This works in a way similar to my description above -- each subgroup is "not too different" from its neighbors to interbreed, but over the whole extent of the line/ring, the far "ends" have diverged enough from each other to be unable to mate.
STILL real easy to SAY!
857 posted on 12/30/2005 10:28:26 AM PST by Elsie
(Heck is where people, who don't believe in Gosh, think they are not going....)