>Hi Tom, Hi Mark.
>
>I am not a respected malacologist..heck, I'm not even a disrespected
>one..but I share Tom's idea. Why wouldn't subspecies appear in the same
>area as parent species..or at the very least in overlapping areas?
>Subspecies apparently share some of the same characteristics as the
>parent species..I can see where geographical separation could have
>caused some of the evolutionary differences that would split them into
>subspecies, but there must be some common link or why would they be
>designated subspecies instead of new species?
>
>Patti "I am so confused" Lounsbury
>New Mexico
>
 
The basic idea is that if two forms belong to the same species, they should
be able to interbreed.  If they occur in the same place at the same time
and interbreed, then the genetic characteristics should be mixed together.
If two distinct forms occur in the same place at the same time, either it's
just different minor forms of one species, or two distinct species.  This
is why geographic (or chronological, in the case of fossils) separation is
thought to be necessary for subspecies.
 
However, in defense of sympatric subspecies, it seems possible that we have
not yet noticed what keeps the two subspecies apart and that individuals
that seem to us to be in the same place and time really do keep apart for
some reason.   Or we could have just happened to sample the boundary region
between two subspecies.
 
David Campbell
 
"Old Seashells"
 
Department of Geology
CB 3315 Mitchell Hall
University of North Carolina at Chapel Hill
Chapel Hill NC 27599-3315
USA
 
919-962-0685
FAX 919-966-4519
 
"He had discovered an unknown bivalve, forming a new genus"-E. A. Poe, The
Gold Bug