Good question! Luckily *full disclosure* my friend Jill Arnel, of Maggie and Geordie the Cairn Terriers fame, is a professional writer who concentrates on dogs. She's just written an article for Suite 101 on the dog-variety subject, and I learned some things.
Did you know
-- why wolves, coyotes, and domestic dogs can interbreed? It's because they have the same number of chromosomes: 78.
-- Nobody's exactly sure where the word "dog" came from? The Old English word for dog, dogca, emerged in the 13th century.
-- The Latin word "canis" for dog gave its name to the Canary Islands?
Learn some more!
If the link won't work try this -- http://dogs.suite101.com/article.cfm/why_dogs_are_so_physically_diverse