Common Descent!

[Furrowed Brow]

This is probably reheating an old theme.

In the God Delusion - Ch 4 Here

Further, creationists do not totally reject evolution. Rather the main issue is the inadequate support for common descent.

I have been thinking about this same point recently as I have been debating the issue on a completely different forum. It is an area I still need to get my head around.

Why do some find common ancestry so unreasonable?
What would count as reasonable support for common ancestry?
What argument/evidence do creationists require?

[Confused]

I'm asking for what they need to see to be able to accept the premise.

The ultimate proof would be to have a genetic map of all extinct and extant life and show what specific mutations are required to go from one life to the next. This probably won't ever happen, but it would definitely prove it.

I'll keep on thinking of what other things would demonstrate common descent to be true.

Do we not already have this form the human genome project in regards to the common ancestry of specific species. In regards to humans specifically, the genetic mapping found the identical ARE sequences exactly where they predicted they would be, this in turn corresponded with new genetic sequences (result of the ancient random errors during replication) that identified with new or enhanced traits of the evolved species. This was all listed in Collins "The Language of God".

[otseng]

I think that current evolutionary thought is that the early mammals were not live-birth but monotremes or monotreme-like. The marsupials and placentals evolved from that more primitive common ancestor.

Is there any evidence to suggest that all the mammals between 200 mya and 110 mya were all "monotreme-like"?

Here is one that suggests they were not.

Discovery of the skull of a shrewlike animal the size of a paper clip pushes back the origin of mammals, including humans, to 195 million years ago.

Teeth in the H. wui skull suggest that this animal suckled its young and, thus, is a true mammal, Crompton notes.

http://www.hno.harvard.edu/gazette/2001 ... ammal.html

[otseng]

the genetics and population biology for the common descent of all organisms from a common ancestor follow the same rules as the common descent of all duck-like birds from a common ancestor of duck-like birds.

Yes, I understand this is the position that common descent proponents hold. From a duck-like bird to another duck-like bird is not the issue. The issue is that given enough time, can a reptile go to a bird?

There are, therefore, several issues here:

• do you accept that some species can have a common ancestor?
• do you accept the genetic mechanisms of inheritance of DNA from the parents, mutation of DNA, the dependence of phenotype on genotype, and the dependence of reproductive success on phenotype?

Yes, I accept these.

• what observations make common descent within certain animal groups acceptable, while the same mechanisms for "deeper" common descent between groups is unacceptable?

This is what it all boils down to. I can accept "shallow" common descent. But, how can "deep" common descent be proved?

You see, genetically, it is impossible to separate deep-level common descent from recent, within-kind common descent.

If it is genetically impossible to demonstrate deep common descent, then another method should be presented to demonstrate deep common descent.

That's a little like asking for the "current-animal name" of the common ancestor of cats and dogs. Since it was neither cat nor dog, it would not have a name as "cat" or "dog."

Since phylum is the highest taxonomic classification of life (next to kingdom), so it would be one of the broadest classification that one can ask for. Supplying the "current animal name" of the animals is not necessary.

In noodling about the literature, I've also learned that early paleontologists tried very hard to shoehorn Cambrian fossils into phyla that were known.

Yes, there are many that are not easily classified. This demonstrates the plethora of extinct and extant body forms that arose only during the Cambrian explosion.

Which part would they disagree with? Do they argue that there is hard data that show that new features really do pop into existence with a single mutation? I bet not. Rather, I bet that they claim that evolutionary theory posits this, and then wax poetic about what a dumb idea it is.

I'm in no position to argue for their positions, esp since I don't subscribe to them.

But not in a single, magical leap in a single mutation in a single generation.

Yes, I realize this is the mainline evolutionary position.

This is not a valid conclusion. The vast majority of biologists--at least, the vast majority of those I know--would go to UCMP to find out what the current thinking is. It doesn't matter what people used to think, except as an interesting study in how our understanding changes as more data are discovered.

What conclusion are you referring to that is not valid?

The only way to justify claiming that organisms appeared suddenly with no prior evolution is if there are no prior fossils.

What I am saying is that common descent would not predict the Cambrian explosion. In which at one period, all the extant and extinct phyla appear (except of course for the Precambrian). No other new phyla appear after the Cambrian. Animals are quite complex in the Cambrian. And there is no evidence of gradualism between all the life forms.

[otseng]

Do we not already have this form the human genome project in regards to the common ancestry of specific species.

I think this is a step, but does not arrive at the final answer.

What would be interesting is understanding the genome sequence of all the primates. Then show what specific mutations are necessary to create the evolutionary tree for all the primates.

[jjg]

The probablilty of different species having similar DNA by chance 1:10E267. To give you an idea what that means, scientists belieleve there is 10E867 particles in the universe. Similar DNA had to happen by common decent.

[Fisherking]

Similar DNA had to happen by common decent.

--or creative design

[QED]

Similar DNA had to happen by common decent.

--or creative design

Don't you mean uncreative design? Why would an infinitely skilled creator keep churning out the same old trick over and over again? Incidentally, I wonder -- do you ever suffer from back-pain?

[honegod]

What would be interesting is understanding the genome sequence of all the primates. Then show what specific mutations are necessary to create the evolutionary tree for all the primates.

sort of like climate models, run it backwards to see if it accurately predicts previous generations ?

given that at least a carbon-14 atom is likely to form part of a DNA molecule, with it's relatively short half life it seems likely that having a chunk of DNA radioactively decay would be a significant source of pretty random mutation.

the only constraint to the 'severity' of the mutation I can see would be the viability of the organism, not any arbitrary classification of species.

[Jose]

the genetics and population biology for the common descent of all organisms from a common ancestor follow the same rules as the common descent of all duck-like birds from a common ancestor of duck-like birds.

Yes, I understand this is the position that common descent proponents hold. From a duck-like bird to another duck-like bird is not the issue. The issue is that given enough time, can a reptile go to a bird?

You miss my point. It is a contradiction to accept a particular class of data for one conclusion, but reject it for another. It's the same kind of data. My question is about the data.

Can a reptile go to a bird? Usually not. Lizards, turtles, and snakes have not. Saursician dinosaurs did not. Pterosaurs did not. Of the ornithiscian dinosaurs, there were a few who did. Will any of the existing reptiles become birds in the future? Almost certainly not. They're too different.

• do you accept that some species can have a common ancestor?
• do you accept the genetic mechanisms of inheritance of DNA from the parents, mutation of DNA, the dependence of phenotype on genotype, and the dependence of reproductive success on phenotype?

Yes, I accept these.

• what observations make common descent within certain animal groups acceptable, while the same mechanisms for "deeper" common descent between groups is unacceptable?

This is what it all boils down to. I can accept "shallow" common descent. But, how can "deep" common descent be proved?

It is proved by exactly the same kind of data as prove shallow common descent...with one interesting quirk. The fossil record strongly supports deep common descent, but there are far too few fossils of most species (hominids excluded) to bring fossil data to bear on shallow common descent. Birds, for example, are particularly difficult. The avian radiation was so rapid that there are hardly any fossils at all to give us clues. So, the data are mostly of two types: morphological similarities, and DNA similarities.

You see, genetically, it is impossible to separate deep-level common descent from recent, within-kind common descent.

If it is genetically impossible to demonstrate deep common descent, then another method should be presented to demonstrate deep common descent.

You've misread what I said. Genetically, it is impossible not to have evolution. The two items in my list above, that you accept, guarantee that evolution must occur. They don't guarantee any particular direction of evolution, though; they simply say that change will happen. Because genetics works out this way, shallow common descent is precisely the same as deep common descent, except for the time scale. My point is that there is no difference in mechanism between the two. Therefore, the data force us to accept both; the data cannot be neatly divided into "within kind" ancestry and "between kind" ancestry. Evolution is, basically, a fractal of Y shapes. If one Y is possible, they all must be.

Of course, in the "real" evolutionary history of the world, some of the branches of some of the Ys were terminated by extinctions. Therefore, evolution has not created a complete fractal image. If we look at the data, we find some "coherent" lineages that we'd call a class of organisms, but these coherent groups are not the same as the biblical "kinds."

That's a little like asking for the "current-animal name" of the common ancestor of cats and dogs. Since it was neither cat nor dog, it would not have a name as "cat" or "dog."

Since phylum is the highest taxonomic classification of life (next to kingdom), so it would be one of the broadest classification that one can ask for. Supplying the "current animal name" of the animals is not necessary.

But isn't that what you and others are asking? "Supply the current phylum name for Ediacaran animals." This can't be done, because the animals are pre-phyla, and can't be sorted into those names.

In noodling about the literature, I've also learned that early paleontologists tried very hard to shoehorn Cambrian fossils into phyla that were known.

Yes, there are many that are not easily classified. This demonstrates the plethora of extinct and extant body forms that arose only during the Cambrian explosion.

You're right that there was a plethora of body plans. The "naming frenzy" attempted to call things by current phylum names, when they probably did not actually represent the phyla whose names they were given. Gzornenplatzes were called chordates because it seemed like a good idea; real chordates may not have come onto the scene until millions of years later.

Even the Cambrian "explosion" is goofy. Go out and look for Cambrian fossils, and see what you find. At the base of the Cambrian, there's darned little--some worm tracks, and occasionally a tiny trilobite-like thing about the size of a baby's fingernail. As you move up, fossils become easier to find, larger, and more diverse. At a minimum, the "explosion" took 5 million years. When we add in the Ediacaran, we're talking more like 100 million. Not much of an "explosion."

But not in a single, magical leap in a single mutation in a single generation.

Yes, I realize this is the mainline evolutionary position.

uhhh...it sounds like you might be disagreeing with me here...as if you might believe that new morphological features do appear by a magical leap in a single mutation. I'm not sure I understand this...perhaps, if there had to be hyperevolution right after the critters got off the Ark, then this is the only way it could occur. There wasn't time for normal genetics to work. [I note that it's not necessarily the "mainstream evolutionary position" here, but a simple fact of how genetics works. A single mutation cannot create a new morphological feature; it can only modify some existing feature. And, of course, if an individual is born with a new genetic variation, it kinda has to have kids, and have those kids have kids, and have everybody else die out, before the whole population can have that variation. Is there any way that a population can change in unison in a single generation? ]

(from prior post) But, after some research, I've determined that the graph is unusable. And as I concluded in that post "there is no reason to doubt what the vast majority of biologists claim in that all the phyla appear during the Cambrian Explosion."

This is not a valid conclusion. The vast majority of biologists--at least, the vast majority of those I know--would go to UCMP to find out what the current thinking is. It doesn't matter what people used to think, except as an interesting study in how our understanding changes as more data are discovered.

What conclusion are you referring to that is not valid?

Hmmm...I was rather vague there, wasn't I? Thanks.

You had concluded that the graph was unusable. The graph came from UCMP. You based your conclusion on the notion hat "the vast majority of biologists" buy the idea that the phyla appeared in the so-called Cambrian Explosion.

I merely noted that the vast majority of biologists (as I said, of the ones I know) would go to UCMP to find the current thinking on the matter. They'd accept UCMP's graph as the current-best interpretation of the currently-available data. They would not say, "no, UC Berkeley is wrong; it's better to stick with the ideas that people had in 1942." That's an awkward thing about science, for non-scientists. There's always new data coming to light, so the old statements are rarely valid any more. Sure, it was once thought that all the phyla appeared in some kind of sudden explosion. Now, it's much more clear that this explosion was very, very slow, and was preceded by lots and lots of ancestral forms. Even the apparent Cambrian origins shown in the UCMP graph are out of date. Some will need to be moved into the Ediacaran (aka Vendian) as researchers get a better handle on divergence times revealed by DNA data.

The only way to justify claiming that organisms appeared suddenly with no prior evolution is if there are no prior fossils.

What I am saying is that common descent would not predict the Cambrian explosion. In which at one period, all the extant and extinct phyla appear (except of course for the Precambrian). No other new phyla appear after the Cambrian. Animals are quite complex in the Cambrian. And there is no evidence of gradualism between all the life forms.

Indeed, common descent would not predict the caricature of the Cambrian Explosion as it has been presented--the sudden appearance of a bunch of phyla. But common descent does predict the actual data: the eventual appearance of phyla after a long history of prior life forms.

Is there anything special about phyla appearing and then hanging around for a very long time? No. If those body plans are successful, they will not be wiped out by extinctions. Is there anything mysterious about other body plans not appearing later? No. If the guys who are already there out-compete new forms, then the new forms won't make it. Once the successful forms have out-competed enough other start-ups, then the only forms that exist for modification are the small array of "phyla" that won the battle.

And, as I've said before, it looks like there's an "explosion" when we look at animals. Look at plants. For them, new phyla appeared on and off throughout the eons. There's no "explosion" of any kind. We can't use the "explosion" argument to get around common descent in the plants. ...and, again, genetics works the same way always, so if it's true for plants, there's no valid argument against the same mechanism operating for animals.

[Jose]

What would be interesting is understanding the genome sequence of all the primates. Then show what specific mutations are necessary to create the evolutionary tree for all the primates.

I think this would be really difficult. The mutation rate in humans is around 200 base changes per person per generation. There will be lots and lots of changes in non-coding sequences, and some phenotypically silent changes in coding sequences. Against this background, there will be mutations that make a difference. Yikes.

We now know from genomic sequence comparisons that there are a great many regulatory RNA sequences. These are genes for RNA molecules that are not translated into protein, but instead interfere with the translation (or stability) of other RNA molecules. There's a huge amount of regulatory information in these RNAs, and we don't know a great deal about them.

The way these RNA-coding genes were found is by evolutionary comparisons. DNA sequences that aren't used don't have constraints on what the precise base sequence is. Sequences that are used, however, have constraints--so mutations that change them are often selected against. As a result, regulatory regions that have the same role in different species tend to have the same or very similar base sequences.

This sort of comparison has been done bazillions of times, in many kinds of organisms. In some "model organisms" that are used in laboratories, it's been possible to test the actual functions of the evolutionarily-conserved sequences. Hook up a regulatory sequence to a "reporter gene," re-introduce the gene construct into the organisms you're working with, and see where the reporter gene is turned on. The most fun reporter gene is Green Fluorescent Protein, which fluoresces with green light under UV illumination. From decades of this kind of work, we know that non-functional regions of DNA suffer mutations at a high rate--and the mutations remain in the DNA because they don't interfere with anything. Mutations occur in functional regions just as frequently, but mutant individuals don't survive and reproduce well, so these types of mutations are weeded out of populations by natural selection.

There are two important lessons here. One is that the data from these kinds of studies confirm the predictions that were made: if evolution happens the way we think it does, then these patterns of mutation are precisely what should be found. When people started looking, that's just what they found. Second, we know that the mutation rate is very high, and that there are lots and lots of differences between species. It is for this reason that I said what I did above--that it will be a serious challenge to figure out which mutations are responsible for the "important" differences among species. Once we have the genome sequences, it will take a long time to understand them at a level that will allow us to address this question.

[Of course, the "creative design" argument that's cropped up here can also explain all of this. We just have to imagine that the creative designer has chosen to design a pattern of DNA base changes that precisely matches predictions based on evolutionary theory. Maybe she did; we'll never know as long as her designs are indistinguishable from natural events.]