But a few indigenous breeds in North America have a purer pedigree — at least one has genetic roots in the continent that stretch back 1,000 years or more, according to a new study. These modern North American breeds — including that current urban darling, the Chihuahua — descended from the continent's original canine inhabitants and have not mixed much with European breeds.

"There is ... archaeological and historical evidence that the native peoples of the Americas had dogs," says Peter Savolainen, an evolutionary geneticist at the KTH-Royal Institute of Technology in Stockholm and an author of the new study. When humans first came to the Americas from Asia, they're thought to have brought with them dogs, whose descendants populated North and South America for centuries.

But those dogs didn't fare too well once Christopher Columbus got here. "It's known that most of these dogs were eradicated when Europeans arrived in America," says Savolainen. Pathogens the Europeans brought killed humans and dogs alike, he says.