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Re: The use of offensive weapons (was Re: ANKYLOSAUR CLUBS *)

Robert.J.Meyerson@uwrf.edu (Rob Meyerson) claims:

> Biologists have been able to show that every part of an animal is
> there for some reason.

I'm afraid that Rob is misunderstanding someone rather badly.  I'm not
certain whether or not that someone is me, but in any case the above
statement is false.  As human beings we seek to find explanations for
patterns and structure, and a 19th century biologist might well have
agreed with Rob's statement because of the manner of explanation
biologists were then comfortable making.  However, a big part of the
Darwinian revolution was the dismissal of teleology -- that is
contemporary evolutionary biologists do *NOT* think that structures
evolve for a reason or purpose.  Instead we look for adaptive
significance; why do animals with a particular character trait
reproduce themselves better than others with different character
traits?  Perhaps it's a subtle difference, but it's an important one.
It's particularly important in the context of this discussion because
Rob seems to think that when a novel structure arises it does so for
*one particular reason*.  Well, unless that one reason is the general
one that bearers of that structure produce more offspring than
conspecifics without that structure then any biologist worth their
salt will disagree.

With one exception I'm not going to bother with the rest of Rob's
message since I think that John and I have been about as clear as we
can be.  However, my one exception is of such major import for this
list that I can't let it go by:

> This has also been shown for many dinosaur groups.  Horns in
> ceratopians, hornlets on theropods, and the thickened skull on
> pachycephalosaurs are simply some of the examples of features found
> on the animal which are primarily used for intraspecies combat.

There are a lot of ideas about how various structures might have been
used by different dinosaurs, but most of those ideas aren't
particularly amenable to testing.  Therefore any conclusions about
which of those ideas are correct must remain extremely tentative.  Rob
appears to be quite missing the major point that John and I are trying
to get across, but I hope that everyone else can see it: there's
little to no reason ever to be certain about any statements regarding
the behavior of extinct animals that left no descendents.  Speculate
all you want, but when you start claiming that the manner in which
theropods used their hornlets supports your contentions about behavior
in other dinosaurs, you've gone far outside the bounds of science.
You'd do just as well to claim ceratopsians could fly because we know
about helium-filled sauropods...

Mickey Rowe     (rowe@lepomis.psych.upenn.edu)