Their skeletal remains curled into sleep-like positions familiar to any dog owner, the 10,000-year-old canines found at a site in Illinois are the earliest known dogs of the Americas. Ever since they were unearthed nearly a half-century ago, the animals have been at the heart of a debate: Were the dogs of the New World descended from Eurasian wolves and then brought here by humans, or were they locally domesticated from American wolves?

New genetic research answers that question — and rev