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|Re: The Death Of Darwin
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Posted by daViper on July 15, 1999 21:50:23 UTC
Ok. Now I have a better understanding of where you're coming from in this. Let's examine it. It gets lengthy at the end but I had to inorder to provide examples, sorry. Take your last paragraph:
: Lets look at the dillemma this way. There are only a certain number of mutations that would occur in a given generation of organisms. ::::: This would not actually be something you could calculate. There could be none at all or there could be many, especially when environmental conditions undergo a radical change such as the proposed asteroid crash into the Yuccatan Peninsula 65 myo (Million years ago) which seems to be the best theory for the extinction of the Dinosaurs though certainly not the only one.
And given the simplicity of the early forms of life, :::::: You do seem to accept that evolution has occured by this statement I take it...
(by the way are we not finding more and more that these organisms were actually complex?) ::::::: I would have to ask "complex" compared to what...
Darwin's theory would dictate that the genome would become increasingly complex. ::::::: Which is what has happened, both in numbers of gene pairs and DNA sequences therein.
This is based on the observence of micro-evolution which does indeed occur and is easily demonstrated. It is a well known fact that bacteria will become resistant to a given antibiotic over time. On the face this would seem to support macro-evolution. ::::::: You have to remember that the terms micro- and macro- evolution were invented several years ago by those who would not accept the fact of evolution, but were shown that it can actually be duplicated experimentally. Some Biologists have taken to using the terms to accomodate these people by trying to explain evolution in terms the doubters can understand. They are not terms normally used in biology however since it would be impossible to define exactly what point in the process constitutes the difference between the two.
However, with the advances in bio-molecular science, this adaptation has found to be more often than not, the result of a loss of genetic information. ::::::: There is really no way to demonstrate this since it could be said that there is a "gain" in genetic information with equal authority. It's actually irrelevant since the resultant adaptation is based on chemical changes in the bacterium's take-up succeptability. It may constitute evolution but whether it represents a long term benefit is questionable since the bacterium is not necessarily evolving into any superior or inferior form, just different. We'll come up with a new antibiotic and get him anyway...:-)
: How can you be so sure that each species of organism doesn't have a finite genetic ability to adapt to environmental pressures? :::::: I'm sure some do. But most show a remarkable ability to adapt very greatly over time. In support of your point here, I might offer the example of Neandertal. DNA analysis has now shown him to NOT be an ancestor to man. Yet here we have this Hominid who evolved into a family structure, made tools for hunting, managed fire, fabricated clothing and even engaged in rituals for funeral purposes. Yet, he went extinct. Some anthropologists suggest he was the victim of genocide since Cro-Magnon (modern) man existed along side him for a while. Either way, I'd have to say he died out due to an inability to adapt. Genocide or no.
But I still don't see how you can say any of this presents a problem in mamillian geneology for Darwinian Theory. Particularly when the fossil record is SO clear and robust in the examples of how the mammals evolved from reptiles. It's one of the most complete sequences there are. Here ar a few highlights.
Protoclepsydrops haplous (early Pennsylvanian) -- The earliest known synapsid reptile. Little temporal fenestra, with all surrounding bones intact. Fragmentary. Had amphibian-type vertebrae with tiny neural processes. (reptiles had only just separated from the amphibians)
Varanops (early Permian) -- Temporal fenestra further enlarged. Braincase floor shows first mammalian tendencies & first signs of stronger attachment to rest of skull (occiput more strongly attached). Lower jaw shows first changes in jaw musculature (slight coronoid eminence). Body narrower, deeper: vertebral column more strongly constructed. Ilium further enlarged, lower-limb musculature starts to change (prominent fourth trochanter on femur). This animal was more mobile and active. Too late to be a true ancestor, and must be a "cousin". Sort of the "Neandertal" of his day......:-)
Biarmosuchia (late Permian) -- A therocephalian -- one of the earliest, most primitive therapsids. Several primitive, sphenacodontid features retained: jaw muscles inside the skull, platelike occiput, palatal teeth. New features: Temporal fenestra further enlarged, occupying virtually all of the cheek, with the supratemporal bone completely gone. Occipital plate slanted slightly backwards rather than forwards as in pelycosaurs, and attached still more strongly to the braincase. Upper jaw bone (maxillary) expanded to separate lacrymal from nasal bones, intermediate between early reptiles and later mammals. Still no secondary palate, but the vomer bones of the palate developed a backward extension below the palatine bones. This is the first step toward a secondary palate, and with exactly the same pattern seen in cynodonts. Canine teeth larger, dominating the dentition. Variable tooth replacement: some therocephalians (e.g Scylacosaurus) had just one canine, like mammals, and stopped replacing the canine after reaching adult size. Jaw hinge more mammalian in position and shape, jaw musculature stronger (especially the mammalian jaw muscle). The amphibian-like hinged upper jaw finally became immovable. Vertebrae still sphenacodontid-like. Radical alteration in the method of locomotion, with a much more mobile forelimb, more upright hindlimb, & more mammalian femur & pelvis. Primitive sphenacodontid humerus. The toes were approaching equal length, as in mammals, with #toe bones varying from reptilian to mammalian. The neck & tail vertebrae became distinctly different from trunk vertebrae. Probably had an eardrum in the lower jaw, by the jaw hinge.
Thrinaxodon (early Triassic) -- A more advanced "galesaurid" cynodont. Further development of several of the cynodont features seen already. Temporal fenestra still larger, larger jaw muscle attachments. Bony secondary palate almost complete. Functional division of teeth: incisors (four uppers and three lowers), canines, and then 7-9 cheek teeth with cusps for chewing. The cheek teeth were all alike, though (no premolars & molars), did not occlude together, were all single- rooted, and were replaced throughout life in alternate waves. Dentary still larger, with the little quadrate and articular bones were loosely attached. The stapes now touched the inner side of the quadrate. First sign of the mammalian jaw hinge, a ligamentous connection between the lower jaw and the squamosal bone of the skull. The occipital condyle is now two slightly separated surfaces, though not separated as far as the mammalian double condyles. Vertebral connections more mammalian, and lumbar ribs reduced. Scapula shows development of a new mammalian shoulder muscle. Ilium increased again, and all four legs fully upright, not sprawling. Tail short, as is necessary for agile quadrupedal locomotion. The whole locomotion was more agile. Number of toe bones is 126.96.36.199.3, intermediate between reptile number (188.8.131.52.4) and mammalian (184.108.40.206.3), and the "extra" toe bones were tiny. Nearly complete skeletons of these animals have been found curled up - a possible reaction to conserve heat, indicating possible endothermy? Adults and juveniles have been found together, possibly a sign of parental care. The specialization of the lumbar area (e.g. reduction of ribs) is indicative of the presence of a diaphragm, needed for higher O2 intake and homeothermy. NOTE on hearing: The eardrum had developed in the only place available for it -- the lower jaw, right near the jaw hinge, supported by a wide prong (reflected lamina) of the angular bone. These animals could now hear airborne sound, transmitted through the eardrum to two small lower jaw bones, the articular and the quadrate, which contacted the stapes in the skull, which contacted the cochlea. Rather a roundabout system and sensitive to low-frequency sound only, but better than no eardrum at all! Cynodonts developed quite loose quadrates and articulars that could vibrate freely for sound transmittal while still functioning as a jaw joint, strengthened by the mammalian jaw joint right next to it. All early mammals from the Lower Jurassic have this low-frequency ear and a double jaw joint. By the middle Jurassic, mammals lost the reptilian joint (though it still occurs briefly in embryos) and the two bones moved into the nearby middle ear, became smaller, and became much more sensitive to high-frequency sounds.
Probelesodon (mid-Triassic; South America) -- Fenestra very large, still separate from eyesocket (with postorbital bar). Secondary palate longer, but still not complete. Teeth double-rooted, as in mammals. Nares separated. Second jaw joint stronger. Lumbar ribs totally lost; thoracic ribs more mammalian, vertebral connections very mammalian. Hip & femur more mammalian.
Sinoconodon (early Jurassic, 208 Ma) -- The next known very ancient proto-mammal. Eyesocket fully mammalian now (closed medial wall). Hindbrain expanded. Permanent cheekteeth, like mammals, but the other teeth were still replaced several times. Mammalian jaw joint stronger, with large dentary condyle fitting into a distinct fossa on the squamosal. This final refinement of the joint automatically makes this animal a true "mammal". Reptilian jaw joint still present, though tiny.
Eozostrodon, Morganucodon, Haldanodon (early Jurassic, ~205 Ma) -- A group of early proto-mammals called "morganucodonts". The restructuring of the secondary palate and the floor of the braincase had continued, and was now very mammalian. Truly mammalian teeth: the cheek teeth were finally differentiated into simple premolars and more complex molars, and teeth were replaced only once. Triangular- cusped molars. Reversal of the previous trend toward reduced incisors, with lower incisors increasing to four. Tiny remnant of the reptilian jaw joint. Once thought to be ancestral to monotremes only, but now thought to be ancestral to all three groups of modern mammals -- monotremes, marsupials, and placentals.
Vincelestes neuquenianus (early Cretaceous, 135 Ma) -- A probably-placental mammal with some marsupial traits, known from some nice skulls. Placental-type braincase and coiled cochlea. Its intracranial arteries & veins ran in a composite monotreme/placental pattern derived from homologous extracranial vessels in the cynodonts. (Rougier et al., 1992)
Cimolestes, Procerberus, Gypsonictops (very late Cretaceous) -- Primitive North American placentals with same basic tooth pattern.
These are but a few highlights in what are several hundred examples of how the various transitions from some of the reptiles to the mammals occured. I wanted to be brief but it's difficult and still catch the major transitory examples. There are, as I said, many hundreds of examples that represent the transitions between these. They are on display in museums throughout the world for all to see for themselves, and the documentation is available at various numerous websites.
So, I really cant see how mamallian genology presents a problem for Darwinian theory. Not when the evidence is known and understood.
Now,.... Regardless of any of this, it still doesn't help us in our quest to determine the existence/nonexistence of God does it. That's a REAL tough one, and all this evolution stuff doesn't solve a thing one way or the other on that issue does it.
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