Man’s best friend was the first of many animals domesticated by humans. But there was no before and after where dogs were suddenly a distinct population of wolves. While some ancient skeletons are clearly canines, there are plenty of obscure skeletons that preceded it. It is possible to get an idea of what happened using the genomes of modern and ancient dogs. But this analysis largely depends on what you think dogs from wolf populations look like.
Now, researchers have drawn a much clearer picture of wolf evolution over the past 100,000 years. The picture it paints is a population that remains a single entity despite being dispersed across continents in the Arctic, with populations sporadically fresh from the core concentrated in Siberia. Many dog breeds seem to have descended from populations of East Asian wolves. But others seem to have received significant input from populations in the Middle East – but it is unclear whether those populations were wolves or dogs.
wolves around the north
This new work required the ability to sequence ancient DNA, which involved obtaining DNA from the skeletons of 66 wolves, which collectively covered about 100,000 years of evolution, including most of the last ice age. Wolves are found in the Northern Hemisphere, and the skeletons used here are closer to the Arctic (perhaps partly because the DNA survives better in cooler climates). But they are widely distributed, with representations from Europe, Asia and North America. The researchers included some genomes from modern wolves as well as five ancient wolf genomes that others had analyzed.
Generally, you expect to find territorial populations that often don’t match their more distant ties. If you map the most closely related genomes, you will usually find that they tend to cluster together. Not so here; Instead, the ancient wolf genomes got lumped together over time. That is, a given wolf was likely to be closely related to other wolves living at roughly the same time, regardless of where those wolves lived on the planet.
Studies of modern wolves indicate that the local population has evolved since the last peak of the last glacial period. But all these populations are more closely related to each other than to wolves before the peak of the ice age.
How did these animals maintain genetic continuity over the vast distances separating them? Apparently, from the repeated expansion of the population in Siberia. Somewhere between 100,000 years ago there was a distinct population of European wolves. But continued arrivals from Siberia gradually reduce the ancestral European presence to anywhere between 10 and 40 percent, depending on the animal. In North America, in contrast, all extant wolves are mainly derived from Siberia, with the rest contributing from interbreeding with coyotes.
One consequence of having a global population is that favorable mutations tend to spread rapidly around the world. The researchers found 24 regions of the genome that seemed to carry useful adaptations, and these useful parts of the DNA appeared in all wolf populations examined.
went to the dogs
So, what can we say about dogs? They also look like Siberian wolves who lived just before the last peak of the Ice Age. But when every wolf older than that point was tested for close association with dogs, the relationship was not strong. This suggests that if dogs were derived from a specific wolf population, we do not have the DNA of that population.
But the researchers found that there was a good match if you had a population that was mostly the Siberian wolf, a fraction of which (between 10 and 20 percent) of its DNA came from a different canid, the dhole, which is also found in Asia. Some breeds of dogs in East Asia seem to have retained this lineage to the present day.
But other breeds in Europe and Africa make up a substantial contribution to the wolf population that is most closely related to an extant wolf from Syria. Researchers estimate that roughly half the genome of a Middle Eastern dog from about 7,500 years ago was from this local source and half from a Siberian ancestor. Many dogs in Africa and Europe have anywhere from 20 to 60 percent of their genomes from this additional ancestor.
Overall, their data support a model where dogs were first domesticated in East Asia, where most of the existing breeds are derived entirely from Siberian ancestors. But as our best friend spread across Asia with us, it came into contact with another population near the Middle East. That population could have been wolves, a dog population that was domesticated separately, or it could have been somewhere in between—there’s no way to tell with genetic data.
In any case, the wolf data provides some context as to why reconciling the ancestry of dogs has been so challenging: genetically, wolves are unusual in being global populations that regularly disrupt stable, long-term regional populations. Ways to brainstorm. , One consequence of this is that it makes no sense to seek wolf populations that are tightly coupled to dogs as a way of identifying domesticated dogs. Even if a population of wolves existed at the time, it would soon mix with other populations.
Nature2022. DOI: 10.1038/s41586-022-04824-9 (About DOI).