pnyikos
2013-06-07 16:52:00 UTC
This is ongoing discussion in talk.origins about big differences in
DNA between taxa (especially sister taxa, and between ancestral and
descendent forms). I've left in some of the context of earlier
exchanges.
Harshman seems to place a lot of stock in molecular clocks. He steers
the discussion to lengths of time next, and a spirited back-and-forth
results.
opossum, or *Sphenodon*, the tuatara.
You understand that the subject is DNA, right? As in the thread title.
Didelphis and Sphenodon most definitely have transformed considerably
over time in genomic terms.
Evidence?
The evidence presented so far is very weak, although Harshman doesn't
see it yet.
isn't it? As for *Sphenodon* the sister taxa departed in the
Jurassic, or maybe even the Triassic.
Yours is a classic case of "begging the question." Do you know the
technical meaning of this term in logic?
IIRC, it was Stephen Jay Gould who wrote that cladistics has a
problem with "stay-at-home" taxa and closely related taxa that went on
a long evolutionary journey.
says [IIRC] is almost indistinguishable from Sphenodon.
Go for it. Still irrelevant, though.
It is Homeosaurus, and Romer did say it is almost identical. So you
still have a long row to hoe to establish your challenged claims.
The way you take refuge in generalities, it only strengthens my
suspicion.
Look at any scientific paper in which there is a phylogenetic analysis
of DNA sequences for which the tree shows a) branch lengths representing
sequence change (not all trees do this; check the figure legend) and b)
at least one of the taxa in question.
You need to have data on sister taxa to conclude anything.
with *Sphenodon* (and, preferably, also *Didelphis*).
Peter Nyikos
Professor, Dept. of Mathematics -- standard disclaimer--
University of South Carolina
http://www.math.sc.edu/~nyikos/
nyikos @ math.sc.edu
DNA between taxa (especially sister taxa, and between ancestral and
descendent forms). I've left in some of the context of earlier
exchanges.
I am not confusing anything. The extinct ancestors are as interesting as
existing species since all had to be fit to survive back their day in
order to evolve. Big gap indicates that lot of middle steps were taken
and none were fit to survive later. Nature feels quite cooperative and
tolerant not at all that competitive and genocidal.
existing species since all had to be fit to survive back their day in
order to evolve. Big gap indicates that lot of middle steps were taken
and none were fit to survive later. Nature feels quite cooperative and
tolerant not at all that competitive and genocidal.
the discussion to lengths of time next, and a spirited back-and-forth
results.
You don't know any of this. There don't have to have been lots of
extinct species; it might be just one lineage that has transformed over
a long time.
Or not, as is possibly true in the case of *Didelphis*, the Virginiaextinct species; it might be just one lineage that has transformed over
a long time.
opossum, or *Sphenodon*, the tuatara.
Didelphis and Sphenodon most definitely have transformed considerably
over time in genomic terms.
see it yet.
The differ considerably from their sister taxa.
So what? The sister taxon of *Didelphis* is far removed from it,isn't it? As for *Sphenodon* the sister taxa departed in the
Jurassic, or maybe even the Triassic.
Yours is a classic case of "begging the question." Do you know the
technical meaning of this term in logic?
IIRC, it was Stephen Jay Gould who wrote that cladistics has a
problem with "stay-at-home" taxa and closely related taxa that went on
a long evolutionary journey.
Much of that difference
can be apportioned along their own lineages. Phylogenetic analysis,
among other things, can estimate branch lengths.
Try it on *Sphenodon,* wise guy.can be apportioned along their own lineages. Phylogenetic analysis,
among other things, can estimate branch lengths.
(They have morphologically too, but that's
irrelevant.)
When I get home, I'll look up a Jurassic rhyncocephalian that Romerirrelevant.)
says [IIRC] is almost indistinguishable from Sphenodon.
still have a long row to hoe to establish your challenged claims.
Colbert called Didelphis a "living fossil" and "a Cretaceous mammal"
in _Evolution of the Vertebrates_. It seems almost an axiom that it
had to have changed a lot genetically in ways of which we know
nothing, but I think this might be a case of begging the question.
in _Evolution of the Vertebrates_. It seems almost an axiom that it
had to have changed a lot genetically in ways of which we know
nothing, but I think this might be a case of begging the question.
suspicion.
No, that's a case of paying attention to the subject.
Prove it.of DNA sequences for which the tree shows a) branch lengths representing
sequence change (not all trees do this; check the figure legend) and b)
at least one of the taxa in question.
Look at the terminal branch
leading to that taxon. If that branch length is not zero, that's
evidence that the lineage has changed. Now of course I can't prove
anything, as science doesn't deal in proof. I can only provide very
strong evidence. And in this case, I'm asking you to do some of the work.
Utterly useless work, unless you can steer me to a site that dealsleading to that taxon. If that branch length is not zero, that's
evidence that the lineage has changed. Now of course I can't prove
anything, as science doesn't deal in proof. I can only provide very
strong evidence. And in this case, I'm asking you to do some of the work.
with *Sphenodon* (and, preferably, also *Didelphis*).
Peter Nyikos
Professor, Dept. of Mathematics -- standard disclaimer--
University of South Carolina
http://www.math.sc.edu/~nyikos/
nyikos @ math.sc.edu