Is convergent evolution evidence against common descent?

Randman, since this sort of follows up a discussion we started elsewhere, I would like to start of with my post from the previous thread. I think it will provide the first step in answering your questions. Again, my intent is to figure out exactly on what we can agree and disagree and then find a way to tie it back into looking at DNA evidence and relatedness of species:

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Alright, so first we have to establish a way to actually get at true closest relations without the use of DNA sequencing and without convergent evolution getting in the way.

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Fortunately, the cladistic system was established before the advent of DNA sequencing, so we actually have such a system. Classic cladistics looks for similarities and differences in organisms in order to determine how closely they are related. They might not always get things completely right, but they certainly can get close.

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And the idea is to not only look for general morphological markers: i.e. has wings, does not have wings or lives in water vs. does not live in water, since these physical attributes can easily be the cause of thhe animal living in water or in the air.

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So, we examine as many external and internal markers as possible. With this data, independent of any DNA analysis we come to the conclusion that humans and chimps are very similar. And even though we are different from a mouse, we do share a number of characteristics: we give birth to live young, we nurse them, we have four limbs, we have a jaw, a cranium, skeleton, ... Using these methods we also find that dolphins, even though they live in the water are more closely related to other mammals than to fish. For example dolphins have flippers (bones covered with skin) while fish do not, dolphins have lungs like mammals, not gills like fish, dolphins give birth to live young and nurse, fish do not, and the list is endless. So, using this system we can find that all mammals seem to be closely related. Interestingly, there is a group of animals that has a placenta like mammals, but differs in a number of other ways: the marsupials. Using similar characteristics, we can determine that marsupials are related to mammals, but it appears that marsupials are more closely related in their group while mammals are more closely related within their group. I.e. a kangoroo is more closely related to a wombat than to a cow or a mouse is more closely related to a cow than to an wallaby.

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Can we agree on this so far?

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Edit: Alright, I gotta run. Please, give this a good read and think about it. If you have questions, you can check out cladistics on the web and see if it makes sense to you. Also, if you don't agree, be specific, does the dolphin vs fish/mammals make no sense or does the mammals/marsupials make no sense, ... and if it does not make sense, exactly what causes it to make no sense. I will get back to you on this. But if it does make sense, then I will take it from there a little later tonight or tomorrow. Cheers.

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