Dogs may have split from wolves in a single domestication event 40,000 years ago, per a new study in Nature Communications. The research challenges an earlier study claiming dogs were domesticated twice — in Asia and Europe.

What they found: Researchers analyzed genomes from dog fossils — including a 7,000-year-old skull found in Germany and a 5,000-year-old specimen from Ireland — and compared them to DNA from modern dogs and wolves. The rates of mutation in the genomes suggest dogs split from wolves about 40,000 years ago and then again into European and Asian breeds about 20,000 years ago, the study says. Domestication happened sometime in between.

• Not so fast: This study follows a 2016 paper suggesting there were two domestication events: one in Europe and one in Asia. The striking genetic differences between European and Asian dogs supports this hypothesis, Gregor Larson, an author of the 2016 paper, told the Washington Post. He added that scientists have not found ancient dog bones in the middle of the Eurasian continent, suggesting there was no split, but in fact two cases of domestication.
• A trend: New technology is allowing scientists to analyze ancient DNA samples with more scrutiny and, as a result, piece together timelines of animal domestication that, in turn, can tell us more about the ancient humans they lived beside.