Real species and ideology

[Michael Bayly]

Hi Richard,

After my last post, I realised I hadn't really addressed your last scenario, i.e.,

>>Now suppose that B & C never actually went extinct, but instead inhabited a
>>part of the earth that Humans have a very difficult time accessing (a few
>>prime examples come to mind...)  For 250 years, we never knew the existence
>>of B & C -- we only knew of A & D, and our genetic data showed them to form
>>a clear monophyletic grouping with respect to all other known taxa.  The
>>zone of gene exchange between A & D could have been thought of either as a
>>morphocline between sister groups, or as introgressive hybridization between
>>sister groups.  But then some intrepid taxonomist goes out and discovers
>>populations of B & C, and genetic data show them to have the phylogenetic
>>relationships as defined above: ((AB)(CD)).  Would we then necessarily
>>eliminate the morphocline option for A & D altogether? What aspect of our
>>knowledge of the existence of B & C changed the relationship between A & D?


I would say that how you revise your assessment depends on the "strength" of the evidence for the relationship ((AB)(CD)).  Additional taxon sampling (or additional data of any sort - taxa or characters), can lead us to revise an assessment of relationships, and of the historical interpretations we associate with them, be they explanations of introgression/clinal variation, or historical biogeography, or co-evolution etc...

A & D have an historical relationship of some kind.  Obviously this doesn't change because we discover B & C, and gather new genetic (or other) data - but our assessment of their relationships and historical scenarios can change.  Still more data might come to hand and we might change our minds again.....

Any explanation is just a theory that the fits the available data.  And, in some sets of circumstances we could argue that introgression is a better supported hypothesis than clinal variation.

cheers,
Mike

----------------
Michael Bayly
Research Scientist in Plant Biosystematics
Museum of New Zealand Te Papa Tongarewa
PO Box 467 
Wellington, New Zealand
Ph: +644 381 7262
Fax: +644 381 7070

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Visit the Te Papa website http://www.tepapa.govt.nz
The email message together with the accompanying attachments may be
CONFIDENTIAL. If you have received this message in error, please notify
mail at tepapa.govt.nz immediately and delete the original message. The
views expressed in this message are those of the individual sender,
except where the sender specifically states them to be views of Te Papa.  
Te Papa employs strict virus checking measures and accepts no liability
for any loss caused either directly or indirectly by a virus arising
from the use of this message or any attached file.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++