Re: Still waiting

In message <0Bwyk.130$YU2.44@xxxxxxxxxxxxxxxxxxxx>, John Harshman
<jharshman.diespamdie@xxxxxxxxxxx> writes
Robert Carnegie wrote:
On Sep 11, 8:48 pm, John Harshman <jharshman.diespam...@xxxxxxxxxxx>
wrote:
Ernest Major wrote: [all snipped out]
In message
<b7195e1b-0290-45c3-bc12-6f6d6c815...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Robert Carnegie <rja.carne...@xxxxxxxxxx> writes

But I think what you want us to accept is that the ancestry of a
living individual or species, or an extinct one, can be traced in a
line back through time and the bodies of ancestors to the common
ancestry of all living things - at least to those microbes that
apparently are happy today indiscriminately to borrow each other's
DNA, at which point ancestry becomes indeterminate.
No, nobody wants you to accept that. We can't do that at all. What we
can do is determine the cladistic relationships among species, and that
implies a line of descent and also a set of ancestral morphologies. We
can compare those inferred ancestral morphologies to fossils and tell
you that this or that fossil resembled the ancestor quite closely, if
you like.
Well - when I say the line can be traced back through ancestors, I
oon't mean /specifically/. But we know where it's going. Or rather,
we know that my line and every other known living thing on earth's
line lead back to the same place.

Ah. We call that "cladistic relationships".

This can be said because all life uses /almost/ the same apparently
arbitrary DNA "word" vocabulary - one slightly variant exception being
mitochondria inside our own cells, with the existence of iariations
supporting the argument that it /is/ arbitrary - so it's evidence of
common descent from some ancient ancestor whose DNA worked like ours.
You can't detect that in fossils, but you can observe from morphology
that the fossils are all our relatives, who would have had DNA like
ours. Because evolution can't fiddle with how DNA works, much - any
change is overwhelmingly liable to break the whole organism.

There are quite a few slightly variant codes, some of them
mitochondrial, some of them nuclear. I believe someone gave a link
recently to a nice tree that shows them all. If not I could look it up
again. They fit the tree of life pretty well, though there is some
homoplasy.


There may be a newer chart by now, but Robin Knight's thesis provides a
good overview.

http://bayes.colorado.edu/
--
alias Ernest Major

.

Relevant Pages

  • Re: Still waiting
    ... living individual or species, or an extinct one, can be traced in a ... DNA, at which point ancestry becomes indeterminate. ... common descent from some ancient ancestor whose DNA worked like ours. ...
    (talk.origins)
  • Re: Still waiting
    ... living individual or species, or an extinct one, can be traced in a ... DNA, at which point ancestry becomes indeterminate. ... common descent from some ancient ancestor whose DNA worked like ours. ...
    (talk.origins)
  • Re: Still waiting
    ... living individual or species, or an extinct one, can be traced in a ... DNA, at which point ancestry becomes indeterminate. ... You can't detect that in fossils, but you can observe from morphology ...
    (talk.origins)
  • Re: Still waiting
    ... living individual or species, or an extinct one, can be traced in a ... DNA, at which point ancestry becomes indeterminate. ... You can't detect that in fossils, but you can observe from morphology ...
    (talk.origins)
  • Re: Still waiting
    ... living individual or species, or an extinct one, can be traced in a ... DNA, at which point ancestry becomes indeterminate. ... You can't detect that in fossils, but you can observe from morphology ...
    (talk.origins)