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Darwin-L Message Log 7:65 (March 1994)

Academic Discussion on the History and Theory of the Historical Sciences

This is one message from the Archives of Darwin-L (1993–1997), a professional discussion group on the history and theory of the historical sciences.

Note: Additional publications on evolution and the historical sciences by the Darwin-L list owner are available on SSRN.


<7:65>From DARWIN@iris.uncg.edu  Fri Mar 18 23:28:28 1994

Date: Sat, 19 Mar 1994 00:28:24 -0500 (EST)
From: DARWIN@iris.uncg.edu
Subject: Hominid evolution and "species" (I)
To: darwin-l@ukanaix.cc.ukans.edu
Organization: University of NC at Greensboro

I have been following the discussion of hominid phylogeny with interest,
and have been learning a lot.  Many thanks to all who are contributing to
it.  I just wanted to add my two cents' as a systematist (though not an
anthropologist) who has an interest in the idea of "species."

Ken Jacobs in a recent posting hit on a very important point that I have
always felt was insufficiently appreciated in the anthropological literature.
He wrote:

  Part of the difficulty in envisioning "H. erectus evolving everywhere
  _simultaneously_ into H. sapiens" is caused by semantics.  Because the
  start point of the single lineage (on this view of the matter) has been
  given a name which is distinct from the _end-point_ of the lineage (i.e.,
  H. erectus versus H. sapiens), one cannot help but tend to see what is
  called H. erectus as being very distinct from what is called H. sapiens.
  Yet in the middle somewhere, at the arbitrary point which divides the two
  taxonomic units, there will be virtually no difference.  The difference
  between a 0.25Mya "H. erectus" and a 0.24Mya "H. sapiens" will be 0.01My
  and not much else.  The taxonomic nightmare which is late Middle
  Pleistocene Europe attests to just this phenomenon.

  Think of it in terms of a long, wide river (the Mississippi, for instance).
  If, for some bizarre reason, it was decided that from now on the river
  south of St. Louis was to be called the Nile, would we then be arguing
  whether the Mississippi turned into the Nile simulaneously on both the
  right and left banks? (not to mention the middle).  I think not, for we
  would be able to recognize the distinction as the arbitrary construct it
  really is.  That we cannot do so quite so readily with respect to H.
  erectus, the "Neadertals," and others of our forebears bespeaks volumes
  IMHO about our persistent inability to come to grips with our origins.

The problem Ken describes is the problem of "group thinking" versus "tree
thinking."  The true history -- the true chronicle of events that a
systematist would be interested in reconstructing -- has no seams: it is a
continuous genealogical nexus extending through time.  When we think in
terms of this genealogical nexus -- the tree -- the questions we ask are of
the form "how is this individual or population genealogically connected to
the other populations and individuals we know?"  If we are "group thinkers"
though, we ask questions like "is this population really _Homo sapiens_ or
really _Homo erectus_, or should we perhaps call it by a new name?"  The fact
that evolution is an historical process means that when we consider evolving
populations in time there aren't "really" any boxes that the individuals fit
into -- there is only the genealogical nexus that connects them.  This is
the reason there has been a "species problem" is systematics since the field
began; "species" is to a considerable extent a classificatory concept, and
when we look at the genealogical nexus up close, classification is sometimes
too blunt an instrument to be useful.

(I should point out in passing that I use the term "tree" in a broad sense:
I do not mean a history that is strictly branching.  When you stand back
and look at evolutionary history at a coarse level of resolution it is
mostly branching, while "up close" it is mostly reticulate; this is all the
same "tree" in my sense.  If I wanted to be really precise I would call it
the Natural System or the evolutionary chronicle, but "tree" is easier to
type.)

In response to Ken Jacobs' message, Kent Holsinger raised some other
important questions about cladogenesis and anagenesis in the context of
this topic.  Let me put some comments on Kent's posting in another message
so that this one doesn't get any longer than it is already.

Bob O'Hara, Darwin-L list owner

Robert J. O'Hara (darwin@iris.uncg.edu)
Center for Critical Inquiry and Department of Biology
100 Foust Building, University of North Carolina at Greensboro
Greensboro, North Carolina 27412 U.S.A.

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