The 2012 winner, crowned on June 22, is eight-year-old Mugly, a bald and beady-eyed crested who sports stringy whiskers weirdly reminiscent of dental floss. (See a picture of Miss Ellie, 2009 World's Ugliest Dog.)

What makes the dog so ugly is its signature hairlessness, said Adam Boyko, an authority on canine genetics at Cornell University.

"If you see a lot of hairless people, for instance, all of a sudden you're going to start noticing moles and weird skin," Boyko said. "It just makes everything else that's weird stand out more." In the case of the Chinese crested, the crinkly, mottled skin is prominently displayed.

"Presumably it's just an ancient mutation that happened one time, and breeders liked it and