For similarities to be conclusive proof of common descent, you need to be able to prove that all other options aren't possible.
If we applied this same criteria to all ideas then nothing could be known for sure. I can't even prove that I woke up this morning since it is possible that the universe was poofed into being just 5 minutes ago, complete with a false history and false memories.
Proof through disproof is a very poor way of seeking knowledge, IMHO. Proof itself, in the absolute sense, is unattainable. What we can do is see if a model makes testable predictions, and then test those predictions. That is what science does. It tests models.
As to common descent v. convergence the test is in the DNA. Convergence can not produce a nested hierarchy at the DNA level for a whole genome. It is possible to do so for a couple mutations here and there, but practically impossible at the genome level. There is simply no mechanism by which a mutation in mice will cause the same mutation to occur in humans, as one example.
Dr. Adequate said earlier that convergent evolution causes only superficial ressemblance but no in depth similarities. I have a hard time accepting this idea as valid, so maybe if it could be explained in detail and how a criteria for convergent evolution can be clearly stated out of this.
A good example is the bill of the platypus and the bill of the duck. These two features do resemble each other superficially, but what happens when we look at the details? It turns out that the two bills are quite different:
1. lower jaw is made up of three bones as in other birds. 2. bill is covered by horn. 3. Nares are near the base of the bill. 4. upper jaw is made of solid bone.
1. lower jaw is made up of a single dentary bone as in other mammals. 2. bill is covered in skin. 3. Nares are near the end of the bill. 4. Upper jaw has a split palate.
Here is a picture of the two skeletal structures:
If all you saw was the skeletal structure you would never suggest that they were anything alike, or at least I wouldn't.
Exactly the point I wanted to make. It would be impossible to disprove every other option to explain the similarities. I was just saying that if you wanted to use similarities as sufficient proof for common descent, this would have to be done.
You didn't get my point. "Sufficient proof" is an oxymoron in the same way that "partial vacuum" is an oxymoron. Either you have absolute proof or you don't. There is no halfway point.
However, we can have evidence. In the case of common ancestry, transitional fossils are evidence, quite compelling evidence IMO. More importantly, it is the pattern of homology in transitionals which evidences common ancestry.
That pattern is a nested hierarchy. This is what makes the theory of evolution a testable model. The theory predicts that there were species with a mixture of non-avian dinosaur features and avian features. The theory also predicts that there were NOT species with a mixture of mammalian and avian features. This allows us to see if fossils fit the predictions or not. They do fit the predictions. Therefore, the theory of evolution is a well evidenced theory.
So you would agree that convergent evolution will only provide superficial similarities, never in depth ones ?
Not always, no. It can be difficult to discern some adaptations as either due to common ancestry or convergent evolution.
I agree this would be expected. However, recently I came across a counter-example where convergent evolution had caused the similarities to be right down to the molecular level. It is about the sonars of bats and dolphins which acquired the same DNA for this characteristics through convergent evolution:
You will notice that I did say this:
"It is possible to do so for a couple mutations here and there, but practically impossible at the genome level."
It is the whole genome comparison between bats and cetaceans which indicates convergent evolution. A good test would be to compare the introns between the prestin genes in both bats and cetaceans.
I disagree. You have 'proof beyond reasonable doubt'. In other words, some things can be proven to a point where any doubt you can have will be unreasonable, illogical. This isn't absolute proof, but it isn't no proof at all either.
Even you seem to reject this idea, as evidenced by this statement:
"I'm afraid I don't find transitional fossils to be compelling evidence at all."
That is unreasonable and illogical. Using your analogy to a court case, it is equivalent to saying "I don't find fingerprint evidence all that compelling". Even worse, this unreasonable doubt is used to cast further doubt on the DNA evidence. "Since I reject the fingerprint evidence all you are left with is the DNA evidence which is just one small piece of evidence, so I reject that as well."
Isn't the coding of a complete structure as complex as a sonar more then just 'a couple of mutations here and there' and is in fact at the genome level.
Yes, it is at the genome level. However, the example you gave was for a single gene, not the whole genome.
Yeah sorry, I misexpressed myself in that sentence. I wanted to say that I don't find the current actual transitional fossils to be compelling, not the general concept of transitional fossils.
What reasonable and logical justification can you give for this position? Staying with the OP, can you justify your reasoning for rejecting multiple half-dinosaur/half-bird fossils as evidence of an evolutionary transition between dinos and birds?
So we have gone from "fingerprints are not compelling evidence" to "what fingerprints?".
Is that how a court of law works? Proof beyond a reasonable doubt once you have ignored the evidence?
The fact of the matter is that there are fossils with dinosaur characteristics not found in any living bird. These same fossils have avian features not found in other dinosaurs. How is this not half dino/half bird?
And I have already mentioned that birds appear before their supposed ancestors in the fossil record, and probably before the vast majority of the supposed transitional fossils.
No one has named the ancestral species of all birds.
Add to that the fact that there are a lot of fake dinosaur-bird fossils out there coming from china as per Alan Feduccia, and it seems that me skeptical is a justified and rational position.
In a court of law can the defending attorney cite a single incident of evidence tampering in a separate case to throw out all evidence?
"Your honor, someone planted John Smith's fingerprints at the scene of the crime in 1945, so surely the fingerprint evidence against my client in 2010 should be dropped."
But in the case of fossils, you have either dinosaurs with feathers, but aside from that are completely dinosaurs.
Modern birds are classified as dinosaurs and are complete dinosaurs, so I really don't see your point. The fact of the matter is that fossils like Archaeopteryx have a mixture of non-avian dinosaur features and modern bird features. Can you please tell us why this is not a transitional fossil? What criteria are you using to determine if a fossil is transitional or not?
If birds are just dinosaur, how can anything be transitional between dinosaurs and birds ?
Obviously, we are talking about a transition between non-avian dinosaurs and avian dinosaurs.
Obviously, there are features that distinguish birds from their dinosaur ancestors. These are the ones that have to be shown transitional.
And that is exactly what we have in these transitionals. Archaeopteryx has teeth and a long tail which are non-avian dinosaur traits.
Non-avian dinosaur traits in Archaeopteryx: 1. Premaxilla and maxilla are not horn-covered (i.e. no beak). 2. Trunk region vertebra are free. In birds they are fused. 3. Cerebral hemispheres elongate, slender and cerebellum is situated behind the mid-brain and doesn't overlap it from behind or press down on it. In birds the cerebral hemispheres are stout, cerebellum is so much enlarged that it spreads forwards over the mid-brain and compresses it downwards. 4. Neck attaches to skull from the rear as in dinosaurs not from below as in modern birds. 5. Center of cervical vertebrae have simple concave articular facets. In birds the vertebrae are different, they have a saddle-shaped surface. 6. Long bony tail with many free vertebrae up to tip (no pygostyle). 7. Premaxilla and maxilla bones bear teeth. 8. Ribs slender, without joints or uncinate processes and do not articulate with the sternum. Birds have stout ribs with uncinate processes (braces between them) and articulate with the sternum. 9. Pelvic girdle and femur joint is archosaurian rather than avian (except for the backward pointing pubis as mentioned above). 10. The Sacrum (the vertebrae developed for the attachment of pelvic girdle) occupies 6 vertebra. The bird sacrum covers between 11-23 vertebrae. 11. Metacarpals (hand) free (except 3rd metacarpal), wrist hand joint flexible. In birds the metacarpals are fused together with the distal carpals in the carpo-metacarpus, wrist /hand fused. 12. Nasal opening far forward, separated from the eye by a large preorbital fenestra (hole). Where a fenestra is present in birds, it is always greatly reduced, and is involved in prokinesis (movement of the beak). 13. Deltoid ridge of the humerus faces anteriorly as do the radial and ulnar condyles. Typical of reptiles but not found in birds. 14. Claws on 3 unfused digits. 15. The fibula is equal in length to the tibia in the leg. This again is a typical character of reptiles. In birds the fibula is shortened and reduced. 16. Metatarsals (foot bones) free. In birds these are fused to form the tarsometatarsus. 17. Gastralia present. Gastralia are "ventral ribs," elements of dermal bone in the ventral wall of the abdomen. Typical of reptiles, they are absent in birds.
I should have better expressed myself. What I mean is that if the fakes are well made enough to fool the paleontologists who examine it into thinking they are real and go up to the publishing.
Which paleontologists were fooled? In which scientific peer reviewed journal was this fossil presented as a real fossil? From what I have read National Geographic (not a peer reviewed scientific journal) presented this fossil without first checking with knowledgable paleontologists. In fact, Storrs L. Olson strongly criticized Nat Geo for publishing the article without it first going through peer review:
quote:Writing in Backbone, the newsletter of his museum, he denounced the publication of a scientific name in a popular journal, without peer review, as a "nightmare". http://en.wikipedia.org/wiki/Archaeoraptor
The only solution is that the publishers require CT scans on every fossil coming from china before publishing it.
The solution appears to be letting real paleontologists take a look at the fossil before letting art directors write stories about it.