Dual Ancestry & Avian Evolution

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darkriddle

darkriddle

Lord Lucien
The movie critic?

King Kandy
If this were the case, it surely would be born out in genetic evidence? We would see two distinct genetic lineages between birds of one line and birds of the other, much like how the Aardvark and Anteater resemble each other, but are genetically distinct.

dadudemon
Originally posted by King Kandy
If this were the case, it surely would be born out in genetic evidence? We would see two distinct genetic lineages between birds of one line and birds of the other, much like how the Aardvark and Anteater resemble each other, but are genetically distinct.


Quite unfortunately, it is not that simple.


The lineages could completely blend and there is literally no evidence, genetically, of a "dual" ancestry.



This can happen in just a few thousand years. We discovered this because some "Germanic" people mixed with some existing European people. They brought tools and methods "north" but the genetic makeup of the modern people does not account for them, at all: it is literally indistinguishable.


We know they mixed because the artifacts and influence are there. We just don't see the genetic evidnce because they blended into "oblivion" into the natives.



If such a problem can occur in a few thousand years, imagine what tens of millions of years can do to a blended ancestry.


We would need to find fossils that occurred shortly after the "blending" occurred. It would have to be so specific (less than a few thousand years) that it is far more likely to be impossible to discover (if any fossils remained from that blending, to begin with) than it is to validate the hypothesis. This does not mean we should not look, however. This also does not mean that there is "blind blending" going on: there could still be some evidence for dual ancestry.


However, we would need genetic evidence from both "ancestors" and then look for those markers in the progeny. Is it possible to do that? Sure...but very unlikely to find anything to support or deny the position...as far as nucleotide sequences are concerned. It is far worse than finding a needle in a haystack.

Omega Vision
Originally posted by dadudemon
Quite unfortunately, it is not that simple.


The lineages could completely blend and there is literally no evidence, genetically, of a "dual" ancestry.



This can happen in just a few thousand years. We discovered this because some "Germanic" people mixed with some existing European people. They brought tools and methods "north" but the genetic makeup of the modern people does not account for them, at all: it is literally indistinguishable.


We know they mixed because the artifacts and influence are there. We just don't see the genetic evidnce because they blended into "oblivion" into the natives.



If such a problem can occur in a few thousand years, imagine what tens of millions of years can do to a blended ancestry.


We would need to find fossils that occurred shortly after the "blending" occurred. It would have to be so specific (less than a few thousand years) that it is far more likely to be impossible to discover (if any fossils remained from that blending, to begin with) than it is to validate the hypothesis. This does not mean we should not look, however. This also does not mean that there is "blind blending" going on: there could still be some evidence for dual ancestry.


However, we would need genetic evidence from both "ancestors" and then look for those markers in the progeny. Is it possible to do that? Sure...but very unlikely to find anything to support or deny the position...as far as nucleotide sequences are concerned. It is far worse than finding a needle in a haystack.
I'll be the first to admit that I have no formal background in science and am little better than the average person in regards to my knowledge therein, but it seems to me like you're using an example of differences between two groups within the same species to forward an argument regarding differences/similarities between separate species or even larger taxonomic groups.

Again, not any kind of expert, but that seems like a logical stretch/imperfect analogy to me.

dadudemon
Originally posted by Omega Vision
I'll be the first to admit that I have no formal background in science and am little better than the average person in regards to my knowledge therein, but it seems to me like you're using an example of differences between two groups within the same species to forward an argument regarding differences/similarities between separate species or even larger taxonomic groups.

Again, not any kind of expert, but that seems like a logical stretch/imperfect analogy to me.

Not really: it's just an example to show why you may not find two legitimate ancestors. The blending could have occured in such a short period of time as to render the idea that you WILL find two ancestors, almost moot. It's even easier among two ancestors of the same species than it would be for two ancestors that are different species (you'd have to know both the original species...which is not quite as easy as it it with humans because we have all three...the theory of the thread starter is two different species...which ones? We only have "one", at best. Even then, we don't know for sure), that are two different species, from tens of millions of years ago. Far more likely is to find a single ancestor (during a period of stability) rather than an ancestor or two during a period of rapid change. Yes, species go through periods of stability and short periods of rapid change (evolution). This is why when Christian apologists (young earth theory) connecting fossils...they just aren't there: rapid change makes it far harder to find them in "perfect" succession.*


It's not as simple as "definitely two ancestors will be found without exception". There's the problem of blending and rapid change with little hope of finding fossils during that rapid change. This is the bane of geneticists that work with extinct species. Not to mention trying to find usable or actual genetic information from fossils (rare, as well).



*There is speciation that occurs in "circles"...I can't explain that too well. Also, two different species producing fertile offspring...how does that even factor in when that should, by some biological definitions, not work (because they would, by some definitions, be the same species if they can produce fertile offspring). I do not buy the theory of two different ancestors for "birds", but I also cannot dismiss it as completely false and still consider that position "completely scientific". The only way to make a sure statement like that is to have all relevant evidence that allows for a perfect and objective conclusion: we do not have such evidence.

darkriddle
I'm a bit more in line of thought with "Omega Vision" here. Mainly on the premise that Protoavis was found not "thousands" of years before Archeopteryx, but "millions." In fact, it was not identified as a bird due to a lack of feather imprints.

The idea of dual evolution could be applied to several different phenomenon in evolution. I, as a person that believes microbial life evolved on earth more than once (meaning that I think early life started and then went extinct billions of years ago, only to evolve again) am a bit biased and predisposed to the dual evolution idea.

But regarding bird evolution, it's more pressing to suggest it here, because there is such a wealth of credible evidence to support both theories of their evolution.

Because one party declares there finds right, and the other does the same, both pointing to credible fossil evidence - it leads more credence that they BOTH may be corect.

The question is, how could this be?

My suggestion was that they might have been a product of two ancestral lines.

As King Kandy pointed out - this would be a problem best dealt with by genetic research.

In fact, genetic gene-tracing would probably be able to distinguish which modern birds came from an elder ancestral line, and which birds had come from a more recent one.

Still "dadudemon" has a valid argument, at some point in time (probably millions of years ago - it's possible (more likely than not) that these two lines may have merged, being as how they would be somewhat closely related to begin with.

If birds did evolve from dinosaurs (as most people believe) then they still share a very similar genetic make-up of the Thecodonts, since dinosaurs themselves evolved from Thecodonts.

But if birds evolved from Thecodonts, they would either predate dinosaurs or appear at the same time in evolutionary history. Strangely, fossil finds like Protavis point directly at this paradox.

I think the key to differentiating the two is in feathers. The fossil finds that suggest a Thecodont origin are as old as the early dinosaurs. These rarely have feathers, (some have down) but have undeniable anatomical features that only birds share today.

Those feathered dinosaurs discovered, appear a great deal of time afterward - and this is what poses that greatest puzzle...how can you be older than your ancestor?

inimalist
Originally posted by dadudemon
The lineages could completely blend and there is literally no evidence, genetically, of a "dual" ancestry.

if there were a dual ancestry of birds, it would be impossible to wash out due to blending

the main crux of the hypothesis would be that birds arose twice in distinct circumstances, meaning, these two streams would be genetically dissimilar to the point where the two lines could not interbreed, one of the definitions of species.

a "dual evolution" situation where the organisms in both evolutionary paths could still interbreed is hardly dual at all, as the organisms they are evolving from are essentially identical. As time goes on, genetic codes tend to become less similar than more, so millions of years with two evolutionary paths is almost certain to produce more dissimilar lines than any sort of convergence on a single genetic code.

In fact, I can't think of any time in evolutionary history something like that could happen... It would be like saying a mouse could evolve to the point that it was genetically similar enough to humans that we could mate... or that chimps and humans may evolve enough that we converge on a point where we could again mate with eachother... idk, but that seems impossible, or so improbable as to be impossible

inimalist
Originally posted by King Kandy
If this were the case, it surely would be born out in genetic evidence? We would see two distinct genetic lineages between birds of one line and birds of the other, much like how the Aardvark and Anteater resemble each other, but are genetically distinct.

Gould made essentially the same argument when talking about fish.

essentially, as a category, they don't exist biologically, given the diversity.

this is the same as the eye appearing several times during evolution, and given what we are learning about the ability of epigenetics to "reactivate" dormant genes based on the environment, should not be unexpected.

King Kandy
Originally posted by dadudemon
Not really: it's just an example to show why you may not find two legitimate ancestors. The blending could have occured in such a short period of time as to render the idea that you WILL find two ancestors, almost moot. It's even easier among two ancestors of the same species than it would be for two ancestors that are different species (you'd have to know both the original species...which is not quite as easy as it it with humans because we have all three...the theory of the thread starter is two different species...which ones? We only have "one", at best. Even then, we don't know for sure), that are two different species, from tens of millions of years ago. Far more likely is to find a single ancestor (during a period of stability) rather than an ancestor or two during a period of rapid change. Yes, species go through periods of stability and short periods of rapid change (evolution). This is why when Christian apologists (young earth theory) connecting fossils...they just aren't there: rapid change makes it far harder to find them in "perfect" succession.*


It's not as simple as "definitely two ancestors will be found without exception". There's the problem of blending and rapid change with little hope of finding fossils during that rapid change. This is the bane of geneticists that work with extinct species. Not to mention trying to find usable or actual genetic information from fossils (rare, as well).



*There is speciation that occurs in "circles"...I can't explain that too well. Also, two different species producing fertile offspring...how does that even factor in when that should, by some biological definitions, not work (because they would, by some definitions, be the same species if they can produce fertile offspring). I do not buy the theory of two different ancestors for "birds", but I also cannot dismiss it as completely false and still consider that position "completely scientific". The only way to make a sure statement like that is to have all relevant evidence that allows for a perfect and objective conclusion: we do not have such evidence.
But you're comparing two lineages of a single species that merged, not the merging of things that were different species to begin with. He is claiming there are lineages from two different types of ancestors, how could they merge when they are unrelated species?

dadudemon
Originally posted by King Kandy
But you're comparing two lineages of a single species that merged, not the merging of things that were different species to begin with.

You want it to be apples to oranges, but it's not.




Originally posted by King Kandy
He is claiming there are lineages from two different types of ancestors, how could they merge when they are unrelated species?

I already asked that question. It's not my theory, ask him.


I was only pointing out that you can't claim that you would see two distinct lineages (in the DNA) when something even easier to see (because it's far younger and from the same species...making it much easier to come up in tests) has blended into oblivion in a far shorter time.


In other words, your criticism is invalid. There' other legit criticisms such as "two different species.....mixed? Then they were two different species: they were subspecies of the same species."

dadudemon
Originally posted by inimalist
if there were a dual ancestry of birds, it would be impossible to wash out due to blending

Actually, that's wrong. I explained why already.

inimalist
Originally posted by dadudemon
Actually, that's wrong. I explained why already.

not... not really...

you just said it would happen really fast... you didn't give any logic about how it could happen in the first place...

King Kandy
Originally posted by dadudemon
You want it to be apples to oranges, but it's not.






I already asked that question. It's not my theory, ask him.


I was only pointing out that you can't claim that you would see two distinct lineages (in the DNA) when something even easier to see (because it's far younger and from the same species...making it much easier to come up in tests) has blended into oblivion in a far shorter time.


In other words, your criticism is invalid. There' other legit criticisms such as "two different species.....mixed? Then they were two different species: they were subspecies of the same species."
Well, if they were subspecies of the same species, then the "two lineages" he spoke of, are naught.

dadudemon
Originally posted by King Kandy
Well, if they were subspecies of the same species, then the "two lineages" he spoke of, are naught.

Nullifying the entire discussion to begin with. thumb up



However, producing fertile offspring...are they the same species? How do you define species at the biological/DNA level?


Man, I do not know how to approach that because it's debated by ACTUAL biologists, still, to this day.

Originally posted by inimalist
not... not really...

you just said it would happen really fast... you didn't give any logic about how it could happen in the first place...

No, no I didn't. *

Go back and re-read that post.


*The "no" refers to the "just" of your post. That's not "just" what I said.

darkriddle
Originally posted by dadudemon
In other words, your criticism is invalid. There' other legit criticisms such as "two different species.....mixed? Then they were two different species: they were subspecies of the same species."


On the premise of species here: there is a bit of confusion regarding the ancestral lines as either subspecies or "unrelated" species, and this falls into conjecture, mainly since the fossils are actually still being debated on concerning their status and classification in science to begin with. (in other words the fossils in question are considered "bird-like" but not fully accepted as birds.)

What is undeniable is that both fossil stocks seem to be transition species - all heading toward bird evolution.

On the idea that two separated species can interbreed:


There are many exceptions to this rule and all have to do with the genetics of the species in question.

If the species are closely related, and in many cases NOT closely related, some times this is possible. My ward against this thought is in the time to which separates the speices.

I was under the impression that if millions of years separated the "diversiance" of species from one another, then they would not be able to interbreed.

Apparently, I was wrong on this notion. As an example, I was told that Neanderthal man and Cromagnon man could have interbred, despite having diverged from a common ancestor over nearly half a million years apart. So I considered them NOT closely related.

It's clear that Neanderthal man was a different species of hominid, then us, and I had figured their genes were too differentiated to be compatible to mix.

Still, even if the birds ancestry did NOT mix, it would not rule out a dual evolution, only that one line went on to become the modern birds we know of today, while the other went extinct.

In fact, some paleontologists hint at this on more than one occasion when talking about the birds "experimental dead-end" species such as the 4-winged Micro-raptor.

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