Real species and ideology

Michael Bayly MichaelB at TEPAPA.GOVT.NZ
Thu Apr 22 09:20:47 CDT 2004

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.


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

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