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The following are quotes added to my Unclassified Quotes database in September 2008. The date format is dd/mm/yy.
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[Index: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Oct, Nov, Dec]
24/09/2008 "It is evident as well that the initial choice of this or that kind of behavior can often have very long-range consequences, affecting not only the species in which it first crops up in rudimentary form, but all its descendants, even if these should constitute an entire evolutionary subgroup. As we all know, the great turning points in evolution have coincided with the invasion of new ecological spaces. If terrestrial vertebrates appeared and were able to initiate that wonderful line from which amphibians, reptiles, birds, and mammals later developed, it was originally because a primitive fish `chose' to do some exploring on land, where it was however ill-provided with means for getting about. The same fish thereby created, as a consequence of a shift in behavior, the selective pressure which was to engender the powerful limbs of the quadrupeds. Among the descendants of this daring explorer, this Magellan of evolution, are some that can run at speeds of fifty miles an hour; others climb trees with astonishing agility, while yet others have conquered the air, in a fantastic manner fulfilling, extending, and amplifying the ancestral fish's hankering, its `dream.'" (Monod, J., "Chance and Necessity: An Essay on the Natural Philosophy of Modern Biology," , Wainhouse, A., transl., Penguin: London, Reprinted, 1997, pp.126-127. Emphasis original) 24/09/2008 "When the mass media first reported the change in my view of the world, I was quoted us saying that biologists' investigation of DNA has shown, by the almost unbelievable complexity of the arrangements needed to produce life, that intelligence must have been involved. I had previously written that there was room for a new argument to design in explaining the first emergence of living from nonliving matter-especially where this first living matter already possessed the capacity to reproduce itself genetically. I maintained that there was no satisfactory naturalistic explanation for such a phenomenon." (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, p.123) 24/09/2008 "These statements provoked an outcry from critics who claimed that I was not familiar with the latest work in abiogenesis. Richard Dawkins claimed that I was appealing to a `god of the gaps.' In my new introduction to the 2007 edition of God and Philosophy; I said, `I am myself delighted to be assured by biologicalscientist friends that protobiologists are now well able to produce theories of the evolution of the first living matter and that several of these theories are consistent with all the so-far-confirmed scientific evidence.' [Flew, A., "God and Philosophy," Prometheus: Amherst, NY, 2005, p.11] But to this I must add the caveat that the latest work I have seen shows that the present physicists' view of the age of the universe gives too little time for these theories of abiogenesis to get the job done." (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, pp.123-124) 24/09/2008 "A far more important consideration is the philosophical challenge Facing origin-of-life studies. Most studies on the origin of life are carried out by scientists who rarely attend to the philosophical dimension of their findings. Philosophers, on the other hand, have said little on the nature and origin of life. The philosophical question that has not been answered in origin-of-life studies is this: How can a universe of mindless matter produce beings with intrinsic ends, self-replication capabilities, and `coded chemistry'? Here we are not dealing with biology, but an entirely different category of problem." (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, p.124) 24/09/2008 "Let us first look at the nature of life from a philosophical standpoint. Living matter possesses an inherent goal or end-centered organization that is nowhere present in the matter that preceded it. In one of the few recent philosophical works on life, Richard Cameron has presented a useful analysis of this directedness of living beings. Something that is alive, says Cameron, will also be teleological-that is, it will possess intrinsic ends, goals, or purposes. - Contemporary biologists, philosophers of biology, and workers in the field of 'artificial life,' he writes, `have yet to produce a satisfying account of what it is to be alive, and I defend the view that Aristotle can help us fill this gap.... Aristotle did not hold life and teleology to be coextensive simply by chance, but defined life in teleological terms, holding that teleology is essential to the life of living things.' [Cameron, R., "Aristotle on the Animate: Problems and Prospects," Bios: Epistemological and Philosophical Foundation of Life Sciences, Rome, February 23-24, 2006]" (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, p.125) 24/09/2008 "The origin of self-reproduction is a second key problem. Distinguished philosopher John Haldane notes that origin-of-life theories `do not provide a sufficient explanation, since they presuppose the existence at an early stage of self-reproduction, and it has not been shown that this can arise by natural means from a material base.' [Haldane, J., "Preface to the Second Edition," in Smart, J.J.C. & Haldane, J., "Atheism and Theism: Great Debates in Philosophy," Blackwell: Oxford, 2003, p.224]" (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, p.125) 24/09/2008 "David Conway summarizes these two philosophical quandaries in responding to David Hume's contention that the life-sustaining order of the universe was not designed by any form of intelligence. The first challenge is to produce a materialistic explanation for `the very first emergence of living matter from nonliving matter. In being alive, living matter possesses a teleological organization that is wholly absent from everything that preceded it.' The second challenge is to produce an equally materialist explanation for the emergence, from the very earliest life-forms which were incapable of reproducing themselves, of life- forms with a capacity for reproducing themselves. Without the existence of such a capacity, it would not have been possible for different species to emerge through random mutation and natural selection. Accordingly, such mechanism cannot be invoked in any explanation of how life-forms with this capacity first `evolved' from those that lacked it." Conway concludes that these biological phenomena "provide us with reason for doubting that it is possible to account for existent life-forms in purely materialistic terms and without recourse to design." [Conway, D., "The Rediscovery of Wisdom," Macmillan: London, 2000, p.225]" (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, pp.125-126) 24/09/2008 "A third philosophical dimension to the origin of life relates to the origin of the coding and information processing that is central to all life-forms. This is well described by the mathematician David Berlinski, who points out that there is a rich narrative drama surrounding our current understanding of the cell. The genetic message in DNA is duplicated in replication and then copied from DNA to RNA in transcription. Following this there is translation whereby the message from RNA is conveyed to the amino acids, and finally the amino acids are assembled into proteins. The cell's two fundamentally different structures of information management and chemical activity are coordinated by the universal genetic code. The remarkable nature of this phenomenon becomes apparent when we highlight the word code. Berlinski writes: `By itself, a code is familiar enough, an arbitrary mapping or a system of linkages between two discrete combinatorial objects. The Morse code, to take a familiar example, coordinates dashes and dots with letters of the alphabet. To note that codes are arbitrary is to note the distinction between a code and a purely physical connection between two objects. To note that codes embody mappings is to embed the concept of a code in mathematical language. To note that codes reflect a linkage of some sort is to return the concept of a code to its human uses. This in turn leads to the big question: `Can the origins of a system of coded chemistry be explained in a way that makes no appeal whatever to the kinds of facts that we otherwise invoke to explain codes and languages, systems of communication, the impress of ordinary words on the world of matter?' [Berlinski, D., "On the Origins of Life," Commentary, February 2006, pp.25, 30-31]" (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, pp.126-127. Emphasis original) 24/09/2008 "Carl Woese, a leader in origin-of-life studies, draws attention to the philosophically puzzling nature of this phenomenon. Writing in the journal RNA, he says: `The coding, mechanistic, and evolutionary facets of the problem now became separate issues. The idea that gene expression, like gene replication, was underlain by some fundamental physical principle was gone.' Not only is there no underlying physical principle, but the very existence of a code is a mystery. `The coding rules (the dictionary of codon assignments) are known. Yet they provide no clue as to why the code exists and why the mechanism of translation is what it is.' He frankly admits that we do not know anything about the origin of such a system. `The origins of translation, that is before it became a true decoding mechanism, are for now lost in the dimness of the past, and I don't wish to engage here in hand-waving speculations as to what polymerization processes might have preceded and given rise to it, or to speculate on the origins of tRNA, tRNA charging systems or the genetic code.' [Woese, C., "Translation: In Retrospect and Prospect," RNA, Vol. 7, No. 8, August, 2001, pp.1055-67, pp,1061, 1056, 1064]" (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, pp.127-128) 24/09/2008 "Paul Davies highlights the same problem. He observes that most theories of biogenesis have concentrated on the chemistry of life, but `life is more than just complex chemical reactions. The cell is also an information storing, processing and replicating system. We need to explain the origin of this information, and the way in which the information processing machinery came to exist.' He emphasizes the fact that a gene is nothing but a set of coded instructions with a precise recipe for manufacturing proteins. Most important, these genetic instructions are not the kind of information you find in thermodynamics and statistical mechanics; rather, they constitute semantic information. In other words, they have a specific meaning. These instructions can be effective only in a molecular environment capable of interpreting the meaning in the genetic code. The origin question rises to the top at this point. `The problem of how meaningful or semantic information can emerge spontaneously from a collection of mindless molecules subject to blind and purposeless forces presents a deep conceptual challenge.' [Davies, P., "The Origin of Life II: How Did It Begin?," Science Progress, Vol. 84, No 1, February, 2001, pp.17-29)" (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, pp.127- 128) 24/09/2008 "It is true that protobiologists do have theories of the evolution of the first living matter, but they are dealing with a different category of problem. They are dealing with the interaction of chemicals, whereas our questions have to do with how something can be intrinsically purpose-driven and how matter can be managed by symbol processing. But even at their own level, the protobiologists are still a long way from any definitive conclusions. This is highlighted by two prominent origin-of-life researchers. Andy Knoll, a professor of biology at Harvard and author of Life on a Young Planet: The First Three Billion Years of Life, notes: `If we try to summarize by just saying what, at the end of the day, we do know about the deep history of life on Earth, about its origin, about its formative stages that gave rise to the biology we see around us today, I think we have to admit that we're looking through a glass darkly here. We don't know how life started on this planet. We don't know exactly when it started, we don't know under what circumstances.' [Knoll, A., "How Did Life Begin? An Interview with Andy Knoll," PBS NOVA, May 3, 2004" (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, pp.129-130) 24/09/2008 "Antonio Lazcano, the president of the International Society for the Study of the Origin of Life, reports: `One feature of life, though, remains certain: Life could not have evolved without a genetic mechanism-one able to store, replicate, and transmit to its progeny information that can change with time.... Precisely how the first genetic machinery evolved also persists as an unresolved issue.' In fact, he says, `The exact pathway for life's origin may never be known.' [Lazcano, A., "The Origins of Life," Natural History, February 2006]" (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, p.130) 24/09/2008 "As for the origin of reproduction, John Maddox, the editor emeritus of Nature, writes, `The overriding question is when (and then how) sexual reproduction itself evolved. Despite decades of speculation, we do not know.' [Maddox, J., "What Remains to Be Discovered," Touchstone: New York, 1998, p.252] Finally, scientist Gerald Schroeder points out that the existence of conditions favorable to life still does not explain how life itself originated. Life was able to survive only because of favorable conditions on our planet. But there is no law of nature that instructs matter to produce end-directed, self-replicating entities. [Schroeder, G.L., "The Hidden Face of God," Free Press: New York, 2001, p.53]" (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, p.130) 24/09/2008 "So how do we account for the origin of life? The Nobel Prize-winning physiologist George Wald once famously argued that `we choose to believe the impossible: that life arose spontaneously by chance.' In later years, he concluded that a preexisting mind, which he posits as the matrix of physical reality, composed a physical universe that breeds life: `How is it that, with so many other apparent options, we are in a universe that possesses just that peculiar nexus of properties that breeds life? It has occurred to me lately-I must confess with some shock at first to my scientific sensibilities-that both questions might be brought into some degree of congruence. This is with the assumption that mind, rather than emerging as a late outgrowth in the evolution of life, has existed always as the matrix, the source and condition of physical reality-that the stuff of which physical reality is constructed is mind-stuff. It is mind that has composed a physical universe that breeds life, and so eventually evolves creatures that know and create: science-, art-, and technology- making creatures.' [Wald, G., "Life and Mind in the Universe," in Margenau, H. & Varghese, A., ed., "Cosmos, Bios, Theos," Open Court: La Salle IL, 1992, p.218] This, too, is my conclusion. The only satisfactory explanation for the origin of such `end-directed, self-replicating' life as we see on earth is an infinitely intelligent Mind." (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, pp.131-132) 25/09/2008 "In my life as scientist I have come upon two major problems which, though rooted in science, though they would occur in this form only to a scientist, project beyond science, and are I think ultimately insoluble as science. That is hardly to be wondered at, since one involves consciousness and the other, cosmology. The consciousness problem was hardly avoidable by one who has spent most of his life studying mechanisms of vision. We have learned a lot, we hope to learn much more; but none of it touches or even points, however tentatively, in the direction of what it means to see. Our observations in human eyes and nervous systems and in those of frogs are basically much alike. I know that I see; but does a frog see? It reacts to light; so do cameras, garage doors, any number of photoelectric devices. But does it see? Is it aware that it is reacting? There is nothing I can do as a scientist to answer that question, no way that I can identify either the presence or absence of consciousness. I believe consciousness to be a permanent condition that involves all sensation and perception. Consciousness seems to me to be wholly impervious to science. It does not lie as an indigestible element within science, but just the opposite: Science is the highly digestible element within consciousness, which includes science as a limited but beautifully definable territory within the much wider reality of whose existence we are conscious." (Wald, G., "Life and Mind in the Universe," in Margenau, H. & Varghese, R.A., ed., "Cosmos, Bios, Theos: Scientists Reflect on Science, God, and the Origins of the Universe Life, and Homo sapiens," Open Court: La Salle IL, 1992, Second printing, 1993, p.218. http://www3.interscience.wiley.com/journal/118640345/abstract) 25/09/2008 "The second problem involves the special properties of our universe. Life seems increasingly to be part of the order of nature. We have good reason to believe that we find ourselves in a uni verse permeated with life, in which life arises inevitably, given enough time, wherever the conditions exist that make it possible. Yet were any one of a number of the physical properties of our universe otherwise-some of them basic, others seemingly trivial, almost accidental-that life, which seems now to be so prevalent, would become impossible, here or anywhere. It takes no great imagination to conceive of other possible universes, each stable and workable in itself, yet lifeless. How is it that, with so many other apparent options, we are in a universe that possesses just that peculiar nexus of properties that breeds life? It has occurred to me lately-I must confess with some shock at first to my scientific sensibilities-that both questions might be brought into some degree of congruence. This is with the assumption that mind, rather than emerging as a late outgrowth in the evolution of life, has existed always as the matrix, the source and condition of physical reality-that the stuff of which physical reality is composed is mind-stuff. It is mind that has composed a physical universe that breeds life, and so eventually evolves creatures that know and create: science-, art-, and technology-making animals. In them the universe begins to know itself. Also, such creatures develop societies and cultures-institutions that present all the essential conditions for evolution by natural selection (variation, inheritance [mainly Larmarckian], competition for survival)-so introducing an evolution of consciousness parallel with, though independent of, anatomical and physiological evolution." (Wald, G., "Life and Mind in the Universe," in Margenau, H. & Varghese, R.A., ed., "Cosmos, Bios, Theos: Scientists Reflect on Science, God, and the Origins of the Universe Life, and Homo sapiens," Open Court: La Salle IL, 1992, Second printing, 1993, p.218. http://www3.interscience.wiley.com/journal/118640345/abstract) 25/09/2008 "NOVA: What is your definition of life? Knoll: I think you can say that life is a system in which proteins and nucleic acids interact in ways that allow the structure to grow and reproduce. It's that growth and reproduction, the ability to make more of yourself, that's important. Now, you might argue that that's a local definition of life, that if we find life on Europa at some time in the future, it might have a different set of interacting chemicals. People have tried to find more general, more universal definitions of life. They're speculative, because we don't know about any life other than ourselves. But one definition that I kind of like says life is a system that's capable of Darwinian evolution. What does it require to have a system that evolves in a Darwinian fashion? First, you have to be able to reproduce and make more of yourself, so that fits with our local definition. You also need a source of variation so that all of the new generation is not identical either to the previous generation or to all its brothers and sisters. And once you have that variation, then natural selection can actually select, by either differential birth or death, some of the variants that function best. That may turn out to be a fairly general definition of life wherever we might find it." (Knoll, A., "How Did Life Begin? An Interview with Andy Knoll," PBS NOVA, May 3, 2004. http://www.pbs.org/wgbh/nova/origins/knoll.html) 25/09/2008 "NOVA: What do you think was the first form of life? Knoll: It's pretty clear that all the organisms living today, even the simplest ones, are removed from some initial life form by four billion years or so, so one has to imagine that the first forms of life would have been much, much simpler than anything that we see around us. But they must have had that fundamental property of being able to grow and reproduce and be subject to Darwinian evolution. So it might be that the earliest things that actually fit that definition were little strands of nucleic acids. Not DNA yet-that's a more sophisticated molecule-but something that could catalyze some chemical reactions, something that had the blueprint for its own reproduction." (Knoll, A., "How Did Life Begin? An Interview with Andy Knoll," PBS NOVA, May 3, 2004. http://www.pbs.org/wgbh/nova/origins/knoll.html) 25/09/2008 "NOVA: Would it be something we would recognize under a microscope as living, or would it be totally different? Knoll: That's a good question. I can imagine that there was a time before there was life on Earth, and then clearly there was a time X-hundred thousand years or a million years later when there were things that we would all recognize as biological. But there's no question that we must have gone through some intermediate stage where, had you been there watching them, you might have placed your bets either way. So I can imagine that on a primordial Earth you would have replicating molecules-not particularly lifelike in our definition, but they're really getting the machinery going. Then some of them start interacting together and pretty soon you have something a little more lifelike, and then it incorporates maybe another piece of nucleic acid from somewhere else, and by the accumulation of these disparate strands of information and activity, something that you and I would look at and agree "that's biological" would have emerged." (Knoll, A., "How Did Life Begin? An Interview with Andy Knoll," PBS NOVA, May 3, 2004. http://www.pbs.org/wgbh/nova/origins/knoll.html) 25/09/2008 "NOVA: In a nutshell, what is the process? How does life form? Knoll: The short answer is we don't really know how life originated on this planet. There have been a variety of experiments that tell us some possible roads, but we remain in substantial ignorance. That said, I think what we're looking for is some kind of molecule that is simple enough that it can be made by physical processes on the young Earth, yet complicated enough that it can take charge of making more of itself. That, I think, is the moment when we cross that great divide and start moving toward something that most people would recognize as living." (Knoll, A., "How Did Life Begin? An Interview with Andy Knoll," PBS NOVA, May 3, 2004. http://www.pbs.org/wgbh/nova/origins/knoll.html) 25/09/2008 "NOVA: Is this an inevitable consequence of the conditions and chemicals and stuff that existed on early Earth? Knoll: We don't know whether life is an inevitable consequence of planetary formation. Certainly in our solar system there is no shortage of planets that probably never had life on them. So it's a hard question to answer. I think the way I'd be most comfortable thinking about it is that you probably have to get the recipe right. That is, you need a planet that has a certain range of environments, certain types of gases in the atmosphere, certain types of geological processes at work, that when you have the right conditions, life will emerge fairly rapidly. I don't think we need to think about inherently improbable events that eventually happen just because there are huge intervals of time. My guess is that it either happens or it doesn't." (Knoll, A., "How Did Life Begin? An Interview with Andy Knoll," PBS NOVA, May 3, 2004. http://www.pbs.org/wgbh/nova/origins/knoll.html) 25/09/2008 "NOVA: Has there been a change in thinking about this over the years? Knoll: People's ideas on the circumstances under which life might emerge have really changed and developed over the last 30 or 40 years. I think it's fair to say that when I was a boy those few people who thought about the origin of life thought that it probably was a set of improbable reactions that just happened to get going over the fullness of time. And I think it's fair to say that most of those people probably thought that we would find out what those reactions were, that somehow we would nail it in a test tube at some point. Now I think, curiously enough, both of those attitudes have changed. I think that there's less confidence that we're really going to be able to identify a specific historical route by which life emerged, but at the same time there's increasing confidence that when life did arise on this planet, it was not a protracted process using a chemistry that is pretty unlikely but rather is a chemistry that, when you get the recipe right, it goes, and it goes fairly quickly." (Knoll, A., "How Did Life Begin? An Interview with Andy Knoll," PBS NOVA, May 3, 2004. http://www.pbs.org/wgbh/nova/origins/knoll.html) 25/09/2008 "NOVA: What is the recipe for life? Knoll: The recipe for life is not that complicated. There are a limited number of elements inside your body. Most of your mass is carbon, oxygen, hydrogen, sulfur, plus some nitrogen and phosphorous. There are a couple dozen other elements that are in there in trace amounts, but to a first approximation you're just a bag of carbon, oxygen, and hydrogen. Now, it turns out that the atmosphere is a bag of carbon, oxygen, and hydrogen as well, and it's not living. So the real issue here is, how do you take that carbon dioxide in the atmosphere (or methane in an early atmosphere) and water vapor and other sources of hydrogen-how do you take those simple, inorganic precursors and make them into the building blocks of life? There was a famous experiment done by Stanley Miller when he was a graduate student at the University of Chicago in the early 1950s. Miller essentially put methane, or natural gas, ammonia, hydrogen gas, and water vapor into a beaker. That wasn't a raixture; at the time he did the experiment, that was at least one view of what the primordial atmosphere would have looked like. Then he did a brilliant thing. He simply put an electric charge through that mixture to simulate lightning going through an early atmosphere. After sitting around for a couple of days, all of a sudden there was this brown goo all over the reaction vessel. When he analyzed what was in the vessel, rather than only having methane and ammonia, he actually had amino acids, which are the building blocks of proteins. In fact, he had them in just about the same proportions you would find if you looked at organic matter in a meteorite. So the chemistry that Miller was discovering in this wonderful experiment was not some improbable chemistry, but a chemistry that is widely distributed throughout our solar system.." (Knoll, A., "How Did Life Begin? An Interview with Andy Knoll," PBS NOVA, May 3, 2004. http://www.pbs.org/wgbh/nova/origins/knoll.html) 25/09/2008 "NOVA: So life is really chemistry. Knoll: Life really is a form of chemistry, a particular form in which the chemicals can lead to their own reproduction. But the important thing, I think, is that when we think about the origin of life this way, it isn't that life is somehow different from the rest of the planet. Life is something that emerges on a developing planetary surface as part and parcel of the chemistry of that surface. Life is also sustained by the planet itself. That is, all of the nutrients that go into the oceans and end up getting incorporated into biology, at first they're locked up in rocks and then they are eroded from rocks, enter the oceans, and take part in a complex recycling that ensures that there's always carbon and nitrogen and phosphorous available for each new generation of organisms. The most interesting thought of all is that not only does life arise as a product of planetary processes, but in the fullness of time, on this planet at least, life emerged as a suite of planetary processes that are important in their own right. We're sitting here today breathing an oxygen-rich mixture of air. We couldn't be here without that oxygen, but that oxygen wasn't present on the early Earth, and it only became present because of the activity of photosynthetic organisms. So in a nutshell, life is really part of the fabric of a planet like Earth." (Knoll, A., "How Did Life Begin? An Interview with Andy Knoll," PBS NOVA, May 3, 2004. http://www.pbs.org/wgbh/nova/origins/knoll.html) 25/09/2008 "NOVA: To get back to these basic chemistry building blocks, is everything from a mouse to a bacterium to you and me made from this simple set of ingredients? Knoll: All life that we know of is fundamentally pretty similar. That's why we think that you and I and bacteria and toadstools all had a single common ancestor early on the Earth. If you look at the cell of a bacterium, it has about the same proportions of carbon and oxygen and hydrogen as a human body does. The basic biochemical machinery of a bacterium is, in a broad way at least, similar to the chemistry of our cells. The big difference between you and a bacterium in some ways is that your body consists of trillions of cells that function in a coordinated manner. Bacteria are single cells, although they're not free agents. In fact, bacteria working in a sediment or in the sea actually live in consortia as well. They're not really lone operators. They work in these very, very highly coordinated communities of organisms that help each other to grow and prosper." (Knoll, A., "How Did Life Begin? An Interview with Andy Knoll," PBS NOVA, May 3, 2004. http://www.pbs.org/wgbh/nova/origins/knoll.html) 25/09/2008 "NOVA: Is it hard to go from these little building blocks to a full-fledged organism? Knoll: Well, we don't know how hard it is to go from the simplest bricks, if you will, in the wall of life to something that is complicated, like a living bacterium. We know that it happened, so it's possible. We don't really know whether it was unlikely and just happened to work out on Earth, or whether it's something that will happen again and again in the universe. My guess is it's not too hard. That is, it's fairly easy to make simple sugars, molecules called bases which are at the heart of DNA, molecules called amino acids which are at the heart of proteins. It's fairly easy to make some of the fatty substances that make the coverings of cells. Making all of those building blocks individually seems to be pretty reasonable, pretty plausible. The hard part, and the part that I think nobody has quite figured out yet, is how you get them working together. How do you go from some warm, little pond on a primordial Earth that has amino acids, sugars, fatty acids just sort of floating around in the environment to something in which nucleic acids are actually directing proteins to make the membranes of the cell? Somehow you have to get all of the different constituents working together and have basically the information to make that system work in one set of molecules, which then directs the formation of a second set of molecules, which synthesizes a third set of molecules, all in a way that feeds back to making more of the first set of molecules. So you end up getting this cycle. I'm not sure we've gotten very far down the road to understanding how that really happens." (Knoll, A., "How Did Life Begin? An Interview with Andy Knoll," PBS NOVA, May 3, 2004. http://www.pbs.org/wgbh/nova/origins/knoll.html) 25/09/2008 "NOVA: In your book, you liken the study of the origin of life to a maze. Knoll: Yes. There are multiple doors that enter the maze, but there's really only one historical path that life took. I think that while we've had some very clever entryways into several of these doors, at this point we still don't know which of these pathways ultimately will thread us through the maze and which end up in a blind alley." (Knoll, A., "How Did Life Begin? An Interview with Andy Knoll," PBS NOVA, May 3, 2004. http://www.pbs.org/wgbh/nova/origins/knoll.html) 25/09/2008 "NOVA: So at this point we're seeing the origins of life through a glass darkly? Knoll: If we try to summarize by just saying what, at the end of the day, do we know about the deep history of life on Earth, about its origin, about its formative stages that gave rise to the biology we see around us today, I think we have to admit that we're looking through a glass darkly here. We have some hints, we have a geologic record that tells us that life formed early on the planet, although our ability to interpret that in terms of specific types of microorganisms is still frustratingly limited. There are still some great mysteries. People sometimes think that science really takes away mystery, but I think there are great scientific mysteries and causes for wonder and, most importantly, things that will, I hope, stimulate biologists for years to come. We don't know how life started on this planet. We don't know exactly when it started, we don't know under what circumstances. It's a mystery that we're going to chip at from several different directions. Geologists like myself will chip at it by trying to get ever clearer records of Earth's early history and ever better ways of interrogating those rocks through their chemistry and paleontology. Biologists will chip at it by understanding at an ever deeper level how the various molecular constituents of the cell work together, how living organisms are related to one other genealogically. And chemists will get at it by doing new experiments that will tell us what is plausible in how those chemical correspondences came to be." (Knoll, A., "How Did Life Begin? An Interview with Andy Knoll," PBS NOVA, May 3, 2004. http://www.pbs.org/wgbh/nova/origins/knoll.html) 25/09/2008 "NOVA: Will we ever solve the problem? Knoll: I don't know. I imagine my grandchildren will still be sitting around saying that it's a great mystery, but that they will understand that mystery at a level that would be incomprehensible to us today. The particulars of the jump from nonliving to living that occurred sometime in our planet's early history is a profound enigma and will likely remain that way for some time to come, says Harvard's Andy Knoll." (Knoll, A., "How Did Life Begin? An Interview with Andy Knoll," PBS NOVA, May 3, 2004. http://www.pbs.org/wgbh/nova/origins/knoll.html) 25/09/2008 "The starting point for Oparin's argument was that the atmosphere of the young Earth was very different from what it is now. In chemical language, it was a reducing atmosphere, virtually devoid of the free oxygen that now sustains the life of animals, ourselves included. What oxygen there was would have been locked up in its chemical compounds with hydrogen (which makes water, or H2O) and carbon (carbon dioxide, or CO2). There would also have been some carbon monoxide (CO), while other carbon would also have been present in the atmosphere in the form of its compound with hydrogen called methane (CH4). Nitrogen, now the predominant component of the atmosphere (to the tune of 80 percent), would also have been present as ammonia (NH3 in the atmosphere of 4,000 million years ago. These are the materials now present in the atmosphere of the planet Jupiter. Oparin guessed that simple organic compounds could be formed from these components of the primeval atmosphere by chemical reactions, perhaps induced by ultraviolet light from the Sun. He went on to argue that the products could have accumulated in the oceans, there to be assembled into life-forms." (Maddox, J., "What Remains To Be Discovered: Mapping the Secrets of the Universe, the Origins of Life, and the Future of the Human Race," Touchstone: New York NY, 1998, Reprinted, 1999, p.128) 25/09/2008 "It fell to Stanley W Miller, a graduate student at the University of Chicago in 1956, to pass a high-voltage electrical discharge through a mixture of gases of that kind and to recover from the bottom of the reaction vessel a mixture of chemicals including several of those called amino acids, the building blocks of proteins. Technically, Miller's experiment was a great success. From different mixtures of methane, nitrogen and water with small traces of ammonia he produced ten of the twenty amino acids that occur naturally in modern protein molecules. The idea was to simulate the effects of lightning flashes. The more common products, the amino acids glycine and alanine, appeared in surprisingly large amounts; some 3 percent of the amount of methane consumed from the reaction vessel was converted into alanine. Miller has calculated that if the Sun's ultraviolet radiation were used with the same efficiency for the production of amino acids on primeval Earth, more than 100,000 tons of alanine would have been produced each year." (Maddox, J., "What Remains To Be Discovered: Mapping the Secrets of the Universe, the Origins of Life, and the Future of the Human Race," Touchstone: New York NY, 1998, Reprinted, 1999, pp.128-129) 25/09/2008 "Even now, the problem that remains to be solved is daunting. It goes without saying that the ultimate test of success will be the replication in some laboratory of processes that might plausibly have led to the formation of living things. Given present ignorance, it is impossible to guess whether that will take several years or several decades." (Maddox, J., "What Remains To Be Discovered: Mapping the Secrets of the Universe, the Origins of Life, and the Future of the Human Race," Touchstone: New York NY, 1998, Reprinted, 1999, pp.128-129) 25/09/2008 "Interestingly-and disconcertingly for some-the key assumption underlying Oparin's argument, that the primeval atmosphere was a chemically reducing atmosphere, is not now so readily accepted as in 1924. The counterargument rests on the comparison of Earth's atmosphere with that of similarly placed Venus and on the attempts made in recent decades to reconstruct the original composition of the nebula of gas and dust from which the solar system is supposed to have formed about 5,000 million years ago. In this view, ammonia in particular would not have been conspicuous in the early atmosphere. This controversy has an obvious bearing on the availability in the primeval seas of the chemicals (whatever they were) from which the first living things were constructed. Researchers in this field, familiar as they are with the Oparin tradition, tend to resist the new arguments. Instead they should welcome them because they may well lead to a better account of what the early atmosphere was like." (Maddox, J., "What Remains To Be Discovered: Mapping the Secrets of the Universe, the Origins of Life, and the Future of the Human Race," Touchstone: New York NY, 1998, Reprinted, 1999, pp.129-130) 25/09/2008 "Meanwhile, the time when life began on Earth has been pinned down. Earth itself is 4,500 million years old. Rocks recovered from the surface of the Moon by the U.S. Apollo missions between 1968 and 1972 revealed that the cratering of the Moon's surface was intense between 4,200 million and 4,000 million years ago, whereupon it almost abruptly ceased. It is unthinkable that Earth, then even closer to the Moon than now, would have escaped the bombardment that so pockmarked the Moon, and equally unthinkable that conditions then would have permitted life to emerge. So life began more recently than 4,000 million years ago. The other end of the time frame comes from dating the earliest plausible fossils found in Earth's surface rocks. Early fossils are necessarily scarce, because much of the early continental crust has already been recycled back into Earth's interior. But the first living things would not have had the bones and skulls that help preserve more recent fossils-those of dinosaurs, for example. Nevertheless, there are not many of them, but there are structures with the size and shape of modern bacteria in sedimentary rocks dating from 3,800 million years ago. A little later in the fossil record, there are structures called stromatolites that appear to be relics of huge agglomerations of single-celled organisms, either bacteria or algae, comparable to the huge bacterial "mats" found floating in modern oceans. Structures of this kind have been found in Australian sedimentary rocks dating from 3,500 million years ago. It seems fair to suppose that life was well established by then and possibly by 3,800 million years ago. By the yardsticks of geological time, that is a narrow window-perhaps no more than 200 million years, and 500 million years at most." (Maddox, J., "What Remains To Be Discovered: Mapping the Secrets of the Universe, the Origins of Life, and the Future of the Human Race," Touchstone: New York NY, 1998, Reprinted, 1999, pp.129-130) 25/09/2008 "The origin of life on the surface of the Earth is a unique historical event whose character cannot be established by experiments in contemporary laboratories: that statement (which equally applies to the evolution of a particular species such as Homo sapiens or, say, to the fact that the geology of central Asia has been shaped, in the past 35 million years, by the collision of the Indian subcontinent with preexisting Asia) has often been used to argue that the origin of life is not and cannot be a proper part of science. For how can we hope to reconstruct the singular circumstances leading to what may have been a unique event? History in general is fraught with the same difficulties: however sophisticated may be historians' understanding of human nature and of public affairs, what theory of history could have predicted that the American War of Independence would have begun as it did? Many scientists have taken this position on the origin of life. Jacques Monod, the distinguished French molecular biologist, said as much in 1970 in his elegant book Chance and Necessity. There is no way, he argued, that an event as improbable as the emergence of life on Earth could be analyzed by science, which is able to deal only "with events that form a class:"" (Maddox, J., "What Remains To Be Discovered: Mapping the Secrets of the Universe, the Origins of Life, and the Future of the Human Race," Touchstone: New York NY, 1998, Reprinted, 1999, p.131) 25/09/2008 "A decade later, Francis H. C. Crick, co-originator of the structure of DNA, put the argument more specifically: the chances that the long polymer molecules that vitally sustain all living things, both proteins and DNA, could have been assembled by random processes from the chemical units of which they are made are so small as to be negligible, prompting the question whether the surface of the Earth was fertilized from elsewhere, perhaps from interstellar space. `Panspermia' is the name for that." (Maddox, J., "What Remains To Be Discovered: Mapping the Secrets of the Universe, the Origins of Life, and the Future of the Human Race," Touchstone: New York NY, 1998, Reprinted, 1999, p.131) 25/09/2008 "The chance of assembling from its component parts one of the large molecules that now plays a vital part in life processes must indeed be exceedingly small. Protein molecules that appear in living things, both as structural elements (muscle fibers, for example) and as enzymes that stimulate vital chemical transformations, are made from just 20 of the many small-molecule chemicals called amino acids linked together in a chemically specific way. Enzyme molecules (which may consist of 100 or many more amino acid units linked together) act as catalysts by accelerating chemical transformations. The effectiveness of an enzyme is usually exquisitely sensitive to the precise arrangement of the amino acid units along the length of the molecule. Mere arithmetic shows that the chance that such a molecule will be assembled from its elementary components by random processes is so small as to be virtually zero. The number of differently arranged protein molecules with 100 units is easily stated (but the arithmetic is not so simple 8): multiply 20 by itself 100 times. The result is unimaginably great-very much greater than the number of particles of matter in the whole of the observable universe. The combined mass of a single copy of each of the possible protein molecules 46 amino acids long would be almost twice the mass of the observable universe." (Maddox, J., "What Remains To Be Discovered: Mapping the Secrets of the Universe, the Origins of Life, and the Future of the Human Race," Touchstone: New York NY, 1998, Reprinted, 1999, pp.131-132) 25/09/2008 "Monod outlines a particularly fiendish version of his argument in relation to the genetic material DNA, whose molecules are constructed from four particular chemical units called nucleotides strung together. 10 The simplest organisms, bacteria for example, may have several million nucleotides arranged in a precise sequence. (The number of different structures of that size is found by multiplying 4 by itself several millions of times, giving an even larger number than that of all possible 100-unit protein molecules.) But when bacterial cells divide, the DNA molecules are also replicated, which requires the intervention of the enzymes whose structures are themselves determined by the arrangement of particular stretches of the original DNA, now identified with genes. How much less likely must it be that DNA molecules embodying that capacity to replicate will emerge from random assembly of the nucleotide units?" (Maddox, J., "What Remains To Be Discovered: Mapping the Secrets of the Universe, the Origins of Life, and the Future of the Human Race," Touchstone: New York NY, 1998, Reprinted, 1999, p.132) 25/09/2008 "What better way of building reproductive isolation into the genome than by a change ensuring, say, that hybrids always produce inviable sperm or even that they cannot be produced at all? There are two difficulties with that question. One is that not much is yet known of the functions of the genes in the X and Y chromosomes, or of the influences upon them of genes located elsewhere, let alone of how the sex chromosomes influence the others. The second difficulty is that the question is improper, implying as it does that natural selection can shape the structure of the genome in the long-term interests of the species. In reality, natural selection looks forward only generation by generation. The question we must ask is `What is the selective advantage of reproductive isolation that accompanies speciation?' or, even, `Why do species exist?' The answer is that reproductive isolation preserves intact the genetic changes that have given an evolving group of animals (or plants) enhanced fitness, ensuring that they are not diluted by the genes from the other creatures in the lineage from which they have separated." (Maddox, J., "What Remains To Be Discovered: Mapping the Secrets of the Universe, the Origins of Life, and the Future of the Human Race," Touchstone: New York NY, 1998, Reprinted, 1999, pp.251-252) 25/09/2008 "The overriding question is when (and then how) sexual reproduction itself evolved. Despite decades of speculation, we do not know. The difficulty is that sexual reproduction creates complexity of the genome and the need for a separate mechanism for producing gametes. The metabolic cost of maintaining this system is huge, as is that of providing the organs specialized for sexual reproduction (the uterus of mammalian females, for example). What are the offsetting benefits? The advantages of sexual reproduction are not obvious. One view is that sexual reproduction makes it easier for an evolving organism to get rid of deleterious genetic changes. That should certainly be the case if there is more than one genetic change and if their combined effect on the fitness of the evolving organisms is greater than the sum of the individual changes acting separately. But there is no direct evidence to show that this rule is generally applicable. Indeed, a recent experiment with the bacterium E. coli suggests otherwise. [Elena, S.F. & Lenski, R.E., Nature, Vol. 390, 1997, pp.395-398] The telling feature of that experiment is that it was reported only in 1997, and concerned the most familiar organism in laboratory genetics. That shows how little has yet been done to found even rudimentary evolutionary speculation on laboratory investigations." (Maddox, J., "What Remains To Be Discovered: Mapping the Secrets of the Universe, the Origins of Life, and the Future of the Human Race," Touchstone: New York NY, 1998, Reprinted, 1999, p.252) "I was particularly impressed with Gerry Schroeder's point-by-point refutation of what I call the `monkey theorem.' This idea, which has been presented in a number of forms and variations, defends the possibility of life arising by chance using the analogy of a multitude of monkeys banging away on computer keyboards and eventually ending up writing a Shakespearean sonnet. Schroeder first referred to an experiment conducted by the British National Council of Arts. A computer was placed in a cage with six monkeys. After one month of hammering away at it (as well as using it as a bathroom!), the monkeys produced fifty typed pages-but not a single word. Schroeder noted that this was the case even though the shortest word in the English language is one letter (a or I). A is a word only if there is a space on either side of it. If we take it that the keyboard has thirty characters (the twenty-six letters and other symbols), then the likelihood of getting a one-letter word is 30 times 30 times 30, which is 27,000. The likelihood of a getting a one-letter word is one chance out of 27,000." (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, pp.75-76) 26/09/2008 "Schroeder then applied the probabilities to the sonnet analogy. `What's the chance of getting a Shakespearean sonnet?' he asked. He continued: `All the sonnets are the same length. They're by definition fourteen lines long. I picked the one I knew the opening line for, `Shall I compare thee to a summer's day?' I counted the number of letters; there are 488 letters in that sonnet. What's the likelihood of hammering away and getting 488 letters in the exact sequence as in `Shall I Compare Thee to a Summer's Day?'? What you end up with is 26 multiplied by itself 488 timesor 26 to the 488th power. Or, in other words, in base 10, 10 to the 690th. [Now] the number of particles in the universe not grains of sand, I'm talking about protons, electrons, and neutrons-is 10 to the 80th. Ten to the 80th is 1 with 80 zeros after it. Ten to the 690th is 1 with 690 zeros after it. There are not enough particles in the universe to write down the trials; you'd be off by a factor of 10 to the 600th. If you took the entire universe and converted it to computer chips-forget the monkeys-each one weighing a millionth of a gram and had each computer chip able to spin out 488 trials at, say, a million times a second; if you turn the entire universe into these microcomputer chips and these chips were spinning a million times a second [producing] random letters, the number of trials you would get since the beginning of time would be 10 to the 90th trials. It would be off again by a factor of 10 to the 600th. You will never get a sonnet by chance. The universe would have to be 10 to the 600th times larger. Yet the world just thinks the monkeys can do it every time. [Gerald Schroeder, `Has Science Discovered God?' After hearing Schroeder's presentation, I told him that he had very satisfactorily and decisively established that the `monkey theorem' was a load of rubbish, and that it was particularly good to do it with just a sonnet; the theorem is sometimes proposed using the works of Shakespeare or a single play, such as Hamlet. If the theorem won't work for a single sonnet, then of course it's simply absurd to suggest that the more elaborate feat of the origin of life could have been achieved by chance." (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, pp.76-78) 26/09/2008 "In my book Darwinian Evolution, I pointed out that natural selection does not positively produce anything. It only eliminates, or tends to eliminate, whatever is not competitive. A variation does not need to bestow any actual competitive advantage in order to avoid elimination; it is sufficient that it does not burden its owner with any competitive disadvantage. [Flew, A.G.N., "Darwinian Evolution," Paladin: London, 1984, p.25] To choose a rather silly illustration, suppose I have useless wings tucked away under my suit coat, wings that are too weak to lift my frame off the ground. Useless as they are, these wings do not enable me to escape predators or gather food. But as long as they don't make me more vulnerable to predators, I will probably survive to reproduce and pass on my wings to my descendants. Darwin's mistake in drawing too positive an inference with his suggestion that natural selection produces something was perhaps due to his employment of the expressions `natural selection' or `survival of the fittest' rather than his own ultimately preferred alternative, `natural preservation.'" (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, pp.78-79) 26/09/2008 "I went on to remark that Richard Dawkins's The Selfish Gene was a major exercise in popular mystification. As an atheist philosopher, I considered this work of popularization as destructive in its own ways as either The Naked Ape or The Human Zoo by Desmond Morris. In his works, Morris offers as the results of zoological illumination what amounts to a systematic denial of all that is most peculiar to our species contemplated as a biological phenomenon. He ignores or explains away the obvious differences between human beings and other species. Dawkins, on the other hand, labored to discount or depreciate the upshot of fifty or more years' work in genetics-the discovery that the observable traits of organisms are for the most part conditioned by the interactions of many genes, while most genes have manifold effects on many such traits. For Dawkins, the main means for producing human behavior is to attribute to genes characteristics that can significantly be attributed only to persons. Then, after insisting that we are all the choiceless creatures of our genes, he infers that we cannot help but share the unlovely personal characteristics of those all-controlling monads." (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, pp.79-80) 26/09/2008 "Genes, of course, can be neither selfish nor unselfish any more than they or any other nonconscious entities can engage in competition or make selections. (Natural selection is, notoriously, not selection; and it is a somewhat less familiar logical fact that, below the human level, the struggle for existence is not `competitive' in the true sense of the word.) But this did not stop Dawkins from proclaiming that his book `is not science fiction; it is science.... We are survival machines-robot vehicles blindly programmed to preserve the selfish molecules known as genes.' [Dawkins, R., "The Selfish Gene," Oxford University Press: New York, 1976, p.x] Although he later issued occasional disavowals, Dawkins gave no warning in his book against taking him literally. He added, sensationally, that `the argument of this book is that we, and all other animals, are machines created by our genes.' If any of this were true, it would be no use to go on, as Dawkins does, to preach: `Let us try to teach generosity and altruism, because we are born selfish.' No eloquence can move programmed robots. But in fact none of it is true-or even faintly sensible. Genes, as we have seen, do not and cannot necessitate our conduct. Nor are they capable of the calculation and understanding required to plot a course of either ruthless selfishness or sacrificial compassion." (Flew, A.G.N., "There Is a God: How the World's Most Notorious Atheist Changed His Mind," HarperCollins: New York NY, 2007, p.80) 26/09/2008 "At some time during the Devonian period, possibly during the later phases of Devonian history, some of the crossopterygian fishes came out on the land. Very likely these were osteolepiforms, of the type represented by the genera Eusthenopteron and Panderichthys. It was a bold step, a venturing of early vertebrates into a completely new environment to which they were only partially adapted. Once having made the step, however, the advanced air-breathing fish soon evolved into a primitive amphibian. With this change vast new possibilities were opened for the evolutionary development of the vertebrates. What were the factors that led the crossopterygians out of the water and on to the land? Professor A. S. Romer has suggested that it was paradoxically a desire for more water that brought about the first excursions of crossopterygians away from their river and lake envr river and lake environments. According to this idea some of the late Devonian crossopterygians may have been forced by excessive drought to seek new freshwater pools or streams in which they could continue to live, and thus they struggled out on the dry ground in an effort to reach the water that was so necessary for their survival. This is certainly a logical explanation of the first stages in the change from an aquatic to a terrestrial mode of life, but there may have been other factors that also contributed to the initial break from life in the water. Perhaps there was a gradual series of changes through time that resulted in increasingly wider excursions away from the water. Perhaps the search for food upon the land may have been as much of a motivating force in this change as the search for fresh bodies of water. We can only speculate about this." (Colbert, E.H. & Morales, M., "Evolution of the Vertebrates: A History of the Backboned Animals Through Time," , John Wiley & Sons: New York NY, Fourth edition, 1990, Second printing, 1992, pp.67-68) 26/09/2008 "At least 377 million years ago a lineage of lobefins arose that was more tetrapodlike than Eusthenopteron. One of these was an animal called Panderichthys. Found in Latvia, this two-foot-long fish had a skull as flat as a coffee table and a smooth back that lacked the dorsal fins of other lobe-fins. Its shoulders-and the fins that attached to them-were so sturdy that it might have been able to move on them like crutches out of the water for short distances. Like coelacanths and lungfish, it probably could move with the left-right, left-right movements that would become our walk. Still, it would be impossible to mistake Panderichthys for a tetrapod. Its toeless limbs were buried inside a ring of fin rays, its braincase was still hinged, and instead of a stapes Panderichthys had a hyomandibular bone that was linked to its jaws and gills." (Zimmer, C., "At the Waters Edge: Fish with Fingers, Whales with Legs, and How Life Came Ashore but Then Went Back to Sea," Touchstone: New York NY, 1998, Reprinted, 1999, p.104) 26/09/2008 "In 10 or 15 million years, however, relatives of Panderichthys reworked their bodies into tetrapod form. Elginerpeton, the beast that Per Ahlberg found hiding in museum drawers, is not only the oldest tetrapod known but the most primitive as well. Its snout turned into a massive snapping trap, ligaments joined its pelvis to its spine. With only fragments of its limbs, it's impossible to know if there were toes yet, but Elginerpeton shows many signs of being an intermediate between lobe-fins like Panderichthys and later tetrapods. Its rear legs were twisted so much that its knees (if it had them) would have pointed to the ground, making the legs useless for walking but good for rowing. Judging from the fact that Elginerpeton was five feet long and hunted on river bottoms, one can assume that the first tetrapods must have been moderately successful at living like a lobe-fin. Within a few million years Elginerpeton was gone, but new kinds of tetrapods were evolving all around the world. One branch included an animal called Ventastega, known from parts of its skull and a few other fragments found in Latvia, as well as the even more obscure Metaxygnathus from Australia. At the time these two landmasses were thousands of miles apart along the equator, indicating that tetrapods were moving quickly along the tropical coasts, invading estuaries and rivers as they went. Yet despite spreading around the planet, this lineage of tetrapods soon died out." (Zimmer, C., "At the Waters Edge: Fish with Fingers, Whales with Legs, and How Life Came Ashore but Then Went Back to Sea," Touchstone: New York NY, 1998, Reprinted, 1999, pp.104-105) 26/09/2008 "Closer to our own heritage were two tetrapods that appeared in Greenland, which was also near the equator: Acanthostega and Ichthyostega. Acanthostega had fingers and toes on its limbs, and its braincase had sealed shut. It had a rigid, long snout that no longer needed a hyomandibular bone for support, and this bone had been reduced to a stapes locked into its skull. It's possible that Elginerpeton had already reached these landmarks, but there's too little of its skeleton to tell for sure. In either case, the fossils speak to a flurry of change, one that-as the work of Neil Shubin and others shows-was based on the vagaries of genes and development. The lobe-fins like Eusthenopteron and Panderichthys used Hox genes to pattern their spine and fins. In the first tetrapods, mutations flipped the Hox pattern in the limb and expressed it along the far edge of the fin, producing a new set of segmented rods." (Zimmer, C., "At the Waters Edge: Fish with Fingers, Whales with Legs, and How Life Came Ashore but Then Went Back to Sea," Touchstone: New York NY, 1998, Reprinted, 1999, p.105) 26/09/2008 "Ichthyostega, once seen as a missing link between fish and tetrapods, now seems to be another weird experiment in limbs. In some respects it was more like later tetrapods-its fishy tail was already half gone, the bones of its forearms were of equal length so that it could walk on them, it had large ribs, and its hips had deep sockets to hold the balls of the femurs. Yet according to one of Jarvik's Swedish colleagues, Hans Bjerring, as well as Coates, its hind legs were thrown back behind its body like a seal's. Although it had sturdy ribs like later tetrapods, it seems to have taken them to extremes, rendering them wide slats. It's possible that it used them as a manatee uses it own oversized ribs, to counteract the buoyancy of its lungs and stay underwater." (Zimmer, C., "At the Waters Edge: Fish with Fingers, Whales with Legs, and How Life Came Ashore but Then Went Back to Sea," Touchstone: New York NY, 1998, Reprinted, 1999, p.105) 26/09/2008 "The feature that many people would pick to distinguish fishes from tetrapods is that which gives the name to the group-the structure of the limbs and the possession of digits. ... it is appropriate here to consider the similarities and differences in structure between the paired appendages of fishes and tetrapods. The fore and hind sets of paired fins of a lobe-finned fish such as Eusthenopteron consist of similar bones. ... In common is first the single element, called the first axial radial, which attaches to the girdle, identifying the animal as a sarcopterygian. From the other end of this element, further elements arise and articulate with it, forming a chain called the metapterygial axis. In Eusthenopteron and tetrapods, there are two of these. In Eusthenopteron, the more posteriorly situated of these in turn gives rise to two more. The precise pattern varies among lobe-fins. Fins of the various lobe-finned fish groups differ more in structure further along the fin than they do nearer the base. Some groups, such as lungfishes, have elongated, paired fins supported by a long series of segments, each with a branching radial springing from it. In most lobe-fins, the branches occur mainly on the anterior (leading) edge of the fin and are called preaxial radials. In lungfishes, both pre- and postaxial radials are found. In osteolepiforms, the fin skeleton remains short, whereas in Panderichthys, the elements are broad and flattened ..." (Clack, J.A., "Gaining Ground: The Origin and Evolution of Tetrapods," Indiana University Press: Bloomington IN, 2002, pp.42-43) 26/09/2008 "The similarities in construction of tetrapod limbs and lobed fins lies in the first three skeletal elements, and the pattern of a single element attaching to the body and giving rise to two more from its far end. These bones can be called by consistent names: in the fore fin or limb, the humerus, radius, and ulna; and in the hind fin or limb, the femur, tibia, and fibula. The humerus of an early tetrapod bears flanges and foramina recognizably the same as those of the same bone in Eusthenopteron. Thereafter, the resemblance breaks down. The divergence in skeletal pattern further away from the body seen among lobe-finned fishes is exaggerated in the contrast between fins and limbs. In most tetrapod limbs, the two elements, ulna and radius or tibia and fibula, articulate distally with each other and with a series of blocklike bones connected by complex joint surfaces, allowing much freedom of movement. These produce the characteristic elbow and knee or wrist and ankle joints ... They allow the ends of the limbs to be brought into contact with the ground at appropriate angles for bearing weight and transmitting thrust. At the ends of each limb, digits arise by sequential budding of a number of radial elements. ... in effect, digits equate in position to the postaxial radials of the fish fin, which have become jointed." (Clack, J.A., "Gaining Ground: The Origin and Evolution of Tetrapods," Indiana University Press: Bloomington IN, 2002, pp.43-44) 27/09/2008 "An animal or plant species will have two names-a binomial. The first is the generic name, and the second is the specific name. For example, one of the animals that features in this book is Panderichthys rhombolepis. Panderichthys is its generic name and rbombolepis is its specific name. Other species of the genus Panderichthys exist, such as stolbovi and bystrowi. Usually the first scientist to describe a new species will name it, unless it turns out to be a member of a genus that is already known, in which case the discoverer will only have to think up a new specific name. Each combination is unique to a species, and the name is designed to reflect something about the animal, such as who found it, where it came from, or some interesting feature of its anatomy. Scientists who name animals often have great fun doing so, although the international rules preclude facetious or vulgar names." (Clack, J.A., "Gaining Ground: The Origin and Evolution of Tetrapods," Indiana University Press: Bloomington IN, 2002, p.11) 27/09/2008 "Panderichthys was, until quite recently, placed within a family called the panderichthyids along with a second genus, Elpistostege. Panderichthys is more closely related to tetrapods than any osteolepidid or even Eusthenopteron. However, although they share several similarities, the most recent work has pointed out differences between Panderichthys and Elpistostege in which Elpistostege is even more tetrapodlike than is Panderichthys (Ahlberg et al. 2000). Indeed, the first specimen of Elpistostege, which consisted just of a partial skull roof, was thought to be a tetrapod when it was first found (Westoll 1938). Confirmation of its true status only came when a second, more complete specimen was discovered in the 1980s (Schultze and Arsenault 1985). Now, both genera are placed as successive genera on the stem lineage close to tetrapods. The family name has become meaningless because they are not uniquely related to each other (as distinct from being branches off the tetrapod stem lineage). Elpistostege comes from the same locality and time period as Eusthenopteron, Escuminac Bay, although, because it is only known from two specimens, its anatomy is not nearly so well understood. Panderichthys comes from a number of localities in Eastern Europe, with the most remarkable specimens from the Frasnian of Lode in Latvia. They include some more or less complete animals. Because these are still covered in their scales, the internal skeleton cannot be seen, so much of their bone structure remains unknown." (Clack, J.A., "Gaining Ground: The Origin and Evolution of Tetrapods," Indiana University Press: Bloomington IN, 2002, pp.63-64) 27/09/2008 "Panderichthys was quite a large fish, with a skull about 300 mm long, and a total body length of over a meter ... . Its body and skull were flattened and the snout rather pointed. The eyes were placed quite close together on the top of its head and were set beneath ridges, giving the impression of eyebrows and creating a subjectively tetrapodlike appearance. Other characters of the skull were also very tetrapodlike (Vorobyeva and Schultze 1991). Elpistostege is still relatively poorly known, and for understanding the story of the origin of tetrapods, Panderichthys will provide a satisfactory guide. By comparing its skull with that of a very early tetrapod such as Acanthostega, those tetrapodlike features that were present already in Panderichthys can be contrasted with those that had yet to evolve. This gives some ideas about the order and timing of the appearance of some tetrapod characters ..." (Clack, J.A., "Gaining Ground: The Origin and Evolution of Tetrapods," Indiana University Press: Bloomington IN, 2002, p.64) 27/09/2008 "Livoniana multidentata is the most recently recognized Frasnian tetrapodomorph ... It is known from only two fragments, both of the anterior end of the lower jaw. It comes from the area around the border between Latvia and Estonia, an area whose ancient name was Livonia. The most striking thing about the jaws is their multiple rows of small, rounded teeth, which give the appearance of a portion of corn on the cob. There are up to five rows of teeth, a feature not known in any other tetrapodomorph. The jaws do, however, show two or three features that are otherwise only found in animals close to true tetrapods like Acanthostega. When all the available information is pooled and put into a computer analysis, Livoniana appears sharing a node with Elpistostege, just below Obruchevichthys on the tetrapod stem lineage. It was probably not a full tetrapod in the sense of having limbs with digits, but it was probably close to the cusp of tetrapod evolution, and so is one of the few concrete pieces of evidence for the range of animals that actually existed between truly `fishlike' stem tetrapods and more fully `tetrapodlike' ones. Its peculiar dentition suggests that there was a radiation of specialized animals at the boundary, of which one went on to produce tetrapods proper." (Clack, J.A., "Gaining Ground: The Origin and Evolution of Tetrapods," Indiana University Press: Bloomington IN, 2002, pp.64-65) 27/09/2008 "This review of the lobe-finned fish groups is not complete without the tetrapods, because this is where, evolutionarily speaking, they (and humans) belong. Modern tetrapods include on the one hand the amphibians-frogs, newts, caecilians, and their kin-and on the other the amniotes-mammals plus the `reptile' groups, including turtles, lizards and snakes, and crocodiles and their closest living relatives, the birds. It includes creatures that, although they do not have legs (limbs with digits) themselves, are descended from some that did. So bats and whales are tetrapods, as are birds and snakes. It also includes all the fossil forms such as dinosaurs, flying or swimming reptiles, and many other more bizarre and less well-known kinds, so long as they are descended from ancestors with legs ... Most current views maintain that tetrapods are a natural group, tied together by numerous unique characters that show that the group had a single common ancestor. Among the unique features that tetrapods share is the possession of limbs with digits ..." (Clack, J.A., "Gaining Ground: The Origin and Evolution of Tetrapods," Indiana University Press: Bloomington IN, 2002, p.66) 27/09/2008 "Although there is a suite of characters unique to most known tetrapods, as this book emphasizes, not all these characters evolved at once, and the sequence of their evolution is unknown in many cases. This is to be expected if tetrapods evolved by a gradual process, which is what most scientists believe happened. Furthermore, the same must be true of limbs and digits-they evolved gradually by stages. Thus, difficult questions arise: when can an appendage really be called a limb, and so at what point does a tetrapod really become a tetrapod? In fact, if evolution is gradual, then there is no precise point in the continuum at which a line can be drawn to distinguish indisputably a limb from a fin, or indeed a tetrapod from a fish. What exactly would one choose? Loss of the fin rays? The evolution of the wrist or ankle bones that interarticulate? The evolution of multiple, jointed, postaxial radials? If so, how many would be the critical number? To add to the difficulties, because there are so many unique characters known for tetrapods, limbs and digits may not be the key feature that most usefully separates them from fishes. Some people might, for example, make the case that the evolution of a neck with loss of the operculogular series makes a more biologically significant character to separate the groups. Or others may choose the changes to the braincase that resulted in the stapes penetrating the wall of the otic capsule." (Clack, J.A., "Gaining Ground: The Origin and Evolution of Tetrapods," Indiana University Press: Bloomington IN, 2002, pp.66-67) 27/09/2008 "In brief, both forms look at the relationships of modern representatives and define tetrapods in terms of these forms. Amphibians and amniotes must have had a common ancestor at some stage among the early tetrapods that was related equally to both but strictly belonged to neither. ... Although this common ancestor will probably always remain hypothetical, it would lie at the node where the lineages of amphibians and amniotes join. Any fossil form that can be shown to belong to either one of these lineages is said to lie above the node, within the `crown group' of tetrapods. Any creature that does not belong to either lies below the node, in the `stem group' of tetrapods. At this point, the crown group definition would admit only creatures above the node into the formal taxon Tetrapoda, with those falling outside it being relegated to stem-tetrapods, even though they have four legs. The stem-based method, also known as the `total group' method, would admit not only the crown group, but a whole suite of other creatures below the crown on the cladogram, but above the node that admits its nearest living relative. For example, with respect to modern tetrapods, this method would look at the nearest living relative of crown group tetrapods, in this case most likely (but not certainly) the lungfishes, and pinpoint the node at which these groups separated as being the next most significant. All animals belonging to the tetrapod stem lineage and falling above the split between lungfishes and crown group tetrapods-such as osteolepiforms and rhizodonts-would be admitted into the formal taxon Tetrapoda, even though they do not have four `legs' ... The conundrum has been partially solved by the decision to call this whole clade the Tetrapodomorpha " (Clack, J.A., "Gaining Ground: The Origin and Evolution of Tetrapods," Indiana University Press: Bloomington IN, 2002, p.68) 27/09/2008 "Some things are clear, however. Both Elginerpeton and Obruchevichthys appear more closely related to tetrapods than was Panderichthys. They are also very closely related to each other, sharing some details that cause them to be placed in the same family (Ahlberg 1995). This family was widely distributed in the Frasnian. They were also different from the slightly later Devonian tetrapods, which will be described in the next chapter. They may represent an early and specialized offshoot from the tetrapod branch. Panderichthys and Elpistostege flourished in the early Frasnian and are some of the nearest relatives of tetrapods. But tetrapods appear only about 5 to 10 million years later in the late Frasnian, by which time they were widely distributed and had evolved into several groups, including the lineage leading to the tetrapods of the Famennian. This suggests that the transition from fish to tetrapod occurred rapidly within this restricted time span. Neither fishlike tetrapods nor tetrapodlike fish body fossils occur in the record before this (Clack 1997a). Indeed, the osteolepiforms as a whole are not found before the Middle Devonian. This lends weight to the suggestion that the tracks from the supposed Late Silurian or Early Devonian are not those of a tetrapod, and those from the Middle Devonian are unlikely to be so. Given our current understanding of phylogeny, tracks made by a terrestrial tetrapod are unlikely to be found before the late Frasnian, and the body fossil evidence conflicts with the interpretation of any pre-Famennian track as terrestrial." (Clack, J.A., "Gaining Ground: The Origin and Evolution of Tetrapods," Indiana University Press: Bloomington IN, 2002, p.96) 27/09/2008 "Most fishes today feed by means of a suction mechanism of some kind. There are exceptions, such as the garpike, which has evolved long, narrow jaws for slicing quickly through water, but the majority of fishes have elaborate mechanisms to draw in as much food as possible with the water they suck in as they open their mouths. This often involves widening the gape as far as possible, brought about by loosening the connections between their skull bones to form a flexible framework for the jaw muscles. It is thought that even early fishes used this method, although their skull adaptations toward it were not as extreme as in later ray-finned fishes. The intracranial hinge ... found in early lobe-fins is thought to be an example of an adaptation to make suction feeding more efficient, although it tends to disappear in longer-snouted forms ... Both Panderichthys and Elpistostege had lost the hinge mechanism and appear to have been rather unspecialized gulpers; they presumably still fed in water. It seems that the lineage leading to tetrapods had found other methods for feeding, which might have been related to a possible adaptation to bottom-dwelling life or life in shallower waters ... Changes to feeding mechanisms will naturally be reflected in changes to jaw structure and operation, so that the lower jaw, often the only clue there is to the existence of Devonian tetrapods, offers evidence of this shift. Accordingly there are many similarities in the jaw structure and dentition of the earliest tetrapods to those of Panderichthys and its close osteolepiform relatives. Indeed, many specimens of lower jaws now known to have belonged to tetrapods were once thought to be those of osteolepiform fishes. The similarities are sufficient to suppose that the earliest tetrapods were, like these fishes, aquatically feeding animals. All of them would have been carnivorous, feeding on other fishes and invertebrates, or-scavenging anything edible that became available. The early tetrapods were probably gulpers like Panderichthys, and with their flattened, broad heads, they may have behaved like the giant Japanese salamanders of today." (Clack, J.A., "Gaining Ground: The Origin and Evolution of Tetrapods," Indiana University Press: Bloomington IN, 2002, pp.284-285) 27/09/2008 "As we look at the historical stages in the evolution of an adaptation, it is possible that at every stage the organ served the same function (the eye is probably an example-all of its stages probably had visual functions), or the earlier stages could have had different functions from the later ones. The classical Darwinian term for the second possibility is preadaptation. In such a case, the earlier stage is described as a preadaptation for the later stage. A possible example of preadaptation is as follows. The most widely accepted theory of how vertebrates invaded the land suggests that lobefinned fish originally walked on the bottom of lakes or stream with their fins, and by degrees came to walk on the muddy surrounds at the water's edge, and finally on dry land as the necessary adaptations for air-breathing and water-retention evolved. Today, two main groups of bony fish are known ..: the ray-finned Actinopterygians (containing almost all of the common fish that we think of as "fish") and the lobe-finned Sarcopterygians (a few oddities, including lungfish and the coelocanth). In a ray-finned fish, the skeleton of its fins comprise a ray of similar bones that are mainly moved by muscles, with one end of the muscle in the fin and the other end inside the body. Lobe-finned fish possess a single main rod of skeletal support in the fin, and their movements are partly controlled within the fin. The difference is interesting because all tetrapods evolved from the lobe- finned fish, and they did so almost certainly because a lobe-fin could evolve into a tetrapod limb, whereas a ray-fin could not. Thus, lobe-finned fish are preadapted for walking on land, while ray-finned fish are not." (Ridley, Mark, "Evolution," , Blackwell: Cambridge MA, Second Edition, 1996, Third Printing, 1999, p.346. Emphasis original) 27/09/2008 "Preadaptation does not imply any futuristic or anticipatory faculty in evolution. Lobe-finned fish did not evolve their skeleton so that they could later give rise to the tetrapods. Sometimes, by chance, an organ that works well in one function turns out to work well in another function after relatively little adjustment. Fins in both fish groups first evolved for swimming. In some lobe-finned species, they probably came to be used for skuttling around near the seashore or on the bottom of rivers or lakes. From this point, only a small change was required for the fish to walk on land. Whatever the details involved, it is a reasonable inference that the lobe-finned skeleton was, unlike a ray-fin, preadapted to evolve into a tetrapod limb. The term preadaptation is applied when a large change in function is accomplished with little change of structure." (Ridley, Mark, "Evolution," , Blackwell: Cambridge MA, Second Edition, 1996, Third Printing, 1999, pp.346-347) 27/09/2008 "A stem form is known for the amphibians, Ichthyostega, appearing about 20 million years into the jawed fish (gnathian) explosion. The amphibian explosion is 30 million years later - with the sudden appearance of 10 families. Ichthyostega is particularly difficult to understand from the model that new morphology is a product of environmentally based `direct selection'. Ichthyostega shows obvious affinities with its contemporaries, the osteolepiform lobefin fish of the late Devonian. They have homologous skull bones, peculiar labyrinthodont teeth, a bone pattern in the fins which suggests the tetrapod limb pattern, etc. Both forms were fresh water fish predators. The amphibian still had lateral lines, a tail fin like the fish, etc. In many ways it might be considered a fish with legs (Carroll, 1988). But yet, Ichthyostega had completed the essential tetrapod adaptive complex. The skull had become fused into a single solid structure movable on the spine. The cleithrum series of bones was detached from the skull and had instead become a separate shoulder girdle articulating with the spine, a skeletal pattern which can still be recognized 365 million years later in the bones of the duck-billed platypus. The pelvis is made of three bones instead of one and is also articulated with the spine. The spine and ribs are reinforced to hold up the body when out of the water. The bones of the limbs are reformed, reoriented, changed in pattern and individuated - a set of individuations which will hold for all future tetrapods. Not only is the pattern changed, but the developmental information density is sharply increased (Carroll, 1988, Stahl, 1974)." (Wilcox, D.L.*, "Created in Eternity, Unfolded in Time," Eastern College: St. Davids PA, 1990, Unpublished manuscript, Chapter 6, pp.23-24) 27/09/2008 "All in all, Ichthyostega is a mystery of the first water. The theory that the direct application of environmental selection can "collect" the necessary morphological information, integrate it into individuated error checked blueprints, and thus create novel structures in organisms seems impossible to apply to Ichthyostega. How can the world of an aquatic predator quickly select, collect and individuate the information for a highly coherent adaptive blueprint of terrestrial limb structure? The theory that the blueprint already existed in some form in the genomes of the osteolepiform fish sounds more reasonable, but sorting it out under water is still difficult. However, if it were true, and if a life style of living on fish stranded on the edge of the swamp could provide a mild selective pressure, the previous encoding of a individuated blueprint could at least explain its tight coherence when it first appears." (Wilcox, D.L., "Created in Eternity, Unfolded in Time," Eastern College: St. Davids PA, 1990, Unpublished manuscript, Chapter 6, pp.23-24) 27/09/2008 "Various sarcopterygian fish, such as some rhipidistians (panderichthyids, osteolepiforms) or dipnoan lungfish, were apparently preadapted for moving out of water onto land. They had functioning lungs and two pairs of bone-strengthened muscular fins on which they could move their bodies and support themselves terrestrially without depending on the buoyancy of water. Although it would seem that many of these fish needed relatively few further changes to attain a primitive terrestrial existence ..., the question of why some of them abandoned their shallow-water habitats and went onto land is difficult to answer with certainty. A classic hypothesis that Romer (1968) popularized suggests that when the shallow, hypoxic habitats of ancient crossopterygians dried up or stagnated further, some varieties that were preadapted to breathing atmospheric oxygen would have searched for new pools of water and probably survived on land for short periods of time. According to Romer, seasonal droughts were common in the Devonian, and selection during such periods would lead to increased intervals of terrestrial exploration until some groups could eventually maintain themselves out of water for significant parts of their life cycle." (Strickberger, M.W., "Evolution," Jones & Bartlett: Sudbury MA, 1990, Third edition, 2000, p.409) 27/09/2008 "Another hypothesis, more commonly accepted now (McFarland et al.), suggests that these aquatic forms escaped to land because of population pressures resulting from predation (probably other fish) as well as from competition for space, food, and breeding sites in these warm, swampy habitats. The transition to land in a moist tropical climate might have produced relatively little stress in such terrestrially preadapted sarcopterygians, and some invertebrate food sources on land may not have been much different from in the swamps themselves. Certainly, throughout the Devonian, land plants were establishing themselves in increasing number and variety ... and arthropods, among other invertebrates, had already made a successful terrestrial transition (Little)." (Strickberger, M.W., "Evolution," Jones & Bartlett: Sudbury MA, 1990, Third edition, 2000, p.409) 27/09/2008 "Whether because of drought or expansion or both, once existence on land was established as an important stage in survival, further selection would operate on many levels to improve air breathing, eliminate carbon dioxide, increase resistance to desiccation, increase head mobility, and enhance further transformations. You can see that such changes were possible in the observation that some present-day fish such as mudskippers, climbing perch, and walking catfish have developed various terrestrial adaptations, even to the point of climbing trees and capturing food." (Strickberger, M.W., "Evolution," Jones & Bartlett: Sudbury MA, 1990, Third edition, 2000, pp.409-410) 27/09/2008 "Although the details are not yet fully known ... many paleontologists agree that land vertebrates, however they first evolved, were related to sarcopterygian lobe-finned fishes. The transition from fish to crawling four-legged tetrapod occurred by the end of the Devonian period, about 360 million years ago during a relatively short geological interval-no more than probably 15 or 20 million years-and encompassed perhaps three or more separate lineages (Carroll 1995)." (Strickberger, M.W., "Evolution," Jones & Bartlett: Sudbury MA, 1990, Third edition, 2000, p.410) 27/09/2008 "The earliest of such identified amphibians in the fossil record, called Acanthostega and Ichthyostega ... show their relationship to rhipidistian forms in a number of features: 1. Many dermal bones in the skulls of panderichthyids and Devonian tetrapods appear similar, occupying relatively similar positions ... Even the remnant of a preopercular bone is present in these primitive amphibia although they possessed no operculum (gill cover). 2. The fins of osteolepiforms and their supporting girdles have bones that we can easily consider homologous to those of early tetrapods ... 3. The tooth structure of both osteolepiforms and Devonian tetrapods shows similar complex labyrinthine foldings of the pulp cavity ... In fact, because of the prevalence of these unusual teeth, paleontologists have given the name Labyrinthodontia to these tetrapods and also to two other orders of fossil amphibians, the anthracosaurs and temnospondyls. (Researchers believe reptiles derive from early anthracosaurs.) 4. The sensory lateral line system of osteolepiforms that extended into the skull appears homologous to a similar pattern of sensory canals embedded in the tetrapod skull ... . 5. The early amphibians possessed a fin-rayed caudal tail that showed obvious fishlike ancestry. 6. The structure of early tetrapod vertebrae had changed relatively little from the vertebral structure of rhipidistian osteolepiforms ..." (Strickberger, M.W., "Evolution," Jones & Bartlett: Sudbury MA, 1990, Third edition, 2000, pp.410-411) 27/09/2008 "The limbs of Acanthostega and Ichthyostega have all the major features of later tetrapods. They bear no trace of dermal scales. Much more extensive areas of articulation have evolved between the pectoral and pelvic girdles and the proximal limb bones. The humerus, radius, and ulna, and femur, tibia, and fibula are massive, potentially supporting elements, and the areas of the carpus and tarsus comprise shorter bones that could have served as zones of hinging and/or rotation. The exact patterns of the carpus and tarsus have not yet been determined and are difficult to compare in detail with those of later Paleozoic tetrapods. The carpals are small and poorly ossified, whereas the proximal tarsals are very large. The metacarpals and metatarsals are not clearly distinguishable from the succeeding phalanges. Clearly, these limbs represent a period of transition, but one that has all the potential for evolving into the pattern of typical tetrapods. Most significantly, the elbow, wrist, knee, and ankle joints, while primitive, unquestionably presage those of later land vertebrates." (Carroll, R.L., "Patterns and Processes of Vertebrate Evolution," Cambridge University Press: Cambridge UK, 1997, pp.231-232) 28/09/2008 "In the 1930s and 1940s, thinking about evolution was only just beginning to take the shape that it has today, in a move called the New Synthesis. This brought together the new sciences of genetics and its spin off, population genetics, with the older discipline of paleontology. Evolution was seen in terms of adaptive radiation, with adaptation to certain environments more important than their phylogenetic descent in determining animal forms. This permitted the idea that, for example, many vertebrate groups could have been descended from more than one ancestor. Mammals, birds, and particularly teleost fishes were considered by some in this way. In this atmosphere, one school of thought became convinced that tetrapods were the product of at least two separate radiations. This school was founded in Stockholm, and its ideas were widely taken up in Eastern Europe. There were two versions of the idea, but both recognized a divergence between salamanders on the one hand, and all other tetrapods on the other. Holmgren (1933) suggested that dipnoans gave rise to salamanders, with all other tetrapods being descendants of osteolepiforms. ... By contrast, Jarvik (1942) suggested that salamanders were the descendants of porolepiforms and that frogs and all other tetrapods arose from osteolepiforms. ... Today, the overwhelming majority of workers accept that the long list of characters held in common by all living and, where known, by almost all fossil tetrapods is evidence that they form a monophyletic clade with a single common ancestor. It is now realized that not all these common characters arose at once, and some of the new preoccupations include questions of which arose first, when, and how." (Clack, J.A., "Gaining Ground: The Origin and Evolution of Tetrapods," Indiana University Press: Bloomington IN, 2002, pp.76-77) 28/09/2008 "Romer insists that amphibians remained aquatic animals much longer than Inger and the Goins suppose. Although he holds to his idea that the earliest amphibians traveled over land to escape their drying pools, he believes that well into the Carboniferous period their normal life was carried on in the water. Not until that time, when insects and land plants radiated with amazing rapidity, would there have been sufficient food material on land to sustain a population of vertebrates. The climate in Devonian years was a far harsher one, he still thinks, than Inger envisions. That seasonal droughts were the rule rather than uninterrupted humidity seems proved by the mud cracks and evaporites that appear in the rocks of the age. Transition to terrestrial feeding and a more or less terrestrial habitat would have been unlikely during a period when desert dryness occurred in alternation with earth-soaking rains. Though the first tetrapods were able, in his opinion, to survive an occasional forced march to new waters, the rigorous conditions which necessitated their migration would have precluded their dallying to catch any scorpions or other arthropods that might have crossed their path. During their early history the amphibians probably stayed in the water, protected from the extremes of climatic change, and developed their taste for invertebrates by eating the aquatic insect larvae which hung upside down from the surface of the pond. Romer adduces more direct evidence for his contention that amphibians emerged from the water relatively late by turning to the fossil record; the oldest members of the class retained the sinuous body of the swimmer and had, with few exceptions, small legs that would hardly have allowed easy locomotion on land. Not until the end of the Carboniferous period did a number of amphibians appear whose strong limbs and stout body were adapted for terrestrial rather than aquatic life." (Stahl, B.J., "Vertebrate history: Problems in Evolution," , Dover: New York NY, Revised, 1985, pp.198-199) 28/09/2008 "Why the amphibians left the water and when constitute only a part of the puzzle to be solved by those who are studying the origin of the first tetrapods. Paleontologists tracing amphibian history have also to analyze the structural modifications necessary to transform a fish into an animal viable on land before they can explain the steps by which rhipidistian forms evolved into the earliest terrestrial species. It is possible to draw such guidelines, because observation of living animals makes patent the different demands on the vertebrate body of watery and aerial environments. Underwater, animals are supported by the medium, kept moist, and supplied with dissolved oxygen. Once they come out into the dry air, they are faced with the necessity of holding themselves up and moving in a much less buoyant substance, of extracting oxygen from a gaseous mixture, and of conserving the water that forms the basis of their protoplasm. The physical forces operative in the terrestrial environment make certain mechanical arrangements a necessity and others an impossibility if the animal is to succeed in these tasks. Determining the time and the order in which the required structural changes took place is a more speculative matter. Although many of the modifications were correlated and so must have occurred simultaneously, paleontologists are not certain of how much alteration took place as protoamphibians were acclimating themselves to land life and how much occurred preadaptively at an earlier time when the animals were still wholly aquatic." (Stahl, B.J., "Vertebrate history: Problems in Evolution," , Dover: New York NY, Revised, 1985, pp.198-199) 28/09/2008 "Although several Devonian fishes possessed lungs, it is not at all clear that elaboration of these structures was an early event in amphibian evolution. Ever since its initial appearance as an outgrowth from the pharyngeal region of the gut, the lung seems to have functioned as a respiratory membrane. Its usefulness to aquatic forms confined in waters of low oxygen content surely explains the perpetuation of the organ in several lines of bony fishes. Although much later in vertebrate evolution the lung itself would increase in complexity as advances in the design of internal organs made possible a higher rate of metabolism, a simple internal respiratory sac not too different from that of the fishes would very likely have sufficed for the cold- blooded protoamphibians. A land vertebrate could not survive, however, without some mechanism for assuring the passage of air from mouth to lungs. In fishes this transport may be a passive process: a fish can gulp air and then plunge head downward, causing the bubbles to rise through the pharynx and so pass backward into the lung. A land animal which remains horizontal must have some way of forcing or drawing air through its respiratory tract. Certain structural innovations which appear in early tetrapods could have arisen in conjunction with the requirement for a respiratory current. The increased length and stoutness of the ribs characteristic of the first known amphibians afforded added surface for the attachment of muscles which could have produced a rise and fall in the body wall, rhythmically changing the pressure around the lungs." (Stahl, B.J., "Vertebrate history: Problems in Evolution," , Dover: New York NY, Revised, 1985, pp.199-200) 28/09/2008 "Elevating the body was also desirable as preparation for easy locomotion over dry ground. A fish moves against the water which buoys it up, generating a minimum of friction, but a tetrapod in contact with the substratum would be considerably hindered by the scraping of its body along the uneven surface unless, like the snakes, it was specially modified for that kind of locomotion. Raising the trunk and tail eliminates at once the necessity of slithering along every rise and fall in the terrain and the danger of scraping the epidermis to shreds in doing so. The transformation of the fins from steering devices to piers for the suspension of the body involved changes in every part of the appendicular skeleton. Besides reorienting at least a portion of the limb in a vertical direction and exchanging for the fin rays feet that could be planted flat on the ground, the relationships of the girdles to the axial skeleton had to be substantially modified ... In fishes, the pelvic girdle always consisted of a pair of bony plates embedded in the ventral body wall. A tetrapod limb, pressing upward against such a structure, would cause it to sink inward and compress the soft organs in the posterior part of the body cavity. If the hind legs were to hold up the animal and push it forward, there had to emerge a rigid connection between the pelvic girdle and the vertebral column. With such an arrangement, the thrusting force of the foot against the ground could be transmitted with little loss to the main axis of the body." (Stahl, B.J., "Vertebrate history: Problems in Evolution," , Dover: New York NY, Revised, 1985, p.201) 28/09/2008 "A union of the appendicular and axial parts of the skeleton in the pectoral region already existed in fishes: from earliest times, the dermal shoulder shield had articulated firmly with the back of the skull. This association, while it was undoubtedly advantageous for fishes, was unsuitable for a tetrapod .... The forelegs are a sort of landing gear in a terrestrial animal: they receive the weight of the body as it is propelled forward by the hind limbs. To absorb the shock generated by the descent of the trunk, the pectoral girdle has to be disconnected from the head. Even if an amphibian had been able to withstand the tension on the skull that would have been created at every step so long as the articulation between girdle and skull remained, another difficulty would have ensued. Because the scapulocoracoid element which receives the limb bone abuts the cleithrum of the shoulder shield along its vertically oriented medial surface, pressure from the leg would set up a shearing stress between the endochondral part of the girdle and the rigidly held dermal portion. Since the skeleton is most vulnerable to shearing forces, the resulting weakness of the suspensory apparatus would limit the weight, and thus the size, of terrestrial vertebrates. Transformation of the girdle into one strong enough to support a walking animal of any mass demanded a loss of the connection of the dermal bones with the skull and a concomitant expansion of the endochondral part to which the legs are attached." (Stahl, B.J., "Vertebrate history: Problems in Evolution," , Dover: New York NY, Revised, 1985, pp.201-202) 28/09/2008 "Freeing the skull from the pectoral girdle surely brought with it other advantages for an animal making its way on land. For the first time, a vertebrate would be able to turn its head and to lift it above the level of the body without tilting its tail downward. This ability made it possible to see beyond small obstacles in the immediate environment and so to choose the most convenient path or to discover enemies lurking nearby. Since the skull, separated from the girdle, remained cantilevered from the front of the vertebral column, its elevation above the ground required its development as an inflexible structure with space available on the posterior surface for attachment of the strong neck muscles that hold it up. Specifically, the braincase would have to become more solid than it was in the ancestral fishes and the occipital region broader." (Stahl, B.J., "Vertebrate history: Problems in Evolution," , Dover: New York NY, Revised, 1985, pp.202-203) 29/09/2008 "Although many fishes flourished with little ossification of the vertebral column, supporting a body in the aerial environment necessitated increasing the amount of bone in that part of the skeleton. While the long-bodied early tetrapods still needed the kind of flexibility conferred by the unjointed but pliant notochord, that structure, reinforced as it was in most ancient fishes by cartilaginous elements, never would have sustained the weight of the whole animal out of water. Evolution of a stronger column was made possible by the appearance in the rhipidistians of small bones that hugged and constricted the notochord: anteriorly in each segment an intercentrum embraced the notochord from below, and, just behind, a pair of nubbins called pleurocentra occupied a dorsolateral position ... . Selected for at first, perhaps, because the intercentrum provided secure footing for the high-spined neural arch, the bones could later expand to share and then entirely accept the stresses projected through the vertebral column of the land animal. Contact between these central elements was apparently insufficient to produce stability, however, for no tetrapod evolved without an accessory articulation more dorsally between the neural arches. The outgrowth fore and aft of paired zygapophyseal, or yoking, processes from the roof of each arch resulted in the development of gliding joints which added strength to the column but interfered little with its flexibility." (Stahl, B.J., "Vertebrate history: Problems in Evolution," , Dover: New York NY, Revised, 1985, pp.203-204) 29/09/2008 "The structural modifications which enable an animal to support itself and to respire in an airy medium would be of no benefit unless the animal could protect its body from desiccation. Since vertebrates, like all living things, are composed of watery protoplasm, this is a formidable task. Eventually, in the tetrapod line, it was to be accomplished in a way similar in principle to that utilized by all organisms adapted for terrestrial life: the body became enclosed in a nonliving coat impervious to water, which exposed moist tissues in as few places as possible. Whereas other forms of life manufactured cork and cuticle, shell, slime, and exoskeleton to retard the loss of water, tetrapods evolved a layer of dead, keratin-filled cells at the surface of the epidermis which confined internal fluid reasonably well." (Stahl, B.J., "Vertebrate history: Problems in Evolution," , Dover: New York NY, Revised, 1985, p.204) 29/09/2008 "Gills, which have to remain moist and exposed if they are to function, had to be abandoned, and respiratory membranes developed in more protected parts of the body. The formation of internal nares was preadaptive for animals that had to restrict contact between the dry air of the environment and their respiratory organs. With a pair of narrow passages that led from the exterior to the front of the oral cavity, protoamphibians could admit in two fine streams the air necessary for respiration rather than exposing the moist interior of the mouth broadly by parting the jaws. In higher tetrapods, protection of the internal tissues mould be increased by further isolating the respiratory stream within the oral cavity and lengthening the distance through which air had to travel before reaching the lungs." (Stahl, B.J., "Vertebrate history: Problems in Evolution," , Dover: New York NY, Revised, 1985, pp.204-205) 29/09/2008 "If the condition of modern amphibians is representative of the level to which the first tetrapods had brought their water-conserving abilities, it is obvious that the bare beginnings of protection against desiccation were sufficient to allow vertebrates to gain the land. In living amphibians, the skin exhibits a keratinized layer but one thin enough in most species to be permeable to water under certain circumstances. The delicacy of the protective laver enables it to serve a double function: covered with mucus, it slows the loss of water when the animal is exposed to the air but permits fluid to enter when the animal submerges itself after a terrestrial excursion. The increase in cutaneous permeability shown on the latter occasion is under hormonal control. Although it is not known whether endocrine activity of this sort is a specialization in modern amphibians or a legacy from ancient forms, it is safe to suppose that physiological mechanisms must have appeared early to supplement the structural alterations which adapted vertebrates for land life. If hormonal regulation of cutaneous permeability did exist in the first amphibians, it would have been effective combined (as it is in extant forms) with endocrine control of the kidney. If the emergent tetrapods secreted hormones that acted to conserve water by inhibiting filtration of fluid from the bloodstream into the urinary tubules or by encouraging the recovery of water by resorption through the tubule wall, the ability of these animals to survive in the atmosphere would have been enhanced." (Stahl, B.J., "Vertebrate history: Problems in Evolution," , Dover: New York NY, Revised, 1985, pp.204-205) 29/09/2008 "Scales disappeared, and other structural defenses against drying out remained limited among the amphibians. These animals assured their viability by behavioral adaptations rather than by paralleling the higher tetrapods in the development of increased physical resistance to desiccation. They frequented moist areas adjacent to streams or lived in marshes, where the heat of the sun made the air steamy rather than dry. When drought was inescapable, they burrowed or lay dormant underground. Undoubtedly, the earliest amphibians fertilized their eggs externally, as many living forms do, laying them in the water, where they were safe from drying if not from the depredations of hungry fishes. Surviving embryos, unprotected by extraembryonic membranes, became gilled larvae that passed through an obligatory aquatic stage before they could step out on land. Those later amphibians which became more terrestrial evolved a variety of special reproductive habits designed to accommodate or abbreviate the larval requirement for water. Their eggs are laid in damp moss, gelatinous froth, or temporary puddles or fertilized and held for a time within the body; the embryos may mature with unusual speed, acquiring adult characteristics before they leave the egg. None of these peculiar inventions permitted the degree of independence from fresh water enjoyed by higher vertebrates, which enclose their embryos in a fluid-filled sac and protect them further with a shell or by housing them internally until they can survive in dry air." (Stahl, B.J., "Vertebrate history: Problems in Evolution," , Dover: New York NY, Revised, 1985, pp.206-207) 29/09/2008 "Although tetrapods were able to spend time on land before they evolved a truly impervious skin and a way of reproducing in the absence of water, they could hardly have managed if their sensory organs had not soon become adapted to functioning in terrestrial surroundings. The eyes of bony fishes, their chemoreceptors, and their lateral-line organs for sensing vibrations in the environment were designed to work in a watery medium. In air, the surface of the lidless eyes would dry in a short time, as would the soft tissue of the lateral-line canals. The olfactory epithelium, usually folded loosely in fishes, would quickly lose its moisture and shrivel. In addition to glands that secreted mucus over the skin, the first vertebrates which were even partially terrestrial required others that continuously bathed the exposed parts of the sense receptors. The nasal lining, recessed within the respiratory passage, was protected sufficiently by this method alone. The eye acquired a lid that could be passed over the surface periodically for instant rewetting of the cornea. With these minor alterations and certain others in the shape of the cornea and lens, the olfactory epithelium and the eye became immensely valuable for the new vertebrates. Since light travels and substances diffuse more rapidly through air than through water, tetrapods could sense changes in their environment at a much greater distance than fishes ever could. That they relied increasingly upon these sensory organs can be inferred from the gradual enlargement of the cranial spaces for the olfactory and optic lobes of the brain, to which impulses from these receptors pass." (Stahl, B.J., "Vertebrate history: Problems in Evolution," , Dover: New York NY, Revised, 1985, p.207) 29/09/2008 "No structural modification, however, could turn the lateral-line system to advantage in a land animal. Its action depended upon the passage through superficial canals of a current of water to deform a gelatinous coating around the cilia projecting from its sensory cells. Even if the gummy coating could have been kept wet, it is unlikely that pressure waves in air would have been forceful enough to disturb it. Because sensitivity to aerial vibrations allows an animal to detect the presence of enemies it cannot see or smell, it was to be expected that a substitute for the lateral-line system, if one appeared, would be selected for. Actually, no new organ arose in the protoamphibians, but by a series of changes in old structures, an arrangement was achieved whereby cells in the inner ear closely related to the sensory cells of the lateral- line system were made responsive to external vibrations. Of chief importance in this renovation was the change that took place in the hyomandibular bone ... In its position behind the spiracular gill slit in ancient fishes, this element of the branchial skeleton had served as a prop for the jaws, bracing the quadrate bone against the otic region of the braincase. When, in the evolution of the protoamphibians, the upper jaw became attached firmly to the skull, the hyomandibula relinquished its articulation with the quadrate and expanded in a lateral direction. A process that already, extended outward to the operculum in rhipidistians broadened and, after the disappearance of the gill cover in the earliest tetrapods, came to rest against the cheek. At its medial end, the hyomandibula remained pressed against the cranial bones that enclosed the inner ear, and thus it constituted a robust prop between the braincase and the cheek in the earliest amphibians. When eventually both the cranial wall and the cheek regions became membranous where the hyomandibula touched them, the old suspensory element, slimmed down, became a functional stapes or columella. Enveloped by an extension of the spiracular pouch, now the cavity of the middle ear, the bone was free to vibrate when the external membrane, or tympanum, against which it rested, was disturbed by vibrations in the air. The new stapes, as it moved, transmitted pressure waves through the membrane at its medial end to the fluid around the inner ear. There, the sensory cells were stimulated, as they always had been, by the agitation of the liquid in which their gelatin-covered cilia were bathed." (Stahl, B.J., "Vertebrate history: Problems in Evolution," , Dover: New York NY, Revised, 1985, pp.207-208) 29/09/2008 "Although it is not possible to tell from the remains of the first known amphibians how far evolution of the ear had progressed, it is clear that by late Devonian times a number of other structural adaptations for land life had been realized. Paleontologists have found in what is now eastern Greenland fossils of vertebrates that were even then robust tetrapods. These animals were not adapted to withstand the arctic conditions that currently prevail in that part of the world. The climate at the end of the Devonian period was far milder. For most if not all of the year, rain water that fell in the highlands ran freely down to the sea, filling the land with streams, shallow backwaters, and rivers that housed a rich variety of lobe-finned fishes. It was an environment conducive to fossilization: not uncommonly, dead fish were carried along with the current until they were buried in sediment at the bottom, often in estuarine areas, where their bones rested side by side with brackish-water placoderms, acanthodians, and sharks. The amphibians that appeared in eastern Greenland were transported downstream in the same way. Alive, they shared the freshwater habitat of their rhipidistian cousins, leaving it from time to time to make forays out onto solid ground." (Stahl, B.J., "Vertebrate history: Problems in Evolution," , Dover: New York NY, Revised, 1985, p.209) 29/09/2008 "circular argument a set of propositions which together constitute an argument and in which one of the premisses is identical with the conclusion. A person who uses a circular argument for the purpose of establishing the conclusion will often be guilty Of BEGGING THE QUESTION." (Mautner, T., ed., "The Penguin Dictionary of Philosophy," , Penguin: London, Revised, 2000, p.95. Emphasis original) 29/09/2008 "begging the question a defect in reasoning which consists in assuming that which one wants to argue for; taking that for granted which is the very point in question. For example, a person wants to argue that God exists. He argues from the two premisses (1) The Bible says that God exists and (2) What the Bible says is true. He supports the second premiss by the two assumptions God is perfectly veracious and the Bible is His word. Each of these presupposes that God exists. This way of arguing begs the question." (Mautner, T., ed., "The Penguin Dictionary of Philosophy," , Penguin: London, Revised, 2000, p.64. Emphasis original) 29/09/2008 "vicious circle ... (Lat. Circulus vitiosus) 1 reasoning which uses a premiss to prove (usually through a number of intermediate steps) a conclusion, but which also uses the conclusion to prove the premiss. 2 a definition in which the definiendum (the expression that is to be defined) is used in the definiens (the defining expression). Especially in mathematics and logic, impredicative definitions, in which the definiens refers to a domain of which the definiendum is an element, are viciously circular. It was Henri Poincare who first used the expression 'cercle vicieux' in his rejection of definitions of this particular kind." (Mautner, T., ed., "The Penguin Dictionary of Philosophy," , Penguin: London, Revised, 2000, p.600. Emphasis original) 29/09/2008 "circle, vicious A definition is viciously circular when the term to be defined reappears in the definition, or where the notion that is being defined is implicitly contained in the definition. The definition that `"x is good" means that we think that x is good' is an example of the former. The definition that `"x is good" means that ideal people like x' is an example of the latter, since although the word `good' does not recur, it seems hidden in the notion of an ideal (= maximally good) person. Reasoning is condemned as viciously circular when the conclusion is improperly concealed in the premises, or is improperly needed to get the conclusion itself from the premises (see also begging the question). It is extremely hard to say when such concealment is vicious, since there is one sense in which in any valid argument the conclusion is concealed in the premises. Controversial cases of circular reasoning in philosophy include Descartes's alleged appeal to God to certify that the clear and distinct ideas that enabled him to prove the existence of God did not deceive him, and the use of the fact that induction has worked well in the past as an argument for supposing that it will work well in the future. For Russell's particular use of the concept, see vicious circle principle." (Blackburn, S., "The Oxford Dictionary of Philosophy," Oxford University Press: Oxford UK, 1994, Reprinted, 1996, p.64. Emphasis original) 29/09/2008 "begging the question The procedure of assuming what is at issue in an argument. Although the charge is commonly made, there is no logical definition of those kinds of argument that beg the question. In the widest sense, any valid argument might be thought to beg the question, since its premises already `contain' its conclusion. Yet valid arguments can and do move reasonable people to accept their conclusions. The best definition is that an argument begs the question if it contains a definite premise or move that would not be accepted by any reasonable person who is initially prone to deny the conclusion." (Blackburn, S., "The Oxford Dictionary of Philosophy," Oxford University Press: Oxford UK, 1994, Reprinted, 1996, p.39. Emphasis original) 29/09/2008 "begging the question, or petitio principii. Literally, requesting what is sought, or at issue. So, requesting an opponent to grant what the opponent seeks a proof of. So, by extension, assuming what is to be proved. A traditional fallacy. Assuming has to be distinguished from entailing, or all valid proofs would beg the question as J. S. Mill thought). But the boundary is sometimes hazy: for example, does an argument of the form `Even if not P, Q; so at any rate Q' assume 'Q'" The expression is sometimes misused: it does not mean `raise the question', or assume without argument'.)" (Kirwan, C.A., "begging the question," in Honderic, T., ed., "The Oxford Companion to Philosophy," Oxford University Press: Oxford UK, 1995, p.81. Emphasis original) 29/09/2008 "vicious circle. An argument assuming its conclusion as a premiss (begging the question), or a definition of an expression in terms of itself. Russell argued that paradoxes in the foundations of mathematics-for example, his paradox of the class of all classes that are not members of themselves depend on a kind of vicious circularity, violating the maxim `Whatever involves all of a collection must not be one of the collection'." (Cohen, M.C., "vicious circle," in Honderic, T., ed., "The Oxford Companion to Philosophy," Oxford University Press: Oxford UK, 1995, p.81. Emphasis original) 29/09/2008 "circular reasoning, reasoning that, when traced backwards from its conclusion, returns to that starting point, as one returns to a starting point when tracing a circle. ... Circular reasoning is often said to beg the question. 'Begging the question' and petitio principii are translations of a phrase in Aristotle connected with a game of formal disputation played in antiquity but not in recent times. The meanings of 'question' and 'begging' do not in any clear way determine the meaning of 'question begging'. There is no simple argument form that all and only circular arguments have." (Sanford, D.H., "circular reasoning," in Audi, R., ed., "The Cambridge Dictionary of Philosophy," Cambridge University Press: Cambridge UK, 1995, Reprinted, 1996, p.124) 29/09/2008 "At first glance, it may not seem that there is a great deal of external similarity between a fish and a mammal, but there is more here than meets the eye. Although a fish has fins and a mammal, like other tetrapods, has limbs, the fish's pectoral fins are in the same position as a tetrapod's forelimbs and its caudal tins are in the same position as the tetrapod's hind limbs. It turns out that in fish, such as the zebra fish, and in tetrapods, such as chickens, mice, and humans, the same homeobox gene clusters are involved in producing both sets of appendages, regardless of whether they are fins supported by rays or limbs supported by bones. The debate that still lingers among developmental geneticists is whether these homeobox genes were present in a distant ancestor and then turned on in specific fore and aft positions to produce two pairs of appendages; or whether the homeobox gene cluster for the front pair of appendages came first. then duplicated, giving rise to the posterior pair of appendages. Each explanation yields the same result, although the first one is the less complicated and perhaps more likely of the two scenarios. But while fish, birds, and mammals share the same homeobox gene clusters that are responsible for the development of pairs of appendages fore and aft, the difference lies in two factors. First, in fish, these genes are active only along the back side of the elongating fin, while in tetrapods they are active along the back and across the front of the developing limb bud. Second, there is one tiny chemical difference that distinguishes one of the homeobox genes of tetrapods from the same gene in fish. In tetrapods, this homeobox gene-the Hoxd-13 gene-has an additional molecular sequence inserted into it that specifies a repeated series of a particular amino acid, alanine. Tetrapods have forefeet and hindfeet. Fish do not have this alanine-encoding insertion, and they do not have feet of any kind." (Schwartz, J.H., "Sudden Origins: Fossils, Genes, and the Emergence of Species," John Wiley & Sons: New York NY, 1999, p.37. Emphasis original) 29/09/2008 "How do we know that this tiny molecular insertion is associated with the development of feet? A bird, which has a reduced number of wrist and fore-foot bones in its wing compared with a mouse or a human, has about one third more alanine repeats than a mammal does. Since we know, as much as we can know anything in the evolutionary past, that there was a reduction in the number of digits and wrist bones during bird evolution, it makes sense that a present-day bird would have a shorter sequence of alanine repeats than would a mammal that has more forefoot bones. The role of alanine in the formation of hands and feet is further indicated by the observation that humans born with developmental deficiencies in the number of hand and finger bones have reduced alanine repeat sequences. If fins become limbs with feet at their ends merely through the turning on of homeobox genes in novel locations and the insertion of a short molecular sequence into one particular homeobox gene, then the evolution of primate hands and feet would be an even simpler evolutionary feat." (Schwartz, J.H., "Sudden Origins: Fossils, Genes, and the Emergence of Species," John Wiley & Sons: New York NY, 1999, pp.37-38) 29/09/2008 "The discovery of homeobox genes involved in limb development was also important for understanding the evolution of the limbs of tetrapods, or four-footed animals. Since tetrapods must have evolved from a fishlike ancestor, the question was: How could forelimbs and hind limbs, with many supportive bony elements in each limb, he derived from the cartilaginous fins of fish, Most living fish--teleosts, such as a trout, or chondrychthyans, such as a shark-are not relevant to unraveling this mystery because they have numerous cartilaginous rays arranged more or less parallel to one another or in a fanlike pattern in each fin. But lungfish and coelacanths are notably different from the typical fish. They have fins that are fleshy at the base and are supported by a series of bones that extend the length of the fin's long axis. The fins of lungfish and coelacanths do contain small, thin fin rays, but these structures adorn the anterior and posterior flanks of the main axis of fin-supporting bones. Fossil relatives of lungfish and coelacanths had similarly configured fins." (Schwartz, J.H., "Sudden Origins: Fossils, Genes, and the Emergence of Species," John Wiley & Sons: New York NY, 1999, p.339) 29/09/2008 "Since the large bones of the tetrapod limb are also arranged in a linear fashion, paleontologists at first thought that the evolution of a limb from a fin involved the simple addition of forefeet and hind feet to the end of this structure, complete with wrist and ankle bones and toes. But in 1986, Neil Shubin, a biologist at the University of Pennsylvania, and Pere Alberch proposed a different evolutionary scheme. They suggested that what had probably happened in the `conversion' of a simple finlike appendage to a tetrapod limb was that the end of the fin had become flexed developmentally, so that it was bent over to the `thumb' side of the limb. Consequently, the toes at the end of a tetrapod's limb are merely derivatives of the rays that would have extended along the posterior side of the ancestral fin. Confirmation of the bent-fin theory of pattern reorganization in the formation of the tetrapod limb came in 1995 from comparative studies by Paolo Sordino, Frank van der Hoeven, and Denis Duboule, all of the University of Geneva, on homeobox gene expression in the tins of zebra fish and the limbs of mice. They found that zebra fish and mice express the same Hoxd genes-Hoxd-11, Hoxd-12, and Hoxd-13-plus one particular Hoxa gene during the early phases of fin and limb development. This finding suggests that the large bones of the tetrapod limb derive from the same homeobox genes that produce the bones that link a fish's fin to its body. But in later phases of development in the mouse, the limb bud expresses Hoxd-11, Hoxd-12, and Hoxd-13 gene activity across the front of the elongating of the limb, whereas the fish's growing fin bud does not. In the mouse, there is not only early homeobox gene activity along the posterior side of the limb but there is also later homeobox gene activity that spreads anteriorly at a right angle to the previous phase of activity. As Sordino and his colleagues pointed out, this difference between the fish and the mouse was due to an asymmetry in cellular activity at the proliferating end of the mouse limb, not necessarily to a physical bending of the original fin axis. Nevertheless, this new cellular field at the end of the developing mouse limb-coursing across the front of the limb bud from the posterior to the anterior side-ultimately leads to the formation of cartilaginous condensations that, in turn, become the wrist and finger bones. Clearly, as represented by the mouse, a novelty responsible for the emergence of the tetrapod foot at the homeobox gene or homeobox gene product level had been introduced in the evolutionary emergence of this group of vertebrates." (Schwartz, J.H., "Sudden Origins: Fossils, Genes, and the Emergence of Species," John Wiley & Sons: New York NY, 1999, pp.339-341) 29/09/2008 "The major supporting structures in the fin of a fish (left), the tin of a lungfish (middle), and the forelimb of a typical four-legged animal. In the fish (represented here by a fossil shark), there are numerous cartilaginous rays, arranged in fanlike fashion, that give stability to the-flare of the thin fin. In the lungfish, the fin is thick and fleshy and is supported by a central series of bones, on each side of which is a series of smaller bones. The tetrapod limb is composed of a single large upper bone (in the ease of the forelimb, the humerus) and two smaller and thinner lower bones (here, the radius and the ulna). In addition, the end of the limb bears toes. In between the toes and the lower-limb bones is a series of small bones (wrist in the forelimb and ankle in the hind limb). The bent -fin theory posited that the lower part of a lungfish-like fin turned in at a right angle and the outer, smaller set of bones became the toes of a tetrapod." (Schwartz, J.H., "Sudden Origins: Fossils, Genes, and the Emergence of Species," John Wiley & Sons: New York NY, 1999, p.340)
* Authors with an asterisk against their name are believed not to be evolutionists. However, lack of
an asterisk does not necessarily mean that an author is an evolutionist.
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Created: 1 September, 2008. Updated: 20 March, 2010.