Okay, I'll bite!

Much of taxonomy does NOT exist in nature - categories
such as Genus, Family, Superfamily, Order, etc. have been
invented for our sense of needing to put order in our view
of nature.  HOWEVER, I thought that the original concept
of "species" is the only thing which does exist, harking
back to the initial definition of individuals which are
able to mate with each other and produce fertile
offspring (and thus eliminating crosses producing animals
such as the Missouri mule, which is a cross between a
horse and a donkey but is sterile).  Granted, this
definition of species has been extended to geographically
isolated populations which could not breed anyway because
they would never get toghether (but what would happen is
we were able to keep a pair of these separated "species"
alive in an aquarium)?

Doesn't this definition still hold as a natural fact, thus
validating the concept of species as not an invention by
man to simplify his thinking about life in genera

Needing a cup of coffee to clear the cobwebs,
Linda