Hello, jbuchanan, and welcome to EvC.
quote:
They then go on and say they know its true because DNA analysis and morphological comparisons demonstrate it.
Actually, "they" know that common descent is true because of all the evidence that supports it.
Evidence, by the way, that
must exist if evolution were true and, if the evidence were different, would show that evolution was false. And evidence that cannot be explained without evolution.
One example of evidence, as you point out, comes from morphological comparisons. By carefully comparing the different species, we know that they can be categorized within a
nested hierarchical scheme. It is obvious that if the theory of common descent were true, we should be able to see such a nested hierarchical scheme; in fact, if we didn't see such a pattern, that would be a serious blow against the theory of evolution. On the other hand, there is no reason to presuppose that a creator would simply created species according to such a pattern.
Now the reason that we think that humans and chimpanzees share a common ancestor is that they sit near each other on the "tree of life". If the tree of life indicates phylogenic relationship (and why else would there be a "tree of life"?) then this indicates that humans and chimpanzees share a recent common ancestor.
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quote:
As far as human evolution is concerned, I have yet to be shown a sufficient mechanism whereby an apelike creature can turn into something like a human.
That's fine. But the evidence suggests very strongly that humans did, in fact, evolve from a common ancestor. That much is certain. We may even call it a fact. What could the mechanism be? Well, the only current theory is that it occurred through natural selection acting on randomly occurring variations. This is because we have actually observed natural selection act in some cases, and so it is a known mechanism. Furthermore, we do not know of anything that would prevent natural selection to produce humans from an apelike creature. And all other mechanisms that have been proposed have been shown to be false.
So where does the inheritable variation on which natural selection acts come from? That, too, is a good question. So far, from what we know about heredity, is that the nuclear chromosomes in our cells are the material through which physical traits occur. Furthermore, we know that the duplication of genetic material that occurs to produce offspring is not perfect; differences occur, differences which cause variations in physical features. So it is logical to deduce that these genetic mutations are the cause of variations in inheritable features.
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So it is possible that the evolution of humans from earlier ape ancestors (which undoubtably did occur, according to the evidence) proceeded through a different mechanism. We currently have someone on another thread trying to resurrect the old idea of orthogenesis, for example. However, the currently accepted model of natural selection on variations in features produced by chromosomes seems to work, and we don't have any other potentially workable models.
Edited by Chiroptera, : Added clause to penultimate sentence in second paragraph.
Actually, if their god makes better pancakes, I'm totally switching sides. --
Charley the Australopithecine
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