The history of how dogs came to be domesticated is the subject of debated and ultimately incomplete research. Though the majority of scientists agree that "the only carnivore ever to be domesticated" originated from wolves, they are split when it comes to where dogs first became dogs and when. Recent research led by evolutionary biologist Robert K. Wayne and conflicting research led by Dr. Peter Savolainen narrowed the two most likely locations to Europe (between 18,000 and 32,000 years ago) and East China (over 32,000 years ago), The New York Times reported.

According to Wayne's theory, dogs evolved from wolves that left their pack to trail ancient nomadic humans for scraps of food. Humans kept them around (at least the friendlier dogs) for protection against larger carnivores like lions and bears as the two formed the beginnings of a mutual relationship that persists until the present day, according to The Washington Post.

Evolution theory has it that these opportunistic wolves became isolated from their packs and bred only with each other, propagating traits relating to congeniality and individualism more trademark to modern day dogs. Physically, however, they "looked like wolves," said Wayne. "It took some time before these proto-dogs started to look different."

As humans became more comfortable with these wolfish dogs, they selectively bred them for certain physical characteristics. Eventually, dogs physically and mentally separated from their ancestors, according to the study.

Wayne and his researchers determined that the first dogs came from Europe based on a 36,000 year old fossil resembling a wolf-dog hybrid.  Comparing the fossil's mitochondrial DNA to living groups of dogs, they found a better match among European dogs than breeds from any other region.

Elain Ostrander of the National Institutes of Health proclaimed Wayne's techniques sound. "When you have an ancient sample, sequencing the mitochondrial DNA is the right first thing to do."

Dr. Peter Savolainen chose to locate the origins of ancient dogs by comparing genomes, according to The New York Times. Based on the premise that dogs evolved from wolves, he measure the DNA of modern dogs against the DNA of modern wolves and found the closest resemblance occurred in East China varieties. Critics of his logic argue that interbreeding among wolves and dogs makes that assertion imprecise. Still, scientists are convinced enough to believe the research is incomplete.

"The fossils spoke for Europe, but the genetics spoke for Asia," said one of Wayne's co-authors and population geneticist at Finland's University of Turku Olaf Thalmann. "At some point, you have to combine the two stories."

"But there have been so many surprises in the history of this research on dog domestication that I'm holding my breath till we get more information," Wayne said.