...the researchers also found that all modern breeds--from poodles to malamutes--derive from at least two population bottlenecks: one that occurred thousands of years ago when humans bred dogs from wolves and one that happened in the last few hundred years as humans bred that ancestral population into the dogs of all shapes and sizes observable today.
Funny, but I was wondering about some of this just the other day. I think getting the Scientific American RSS feed was a REALLY good idea.