Comb Jellies Countering Notions Of Evolution?

[mcpng]

I was surfing on apologetic sites (wait, don't switch off now), when I saw something about how comb jellies are evidence against our notions of evolution. I did some minor research, and yeah apparently it's true, it is a problem with the notion of evolution. Doesn't refute it, but is a problem. Sure it can be explained by evolution, but it's a little bit of a bend.

 

Comments?

 

Link to the original place i saw it here: (apologetics site) but you can research it more elsewhere.

 

http://www.apologetics.org/COMBJELLIESATTHEBASEOFTHEEVOLUTIONARYTREE/tabid/162/Default.aspx

[Snakefoot]

"...a mysterious creature whose characteristics can only be inferred from fossils...

 

The article and its supposed "bombshell" are bullshit.

[oddbird1963]

First, the paradigm for the evolutionary process is a bush, not a tree. There can be several different lines of descent among species that branch off and then die off, leaving no descendants.

 

Secondly, this is not a problem for "evolution." The evidence in support of evolutionary theory is overwhelming.

 

This is a "problem," if that is the right word, for one portion of evolutionary theory, if indeed your article was correct. It is an issue for peer review and discussion in academic journals.

 

So, you are attributing way to much significance to the comb jelly fish. It in no way demolishes or creates a problem for the theory of evolution. There are always discoveries that cause scientists to change ideas they once held about the origins of specific species.

 

I believe the article and others like it pointed out that they can trace sponges back further than comb jellies. In other words, there were probably less complex ancestors of the comb, but there is nothing in the fossil record that has been found yet.

[skepticalme]

That link was painful to read. It has been stated that if paleontologist found fossils of a Cambrian horse that it would be very strong evidence against evolution. And that is entirely correct, fossils of a modern animal in Cambrian rock WOULD be strong evidence. Apperently the people who wrote those two articles think that such a fossil has now been found, but they actually have it completely backwards. The example they have isn't a modern animal in the Cambrian, it is a Cambrian animal that has survived to modern day with very little change. The fact that so little change has occured isn't really suprising. Sharks have been relatively unchanged for 200 million years. The oceans, deep oceans in particular, are the most stable habitats on the planet. There isn't much climate change down there. The bottom of the ocean is essentially an ecosystem in a time capsule.

 

To use an analogy, it would be like a person seeing a P-51 Mustang in an airshow then finding a picture of one from the 1940's and watching that person conclude that since the P-51 was built in the 1940's and exist today, then all planes that exist today must have been built over a 6 day period in the 1940's. That is the kind of logic that these people are using.

[Shyone]

The example they have isn't a modern animal in the Cambrian, it is a Cambrian animal that has survived to modern day with very little change.

 

This is it.

 

People who do not understand that animals that evolve do so from smaller subsets of a larger species that may undergo little change.

 

IOW, the existence of single celled animals today does not mean that more complicated animals did not evolve from single celled animals, and this is the Apologist equivalent of the statement, "If Man evolved from Monkeys, then why are there still monkeys around?"

[Petrel]

I guess this thread's a little stale now, but I'll post in it anyway. . .

 

The basis for this story was a paper published recently in Nature, entitled "Broad phylogenomic sampling improves resolution of the animal tree of life". The paper largely supports previous ideas regarding the branching of the tree of life, answers some questions previously controversial, and also proposes this controversial notion. The paper does not say that ctenophores were the first multicellular animals. It says that ctenophores are the outgroup to the sponges plus all other metazoans. The significance of this is that sponges were initially placed as the outgroup, consistent with the genetic and morphological data. The idea is that the common ancestor of sponges and all other metazoans was similarly structurally "simple" (although I hate to use that word), and the derived traits of other metazoans such as bilateral symmetry, limbs, and so forth evolved later.

 

If ctenophores are the outgroup, then that means that the common ancestor of ctenophores and all other metazoans, including sponges, must have had a more elaborate genetic toolbox than expected, and when sponges evolved they lost some of this toolbox. This is not impossible, if you look at a phylogenetic tree there are all sorts of deletions of genes from one group to another. It is, however, unexpected, just because it's not what you would think immediately is the most straightforward explanation.

 

However, the support for this outgroup was not very good, and I read at least one paper recently concluding that sponges are properly placed as the outgroup to all other metazoans. I can track this down if someone wants to see it. So this paper provided valuable information on the branchings of the metazoan phylogenetic tree, but this particular detail is probably not accurate, and will be corrected when we have more genetic data to work with.

[Shyone]

 

If ctenophores are the outgroup, then that means that the common ancestor of ctenophores and all other metazoans, including sponges, must have had a more elaborate genetic toolbox than expected, and when sponges evolved they lost some of this toolbox. This is not impossible, if you look at a phylogenetic tree there are all sorts of deletions of genes from one group to another. It is, however, unexpected, just because it's not what you would think immediately is the most straightforward explanation.

 

However, the support for this outgroup was not very good, and I read at least one paper recently concluding that sponges are properly placed as the outgroup to all other metazoans. I can track this down if someone wants to see it. So this paper provided valuable information on the branchings of the metazoan phylogenetic tree, but this particular detail is probably not accurate, and will be corrected when we have more genetic data to work with.

The "toolbox" notwithstanding, I would still expect to see more complex DNA as animals evolved. You're right that deletions occur, and that would explain a "simpler" species evolving from a more "complex" creature, but that's got to be as rare as hen's teeth (which are genetically possible).

 

Assuming a large number of deletions would be necessary, that would make it even more unlikely.

 

When "simpler" creatures evolve from more "complex" creatures, the DNA is more often silenced than deleted. DNA, and nature, are very conservative with DNA, and old modifications usually remain, but the are "turned off."

 

I may not have an accurate mental picture of the tree the article is suggesting. My comparative invertebrate anatomy course didn't even include information on genetics (in the early 1970s).

[Petrel]

In general, yes. But at the moment we're working with fragmentary genomes, so it would be hard to tell just how far the gene loss extended. There are full genomes for only a small number of organisms, and those concentrated among not just the vertebrates, but the mammals! If you want to know much about other organisms, you either have to hope someone else looked at that particular gene already or go sequence it yourself. We have two cnidarian genomes sequenced, but none completed for the sponges (although I understand one should be published soon).

 

We know that gene loss does happen, our model invertebrates are especially plagued by this, and the ancestor of the cnidarians had some genes for innate immunity which were lost in cnidarians. With more data it becomes easier to tell where genes were lost and where they were never present in the common ancestor in the first place.

 

Of course the question is moot because it appears that this conclusion was incorrect, and the phylogenetic tree branches as we'd expect.

[Shyone]

In general, yes. But at the moment we're working with fragmentary genomes, so it would be hard to tell just how far the gene loss extended. There are full genomes for only a small number of organisms, and those concentrated among not just the vertebrates, but the mammals! If you want to know much about other organisms, you either have to hope someone else looked at that particular gene already or go sequence it yourself. We have two cnidarian genomes sequenced, but none completed for the sponges (although I understand one should be published soon).

 

We know that gene loss does happen, our model invertebrates are especially plagued by this, and the ancestor of the cnidarians had some genes for innate immunity which were lost in cnidarians. With more data it becomes easier to tell where genes were lost and where they were never present in the common ancestor in the first place.

 

Of course the question is moot because it appears that this conclusion was incorrect, and the phylogenetic tree branches as we'd expect.

That is truly fascinating. One thing we don't discuss often here is the evidence for evolution. There are fewer and fewer "deniers", but they can be a stubborn lot. Genetics research has been (and will continue to be) as fruitful or even more fruitful than classical taxonomy based on morphology. Glad to have you here.