Creation vs. Evolution

[H2Andy]

I had thought that the dino to bird issue had been discounted. From everything that I have read archaeopteryx was only a bird, but perhaps I am wrong. Could you provide your source?

"the evidence is overwhelmingly in favor of birds being the descendants of a maniraptoran dinosaur, probably something similar (but not identical) to a small dromaeosaur."

http://www.ucmp.berkeley.edu/diapsids/avians.html


"A particulary important and still contentious discovery is Archaeopteryx lithographica, found in the Jurassic Solnhofen Limestone of southern Germany, which is marked by rare but exceptionally well preserved fossils. Archaeopteryx is considered by many to be the first bird, being of about 150 million years of age. It is actually intermediate between the birds that we see flying around in our backyards and the predatory dinosaurs like Deinonychus. In fact, one skeleton of Archaeopteryx that had poorly preserved feathers was originally described as a skeleton of a small bipedal dinosaur, Compsognathus. A total of seven specimens of the bird are known at this time.

It has long been accepted that Archaeopteryx was a transitional form between birds and reptiles, and that it is the earliest known bird. Lately, scientists have realized that it bears even more resemblance to its ancestors, the Maniraptora, than to modern birds; providing a strong phylogenetic link between the two groups. It is one of the most important fossils ever discovered.

Unlike all living birds, Archaeopteryx had a full set of teeth, a rather flat sternum ("breastbone"), a long, bony tail, gastralia ("belly ribs"), and three claws on the wing which could have still been used to grasp prey (or maybe trees). However, its feathers, wings, furcula ("wishbone") and reduced fingers are all characteristics of modern birds.

http://www.ucmp.berkeley.edu/diapsids/birds/archaeopteryx.html

 

[sandjeep]

H2Andy said

"the evidence is overwhelmingly in favor of birds being the descendants of a maniraptoran dinosaur, probably something similar (but not identical) to a small dromaeosaur."

Contentious is an understatement, but thanks for posting your source. There is actually two schools of thought currently in the scientific community. One is, as you have said, it's a transitional link. The second is that it is a bird, and that is from highly regarded scientists like Alan Feduccia. He is an evolutionist as well, so no argument with him concerning ToE as a whole. He just discounts this Archaeopteryx as being the smoking gun. Feduccia's bio is on the Chapel Hill NC site.

 

[sandjeep]

It is especially unsatisfying to attempt a discussion of the metaphysical with a monkey.

They are most likely to just fling feces at you, grin and hoot wildly.

Classic!!, I hope you don't mind if I use this quote

 

[H2Andy]

There are currentlly two schools of thought currently in the scientific community. One is, as you have said, it's a transitional link. The second is that it is a bird, and that is from highly regarded scientists like Alan Feduccia.

Feduccia states that birds descended from dinosaurs; he just thinks they descended from a different kind of dinosaur (thecodonts as opposed to theropods, both subsets of archosauria)

there's almost always going to be competing views as to almost any scientific idea out there. that's part of the scientific process, and one of its great strengths: it is constantly challenged from within.

while respected for other work with birds, Feduccia does not represent the majority view when it comes to bird origins. His views are certainly those of the minority.

right now, the majority of scientists believe the evidence indicates what i quoted above

there is no issue as to whether birds descended from dinosaurs (i'm just repeating for emphasis). Creationists love to misquote Feduccia on this point. or, more accurately, to quote him out of context.

this is the quote:

"It is biophysically impossible to evolve flight from such large bipeds with foreshortened limbs and heavy, balancing tails" (because as noted by the writer of the article, that is exactly the wrong anatomy for flight). Feduccia stated, "In my opinion, the theropod origin of birds will be the greatest embarrassment of paleontology in the 20th century."

what they don't quote is when he goes on to make a case for the thecodont origin of birds. thecodonts, let's remember, are a different kind of dinosaur.

and, again, both thecodonts and theropods are groups of archosauria, a subclass of reptilia

so the argument is whether birds came from this dinosaur over here, or from that, rather similar dinosaur over there ... gee...

 

[Thalassamania]

There are those of us who put the birds in the Dinosauria.

 

[H2Andy]

well, theropods are within dinosauria

so a theropod origin of birds is a dinosauria origin of birds

(as best as an amateur can understand this stuff)

 

[Thalassamania]

I'm comforted by the idea that the dinos are still with us<G>.

 

[MikeFerrara]

there were three values being compared, of which SCI was one (stratigraphic consistency index). when compared to the other two indexes, SCI is consistent with what the other two show.

an SCI mean of .551 does not mean that it is right 50% of the time. it has nothing to do with that. it's not a prediction tool. it's an internal measurement to the index.

it means that, on average over the years, the SCI levels of consistency is .551, and it holds close to there from the eldest fossils to the younger fossils

meaning that the fossil record is fairly stable over the years, and we have a good picture of the older fossils

(he was arguing against the notion that the older fossils don't give a good picture of what was happening then)

I guess I got what he was trying to show. From the article...

Here we show that new assessment methods, in which the order of fossils in the rocks (stratigraphy) is compared with the order inherent in evolutionary trees (phylogeny), provide a more convincing analytical tool: stratigraphy and phylogeny offer independent data on history....

AND...

SCI is the ratio of consistent to inconsistent nodes in a cladogram.

A range of 0.493 - 0.618 may show that the percentage of consistant nodes doesn't vary much with age of the fossils but it doesn't look like the percentage of consistant nodes is very high at any point.

 

[MikeFerrara]

My last post continued sort of...

In regard to genetic sequencing. Is this a reasonable (though partial) explanaition of how DNA sequencing is used?

From http://www.talkorigins.org/faqs/faq-intro-to-biology.html

The degree of similarity in nucleotide sequence is a function of divergence time. If two populations had recently separated, few differences would have built up between them. If they separated long ago, each population would have evolved numerous differences from their common ancestor (and each other). The degree of similarity would also be a function of silent versus replacement sites. Li and Graur, in their molecular evolution text, give the rates of evolution for silent vs. replacement rates. The rates were estimated from sequence comparisons of 30 genes from humans and rodents, which diverged about 80 million years ago. Silent sites evolved at an average rate of 4.61 nucleotide substitution per 109 years. Replacement sites evolved much slower at an average rate of 0.85 nucleotide substitutions per 109 years.

It appears that sequencing data is calibrated or scaled (in regard to time) based on assumptions originally infered from the fossil record in order to infer time lapsed since diversion. Genetic difference is what is measured.

This assumes, rather than establishes, that there was a common ascestor and that there ever was ever a divergence in the first place. Going back to the study that we've been discussing I'm not sure that we can really consider DNA sequencing as being independant of stratigraphy with regard to a "time lapsed since diversion" estimation.

From a "measurement system analysis" point of view (for 17 years that was my field) some of the problems here seem pretty clear. Unfortunately I have to be off-line for a couple of days (work stuff) but when I get back I'd like to go further into this. I'd also like to bring fossil dating methods into this. Due to the number of methods being used, I'm not sure how easy that will be so I might hold off on that.

 

[H2Andy]

This assumes, rather than establishes, that there was a common ascestor and that there ever was ever a divergence in the first place.

the genetic data does in fact show splits in species over time. the greater the time since it happened, the greater the divergence

it is in fact a test of evolution.

how?

1. evolution says all beings come from the same organism, but change over time.

2. does the genetic data show that?

3. yes. it shows that "more different" beings, such as humans and rats have widely varying DNA, while "less different" beings, such as apes and humans have much closer DNA (about 96% in common, perhaps as high as 98.5%)

if evolution were not true, you would have no such patterns.

thus, DNA could have killed evolution if the results had come out different. they did not. DNA tells us (again) that evolution is real, and it confirms the "eyeball" approach (clearly, apes and humans are alike; humans and roaches are not) and the
fossil approach (before we get to humans, we have a long sequence of more-and-more human-like beings until finally human beings appear)

I'm not sure that we can really consider DNA sequencing as being independant of stratigraphy with regard to a "time lapsed since diversion" estimation.

but it is independent. basically, you can see from the DNA analysis that rats and human DNA are WIDELY DIVERGENT. then you look at the DNA of humans and apes and they are VERY CLOSE TO EACH OTHER.

so you can calibrate the "time" from well established divergences in the fossil record. rats and humans diverged 80 million years ago (a lot more than the 5 million between humans and apes) so that was used for a calibration. now they have a good picture of how time = DNA variance. that's all they did.

then you test that on other known "splits" to see if it works, and what do you know?
it does work.

as a result of the DNA testing, changes had to be made to some of the accepted taxonomy and classifications. but it just so happens that it gives a darn close picture to what was there before. again, it confirms what we knew.

under any circumstances, evidence that is confirmed by taxonomy, the fossil record, and independent DNA testing is pretty darn good.

in this case, it is also subject to peer review and quite lively intellectual debate.

the data stands. evolution works.