I have often found that the more I learn about biology, the more easier it becomes to beco

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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! :)


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