Enlarge / Eastern Gray Wolf is a mixture of Siberian origin and coyote DNA.
Man’s best friend was the first of many animals that humans domesticated. But there was no clear moment before and after, when dogs suddenly became a separate population of wolves. While some ancient skeletons are apparently dogs, there are many ambiguous skeletons earlier than that. It is possible to get an idea of what happened with the help of the genomes of modern and ancient dogs. But this analysis depends largely on what the wolf populations from which the dogs are derived look like.
Researchers have now created a much clearer picture of the last 100,000 years of wolf evolution. The picture he paints is a population that remains intact, even though it is scattered across the continents of the Arctic, with the population sporadically refreshed by the nucleus concentrated in Siberia. Many dog breeds appear to be derived from a population of East Asian wolves. But others also appear to have received significant contributions from a population in the Middle East – but it is not clear whether this population was wolves or dogs.
Wolves to the north
The ability to sequence ancient DNA was essential to this new work, which involved obtaining DNA from 66 wolf skeletons that together span 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 usually closer to the Arctic (probably in part because DNA survives better in cooler climates). But they are widespread, representing Europe, Asia and North America. The researchers also included five genomes of ancient wolves that others have analyzed, along with some genomes of modern wolves.
Advertising
You would usually expect to find regional populations that do not often mix with their more distant relationships. If you draw the most closely related genomes, you will usually find that they are grouped together. This is not the case here; instead, the ancient genomes of wolves have come together over time. That is, a wolf is most likely to be closely related to other wolves living at about the same time, no matter where those wolves live on the planet.
Studies of modern wolves show that local populations develop after the last peak of the last ice age. But all of these populations are more similar to each other than the wolves around before the peak of the ice age.
How have these animals preserved the genetic continuity of the vast distances that separate them? Apparently through the repeated expansion of the population in Siberia. Some 100,000 years ago, there was a separate population of European wolves. But continued arrivals from Siberia are gradually reducing the European ancestral presence to somewhere between 10 and 40 percent, depending on the animal. In North America, in contrast, all wolves today are mostly from Siberia, and the rest are the contribution of coyote crossings.
One consequence of having a global population is that beneficial mutations are spreading rapidly around the world. The researchers found 24 areas of the genome that appear to carry useful adaptations, and all of these useful regions of DNA appear in all wolf populations studied.
He went to the dogs
So what can we say about dogs? They also resemble Siberian wolves, which were alive just before the last peak of the ice age. But when any wolf older than this point was tested for close contact with dogs, the relationship was not stable. This suggests that if dogs are derived from a specific wolf population, we do not have DNA from that population.
Advertising
But the researchers found that there was a good match if you had a population that was predominantly a Siberian wolf with a piece of DNA (between 10 and 20 percent) coming from a different dog, the jule, which is also found in Asia. Some dog breeds in East Asia seem to have preserved this lineage to this day.
But other breeds in Europe and Africa appear to have made a major contribution from the wolf population, which is most closely related to today’s wolf in Syria. Researchers estimate that a dog from the Middle East about 7,500 years ago has about half the genome of this local source and half of Siberian ancestors. Many dogs in Africa and Europe have 20 to 60 percent of their genomes from this extra ancestor.
In general, their data support a model in which dogs were first domesticated in East Asia, where most of the breeds present are descended solely from Siberian ancestors. But as our best friend spread across Asia with us, he came into contact with another population, probably near the Middle East. This population may have been wolves, it may be a population of dogs that have been domesticated separately, or it may be somewhere in between – there is no way to tell by genetic data.
In any case, data on wolves provide some context for why the origins of dogs have been so difficult to rank: Genetically, wolves are unusual because they have a global population that regularly accumulates in a way that disrupts stable, long-term regional populations. One consequence of this is that it does not make much sense to look for a wolf population with which dogs are closely related as a way to identify where the dogs have been domesticated. Even if this wolf population existed at the time, it would probably mix with other populations soon after.
Nature, 2022. DOI: 10.1038 / s41586-022-04824-9 (For DOI).
Add Comment