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RE: Progress schmogress (was Re: competition)



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Edels
>
> Tim, etc:
>
> In case you haven't checked cranial capacities lately,
> _Homo sapiens neanderthalensis_ actually had an average braincase size
> that was 7-10% larger than _Homo sapiens sapiens_ (average).

This MAY have to do with Neanderthalers generally more massive proportions,
but there is indeed a larger endocranial volume in those guys then us.

Incidentally, almost all paleoanthropologists now regard Neanderthalers as a
distinct species _H. neanderthalensis_ rather than a subspecies of modern
humans.  There are a number of anatomical features found in Neanderthalers
that are not present in us, and vice versa.

As many evolutionary biologists have shown, it is VERY hard to test
hypotheses of competitive exclusion in the fossil record.  It is an
appealing story, and it is quite likely the case in many instances, but it
is very difficult to demonstrate.  Furthermore, there might be some
attributes involved in competitive exclusion (for example, physiological or
behavioral features) which would not be obvious in the osteological or shell
or hard plant tissue remains that make up most fossils.

Finally, the "progressive" state is sometimes hard to establish.  In come
cases it is more clear: a fully marine whale without external hindlimbs vs.
one with them.  In other cases, though, it seems that people tend to assume
"current = progressive".  Okay, but that is not the same as "specialized =
progressive", another possible formulation.  For example, sphenodontians
today are represented by only a relatively unspecialized (and possibly
recidivist!) form, compared to a much higher ecomorphological diversity in
the past.  Similarly, crocodylomorphs in the Cretaceous and Tertiary
represented a wider range of ecomorphotypes than at present.  Same with
horses and rhinos and proboscideans of the Tertiary (much greater diversity
of ecological habit in a given time slice than at present).

So, as always, be cautious with "why" statements in evolutionary biology
(i.e., this is why this happened).  Our first order of business is
establishing the "what" statements: describing the details and patterns that
are out there.  "Why" statements are often more speculative, and are harder
to test against alternative "why" statements.

Hope this helps.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796