This scientific study has just been published by Laura Shanno, Postdoctoral Research Associate in Biological Sciences, Cornell University
“The story of the origin of the dog is generally told as follows: between 30,000 and 16,000 years ago, wolves found themselves under pressure, hungry, their hunting territory having been taken over by humans. Strong fortunately, these resourceful wolves had spotted that the men had a tendency to leave good things to eat around. Collecting the leftovers seemed easier to them than going out to hunt, so they spawned with the human population.
Wolves are rather annoying neighbors. However, some of them less than others. Humans were more likely to tolerate the proximity of less aggressive, more self-oriented wolves. Also, other predators are less likely to attack you when you are surrounded by wolves. Thus, humans and the most sociable wolves have made a kind of agreement: tolerance and food for the most docile and useful wolves.
The docile and intelligent wolves had even more docile and intelligent cubs, and over time it was more and more enjoyable to be around them. Obviously, friendly and helpful wolves frolicking among people and eating leftovers aren’t really wolves. We have a word to describe them: they are dogs.
Here is the most probable hypothesis put forward by biologists on the “how” of the appearance of dogs. We have an idea of “when” it happened, but it was more difficult to know “where”. Who was the first to turn marauding gray wolves into real dogs?
In search of geographical origin
To find out more, the scientists looked at mitochondrial DNA, inherited exclusively from the mother’s side, and the Y chromosome, representative of paternal DNA. They drew the following suggestion: dogs were first domesticated in China, south of the Yangtze River.
However, the oldest dog bones that could be found were unearthed on the other side of Eurasia, in Northern Europe. Additionally, the mitochondrial DNA of modern dogs is similar to that of ancient European wolves.
Finally, Middle Eastern wolves share a large number of genetic sequences with today’s dogs, suggesting that these Middle Eastern wolves are the ancestral wolves.
All of this evidence points to the dogs coming from somewhere in Eurasia. But my colleagues and I wanted to narrow the field a bit. And to do that, we thought that for our new study, we would need to get DNA from as many dogs as possible.
dogs are everywhere
Dogs are found almost anywhere there are people. Over time, we bred them to do everything from herders to fishing dogs. The breeds we have created come in a wide variety of sizes and appearances, from small Chihuahuas to giant Danes. The vast majority of these canine breeds are no older than 200 years, and come from Europe. But these pedigree dogs, or even animals hybridized with them, are a minority on the planet.
Most dogs are animals that are found roaming villages, living around and among people, but not necessarily looking like what you might consider a house pet. You can learn a lot from ancient dogs by studying these village animals, compared to purebred dogs, because they have more genetic diversity. Thus, the number of variants of a single gene of a village dog is greater than that of a purebred animal.
All dogs are descended from a certain group of wolves, and thus benefit from some of the genetic diversity of wolves. As purebred dogs were formed from a select group of dogs, they carry only a small portion of canine genetic diversity.
On the trail of DNA sequences
Scientists in our lab have traveled to a wide variety of destinations to collect blood or saliva samples from dogs. In other places where we were unable to go, collaborators sent us samples. It wasn’t too difficult: the village dogs are quite easy to approach by searchers bringing some food.
In total, we extracted DNA from samples from 549 dogs from 38 countries representative of the entire planet, as well as DNA from 4676 purebred dogs. Our lab at Cornell University is located in the same building as a veterinary clinic, which came in handy since most of our purebred dogs came here for treatment.
Once our samples were collected, we were able to determine the genotype of each dog on approximately 180,000 points of its genome. This was the largest collection of data ever used to examine the question of dog origins.
We were looking for a very specific pattern of genetic diversity forged by history. When a given group of wolves became a group of dogs, the genetic diversity of the latter was only that of the group of wolves. When some of these dogs traveled with humans to other regions, or were sold to other inhabitants in other regions, they carried with them only part of the genetic diversity of the group of dogs. of origin, and, by extension, only part of the total diversity.
Thus, we expected the original dog population to be the most genetically diverse. One should be able to spot a decreasing diversity gradient for dog populations as they move away from the origin.
And that’s what we observed when we compared the genomes of dogs from different populations. Dogs from Central Asia, Mongolia and Nepal are the most diverse, with genomes corresponding to the oldest variations just after the start of domestication. When we look at the same DNA markers in dogs from neighboring regions, the diversity is in decline. And it decreases further as one moves away from Central Asia. That’s what you’d expect if the first humans who turned a population of marauding gray wolves into dogs were from Central Asia.
Looking at the large body of dog data that has been collected, we can detect a very clear signal that most of the dogs living on the planet today are descended from Central Asian dogs. However, our study only concerns current dogs. We do not have information about past animals that did not leave descendants. Moreover, the patterns of diversity we observed reflect the origins of dogs but also everything that has happened to their populations since their domestication.
Other scientists have extracted DNA from the bones of ancient dogs and these samples should yield interesting evidence for time periods even closer to domestication. However, studies of ancient DNA are limited by the number of bones available, material that varies for many reasons other than the historical distribution of dog populations. For example, some environments are more conducive than others to the preservation of bones and DNA. Similarly, some areas have been seriously excavated by archaeologists, and others have not.
In conclusion, if we are able to spot common traits in ancient and modern dogs, we will clarify the history of the dog and its best friend, the human.”