Re: An end to miracles (was Re: New alvarezsaurid)

[Dinogeorge <Dinogeorge@aol.com>]

In a message dated 98-03-31 08:45:50 EST, th81@umail.umd.edu writes:

<< Okay, George, we've let you go on and on and on about this. You've had your
say.
 
 Now, time for you to clarify:
 
 What is so miraculous about evolution?  Evolution BY NECESSITY can only
 operate from previously existing structures.>>

I never said I consider evolution miraculous. What strikes me as miraculous
about BADD is the picture that has developed of theropods accumulating a
>series< of characters, each of which has its own ad hoc reason for existence
unrelated to flying, and then, suddenly, when the string of accumulated
characters attains a certain "critical mass" (or whatever), the creature in
which these characters have accumulated takes wing. This is a miracle, like
having a broken teacup reassemble itself and pop onto the tabletop from which
it fell.

In the birds-are-not-dinosaurs picture developed by the ornithologists (e.g.,
Alan Feduccia), we have to accept a similar miracle: that the same set of
characters evolved twice, once in the arboreal bird ancestors, where it led to
flight, and once again, in theropods, where it led in quite the opposite
direction! I of course accept the evolution of flight features in arboreal
archosaurs, but I cannot accept the idea that these same characters appeared
virtually simultaneously in theropods without there being a close phyletic
relationship between the two groups.

In BCF, I argue that the aforementioned series of characters develops in
theropods that have taken to (actually, retained from pre-dinosaurian
archosaurs) an arboreal lifestyle. Each character may then be understood as an
incremental improvement to (or at least, in the context of) this lifestyle--it
has a reason for existence that is related to flight (in the broad sense:
parachuting, gliding, what have you; powered, flapping flight appeared much
later, after many evolutionary "steps"). This is >not< to say that any
character appeared because, sometime down the road, the animals were going to
become powered, flapping fliers, but only that, whatever kind of flying the
animals were doing was improved (somehow) by the appearance of the character.
To me this makes more sense than having a character appear because, say, it
made a dinosaur a better runner, and having it turn out later that the
character also made the dinosaur a better flier. Not that this is impossible,
of course--as you note below--only that it seems astonishingly (unnecessarily)
unlikely to have happened with a >whole series< of characters.
 
<< Take insect flight:  Either modified gills or modified body lobes are
 present for some other reason, but are selected for so that (in one lineage)
 they become used for flight.  No "miracles" required.  A posteriori it might
 look "unlikely", but the same can be said of almost any complex structure.>>

The wings of insects may have started out as modified gills or body lobes, but
once these structures became exapted for the kind of wind-blown, rudimentary
flying that insects may have been capable of at that stage of the evolution of
insect flight, >further< modifications were undoubtedly related to improving
insect flight. There is a >long< series of modifications required to change
gills/body lobes into the kinds of wings that insects have. I cannot believe
that most of these modifications occurred or were selected for for reasons
other than flying.

Yet this is exactly what the BADD paleontologists are trying to say, with
regard to dinosaurs and birds. Your example is >highly illuminating<.

<<snip>>
 
<< Your argument is precisely the argument used by creationists.>>

No, because to them all of this is miraculous. Or so they would have us
believe. My point is that miracles are >not< required to explain evolutionary
events.
 
<< So, now the test of science: would you change your position on the origin
of
 avian flight if presented with evidence which contradicted your model? (I'm
 not saying that that evidence exists; I am only setting up a hypothetical
case).>>

Absolutely. Of course. But I've done my homework, and so far I haven't found
anything that flatly contradicts the model. For example, I like the fact that
so many >small< theropods and such are being unearthed and described these
days. A facet of BCF is that flight developed in small, lightweight
archosaurs--animals with a body length measured in inches rather than feet (or
centimeters rather than meters, if you're metrified)--not in the somewhat
larger forms the size of _Eoraptor_ or _Coelophysis_. It is not a coincidence
that most (though not all) of the smallest dinosaurs known are theropods.