Cladistic language concepts

[Sean Brady]

----------------------------Original message----------------------------
Just a note on DNA sequence data.
 
        The rate of change in a particular sequence (e.g. a gene) must be
conceptually kept separate from the rate of branching.  This latter rate
involves speciation, while the former rate probably has nothing to do with
speciation.  People have certainly tried to tie these two together, but
such a link, if it exists, has not been demonstrated yet.
 
        In terms of using DNA sequence as comparative evidence for the
history of speciation (i.e. building a tree), the main concern is finding a
sequence of DNA that changes slow enough to preserve comparative
differences, but without changing so fast that these differences 'pile up'
on each other and obscure their history.  Unfortnately, if the true history
is more like a bush than a tree, as Ghiselin discusses, any gene we may
pick will probably contain too few changes (i.e. be too slow) to
reconstruct this history.
 
        A crucial question in both biological and linguistic reconstruction
seems to be this:  Does our analysis yield a bush-like structure 1) because
there really is a bush-like structure; or 2) because our data and/or
methods of analysis cannot resolve the (true) tree-like structure.  This is
a huge, and unsolved, problem in biological systematics.  We simply cannot
distinquish between these two scenarios yet, although with the rapid influx
of DNA data, some people are beginning to tackle this problem.
 
        I wonder what the state-of-the-art is on this issue regarding
linguistic reconstruction.
 
 
 
\>----------------------------Original message----------------------------
>Can you segregate the slowly developing parts of the genome from the oth
>ers, or more broadly, can you classify sections by their rates of
>branching?
>
 
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Sean Brady                              sgbrady at ucdavis.edu
 
Population Biology Graduate Group       tel. (530) 752-9977
Department of Entomology                fax. (530) 752-1537
University of California
One Shields Avenue
Davis, CA 95616-8584
 
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