Dogs are too pure for this world. This fact is known. If supernatural explanations were sufficient, we could safely say that dogs descended from the heavens to bring us joy.
Reality, as ever, gets in the way with its need for “logic” and “evidence.” The truth is that we created dogs gradually by unconsciously selecting for traits that made wild wolves increasingly puppy-like. Yes, modern dogs are essentially just perma-puppies. That much is clear. What we’re not quite certain about is where and how this happened. Was there one uber dog who became the common ancestor for all future pups? Did the humans of one particular region successfully get wolves to cooperate? Or did that happen multiple times around the world, such that dogs converged into one species with many breeds?
One new study has a theory, but it doesn’t resolve the debate. A group of biologists, geneticists, and archaeologists looked at some of the oldest dog remains and performed a genetic analysis to figure out how related they were to each other. They published those findings on Tuesday in Nature Communications.
But first, a quick recap. To understand these new results, you have to understand last year’s big study on dog origins. That paper, written by an entirely separate group, proposed an idea that was new at the time: that dog domestication actually happened twice. It argued that there was a dog population in the east and another in the west. The researchers estimated that around 14,000-6,000 years ago, that divide between dog groups already existed—but since the oldest dog fossils in both the east and west are older than that, it follows that the populations were already separate. That is, they was never one big group of dogs that split into two over time. Rather, domestication happened twice, such that by 14,000-6,000 years ago there were already two distinct populations. Then, as humans migrated from east to west, eastern dogs mixed with the western dogs, largely supplanting the western population and creating the illusion of a single lineage.
This new study essentially argues against that hypothesis. The ancient German dog remains they looked at are separated by several thousand years, but in that time there’s been little genetic change. That suggests that there’s little evidence of the huge population overhaul you’d expect from the intermingling of two entirely separate dog groups. And what’s more, the new study argues, last year’s group miscalculated the east-west divide. It didn’t happen 14,000-6,000 years ago—it was more like 17,000-24,000 years ago.
If the divide happened that long ago, you don’t run into the issue of having fossils from before dogs should have spread around the globe. So you don’t need the explanation of two domestication events. Instead, you have a much simpler explanation: domestication happened once, about 20,000 to 40,000 years ago, and dogs spread out from there. The populations in the east and west grew more genetically distinct from each other over time, but the east-west migration simply allowed two formerly-connected groups to mix with each other again. That would explain why you don’t see a huge shift in the genetic composition of the western dog population. There was no new eastern dog group that entered the mating fray, it was just a big family reunion.
None of this means that the debate is over. It just means there’s more information to digest and discuss. And really, isn’t that the beauty of science? We can all love and appreciate dogs for the good good boys that they are, while still disagreeing over where they came from. The arc of scientific progress may be long, but it bends towards truth. And belly rubs.