From: lip@s1.gov (Loren I. Petrich)
Newsgroups: talk.origins
Subject: Molecular Homologies? (was Re: some stuff about fruit flies)
Date: 12 Oct 92 06:08:30 GMT
Organization: LLNL


	I'm no professional geneticist, but...

In article <7228@tekig7.PEN.TEK.COM> alanf@tekig6.PEN.TEK.COM (Alan M Feuerbacher) writes:
>    Indeed, in a larger perspective, the close resemblance of human
>    and chimp DNA really represents another evolutionary problem,
>    rather than a solution.  Comparisons of DNA in frogs show that
>    there is much greater DNA variation among them than there is
>    between the bat and the blue whale; yet the world's three
>    thousand species of frogs are all much more similar to each
>    other than man is to any of the other primates, to say nothing
>    about comparing bats and whales.

	Good grief!!!

	In macroscopic features, the batrachians (frogs and toads) are
more similar in overall appearance than our species and the great
apes. There was even an article in _Science_ some years back that
reported on comparing human and chimp skeletons by the same kinds of
measurements as are used to classify frogs. The result: more
difference.

	This is only proof that evolution works at different rates
along different lineages, and on different features. Even in cases of
almost constant evolution rate, such as with certain molecules, the
variation rate differ from molecule to molecule. Thus, a certain
fibrinopeptide (involved with blood clotting) evolves faster than
hemoglobin, which evolves faster than cytochrome c, which evolves
faster than ribosomal RNA.

	I don't know how old frogs are supposed to be, but they must
be at least Mesozoic, since they don't like salt water and are not
found on isolated islands, and also since they are found on most of
the continents, where started to separate in the late Paleozoic /
early Mesozoic (don't quite remember exactly when). After the late
Mesozoic (at least!) and probably the early Mesozoic, the continents
would have been too far apart. This dispersion hypothesis can be
tested by constructing a frog family tree. Has anyone done so?

	This early-Mesozoic age (~200 myr) is greater than the
late-Mesozoic/early-Cenozoic mammalian radiation (~65 myr) (bat-whale
separation, among others), and certainly much greater than the
human-chimpanzee separation (5-7 myr).

	In an even more spectacular example, molecular-evolution
studies reveal that outwardly similar strains of bacteria may have
_very_ great molecular distance between them, which may indicate a
separation time of hundreds of millions of years ago, way back in the
Precambrian. Has anyone tried to _estimate_ when the different strains
of (say) methanogens diverged?

>    If we are drawing conclusions about man's evolution using DNA
>    comparisons, we then have to do a lot of explaining about those
>    variations found in nearly identical frogs.

	No problem. See above.

>    ... The author of virtually every
>    contemporary book supporting evolution trots out the human-chimp
>    DNA comparison, but very few mention the frogs or another
>    discovery of microbiology that has been known for some time.

	Give me a break. Why this conspiracy-mongering? Human
evolution is _the_ interesting evolutionary question among
non-specialists.

	And among the pros, evolutionary rate variation is well-known.

>    ... John Randall has done it as
>    succinctly as anyone:

>	The older text-books on evolution make much of the idea of
>	homology, pointing out the obvious resemblances between the
>	skeletons of the limbs of different animals.  Thus the
>	`pentadactyl' limb pattern is found in the arm of a man, the
>	wing of a bird, and the flipper of a whale, and this is held
>	to indicated their common origin.  Now if these various
>	structures were transmitted by the same gene-complex, varied
>	from time to time by mutations and acted upon by environmental
>	selection, the theory would make good sense.  Unfortunately
>	this is not the case.  Homologous organs are now known to be
>	produced by totally different gene complexes in the different
>	species.  The concept of homology in terms of similar genes
>	handed on from a common ancestor has broken down....
>	[Randall, John L., _Parapsychology and the Nature of Life_,
>	New York: Harper & Row, 1975]

	"Now known to be produced by totally different gene complexes
in the different species"???

	Does he have one speck of evidence???

	It is still far from understood how genes control development,
but what has been learned is contrary to JLR's assertion. Example: the
homeobox gene complex, which works similarly across the animal kingdom
(or at least among those species that have been studied, such as fruit
flies and mice). Any refs?
Newsgroups: talk.origins