To: All Msg #369, Sep2193 06:22AM Subject: Repost: Evolution of three and fourchambered he

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From: Joel Roth To: All Msg #369, Sep-21-93 06:22AM Subject: Repost: Evolution of three- and four-chambered hearts Organization: Aegis Society, Kyoto Japan From: (Joel Roth) Message-ID: <> Newsgroups: Julie Thomas' critique of theories of heart evolution, posted about one year ago, strike me as well written and referenced enough to merit reposting. She argues against, in her words, a 'just-so' scenario for evolution of the heart that conceals what appear to her to be mortally maladaptive transitional stages, and stages that differ dramatically (in her opinion) from developmental sequences. These articles underscore a major difficulty I have in accepting the evolutionary hypothesis: I have not yet heard sufficient evidence to believe that every step in the hypothetical development of biological systems over time would have necessarily improved or maintained the viability of the organism--which I understand is a precondition of evolutionary scenarios based on selection or drift. My experience is that macro-size systems that we see in the world around us require substantial *investment* of energy, skill, and material resources as a rule before any return is achieved. (A factory or business is a good example.) Evolution theory, OTOH, seems to say that biological "factories" ranging in size from organelles to organs can develop without benefit of skill or information resources, and without the need of even short-term compromises in productive use of energy or nutrient resources. The validity of this assumption seems to me at least as difficult to prove as the various scenarios for abiogenesis. ~From: bk186@cleveland.Freenet.Edu (Julie Thomas) ~Newsgroups: ~Subject: More on three and four chamber hearts ~Message-ID: <> ~Date: 9 Apr 92 05:04:22 GMT ~Organization: Case Western Reserve University, Cleveland, OH (USA) ~Lines: 85 I have often found that the more I learn about biology, the more easier it becomes to become skeptical of evolution. Let's consider our three to four chamber heart transition in more detail. At first, I must confess that I thought this was really not a big deal. I could envision some regulatory mutation working to to simply extend the interventricular septum so it completely seperated the right and left ventricles (although typical neo-Darwinian gradulism seemed out of the question). My problem was that I could see no selctive advantage in this. The standard line about increased efficiency (meaning evolution works to increase efficiency?) didn't hold up to scrutiny (as far as yours truly was concerned). But now I must change my tune and become even more skeptical as evolving a four chamber heart was MUCH more than just completely the interventricular septum. See my cartoons below for a schematic of the two types of heart. Reptilian heart 1 ! ! 2 3 !***! !*/ /* * * * ! * * R ! L * * ! * * ! * ****** Mammalian heart 1 ! 2 3 ! / / !*/**** /* * ! * * ! * * R ! L * * ! * * ! * ****** 1 = Pulmonary trunk (blood leaves for the lungs) 2 = Right atrium (blood enters from the lungs) 3 = Left atrium (blood enters from the body) R = Right ventricle L = Left ventricle ! = Interventricular septum If you look at these figures, it becomes quite obvious that the ol' "complete the septum" story just won't work. For if the reptilian septum was completed, this would kill the reptile since the blood from BOTH the right and left atrium could not enter the right ventricle, thus it could not be oxygenated by the lungs. In other words, blood from the right atrium must first travel through a portion of the left ventricle. In mammals, not only is the interventricular septum complete, but the right atrium opens into the right ventricle. Thus, the change that would have to occur is far more than a growing septum. The plumbing of the heart would also have to change simultaneously. Any tales about how a shifting atrium occurred? But let's also look at interesting developmental consideration. In humans, when the interventricular septum is completed in about 3 months gestational age, the atrial septum still possesses a discontinuity where there is cross-talk between the two atria. Thus, development does not show a "2 complete atrial chambers /1 ventricular chamber --> 2 complete atrial chambers/2 compete ventricular chambers" transition which is what was supposed to have happened in the reptile heart to mammal heart transformation. ~It always seems that if we find a similar pattern in embryological development, we are supposed to have evidence for evolution. But if the pattern differs, well........ Evolution can be such a paradigm! :) ~From: bk186@cleveland.Freenet.Edu (Julie Thomas) ~Newsgroups: ~Subject: Re: More on three and four chamber hearts ~Message-ID: <> ~Date: 14 Apr 92 01:53:25 GMT ~References: <> ~Lines: 88 In a previous article, salem@pangea.Stanford.EDU (Bruce Salem) says: >Did you see my posting from a couple of days ago in the >developmental sequence of the four chambered heart in >humans and its relation to the anatomy of two and three >chambered hearts? Yes I did. Thank you. However, I did not find it to be all that helpful. If I recall, you posted about the human heart developing from a "primitive" structure into the four-chambered heart in a manner somewhat suggestive of the evolutionary procession. But unless the null hypothesis would be that the heart should develop in a different manner, I fail to see how this is evidence of the supposed transformation. Are you suggesting that without evolution, we should expect, for example, the heart to develop from some 12 chamber stage? And considering that development proceeds from a single cell towards a complete multicellular organism, I would expect earlier structures to be less defined. >That account (Arey, 1942 Developmental Anatomy pg. 316 ff) >sayes that the development proceeds in stages roughly analogous >with the enchancements from fish to mammalian form. Right. "Roughly analogous". That does not give me reason to suspect this must reflect some ancient phylogenetic transformation. The heart >begins as a thickening in vascular structures in the crainial >area of the embryo, develops into a three chambered affair >with atruim, ventricle, and bulbus. Well, the fish heart consists of a four chambered affair in series. A forth and smaller segment, >the sinus venoosus, which developed out of a different structure >than the rest of the heart, unites with the right side of the >atrium. If this is true, then the fish heart is most different. As the heart developes the atrial and ventricular partitions >begin to appear at the same time that the bulbus is absorbed by >the ventricle. Out of the bulbus both the aorta and pulmonary arteries >are formed, and this is not due to a partition of the atrium. At >this point the venous circulation enters the atrium and the >arterial leaves from what used to be the bulbus. The heart is >still three chanbered. It is the transformation of the bulbular >region and ajoining parts of the right ventricle into the >right ventricle and the simutaneous fornation of the remaining >septa that results in the four chambered heart. The partitioning >occurs after the antrial and venous circulation have become >isolated at opposite ends of the heart. So the transformation >of the pulmonary function predates in the development, at least, >the greater efficiency effected by partitioning and formation of >valves. How does this help the reptile to mammal heart transformation? Recall that in the reptile (with a three chambered heart) both atria enter into the left ventricle. What you need is the two atria dumping into the left ventricle, then the right one shifting to the right as the intervenricular septum completes its growth. The funny thing is that when it does, there remains an opening between atria. > Now, I hasten to add that I an not making a case for >recapitulation, as Gould makes a good case that the relation >between development and phylogenetic steps is very much >more complicated than that. > Covering the bases, eh? I have a great deal of difficulty accepting ontogeny as evidence for evolution when the cards are stacked so that similarities supposedly mean relationship and differences are assigned to some "special" category where ad hoc explanations reign. The whole endeavor is set up so that only evidence for evolution can be found. I reject this methodology. If similarities count for, differences count against. (of course, similarities might not count for and differences might not count against; subjective interpretations are everywhere!). ~From: bk186@cleveland.Freenet.Edu (Julie Thomas) ~Newsgroups: ~Subject: Developing ideas on hearts. ~Message-ID: <> ~Date: 16 Apr 92 00:36:37 GMT ~Lines: 144 Let's look at the development of the human heart in more detail to determine if it really helps the notion that "hearts evolved". For my primary source, I'll use the text "The Developing Human" by Keith Moore. The first thing to note is the cardiovascular system is the first to form. Blood actually begins to circulate in the embryo by three weeks. Moore writes, "this precocious development is necessary because the rapidly growing embryo needs an efficient method of acquiring nutrients and disposing of waste products". Now recall that the human heart begins functioning in a so-called primitive form. This is usually seen as some kind of phylogenetic evidence. I doubt this, as what it could also mean is that the embryo needs a pump as soon as possible, and it employs the "primitive" pump because it can't wait around for it to develop into the more complex pump. Thus the "primitive" heart need not reflect phylogeny, it may very well reflect the developmental need for some kind of pump as soon as possible. Secondly, the heart forms by first forming a heart tube. Ah, says the evolutionist. This stage reflects that first "just so" story about a blood vessel becoming enlarged, incorporating valves, and becoming a primitive heart, that was brought up earlier. Unfortunately for the tale, the details don't support the story line. First it should be noted that the heart tube actually forms from the merging of TWO smaller heart tubes which are laterally opposed. The two tubes fuse to actually create a tube within a tube. Between the tubes is a gelatinous tissue called 'cardiac jelly'. Now, given these details, the story about an evolving blood vessel becomes quite a long shot. If the story was true, the bipartite structure is not explained. What is even more significant is that in some fish and amphibians, the heart does start as a single tube. But in all other vertebrates, the heart starts with the fusion of two regions. Thus at the beginning, the hearts of fish/amphibia and other vertebrates differ radically in development. How and why did this state of affairs evolve? We are not talking about modifying later states of development, but we are talking about starting off from a different subroutine. Finally, I can't resist going back to the evolving vessel story. Measurements in the chick embryo show that while the heart tube can easily fill with blood while it is relaxed, it cannot contract sufficiently to reduce the lumen of the tube to provide for efficient propulsion. This mechanical difficulty is resolved by the cardiac jelly. It provides the medium by which a force of relatively modest contraction of the myocardium is transmitted radially toward the endocardium with resultant closure of the lumen. Once the musculature of the ventricle builds up, this jelly is no longer needed. Thus it seems that notions of contracting blood vessels are far too simplistic. Even if they contracted, they might not have been able (as seen by this evidence) to reduce the lumen enough to give a substantial force of propulsion. Now lets turn to the development of the chambers. Moore emphasizes that these events occur concurrently. After fusing the two tubes, the tube within a tube elongates and develops alternate dilations and constrictions resulting in the formation of the various chambers. The atrial chamber grows a septum and the completion of this septum is actually quite involved and depending on the stage, various perforations are made and discarded. In fact, because of fetal circulation, a perforation (the foramen ovale) is maintained throughout fetal life as the lungs are bypassed. It isn't until birth that this hole closes and pulmonary circulation is established. The right atrium forms by incorporating part of the sinus venosus. The left atrium forms mostly by incorporating proximal parts of the pulmonary vein. The interventricular septum concurrently grows to divide the ventricles. Now at no time does the septum grow so that the two atria pour into the left ventricle. The system develops so that with the growing interventricular septum, the right atria pours into the right ventricle and vica versa. I find this significant since this does not reflect the supposed reptile to mammal change (as outlined in my previous posts). Furthermore, the manner in which the left atria forms is most instructive. It's formation is tied to the prior existence of the pulmonary vein. Yet a pulmonary vein clearly implies an oxygenating organ, and pulmonary artery. Now a pulmonary artery obviously implies that the heart must be sending blood in two directions: to the body AND the oxygenation organ. Thus, the development cannot be reduced to pieces and parts. The whole thing has to be there. If this evolved, surely some sort of saltation is called for as gradualistic microevolutionary changes must travel through many levels which are not only lacking advantages, but would actually be disadvantageous. Does all this really help the notion that "hearts evolved"? I really don't think so. First, let me sound like a creationist. In this case, ALL mutations which affect the heart in an observable manner are deleterious (although I'm quite sure there are many neutral ones which are not picked up due to a lack of mutant phenotype). When development is changed, we get a heart DEFECT. Thus, the development of the heart must be fine-tuned so that significant changes result in deleterious effects. This is certainly not a friendly environment for notions of reshaping the system due to mutations. Secondly, the development of the heart underscores the final forms of different hearts, namely, there are significant differences. If similarity counts as evidence for evolution, differences ought to count against. None of this is certain, of course, however it ought to raise some red flags when we hear stories about hearts "a-changin". Thirdly, the similarities need not imply relationship. For example, the heart tube might not reflect some ancient form. In fact, it probably exists only because the embryo needs to recruit a pump as soon as possible to continue development. And a tube can form more quickly than a complicated four chambered heart. In the end, since the evidence is only circumstantial, it's basically a judgment call. For my part, speaking from my heart, in an attempt to circulate some ideas, I am not convinced by the evolutionary story even when it is pumped up with similarities. :) I am unable to simply hand-wave away the differences, the similarities are not compelling, and the empirical data gives us reason to suspect that developing hearts don't like to change patterns, and no reason to suspect they do or ever have. Add to this all the problems with the "just so" explanations. Would the three to four heart chamber transition really be such an advantage? I already brought up runnin lizards and lazy crocs which seem to throw a monkey wrench in this little story. But there is another aspect. Mixing blood simply means the concentration of dissolved oxygen in the blood is going to be less. Now increasing the efficiency of the heart usually means getting more oxygenated blood to the body. But instead of going through all this organ restructuring, an organism could enjoy the same benefit with a few simple point mutations in the hemoglobin so that it would be saturated at lower concentrations of dissolved oxygen. In other words, the oxygen dissociation curve could be shifted to the left by such a mutation making it possible for the hemoglobin to load and unload oxygen at lower concentrations. Thus, if efficiency was the selective pressure, one would expect this route to have been monopolized instead of organ transformation since it is more likely ~to arise because it involves simpler changes giving the same benefit s. These considerations cause me to suspect that evolutionary reductionism is missing the mark. Notions of reptiles evolving mammalian hearts treats organisms as pieces and parts, while if anything is to be learned from development, it is that organisms develop and exist as whole beings. Perhaps the mammalian heart exists because it exists in a mammal. ~From: bk186@cleveland.Freenet.Edu (Julie Thomas) ~Newsgroups: ~Subject: Another heart attack. ~Message-ID: <> ~Date: 18 Apr 92 12:56:30 GMT ~Lines: 215 Well, I was about to leave this topic, but it seems another actor has walked onto the stage, Mr. Lungfish. Let's set the context for his part in the story. (Using Torey's and Feduccia's "Morphogenesis of Vertebrates). The structure of the heart in the Chondrichthyes and actinopteryian Osteichthyes conforms to the general pattern of four-chambers-in series. Blood from the body enters the sinus venosus, then the single atria, then the single ventricle, and leaves via the truncus to travel to the gills, where it is oxygenated, and then goes to the body WITHOUT returning to the heart. As we know, terrestrial vertebrates have pulmonary and systemic circuits operating in parallel along with divided hearts. How did this rather major change come about? To put it simply, what good is 1/2 a pulmonary artery, 3/2 of atria, or a 'lung' that is not connected to the circulatory system? Well, we don't have any living rhipidistian crossopterygians which are said to have been the ancestors of the first amphibians. But wait, we do have that living fossil, that member of the other group of Crossopterygii, the coelacanth. Since this critter hasn't changed over the hundreds of millions of years, and it is another crossoptterygian, you would sort of expect some crucial insight from this critter's heart. According to T&F (pg 422) their: "internal anatomy specialized as to be little indicative of the basic conditions we should like to know". Now I don't know about anyone else, but this looks like hand-waving in response to information that is not supportive or even contradictory of our story, "The Heart That Evolved". It probably has only a fish heart! Oh well. Anyway, have no fear, as we do have the living relatives (so it is said) of the crossopterygii, the Dipnoi, or lungfishes. Yes, indeed, the lungfish have a four-chambered heart which operates with a parallel circulatory system. According to this twist in the plot, the lungfish reflect the state of the original amphibian ancestor, and the reptilian ancestor, along with the bird and mammal ancestor. Thus, the origin of the four-chambered heart has been solved, and they all lived happily ever after. But hold on a minute. If you ask me, Mr. Lungfish makes the heart story even more implausible. Why? Because we are STILL left with a lungfish which evolves a 2 atria/2 ventricle heart with pulmonary circuit system from fish with a 1 atrium/1 ventricle heart and NO pulmonary circuit. The origin of this four chambered heart is still not resolved, and in fact, the situation is worse. For now it is no longer possible to appeal to the three-chambered hearts of amphibians and reptiles to serve as intermediate structures! We are left with the same problem, but now we're empty handed. The amphibian/reptilian heart evolved AFTER the the lungfish heart, so certainly any information from these systems is not applicable. In short, not only do we have no fossil evidence, but we have now lost our developmental evidence. Thus, we have NO evidence, but we have a belief that is supposed to be scientific. Now, I suppose one could appeal to the amphibian heart/reptile heart as "possible" states which "might have occurred". But I wouldn't even accept these speculations. Why? For one thing, it's easier to lose a structure than gain one. That is, the amphibian/reptilian heart would be "intermediate" examples where the four chamber structure was LOST, not acquired. A situation where a heart is changed so that the septum no longer completely forms is NOT evidence for the ability to acquire new chambers and new circulatory systems. It is no longer possible to use the amphibian/reptilian systems as intermediates to explain how some fish evolved a four-chamber heart in parallel. Mr. Lungfish, while thinking himself the hero of the story, really turns out to be a villain. But what of our reptile to mammal transition? Let's not forget to let Mrs. Crocodile play her part. She too has a four chamber heart, much like that of mammals and birds, making her heart more similar to a humans than to a lizard. In fact, her interventricular septum is structured differently than other reptiles, causing T&F to assert: "this septum is a vertical septum rather than a horizontal one , and appears to be a new evolutionary development, which is not to be homologized with the interventricular septa of lizards, snakes, and turtles". (pg 425). Now I'm confused. How is this septa a new evolutionary development if it, like that of the bird and mammal, supposedly reflects that lungfish to mammal/bird line? Anyway, the significant point is that the septa are not homologous. Now let's go back to that old reptile to mammal transition problem. If you'll recall, the problem I alluded to was that in reptiles (but not crocs) BOTH the right and left atria empty into the left ventricle. If Mr. Lungfish's contribution to the plot is considered, the problem is not how to separate the atria, but now it's how to sequester them. Either one seems like trouble to me. What selective advantage was there in taking a heart where the the right atrium enters the right ventricle and shifting it so that it enters the left ventricle where the blood can now mix? This problem is further emphasized in the amphibians. According to T&F, (pg 423): "modern Amphibia, with their incompletely divided hearts, may illustrate degeneracy rather than primitive intermediacy between fishes and amniotes". Well, there goes the infamous story line! No more can we use "efficiency" as our selective guide. For hearts in amphibians and reptiles evolved to a state of inferior efficiency. But what about all that talk about efficiency? Didn't people REALLY believe it? Or was it a smokescreen? Wouldn't some amphibian which developed a less efficient heart be at a disadvantage than one that did not? Afterall, we heard time and again about how a more efficient heart would be a selective advantage. If a completely separated heart was an advantage, then an incompletely separated heart would be a disadvantage. Thus, if I was supposed to seriously entertain that just so story, it seems only fair to expect those who believed it to also take it seriously and explain how evolution worked to select for an inefficient system among those with efficient systems. As it turns out, the heart story has taken a turn over some figurative aortic arch for the worse. But there is one more aspect of Mr. Lungfish that I want to look at. Mr. Lungfish has lungs and an efficient circulatory system. These come in handy when droughts occur. Wait a minute! Isn't this the scenario for the fish to amphibian transformation? It sure is, yet Mr. Lungfish hasn't evolved one bit towards wandering onto the land in over 300 million years of evolution! In fact, Mr. Lungfish has hardly changed although he has sat poised for 300 million years at the state and environment which supposedly gave rise to amphibians. These facts make you wonder about that other story about fish and amphibians. Now in response to some of the complaints I've been getting, let me outline some of the points which I have gotten out of this inquiry. 1. Many believe "hearts evolved". They consider this a scientific belief. Yet they admit that our evidence for this belief is meager. So why are people getting upset about me not accepting a belief which is supposedly scientific yet which lacks good evidence? 2. I have learned again that similarity need not reflect some phylogenetic relationship. We saw this with sharks and mammals when it came to the circulatory pattern associated with the yolk sac. In my mind, this weakens the appeal to similarities to support evolution. If the vessels of the reptile were not descended from the shark even though they are identical, then it becomes entirely plausible that the heart of the mammal was not descended from the lungfish even thought they are quite similar. 3. The hearts of amphibians and reptiles start out from different initial states. Thus, this is not an example of "tweaking at the peripherals". This weighs heavily in my mind against some evolutionary transformation. On this point, I have proceeded from agnosticism to skepticism. 4. We are still left with no account of how the four-chambered heart arrived on the scene. Mr. Lungfish has actually worked to remove all the developmental circumstantial evidence by placing this transformation in the fish. If you don't have a clue as to how it happened, I see no good reason to think it could have happened. 5. The ad hoc nature of "just so" stories have been exposed. Their only limit is one's imagination. Here is a case where the definitive word is supposed to rest on someone's musings. Furthermore, the just so story about efficiency actually turns in on itself when we realize that hearts evolved to less efficient states. The take home message is that just so stories are quite like the creationsist's "God did it" story. In both cases, the "explanation" seems to be able to explain anything. The only thing just so stories have on the creationist's stories is that the former are more imaginative. In all honesty, they usually read like modern myths (to me), an analogue to the camp fire stories about the distant past which tell us why things are like the way they are today. 6. I've also learned that the fallacy of card stacking is common in evolutionary thought. If differences are found which do not support the story, or even are contrary to the story, we either complain about them being found in cousins (although this doesn't stop us from using cousins to support ancestry), or we give them a label and assign them to a "special" category (an effective way of dismissing contrary evidence) like "regressive evolution" or "highly specialized". 7. I've learned that a creature can be poised to transform, yet can refuse to transform for hundreds of millions of years. 8. Finally, while I fully concur that the creationists are just plain wrong when they say there is no such thing as an advantageous mutation, here is a system where all phenotypically observable mutations are deleterious. To date, the expirical evidence certainly supports the following hypothesis: -->Concerning the development of the circulatory system, there is no such thing as an advantageous mutation<--. I wonder how many other systems this hypothesis would apply to (BTW, it's both predictive and falsifiable for those who worry about such things)? Now if you take this hypothesis, with it's supporting set of data and add it to the considerations concerning "teaking" in #3, and consider the lack of evidence and an explanation for the belief that hearts did evolve, we seem to be falling into a position where it looks like hearts did not evolve, at least in a neo-Darwinian sense. All in all, this has been an experience which has shown me more than the specifics associated with hearts. I've gained insight into the aspects of the biological world as a whole and have also seen how the paradigm of evolution functions as a guide. I have enjoyed this. Now, I'll try to get back to that other topic and post on it later. Thanks to all those who have interacted! -- Joel Roth (international) Brahma Kumaris World (within Japan) Spiritual University 1-2-15-501 Nakamichi, Higashi Nari ku, Raja Yoga Center, Osaka Osaka, Japan 537, 81-6-971-7251


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