Cladistic language concepts

[H.M.Hubey]

----------------------------Original message----------------------------
Sean Brady wrote:
>
>         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.
 
There was recently a science article in which the short-term mtDNA
mutation rate was found to be much higher than the long-term mutation
rate was thought/accepted to be. In the article it said/hinted that it
could be because there was a limited number proteins that could occur
and that some mutations went back to some older ones. What is the
latest on this?
 
I can see how something similar can account for the great disagreement
in linguistics. For example, there is nothing to prevent a change
r > z to change later to z >r and then look as if nothing happened.
When we look at the results of the diffusion equation (the one that
creates the Gaussian i.e. normal density) we see that if the changes
in linguistics also obey this equation at least approximately (and they
probably do because almost all math models implicitly use this Gaussian
distribution) then if we examine intensities of change, then the largest
number is always no change. IOW, if we could measure change and could
assign numbers like level 1 change, level 2 change etc, then level 0
change
(i.e. no change) is always greater than level 1 change, and it is also
greater than level 2 change etc. So this means that it is a mistake to
assume that if we see two words that seem exactly alike after 5,000
years
that it is due to chance because after all, we expect more of no-change
than one-sound-change, and more no-change than 2-sound-changes etc.
 
This is a common belief that is exacerbated because many linguists also
seem to assume that all changes in all languages should be occurring
at the same rate as in the IE languages whereas other languages might
be many times more stable.
 
>         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.
 
This is also a huge unsolved problem in linguistics :-)
 
 
> Sean Brady                              sgbrady at ucdavis.edu
>
> Population Biology Graduate Group       tel. (530) 752-9977
 
--
Best Regards,
Mark
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