Charles Darwin

quote:
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if it were discovered that there was some reason for the design, would you reject evolution?
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My point was (a) to make you think seriously about the possibility that a reason may be discovered, as it has for so many other so-called function-less designs, (b) to make you realize that this is not really how weak this "evidence" is. If you would be perfectly willing to live with the finding of function and this would not put so much of dent in your theory (as so many other findings of function have failed to do), then its apparent lack of function cannot serve as such strong positive evidence. Your theory has too much plasticity.

Charles Darwin

I really don't know that much about linguistic evolution, so I'd prefer to not engage in that analogy. Regarding your second point, I don't know what Behe's arguments are for common descent, so I can't say why he accepts it.

RufusAtticus

Charles Darwin,

Yeah, so what? How does this support your contention that originally biology defined vestigal structures as "functionless" structures.

If you've read Wiedersheim enough to claim that it supprts you then you should know what the citation is. However, since you do not I suspect that you haven't read it, nor any of these others. I suspect that you are just parroting references you found on a creationist webpage somewhere. To copy them without attribution is academically dishonest.

Quotes in context please, that support your point.

All I see is a quote that says that "vestigial" is not the same as "functionless." It doesn't support your contention that the biological usage was changed because they were finding function is previously declared "functionless" organs.

Well then since you have claimed to have read this, how about you give us a summary of the argument of the paper.

I asked for primarary scientific literature, not secondary literature. I'd like you to expalain to this evolutionary geneticist how the molecular biology of evolution shows that variation is "preprogrammed."

I guess this handwave is your way of conceeding that you don't have a reference. If it is so well accepted, then it should be easy for you to find references from the biological literature to support your claim. Your failure to do so says much about how much support you can muster.

This is not a spontaneous process, it is an iterative process. I suspect that you are using "spontaneous" without its typical connotation of suddenness. If this is true, then this objection to evolution completely falls apart since we are well aware of nonsenient processes and natural forces that without any external input or preprogramming produce complexities.

Wounded King

Dear Ipetrich,

Arthropod smarthropod, the most interesting thing about the HOX genes from an evo/devo point of view is how massively ubiquitous, and highly conserved, they are in all the bilateria both vertebrate and invertebrate.

I admit that the homeotic mutations seen in mammalian HOX knockouts in mice are not quite as dramatic as antennapedia, but then the mammals have a lot more HOX genes to look after (four HOX clusters to drosophilas one).

My favourite evolutionary HOX example was the switch from dipteran haltere to the more 'primitive' wing structure in ultabithorax mutants.

Of course the craziest thing about the HOX cluster is its spatial and temporal colinearity, whats all that about?

TTFN,

Wounded

NottyImp

That's a nice definition - and I'd like to know (beyond personal incredulity) what your problem with it is. In the non-biological world there is enormous self-organising complexity (from snow-flakes, to galaxies, to highly complex organic molecules).

You were asked in an earlier post to develop a theory that clearly gives reasons why that complexity should be limited, and could not lead to the variety of biological species we see today. So, again, what is it CD that you think sets a limit on complexity?

lpetrich

"Charles Darwin":
Responding to my comment that homologies often arise from different development paths, you wrote:

RufusAtticus :
Unless you can provide a reference from a paper in the scientific literature, we can only assume that you are making this up.

I'm sorry to see that you are increduluous to this, frankly, non controversial fact. Sorry, I do not have a reference handy, but I shouldn't need to. Do you need a reference that the earth is round?

"Charles Darwin", that is pure snottiness. Just because it seems self-evident to you does not mean that it is equally self-evident to others.

Is this sarcasm? I don't think so. This is a discussion about evolution and you are claiming it to be a fact, and you are citing homology as a major evidence. You ought to be familiar with the evidence.

More of the same sort of snottiness.

Evolutionists routinely cite homology as powerful evidence, yet rarely deal with the fact that "homology" has been granted a special status; it is not subject to a developmental check. In fact, they sometimes are not even aware of these details.

Actually, homology has held up rather well --- and one very surprising result has been the discovery of "deep homology" -- of patterning mechanisms shared by much of the animal kingdom, and especially by arthropods and vertebrates.

Hox genes are found over much of the animal kingdom, specifying front-to-rear identity, and their order in the genome reflects their front-to-rear order in every case. Those mutant fly heads, above, show the effect of Hox-gene mutations; the antennae and mouthparts develop as if they were elsewhere on the fly's body.

The Geoffroy St. Hilaire hypothesis of dorsoventral homology states that the ventral side of annelids and arthropods is homologous to the dorsal side of vertebrates, and vice versa. This would be proposed every 20 years and then debunked for such reasons as the difficulty of imagining the homology between a ladder and a tube, the respective shapes of arthropod and vertebrate central nervous systems. However, discoveries of development-control genes have shown St. Hilaire to be right about this after all.

Muad'Dib

Sorry, I wasn't responding specifically to you, but to whoever was saying that CD may not be coming back. I should have quoted someone to avoid confusion.

Those are really cool fly heads, though!

Wounded King

I'm sure there was a genitals for mouthparts mutant as well.

Maybe CD is thinking of structures which have been considered homologous on purely morphological grounds and have later been shown to be genetically/ developmentally and really only analogous structures.

There are some strange half-caste cases of course. The fact that the PAX6 gene patterns prospective eye tissues across both the vertebrates and invertebrates despite the fact that the eyes of say an octopus and a human, to pick a well worn example, are generally only considered analogous.

It might be easier if CD were to give some of his objections to examples of homology in specific detail rather than casting his net over the whole of morphology and development.

TTFN,

Wounded

lpetrich

The Pax6 gene is involved with starting eye development; what comes later is under the control of other genes. Thus, one can induce ectopic eyes in fruit flies with mouse Pax6 -- but those eyes look like regular fruit-fly eyes rather than mouse eyes.

But this is still consistent with the proposition that the details of vertebrate and cephalopod eyes were independently invented. Their development and anatomy are different, and the closest relatives of vertebrates and cephalopods have much simpler eyes.

lpetrich

Wounded King:
My favourite evolutionary HOX example was the switch from dipteran haltere to the more 'primitive' wing structure in ultabithorax mutants.

What happens there is that the third thoraic segment develops like the second one.

Of course the craziest thing about the HOX cluster is its spatial and temporal colinearity, whats all that about?

I think that this provides clues as to how these genes originated. I haven't seen any of this in the literature; these are my speculations.

First, note that these genes have rearward dominance; the Hox gene which starts its expression the farthest back is the one which tends to dominate.

Also note that Hox genes are recognizably related.

So here's my scenario:

The ancestral Hox gene specified only behind-the-head -- generalized rearward -- identity.

It got duplicated, and the forward expression boundary got moved backward for the duplicate. This enabled the duplicate to specify more-rearward identity. However, it overlapped the original gene's expression, meaning that it had to dominate the original gene in order to work properly.

This process was repeated about 8 or so times, producing a gradient of increasing rearwardness specification.

Edited to add:

I note also that the ancestral mode of growth in arthropods, annelids, and vertebrates is to add segments at the rear end. This is consistent with my rearward-evolution scenario for Hox genes.