Looking for Refs for Reality of Species

[Mike Taylor <mike@indexdata.com>]

Dear DMLers,

It seems to be established wisdom that for extant taxa, species are
objectively real while genera are merely a convenient abstraction.
But can anyone send me any references (or better still, PDFs) in which
this stance is actually argued for rather than merely being stated?
Please respond off-list; I will summarise to the list.  Many thanks.

 _/|_    _______________________________________________________________
/o ) \/  Mike Taylor  <mike@indexdata.com>  http://www.miketaylor.org.uk
)_v__/\  "Observations on becoming a good writer: 1) The most important
         virtue in a writer is the will to write" -- Greg Gunther.