's quotes from the creationist Menton give some correct information but are intended to deceive in the long run.

     Response to Paul Rothberg

     Posted by Mockingbird1 on September 14, 1998 at 23:24:27:

     :PR: Kevin's quotes from the creationist Menton give some correct information but are intended to deceive in the long run.

     PK: I recognized Dr. Menton's statements on Pharygeal pouches, or whatever they are, to be correct. I could care less if the man believes the earth is 5998 years old. I must thank you for pointing out the affiliation of the correct party. I recognized the statements of the professors to be incorrect. If they did not say that mammal babies had gills, they certainly suggested it. If they were not borrowing from Haeckel in ignorance, I would categorize their statement as intentionally deceptive. Obviously, I'm no expert, and I am suspicious of many of their claims. I do think they have a fair description of the theory though.

Response to Paul Rothberg

     Posted by Kevin Kamberg on September 15, 1998 at 00:28:24:

     Paul: Kevin's quotes from the creationist Menton give some correct information but are intended to deceive in the long run.

     ***Kevin: Actually I spent some time digging thru medical university libraries (online libraries) and even an essay by an evolutionary biologist/associate professor of biology from North Carolina that I found online. Menton's site was one of the last ones that I found and though I left a link to it at the bottom of my post, that was only because he provided a concise summary of the issue.
     BTW, I only quoted him once and except for that and the quote from the white paper, nothing was plagerized or reworded from anywhere else!
     I carefully compared Menton's stuff with the medical library’s stuff before using it also. If you attack him, you are attacking mainstream medical knowledge. Believe it or not, I found an undergraduate pre-med biology book the most informative. It was only a 200 level class too. This stuff really is pretty basic biological knowledge.

     Posted by Deb on September 15, 1998 at 09:14:54:

     I read some of Menton's stuff a while back (but in another context), and I have to confess to finding it woefully lacking (in the particular area I was looking at at the time--something to do with anatomy). I think the main problem is the assumption that just because one has medical training, one is an expert on evolution. This is actually quite false--it's very easy to become a doctor with virtually no real exposure to evolutionary theory.

     Posted by Kevin Kamberg on September 15, 1998 at 14:21:35:

     Deb: ). I think the main problem is the assumption that just because one has medical training, one is an expert on evolution. This is actually quite false--it's very easy to become a doctor with virtually no real exposure to evolutionary theory.

     Kevin: Exactly! Medical training deals in verifiable facts. This stuff on the "non-functional appendix", spontaneous generation, Haeckel's garbage, "gill slits", etc... all were debunked with facts. The kind of verifiable stuff that medical professionals deal with on a daily basis. I fail to see how your statement above helps your cause in any way. It seems to me that you've made an excellent case for science being science and the TOE being....?

Second Response

     Posted by Pat on September 14, 1998 at 23:03:16:

     The fact remains that these structures which form gill arches in agnathans, form other structures in jawed fishes and tetrapods. Haeckle's recapitualization theory was wrong, but vertebrates have no choice but to build on what went before. The fact that this occurs is overwhelming evidence for evolution. There is no other explaination that accounts for the facts.

     Kevin:

     Rather than having anything to do with vestigal apparatus for breathing or respiration, the pharyngeal "pouches" develop into parts of the face, neck, and important glands! "In man and other mammals, these arches and pouches develop into part of the face, muscles of mastication and facial expression, bones of the middle ear, and endocrine glands" - Dr. David Menton.

     Pat:

     Precisely. When creationists ask for some completely new organ formed by evolution, they are missing the point. It doesn't work that way. Old structures are reworked to new functions. For example, jaws were not initially for biting, but were only modified gill arches to create an exaggerated flow of water into the mouth. Fish still feed that way, in many cases. Teeth and biting or seizing came later.

     Kevin:

     MEANWHILE, the embryo's lungs develop quite independently of these "gill slits."

     Pat:

     Of course. Different system entirely. Organ systems often become modified for new purposes. It's no surprise that evolutionary theory was developed to conform to that reality.

     Kevin:

     It appears that the White Paper is a fairy tale for adults.

     Pat:

     I think you still don't understand what this issue means in terms of science.

     Posted by MEYER on September 14, 1998 at 23:10:09:

     Pat; Haeckle's recapitulation theory was wrong,

     Pat again; Old structures are reworked to new functions. Again Organ systems often become modified for new purposes.

     Mighty close to the same thing as recapitulation ain't it Pat?

Response to Pat

     Posted by Mockingbird1 on September 14, 1998 at 23:15:22:

     PK: I'm not sure if you feel sorry for the Prof's who are getting pasted and you want to speak up for them, or if you really are agreeing that these are gill slits on mammal embryos. Are you just saying you can understand how they wrote that or are you really agreeing with them?

     Posted by Paul Rothberg on September 14, 1998 at 23:32:12:

     What you call them doesn't matter. There are similar structures in the embryos of all vertebrates. What develops into a gill support in one develops into a jaw in another. It is still homology. The evidence for this is getting stronger still.
     Kevin's comments and quotes were designed to deceive. You have been deceived. If you want to argue development you and Kevin need to learn some.
     I am reading Developmental Biology by S.F. Gilbert to remedy my deficiencies in this area. That way I can understand better what I read in Nature and Science.

     Posted by Mockingbird1 on September 14, 1998 at 23:46:28:

     PR: What you call them doesn't matter.

     PK: Words can have specific meanings, often two words or terms have the same specific meaning. The gill slits is where rich Americans cut off a fishes head before they cook and eat it (we just don't have the palate to appreciate the head). Pharyengeal pouches or whatever they are, are structures on vertebrate embryos on or near the head.

     PK: What you call them certainly does matter if you want to believe that mammal embryos are just like fish, amphibian, reptilian and avian embryos.

Response to Paul Rothberg

     Posted by Pat on September 15, 1998 at 07:49:35:

     Kevin's comments and quotes were designed to deceive.

     Pat:

     I have to disagree with you there. Kevin is wrong sometimes, but he does not intentionally mislead anyone, IMO.

     Paul:

     You have been deceived.

     Pat:

     Nope. I don't agree with Kevin. Neither do I agree with Haeckel. But there is a reason that our development shares features with other classes of vertebrates.

     Paul:

     If you want to argue development you and Kevin need to learn some.

     Pat:

     While I've taken only one course in vertebrate embryology, I have continued to read on it from time to time.

Response to Mockingbird1

     Posted by Pat on September 15, 1998 at 07:43:17:

     PK: I'm not sure if you feel sorry for the Prof's who are getting pasted and you want to speak up for them, or if you really are agreeing that these are gill slits on mammal embryos. Are you just saying you can understand how they wrote that or are you really agreeing with them?

     Pat:

     It appears that you've confused this with recapitulation. Our jaws and ears form out of the same structures that form gill arches in other classes, because evolution doesn't create new structures. It remodels old ones. This doesn't mean that humans are fish at some point, but it does mean that our development is constrained by what went before. If our ancestors were fish at some point, then it's understandable that our anatomy uses the same pathways as fish, early on. Nothing else makes any sense of the facts. But no, we do not recapitulate our evolution in utero. "Gill slits", I've heard used informally from time to time, but that's not what they are, in fish or in humans.

     Posted by Mockingbird1 on September 15, 1998 at 10:16:42:

     PK: I appreciate your direct and informative answer.

Third Response

     Posted by Helen on September 15, 1998 at 00:21:24:

     You might be interested in this article, which was published (with some additions by Paul Nelson) in Origins and Design 18:2 (Fall 1997).
     Conference on Naturalism, Theism and the Scientific Enterprise University of Texas, Austin, February, 1997

     ABSTRACT Before Darwin, homology was defined morphologically and explained by reference to ideal archetypes, - that is, to supernatural design. Darwin reformulated biology in naturalistic* rather than idealistic terms, and explained homology as the result of descent with modification from a common ancestor. Descent with modification, however, renders design unnecessary only if it is due entirely to naturalistic mechanisms. Two such mechanisms have been proposed, genetic programs and developmental pathways, but neither one fits the evidence. Without an empirically demonstrated naturalistic mechanism to account for homology, design remains a possibility which can only be excluded on the basis of questionable philosophical assumptions.

     1. MORPHOLOGICAL AND PHYLOGENETIC HOMOLOGY

     From at least the time of Aristotle, people who study living organisms have noted some remarkable similarities among very diverse creatures. Bats and butterflies are quite different from each other, yet both have wings to fly; bats fly and whales swim, yet the bones in a bat's wing and a whale's flipper are strikingly alike. The first kind of similarity involves different structures which perform the same function, and in 1843 anatomist Richard Owen called this "analogy." In contrast, the second kind of similarity involves similar structures which perform different functions, and Owen called this "homology." Owen (and other pre-Darwinian biologists) attributed homology to the existence of archetypes: biological structures are similar because they conform to pre-existing patterns. (Bowler, 1989; Panchen, 1994)
     In 1859, Charles Darwin offered a different explanation for homology. According to Darwin, bats and whales possess similar bone structures because they inherited them from a common ancestor, not because they were constructed according to the same archetype. By replacing archetypes (which imply design and supernatural agency) with a natural mechanism such as common descent, Darwin hoped to render idealistic explanations unnecessary and to place biology on a securely naturalistic basis.
     [* In this paper, "naturalism" and "naturalistic" refer to the philosophical doctrine that nature is the whole of reality, and that ideas and supernatural entities are human projections.]
     Not all structural similarities, however, are inherited from a common ancestor (as Darwin and his followers recognized). For example, the eye of a mouse is structurally similar to the eye of an octopus, yet their supposed common ancestor did not possess such an eye. In 1870, Ray Lankester coined the term "homoplasy" to describe such features. Implicit in this distinction was a new definition of homology. As evolutionary biologist Ernst Mayr put it, after Darwin the "biologically most meaningful definition"" of homology was: "A feature in two or more taxa is homologous when it is derived from the same (or a corresponding) feature of their common ancestor." (Mayr, 1982) In other words, what Darwin proposed as the explanation for homology became its definition. For many biologists, the post-Darwinian (or phylogenetic) definition of homology has replaced the structural (or morphological) definition. (Hall, 1992; Panchen, 1994)
     The concept of homology can thus function in several ways, which can be brought into sharper focus by placing them in the context of syllogisms:
     A. Classical (morphological) view:
     Premise 1 (Definition). Features are homologous if and only if they have similar structures.
     Premise 2 (Empirical observation). A bat's wing and a whale's flipper have similar structures.
     Conclusion. Therefore, a bat's wing and a whale's flipper are homologous features.

     A'. Darwin's extension of the morphological view:
     Premise 1 (Conclusion from classical view). A bat's wing and a whale's flipper are homologous features.
     Premise 2 (Proposed explanation). Features are homologous because they are inherited from a common ancestor.
     Conclusion: Therefore, a bat's wing and a whale's flipper are inherited from a common ancestor.

     B. Post-Darwinian (phylogenetic) view:

     Premise 1 (Definition). Features are homologous if and only if they are inherited from a common ancestor.
     Premise 2 (Assumption? Empirical inference?). A bat's wing and a whale's flipper are inherited from a common ancestor.
     Conclusion. Therefore, a bat's wing and a whale's flipper are homologous features.

     Ironically, the post-Darwinian (phylogenetic) definition of homology undercuts one of Darwin's own arguments for evolution, since it requires that common ancestry be established (or assumed) before features can be called homologous. Logically speaking, it is a fallacy to infer evolution from phylogenetic homology: once one determines (or assumes) that features are homologous because of common ancestry, it would be circular reasoning to claim that homology demonstrates common ancestry. This does not mean, however, that structural similarities can no longer be used to infer homology, but only that they must be traced back through a fossil lineage to a common ancestor. For example, the similar bone structures in a bat's wing and a whale's flipper cannot, by themselves, justify an inference of phylogenetic homology. But if one could establish that fossil bats and fossil whales are more similar in this regard than extant organisms, - especially if the fossils suggest gradual divergence from a presumed common ancestor, - then one could infer that they are phylogenetically homologous.

     2. THE NEED FOR A NATURALISTIC MECHANISM

     It turns out, however, that tracing structural similarities back through fossils to a presumed common ancestor is insufficient to exclude archetypes or design-based explanations. The problem is unintentionally illustrated by biologist Tim Berra in his 1990 book, Evolution and the Myth of Creationism (Stanford University Press). According to Berra, "If you look at a 1953 Corvette and compare it to the latest model, only the most general resemblances are evident, but if you compare a 1953 and a 1954 Corvette, side by side, then a 1954 and a 1955 model, and so on, the descent with modification is overwhelmingly obvious. This is what paleontologists do with fossils, and the evidence is so solid and comprehensive that it cannot be denied by reasonable people.." (p. 117; emphasis in the original) As the title of his book indicates, Berra's primary purpose is to show that living organisms are the result of naturalistic evolution rather than Supernatural design. Structural similarities among automobiles, however, - even similarities between older and newer models (which Berra calls "descent with modification"), - are due to construction according to preexisting patterns, i.e., to design. Ironically, therefore, Berra's analogy shows that phylogenetic homology is not sufficient to exclude design-based explanations. In order to demonstrate naturalistic evolution, it is necessary to show that the mechanism by which organisms are constructed (unlike the mechanism by which automobiles are constructed) does not involve design. One could simply postulate that the mechanism of biological evolution is naturalistic, arguing that the postulate is justified because science is limited to studying natural mechanisms. Although such a philosophical move may seem very reasonable, however, it compromises the status of evolutionary biology as an objective science. Asserting that something is objectively true implies that it is based on empirical evidence, not merely assumed a priori on philosophical grounds. A methodological exclusion of design-based explanations constitutes a limitation on one's discipline, not a description of objective reality. If evolutionary biologists want to show that the actual mechanism of evolution does not involve Supernatural design, they cannot merely exclude the possibility a priori, but must take the more difficult approach of proposing and corroborating a naturalistic alternative.
     This alternative must account naturalistically for what evolutionary biologist Leigh Van Valen has called "continuity of information." (Van Valen, 1982) According to Van Valen, homologous features are produced during the development of each individual organism by information which has been inherited, with modification, from the organism's ancestors. Thus the first step toward understanding the mechanism of evolution would be to determine the nature of the information which controls the development of the embryo.

     3. HOMOLOGY AND GENETICS
     One possibility is that this information is encoded in the organism's genes. In the 1930's, the synthesis of Darwin's theory and population genetics explained evolution as a change in gene frequencies, and several decades later the discovery of the structure and function of DNA extended this explanation to the molecular level.
     According to the neo-Darwinian synthesis, a genetic program encoded in DNA directs embryonic development; the process of reproduction transmits this program to subsequent generations, but mutations in the DNA sometimes modify it ("descent with modification"); thus descendants of the original organism may possess structures which are similar but not identical ("homologies"). No design is required, so the explanation is thoroughly naturalistic. By 1970, molecular biologist Jacques Monod felt justified in announcing that "the mechanism of Darwinism is at last securely founded," and that as a consequence "man has to understand that he is a mere accident." (quoted in Judson, 1980, p. 217)
     Efforts to correlate evolution with changes in gene frequencies, however, have not been very successful. Detailed studies at the molecular level fail to demonstrate the expected correspondence between changes in gene products and the sorts of organismal changes which constitute the "stuff of evolution." (Lewontin, 1974, p. 160). According to Rudolf Raff and Thomas Kaufman, evolution by DNA mutations "is largely uncoupled from morphological evolution;" the "most spectacular" example of this is the morphological dissimilarity of humans and chimpanzees despite a 99% similarity in their DNA. (Raff and Kaufman, 1983, pp. 67, 78).
     Some biologists have proposed that the remaining 1% consists of "regulatory genes" which have such profound effects on development that a few mutations in them could account for dramatic differences. For example, mutations in homeotic genes can transform a fly's antenna into a leg, or produce two pairs of wings where there would normally be only one, or cause eyes to develop on a fly's leg. Furthermore, genes similar to the homeotic genes of flies have been found in most other types of animals, including mammals. Based on the profound developmental effects and almost universal occurrence of such genes, biologist Eric Davidson and his colleagues recently wrote that "novel morphological forms in animal evolution result from changes in genetically encoded programs of developmental regulation." (Davidson et al., 1995, p. 1319).
     According to this view, homologous features are programmed by similar genes. Assuming that genes with similar sequences are unlikely to originate independently through random mutations, sequence similarity would indicate common ancestry. Features produced by similar sequences could then be inferred to be phylogenetically homologous. The very universality of homeotic genes, however, raises a serious problem for this view. Although mice have a gene very similar to the one that can transform a fly's antenna into a leg (Antennapedia), mice do not have antennae, and their corresponding gene affects the hindbrain; and although mice and flies share a similar gene which affects eye development (eyeless), the fly's multifaceted eye is profoundly different from a mouse's camera-like eye. In both cases (Antennapedia and eyeless), similar homeotic genes affect the development of structures which are non-homologous by either the classical morphological definition or the post-Darwinian phylogenetic definition. If similar genes can "determine" such radically different structures, then those genes aren't really determining structure at all. Instead, they appear to be functioning as binary switches between alternate developmental fates, with the information for the resulting structures residing elsewhere. (Wells, 1996)
     Not only are non-homologous structures produced by organisms with supposedly homologous genes, but organisms with different genes can also produce similar structures. The most famous examples involves the genes, mentioned above, which affect wing and eye development in flies. Fly embryos with a normal gene for wing development, when treated with ether, can be induced to grow a second pair, just as though they possessed the mutant form of the gene. (For a review, see Hall, 1992) Flies with a mutant form of the eye gene fail to develop eyes; but if eyeless flies are bred for many generations, some of their descendants will develop eyes even though they still possess the mutant form of the gene. Such anomalies led embryologist Gavin de Beer to conclude that "homologous structures need not be controlled by identical genes," and that "the inheritance of homologous structures from a common ancestor ... cannot be ascribed to identity of genes." (de Beer, 1971, pp. 15-16).
     The underlying assumption that a genetic program directs embryonic development has been seriously questioned by developmental biologists. (For a review, see Wells, 1992) Sydney Brenner, who originally proposed genetic programs in 1970, repudiated the idea when he realized that the information required to specify the neural connections of even a simple worm far exceeds the information content of its DNA. (Brenner, 1973) A decade later, developmental biologist Brian Goodwin noted that "genes are responsible for determining which molecules an organism can produce," but "the molecular composition of organisms does not, in general, determine their form." (Goodwin, 1985, p. 32) And in a 1990 critique of the notion of genetic programs, H.F. Nijhout concluded that "the only strictly correct view of the function of genes is that they supply cells, and ultimately organisms, with chemical materials." (Nijhout, 1990, p. 444)
     Clearly, the genetic explanation for homology is inadequate. As an alternative, some biologists have suggested that homology results from complex developmental mechanisms which are not reducible to a genetic program.

4. HOMOLOGY AND DEVELOPMENTAL PATHWAYS
     Since homologies cannot be explained by equating developmental information with DNA sequences, some biologists have attempted to explain it by attributing it to similar developmental pathways. Although DNA determines the amino acid sequence of proteins essential for development, such pathways also involve other factors, such as the localization of cytoplasmic constituents in the egg cell, physical constraints resulting from the size of the embryo, and so on. (Wells, 1992)
     Efforts to correlate homology with developmental pathways, however, have been uniformly unsuccessful. First, similar developmental pathways may produce very dissimilar features. At the molecular level, it is well known that virtually identical inducers may participate in the development of non-homologous structures in different animals. (Gilbert, 1994) At the multicellular level, the pattern of embryonic cell movements which generates body form in birds also generates body form in a few species of frogs. (Elinson, 1987) And even at the organismal level, morphologically indistinguishable larvae may develop into completely different species. (de Beer, 1958) Clearly, similar developmental pathways may produce dissimilar results.
     Second, and more dramatically, similar features are often produced by very different developmental pathways. No one doubts that the gut is homologous throughout the vertebrates, yet the gut forms from different embryonic cells in different vertebrates. The neural tube, embryonic precursor of the spinal cord, is regarded as homologous throughout the chordates, yet in some its formation depends on induction by the underlying notochord while in others it does not. (Gilbert, 1994) Evidently, "structures can owe their origin to different methods of induction without forfeiting their homology." (de Beer, 1958, p. 151) Indeed, as developmental biologist Pere Alberch noted in 1985, it is "'the rule rather than the exception" that "homologous structures form from distinctly dissimilar initial states." (Alberch, 1985, p. 51)
     Production of similar forms from dissimilar pathways is also common at later stages of development. Many types of animals pass through a larval stage on their way to adulthood, a phenomenon known as indirect development. For example, most frogs begin life as swimming tadpoles, and only later metamorphose into four-legged animals. There are many species of frogs, however, which bypass the larval stage and develop directly. Remarkably, the adults of some of these direct developers are almost indistinguishable from the adults of sister species which develop indirectly. In other words, very similar frogs can be produced by direct and indirect development, even though the pathways are obviously radically different.
     The same phenomenon is common among sea urchins and ascidians. (Raff, 1996)
     Even the classic example of vertebrate limbs shows that homology cannot be explained by similarities in developmental pathways. Skeletal patterns in vertebrate limbs are initially laid down in the form of cartilage condensations, which later ossify into bone. The sequence of cartilage condensation is the developmental pathway which determines the future pattern of bones in the limb. Yet similar bone patterns in different species (i.e., homologies) arise from different sequences of cartilage condensation. (Shubin, 1991) In the words of biologist Richard Hinchliffe: "'Embryology does not contribute to comparative morphology by providing evidence of limb homology in the form of an unchanging pattern of condensation common to all tetrapod limbs." (Hinchliffe, 1990, p. 121)
     The constancy of final patterns despite varying pathways has prompted developmental biologist Gunter Wagner to suggest that homology might be due to conserved developmental "constraints". (Wagner, 1989) Wagner's critics, however, object that this notion is too vague to be useful. Although developmental constraints emphasize the fact that embryos are capable of producing similar end-points by a variety of routes, they do not constitute a naturalistic mechanism accessible to empirical investigation.
     So embryology has not solved the problem of homology. In 1958, Gavin de Beer observed that "correspondence between homologous structures cannot be pressed back to similarity of position of the cells in the embryo, or of the parts of the egg out of which the structures are ultimately composed, or of developmental mechanisms by which they are formed." (de Beer, 1958, p. 152).  Subsequent research has overwhelmingly confirmed the correctness of de Beer's observation. Homology, whether defined morphologically or phylogenetically, cannot be attributed to similar developmental pathways any more than it can be attributed to similar genes. So far, the naturalistic mechanisms proposed to explain homology do not fit the evidence.

5. CONCLUSION
     In 1802, William Paley wrote that someone crossing a heath and finding a stone could reasonably attribute its presence to purposeless natural causes. Upon finding a watch, however, and seeing that "its several parts are framed and put together for a purpose," one could conclude that the watch had been designed. By analogy, Paley argued, one could also conclude that living things are designed. (Paley, 1802, p. 2) In 1859, Charles Darwin argued that living things are more like Paley's stone than Paley's watch, and claimed that everything which Paley attributed to design could be accounted for naturalistically, by descent with modification.
     As Berra's automobile analogy shows, however, descent with modification is not enough to exclude design. It is necessary, in addition, to show that the mechanism of descent with modification is thoroughly naturalistic. Darwin thought he had done this with his theory of natural selection, but as the problem of homology demonstrates, he failed to accomplish his goal.
     Diverse organisms possess homologous features. Homology may or may not be due to inheritance from a common ancestor, but it is definitely not due to similarity of genes or similarity of developmental pathways. In 1971, Gavin de Beer wrote: "What mechanism can it be that results in the production of homologous organs, the same 'patterns', in spite of their not being controlled by the same genes? I asked this question in 1938, and it has not been answered." (de Beer, 1971, p.16) Twenty-five years later, the question still has not been answered.
     Without a naturalistic mechanism to account for homology, however, Darwinian evolution cannot claim to have demonstrated scientifically that living things are undesigned, and the possibility remains that homologies are patterned after idealized archetypes. Without a demonstrated mechanism, naturalistic biologists are left with only one alternative: exclude design a priori, on philosophical grounds.
     This exclusion could be taken as a statement that supernatural design does not exist, or it could be taken as a statement that supernatural design is beyond the reach of empirical science. The first is a theological statement, and warrants a theological response. The second is a methodological limitation which cannot be logically extrapolated to a limitation on reality. In other words, a scientist who makes the first move is engaging in theological disputation, while a scientist who makes the second is declining to investigate a possible aspect of reality.
     Unfortunately, many biologists make both moves, but fail to distinguish logically between them. While justifying their exclusion of supernatural design on methodological grounds, they act as though science has disproved its existence by providing a naturalistic explanation for homology. When confronted with the fact that science has failed in this regard, they reaffirm their methodological commitment and express faith that a naturalistic mechanism will someday be discovered.
     And perhaps it will. But what if living things really are designed? Someone who finds a watch on the ground, and wants to investigate its origin, would be mistaken to rule out design a priori. Having already jumped to the wrong conclusion, that person might go on to waste an entire lifetime dabbling in spurious explanations. If science is truth-seeking, then this is a strange way to do science.

     According to an old joke, a passer-by walks up to a drunk stumbling around under a street light. The passer-by asks the drunk what he's doing, and the drunk replies, "Looking for my watch." "Oh, did you lose it here?" asks the passer-by. "No," the drunk replies, "I lost it across the street, but there's no light over there!" Letting naturalistic philosophical assumptions limit one's search for the cause of homology may not be the best way to study living things.

REFERENCES

• Alberch, Pere (1985). "Problems with the Interpretation of Developmental Sequences," Systematic Zoology 34 (1): 46-58
• Berra, Tim M. (1990). Evolution and the Myth of Creationism. Stanford, CA: Stanford University Press.
• Bowler, Peter J. (1989). Evolution: The History of an Idea. Revised edition. Berkeley: University of California Press.
• Brenner, Sydney (1973). "The Genetics of Behaviour," British Medical Bulletin 29: 269-271.
• Davidson, E. H., Peterson, K. J. and Cameron, R. A. (1995). "Origin of Bilaterian Body Plans: Evolution of Developmental Regulatory Mechanisms," Science 270:1319-1325.
• de Beer, Gavin (1958). Embryos and Ancestors, 3rd ed. Oxford: Clarendon Press.
• de Beer, Gavin (1971). Homology: An Unsolved Problem. London: Oxford University Press.
• Elinson, Richard P. (1987). "Change in Developmental Patterns: Embryos of Amphibians with Large Eggs." In Rudolf A. Raff and Elizabeth C. Raff, eds.,Development as an Evolutionary Process, vol. 8, pp. 1-21. New York: Alan R. Liss.
• Gilbert, Scott F. (1994). Developmental Biology, 4th ed. Sunderland, MA.: Sinauer Associates.
• Goodwin, Brian C. (1985). "What Are the Causes of Morphogenesis?" Bioessays 3: 32-36.
• Hall, Brian K. (1992). Evolutionary Developmental Biology. London: Chapman & Hall.
• Hinchliffe, Richard (1990). "Towards a Homology of Process: Evolutionary Implications of Experimental Studies on the Generation of Skeletal Pattern in Avian Limb Development." In J. Maynard Smith and G. Vida, eds., Organizational Constraints on the Dynamics of Evolution, pp. 119-131. Manchester, UK: Manchester University Press.
• Judson, Horace Freeland (1980). The Eighth Day of Creation. New York: Simon & Schuster.
• Lewontin, R.C. (1974). The Genetic Basis of Evolutionary Change. New York: Columbia University Press.
• Mayr, Ernst (1982). The Growth of Biological Thought. Cambridge, MA: Belknap Press.
• Nijhout, H.F. (1990). "Metaphors and the Role of Genes in Development," Bioessays 12: 441-446.
• Paley, William (1802). Natural Theology. Reprinted in 1972. Houston, TX: St. Thomas Press,.
• Panchen, Alec L. (1994). "Richard Owen and the Concept of Homology." In Brian K. Hall, ed., Homology: The Hierarchical Basis of Comparative Biology. San Diego: Academic Press, pp. 21-62.
• Raff, Rudolf A. (1996). The Shape of Life: Genes, Development, and the Evolution of Animal Form. Chicago: The University of Chicago Press.
• Raff, Rudolf A. and Kaufman, Thomas C. (1983). Embryos, Genes, and Evolution. New York: Macmillan.
• Shubin, Neil H. (1991). "The Implications of 'The Bauplan' for Development and Evolution of the Tetrapod Limb." In J.R. Hinchliffe, J.M. Hurle, and D. Summerbell, eds., Developmental Patterning of the Vertebrate Limb, pp. 411-421. New York: Plenum Press.
• Van Valen, Leigh M. (1982). "Homology and Causes." Journal of Morphology 173:305-312.
• Wagner, Gunter (1989). "The Biological Homology Concept," Annual Review of Ecology and Systematics 20: 51-69.
• Wells, Jonathan (1992). "The History and Limits of Genetic Engineering," International Journal on the Unity of the Sciences 5: 137-150.
• Wells, Jonathan (1996). "Unseating Naturalism: Recent Insights from Developmental Biology." Presented at a conference on Mere Creation: Reclaiming the Book of Nature, Biola University, Los Angeles.

* * * *

     Also from Dr. Wells:

     Darwin considered some of the best evidence for his theory to be the striking resemblance of vertebrate embryos at an early stage of their development. He wrote in The Origin of Species that "the embryos of mammals, birds, fishes, and reptiles" are "closely similar, but become, when fully developed, widely dissimilar." He argued that the best explanation for their embryonic similarity was that such animals "are the modified descendants of some ancient progenitor." According to Darwin, "the embryonic or larval stages show us, more or less completely, the condition of the progenitor of the whole group in its adult state." (Darwin, 1859, pp. 338, 345).
     Darwin believed that evolutionary changes tend to occur in the later stages of development and are gradually pushed back into embryogenesis, with the result that embryonic development bears the imprint of past evolution (in Ernst Haeckel's words, "ontogeny recapitulates phylogeny"). The doctrine of recapitulation fits so nicely with Darwin's theory that it has endured to the present, and can be found in many modern biology textbooks. But it was clear to embryologists even during Darwin's lifetime that it did not fit the facts. Nineteenth-century embryologist Karl Ernst von Baer pointed out that although vertebrate embryos resemble each other at one point in their development, they never resemble the adult of any species, present or past. The most that can be said is that embryos in the same major group (such as the vertebrates, which include fishes, reptiles, birds, and mammals) tend to resemble each other at a certain stage before they develop the distinguishing characteristics of their class, genus and species. (Gould, 1977; Hall, 1992; Raff, 1996).
     Darwin and his followers ignored these difficulties, however, and the modern synthesis excluded embryology entirely. Only in the past twenty years, with the rise of developmental genetics, has comparative embryology attracted significant interest from evolutionary biologists. One result of this renewed interest has been the recognition that patterns of early development do not fit the Procrustean bed of recapitulationism.
     Although it is true that vertebrate embryos are somewhat similar at one stage of their development, at earlier stages they are radically dissimilar. After fertilization, animal embryos first undergo a process called "cleavage," in which the fertilized egg divides into hundreds or thousands of separate cells. During cleavage, embryos acquire their major body axes (e.g., anterior-posterior, or head-to-tail, and dorsal-ventral, or back-to-front). Each major group of animals follows a distinctive cleavage pattern; among vertebrates, for example, mammals, birds, fishes, and reptiles cleave very differently. (Gilbert, 1994).
     Animal embryos then enter the "gastrulation" stage, during which their cells move relative to each other, rearranging themselves to generate basic tissue types and establish the general layout of the animal's body. The consequences of this process are so significant that embryologist Lewis Wolpert has written that "it is not birth, marriage, or death, but gastrulation which is truly the important event in your life." (Wolpert, 1991, p. 12) Like cleavage patterns, gastrulation patterns vary markedly among the major groups of animals, including the different classes of vertebrates. (Elinson, 1987).
     Only after gastrulation do the embryos of mammals, birds, fishes, and reptiles begin to resemble each other. In the "pharyngula" stage, every vertebrate embryo looks vaguely like a tiny fish, with a prominent head and a long tail. The neck region of a vertebrate pharyngula also has a series of "pharyngeal pouches," or tiny ridges, which recapitulationists misleadingly refer to as "gill slits." Although in fish embryos these actually go on to form gills, in other vertebrates they develop into various other head structures such as the inner ear and parathyroid gland 2E (Lehman, 1987) The embryos of mammals, birds and reptiles never possess gills.
     Therefore, Darwin's belief in recapitulation is belied by the evidence.Embryologists have occasionally pointed this out (Garstang, 1922; deBeer, 1958), but their admonitions have fallen mostly on deaf ears. As recently as 1976, biologist William Ballard (who, according to Richard Elinson, coined the term "pharyngula" [Elinson, 1987]), lamented the fact that so much energy continues to be "diverted into the essentially fruitless 19th century activity of bending the facts of nature to support second-rate generalities." Ballard concluded that it is "only by semantic tricks and subjective selection of evidence" that one can argue that the early stages of the various classes of vertebrates "are more alike than their adults." (Ballard, 1976, p. 38)

REFERENCES

• Ballard, W. W.: 1976."Problems of Gastrulation: Real and Verbal." BioScience, 26: 36-39.
• Darwin, C.: 1859. On the Origin of Species, reprint. New York: Modern Library.
• de Beer, G.: 1958. Embryos and Ancestors, 3d ed. Oxford: Clarendon Press.
• Elinson, R. P.: 1987. "Change in Developmental Patterns: Embryos of Amphibians with Large Eggs." In Development as an Evolutionary Process,ed. R. A. Raff and E. C. Raff, Vol. 8, pp. 1-21. New York: Alan R. Liss.
• Garstang, W.: 1922. "The Theory of Recapitulation: A Critical Re-statement of the Biogenetic Law." Journal of the Linnean Society (Zoology), 35:81-101.
• Gilbert, S. F.: 1994. Developmental Biology, 4th ed. Sunderland, MA.: Sinauer Associates.
• Gould, S. J.: 1977. Ontogeny and Phylogeny. Cambridge, MA.: Belknap Press.
• Hall, B. K.: 1992. Evolutionary Developmental Biology. London: Chapman & Hall.
• Lehman, H. E.: 1987. Chordate Development, 3d ed. Winston-Salem, NC: Hunter Textbooks.
• Raff, R. A.: 1996. The Shape of Life: Genes, Development, and the Evolution of Animal Form.
• Chicago: The University of Chicago Press.
• Wolpert, L.: 1991. The Triumph of the Embryo. Oxford: Oxford University Press.

     Posted by scott on September 15, 1998 at 11:05:19:

     Sorry Helen, but I think an embryologist worth his salt would know that pharyngeal pouches are POUCHES not ridges.  Besides, Wells got his first doctorate in theology, so one has to wonder where his true interests are.

Fourth Response

     Posted by Sumac on September 15, 1998 at 02:01:57:

     I'm going to have to go with Paul and Pat P. on this one. Gill slits (or gill clefts) are only called that because they resemble the same structure in developing fish. They have the same origin, but are used for different purposes. I defy any of you to find any current source that says human embryos have gills. Gill slits and gills are two different things.
     As far as Dr. Wells' essays go, it is widely recognized that early and late developmental stages are more divergent than the intermediate stages. There is sort of an hourglass shape in terms of the similarity of vertebrate embryos during the course of development. It is even recognized that individual characteristics are most similar at different times. We have gone over all this before. None of these facts put into question the idea that previously established forms have been modified for new functions. In fact, the data indicates that major changes can be established by very subtle changes in just the timing of development.
     By the way (this is for MEYER), Haeckel said that human embryos pass through the adult stages of ancestral forms. That is what he meant by recapitulation. The current theory (which is upheld by the data) is one of embryonic recapitulation such that evolutionary changes occur through successive modifications in development.

     Posted by Mockingbird1 on September 15, 1998 at 11:29:32:

     S: I'm going to have to go with Paul and Pat P. on this one.

     PK: Sumac, agreeing with the smart people is a good tactic, that is why I want to agree with you. Pat P has said that the pharygeal pouches or ridges or whatever they are, are not gill slits. Paul seems to be saying that suggestions that they are not gill slits are part of a fraud.

     S:Gill slits (or gill clefts) are only called that because they resemble the same structure in developing fish.

     PK: Not exactly. Gills slits are called 'gill slits' because they allow water out after flowing through the gills. Gill slits are a feature in adult fish. This is where we often behead boney fishes. Though something is homologuous to what will develop into gill slits, might not make it a gill slit. The absence of gills beneath the structure indicates that it is not and can not be a gill slit. To insist on calling the mammalian structure a gill slit, is to suggest gills which we all know are not there at all.

     PK: What the White Paper says (the bolding is mine):

     "Thus, while much of biology addresses proximate causation of observed phenomena, evolutionary biology addresses ultimate causation. Answers to questions regarding ultimate causation might include "because this species inherited the feature from distant ancestors" or "because a history of natural selection favored this feature over others in the recent past." That a human embryo has gill slits can be understood only by inheritance from early vertebrate ancestors; that we walk upright can be understood as an adaptation, a trait favored by natural selection in our more recent ancestors. In emphasizing history, we must, at the same time, recognize that evolution is an active, ongoing process."

     PK: Your past ability to recognize and correct evolutionist mistakes, your recent recognition of the appendix as a non-vestigial structure, has distinguished you. I do not doubt your integrity or knowledge here. I suspect that our differences may be semantic.

     Posted by Sumac on September 15, 1998 at 12:18:33:

     I have not seen any textbook that says gill slits in mammalian embryos have anything to do with functional gills. The term is a historical one and, unfortunately, can be confusing (as common names often are). Developmental biologists recognize that what they call gill slits are not slits and are not gills. It's just that that is what they were called when they were first described and the name has stuck. Most, if not all, textbooks will refer to the structures as pharyngeal poiuches, but they will also give you the common name which is gill slits or clefts. Oftentimes, in science, the original name for something is based on what the current thinking of the function is (like that syntax?). Later, when we understand it better, the name may not make sense anymore, but the name will stay. Attempts to change the name can be successful or not. In this case, we are stuck with several names for the same structure.

     Posted by Mockingbird1 on September 15, 1998 at 12:42:50:

     PK: I cringe when folks find the Bible, and other sacred texts referring to the Sun rising in the east, and going on to add that that is wrong, when the term is in common use.

     PK: For those who read about the evolution of structures and who may be unfamiliar with the absence of actual gills in human embryos, the term may be misleading. Quite likely, the professors did not intend to mislead or perpetuate Haeckelian notions in any deliberate manner. My inferences on the use of the term are colored by our past discussions re: Haeckel.

     PK: Perhaps the lines in question could be rewritten (italicization is my proposed insertion):   "Thus, while much of biology addresses proximate causation of observed phenomena, evolutionary biology addresses ultimate causation. Answers to questions regarding ultimate causation might include "because this species inherited the feature from distant ancestors" or "because a history of natural selection favored this feature over others in the recent past." That a human embryo has" structures resembling gill slits, even though it has no gills, nor ever will have gills, " can be understood only by inheritance from early vertebrate ancestors; that we walk upright can be understood as an adaptation, a trait favored by natural selection in our more recent ancestors. In emphasizing history, we must, at the same time, recognize that evolution is an active, ongoing process."

Fifth Response

     Posted by scott on September 15, 1998 at 11:08:04:

     Gills in fish and the vasculature and facial structures of humans derive from the same embryonic structures.

Is the Human Embryo Essentially a Fish with Gills?
by Dr. David N. Menton, Ph.D.
Copyright © 1997 Missouri Association for Creation, Inc.

     Almost from the beginning, evolutionists have attempted to equate the process of evolution with the progressive development of the embryo. During the famous Scopes "Monkey Trial" in 1925, for example, lawyers and expert witnesses defending teaching Darwinism in public schools, repeatedly confused evolution with embryology. The lawyers even insisted that evolution must be taught if physicians are to understand the development of babies in the womb! The very word "evolution" (which means "unfolding"), was taken from the name of an early theory of embryonic development which proposed that humans are completely preformed in miniature in the fertilized egg, simply "unfolding" during the development of the baby. Obviously, the blind-chance process of Darwinian "evolution" has nothing whatever to do with the exquisitely-controlled process of embryological development. Still, evolutionists have long attempted to relate embryology to evolution, presumably in an effort to extrapolate the readily-observable process of embryonic development into the unobservable process of macroevolution. Embryology continues to play a role in current evolutionary dogma. Generations of students have been told, for example, that the human embryo developing in the womb passes through stages of its evolutionary ancestry -- even at one point having gills like a fish!
     Like most students of biology, I was required to memorize the "biogenetic law" which states that "ontogeny recapitulates phylogeny." This means that the developing embryo (ontogeny) of each vertebrate species retraces (recapitulates) its evolutionary history (phylogeny). Specifically, each embryo in the course of its development, is said to pass through a progression of abbreviated stages that resemble the main evolutionary stages of its presumed ancestors. Thus, in the case of the human embryo, recapitulation scenario goes something like this: 1) The fertilized egg starts as a single cell (just like our first living evolutionary "ancestor"). 2) As the fertilized egg repeatedly divides it develops into an embryo with a segmented arrangement (the "worm" stage). 3) These segments develop into vertebrae, muscles and something that sort of looks like gills (the "fish" stage). 4) Limb buds develop with paddle-like hands and feet, and there appears to be a "tail" (the "amphibian" stage). 5) By about the eighth week of development, most organs are nearly complete, the limbs develop fingers and toes, and the "tail" disappears (the human stage). Now the mother can finally claim the baby as her own, or at least one of her own species. This ludicrous scenario has actually been used as a justification for abortion -- after all you are only killing lower animals!
     The "biogenetic law" was first promulgated in the late 1800's by the German biologist Ernst Haeckel, a committed disciple of Darwin. Impressed by the general similarity among vertebrate embryos, Haeckel chose to ignore their differences. (Haeckel was a scientific charlatan who even stooped to publishing two copies of the same woodcut side by side to demonstrate the "remarkable similarity" between human and dog embryos!) Haeckel's "law" was shown to be unsound by many of the most distinguished embryologists of his own day, but its appeal to evolutionists was so great that it remained impervious to scientific criticism. In her book Essays in the History of Embryology and Biology (MIT Press, 1967 p. 150), Jane Oppenheimer said that the work of Haeckel "was the culmination of the extremes of exaggeration which followed Darwin." She lamented that "Haeckel's doctrines were blindly and uncritically accepted," and "delayed the course of embryological progress." Embryologist Erich Blechschmidt, considered Haeckel's biogenetic "law" to be one of the most serious errors in the history of biology. In his book The Beginnings of Human Life (Springer-Verlag Inc., 1977, p. 32), Blechschmidt minced no words in repudiating Haeckel's "law":

     "The so-called basic law of biogenetics is wrong. No buts or ifs can mitigate this fact. It is not even a tiny bit correct or correct in a different form. It is totally wrong."

     We could ignore this whole sorry chapter in the history of evolutionism, were it not for the fact that the biogenetic "law" is still being taught as a fact in our public schools! Of 15 high school biology textbooks being considered for adoption by the Indiana State Board of Education in 1980, nine offered embryological recapitulation as evidence for evolution.
     Evolutionists themselves have conceded that the biogenetic "law" has become so deeply rooted in evolutionary dogma that it cannot be weeded out. For example, Paul Ehrlich said "it's shortcomings have been almost universally pointed out by modern authors, but the idea still has a prominent place in biological mythology" (The Process of Evolution, 1963, p. 66). Even Dr. Benjamin Spock saw fit to perpetuate Haeckel's recapitulation myth in his well-known book, Baby and Child Care (Cardinal Giant Edit 57 p. 223). Spock confidently assured expectant mothers that:

     "each child as he develops is retracing the whole history of mankind, physically and spiritually [sic], step by step. A baby starts off in the womb as a single tiny cell, just the way the first living thing appeared in the ocean. Weeks later, as he lies in the amniotic fluid of the womb, he has gills like a fish."

     It is a well-established fact that the human embryo (like all mammalian embryos) never has gills in any sense of the word. The fanciful notion of gills is based upon the presence of four alternating ridges and grooves in the neck region of the human embryo (called pharyngeal arches and pouches) that bear a superficial resemblance to gills. While similar arches do give rise to gills in certain aquatic vertebrates such as fish, their developmental fate in mammals has nothing to do with gills or even breathing. In man and other mammals, these arches and pouches develop into part of the face, muscles of mastication and facial expression, bones of the middle ear, and endocrine glands.
     The embryological development of the heart has been another popular textbook example of embryonic recapitulation, and thus "proof" of evolution. Evolutionists argue that as the human heart develops, it goes from a two-chambered "fish heart," to a three-chambered "amphibian heart" and, finally, forms the four-chambered mammalian heart. In his book Comparative Anatomy and Embryology (Ronald Press, 1964, p. 509), William Ballard said "no false biological statement has had a longer or more popular life than the one about the ontogeny of the four-chambered heart." Ballard pointed out that "in real life, all vertebrate hearts are composed of the same four chambers at the pharyngula stage." As the heart develops, these four chambers become specialized in different ways which are uniquely suited to the demands of aquatic, amphibious or terrestrial life.       Embryologists are now aware that the embryos of each species of animal are unique and dynamically functional systems. The human embryo does not become human at some point during its development, rather it is uniquely human at every stage of its development. While scientists continue to learn much about the marvelous process of development in the embryo, the inspired words of King Solomon (Ecclesiastes 11:5) remain true:

     "As you do not know the path of the wind, or how the body is formed in a mother's womb, so you cannot understand the work of God, the Maker of all things."

     Originally published in St. Louis MetroVoice, December 1993, Vol. 3, No. 12

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