How do we know that homologous structures really do support evolution?

In message 142 of What happens after death for an atheist?, LDSdude references several examples of things that many consider to be evidences for evolution, but turns them around, saying that they are evidence for a divine creator. For example: It is conceivable that a supreme being who was in the process of creating all the organisms of the world would use the same basic structures over and over again, since this would probably be easier than redesigning the wheel every time he wanted to make something new. Studies of anatomy support the common sense assertion that related organisms do have similar anatomy — for example, the arms of humans, the wings of bats, and the fins of whales all have similar bones in similar configurations.Those in support of evolution might suggest that this is evidence of common descent. I believe that this assertion is supported by the fossil record, and that animals which are presently lumped together in taxonomic groups are related through common ancestors rather than through design by the same creator. I will give an example:The fossil record supports the evolution of whales and other sea mammals from mammals which lived on land. One can start with Pakicetus, a mammal similar to today’s wolves, but with a longer snout. This animal lived about 52 million years ago, and was adapted for life near water, with ears adapted to hear underwater and a strong tail, which may have been helpful while swimming. Its feet were similar to those of other animals which are adapted to running.Pakicetus fossils have been found in Pakistan. Later fossils that evolved from Pakicetus were also found in this area. Ambulocetus was a crocodile-like mammal which lived in shallow water in what is now Pakistan. It lived about 49 million years ago, and can be linked to Pakicetus by its ear bones, teeth, and other aspects of anatomy. These were succeeded by the Rodhocetus, animals living 45 million years ago. Another discovery in Pakistan, these had the characteristic ear bones and teeth, but with reduced hind limbs and a closer resemblance to modern whales in terms of its fin anatomy. It still had the ankles of an animal like the Pakicetus, however, linking it to them. Later fossils include Basilosaurus, found in many places throughout the world, which had even more reduced hind limbs, as well as most of the characteristics of modern whales.Modern whales have larger brains and more developed organs for sound than did Basilosaurus. These allow them to have more complex social structures. Their hind limbs are reduced almost to nonexistence.It is easy to see here that the anatomy of fossils supports the story of land animals which lived in one part of the world changing over time to later become a group which spread all over the oceans. It is important to note that animals with body types most different from their most modern descendants appear to be older than the ones which are more similar to modern whales.The biogeography and fossil record of whale evolution does not support the concept of a creator that did not use evolution to create these animals. If that were the case, it would be likely that Ambulocetus and Pakicetus, for example, might live in different parts of the world at the same time, without evidence that one lived millions of years prior to the other. Though reasonable it may be for the creator to use similar body plans, I see no reason for him to include similarities that obviously hide his work such as the similarities between the feet of Pakicetus and Rodhocetus.

Thread moved here from the Proposed New Topics forum.

Talkorigins has an article on homologous structures that I thought was awesome. Its point was that homologous structures might argue for common design, but homologous errors argue against it. I remember one of his examples was the damaged vitamin C gene that is in apes and humans. It's understandable that the Creator (and I'm a believer) would design similar structures in two different species, but why similar errors? That doesn't make any sense at all.You add to that argument quite well with your post.

Thanks, that is an excellent point.

Hi Gary,I'm not sure that "homologous structures support evolution" but rather that the hypothesis of evolution best explains the existence of homology. Neither creationists nor evolutionary biologists doubt that homology exists. But it's clear that the origin of species by direct descent best explains the homologous traits that exist in nature.As I see it, the creationist hypothesis can account for the existence of homology in some functional traits (i.e our human hemoglobin gene looks similar to the hemoglobin gene of the rat because it does the same job, so it has to have a similar structure). But the creationist argument fails to account for non-functional homology. Truthlover gave an example with the origin of errors. There are plenty of other examples.The fact that SINEs and LINEs appear in mammalian genomes in a characteristic distribution that exactly fits the hypothesis of mammalian evolution that we get from DNA phylogenies and morphological taxonomies can be explained by evolution but not by creationism. SINEs and LINEs exhibit an epidemiological distribution pattern that is perfectly explained by evolutionary theory. But no creationist can explain the epidemiological nature of these characters. How could one species "infect" another with its repetitive elements unless by direct descent? Other non-functional homologies include silent site mutations - that is mutations in DNA sequences that do not make any difference whatsoever to the amino acid structure of the coded protein. Creationists can give no answer to why these silent mutations should be distributed through animals exactly as our existing theories of taxonomy and phylogeny would predict.Mick

yes it is!If however there was an infinite symmetric basis we do not apprehend but might be able to enumerate further it might be that two errors in different species could find a common gene survival genically through a niche IF (the big iffff) the two errors make inverted divisions in the populations' geneotypes and phenotypes.It seems that historically it was an issue that creationists never thought of why organons' life might be poorly designed but this thread takes that history to a future we can but dimly recognize.

Christian theology predicts serious "errors" along with astounding beauty and design. The error is due to the corruption that the whole earth is subordinated to.It is sort of absurd for evolutionists to continually ignore this element in pretending seeming "flaws" are arguments against a Creator.In fact, the same thing could be argued against common descent, that with such vast amounts of time envisioned by evolutionists, that we should expect more perfect designs due to the amount of time for evolution to work.

The point seems to have just sailed clear over your head. This isn't Darwin's Terrier's argument from bad design.The existence of flaws is not being put forward as any sort of argument against creation, what is being pointed out is that the patterns of errors/flaws that we see correspond remarkably well to the already independently derived phylogenies.The point isn't that these flaws couldn't be due to 'the fall', or whatever, but that if they are they show a remarkable pattern of consistency which suggests that whatever directed the corruption of the whole Earth did so in such a manner as to carefully reflect the elements of common design already apparent in creation which have subsequently so mislead biologists to assume common descent. Its not impossible, especially if God is micro-managing the ongoing corruption to ensure consistency, but why on Earth is it needed? Not if you actually understood evolutionary theory. Perhaps if we had had a consistent, effectively stationary, environment for a billion years or so we might find some lifeform which was optimised for that environment and which couldn't be outcompeted by any other lifeform, but I'd suspect that even then you would be more likely to find a thriving ecology which would continue to drive evolution by its own internal dynamics.All we can say really is that, as S.J. Gould observed, starting off from very simple organisms, i.e. unicells, we can expect evolution's random walk to gradually take certain elements of life into avenues of increased complexity, at least in terms of cellular number and integration.TTFN,WKThis message has been edited by Wounded King, 07-11-2005 05:38 AM

It's about correlations rather than just errors. the correlations of errors with common descent and the absence of errors that don't correlate.Thus the vitamin C error correlates between humans and chimps but there is no similar error between humans and ostriches (that isn't overlaid with changes in both lineages since their common ancestry).

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I don't see that at all. That's the claim of evolutionists, but at the same time, there seems to often be a refusal to properly assess the data, at least from my perspective, and without certain basic questions answered, I don't see how anyone can make that claim.For example, and these are just some questions that ought to be fully answered before concluding anything on the data:Were the flaws genuinely ignored when creating phylogenies? (The claim of independent phylogenies is dubious, imo, unless you are perhaps talking of molecular "flaws", and then we need to delve more into what causes those flaws.To what degree are mutations random, non-random, etc,...?Are mutations and flaws, for species with certain similarities, more likely for those species, and thus common flaws can arise independently and not be the result of those traits being passed on by a common ancestor?What are the limits of convergent evolution? Is it reasonable to expect that convergent evolution can be responsible for the ear bones independently evolving? What about DNA code?Can non-coding DNA exhibit convergent properties? To what degree, and what are the mechanisms of that?Same for coding DNA?Are there predispositions towards the same flaws in DNA?Note: If similar traits arise that are considered highly unlikely to have arisen via common ancestry, evolutionists do not consider that a falsification of common descent, but that is simply assigned to convergent evolution. However, if convergent evolution is a plausible explanation for common traits, then assuming common descent because it seems more likely for evolutionists is, once again, using a basic assumption to argue for the basic assumption, and is, imo, circular reasoning.It is not surprising when such circular reasoning is applied across the board that the results would be in line with it.

Did you even read any of the thread before regurgitating your usual bugbears? These are quite explicitly molecular level 'flaws', i.e. chromosomal fusions/breaks and retroviral insertions. I think you are making a point here that is hard to discern. Could you differentiate between common ancestry and common descent. I assume by common ancestry you mean parallel evolution, where the same trait occurs through a similar pathway in two now distinct lineages which nevertheless had a relatively recent common ancestor, recent enough to arguably give them a specific predisposition to that particular mechanism of origin for that trait. In contrast we would have convergent evolution where a functionally equivalent/identical trait arises in two highly unrelated lineages. And in the final case, common descent, the trait would be shared because it arose in a shared ancestral organism. You haven't shown any circular reasoning, just asked a lot of vague questions. A number of these question are already in the process of being investigated, as you might know had you ever actually tried to familiarise yourself with the relevant literature. I would recommend you to look at the literature on mutational hotsposts.TTFN,WK

No. I'll explain. If one accepts evolution, then traits cannot arise totally independently since the evolutionist position is that a priori all living things are interdependent and share a common ancestor.So I use the phrase shared traits from a common ancestor to be precise, meaning that it's clear that the trait appeared independently of being passed on, at least morphologically, from a common ancestor.On the face of it, this would seem to falsify evolution, but evolutionists have proposed that such independent appearance of similar traits is the result of convergent or parallel evolution. I am not aware of a distinction between convergent and parallel evolution. I am interested in the concept of a specific predisposition across species towards similar traits and think until we understand that very, very well, we cannot safely draw conclusions based on evolutionary models of what the data actually means. I just see that as a broader range of parallel and convergent evolution, or proposed convergent evolution. That's what I mean when I refer to common ancestry or common descent. I am aware that these basic and not at all vague questions have not been answered, but are in the investigative stage, which is why I repeatedly bring that up.Heck, if you cannot even define how and to what degree mutations are random and non-random, then you cannot possibly make such dogmatic claims as evolutionists do about the preponderance of the evidence.The basic questions I keep bringing up are the questions that need to be answered to understand things like how we should properly treat the data, which assumptions are correct, etc,...I am glad there is some research into these issues. Maybe when we have a better understanding and more comprehensive assessment, soem more assertive claims could be appropiate. They certainly are not appropiate at present.

How can you possibly evaluate how appropriate the claims are when you are unfamiliar with the research into the very issues you claim are of key importance.TTFN,WK

Hi randman, This is just plain wrong. Vertebrate wings evolved in various lineages completely independently. The ancestral vertebrate did not have wings. But birds and bats both evolved wings, without inheriting them from a common ancestor. Accepting evolution does not entail "that traits cannot arise totally independently". You're wrong - see above. That predisposition - or, more accurately, disposition - is imposed by the environment. For example, the long proboscis of the honey bee and the long beak of the humming bird. There was no "predisposition" towards having a long face. But there was a "disposition" imposed by the structure of flowers. You have asked a good question and it's the basis of adaptationist behavioral ecology.Mick

I don't see why it is that important that we understand which mutations are and aren't random. Some mutations tend to be more likely to get filtered out of the gene pool, which is why ubiquitin, a small protein involved in removal of misfolded proteins, has stayed almost the same in a wide variety of organisms. Because it is so small, modifying it doesn't often make it more efficient, but rather causes it to not work at all. Does the probability of a mutation in ubiquitin's gene sequence affect whether or not such a mutation would result in nonviable offspring?If ubiquitin's sequence was more or less likely to change than other genes, that likelihood wouldn't affect much, since most mutations to it cause the organism to die.