Dogs may have joined humans more than once, DNA from ancient wolves shows

(ORDO NEWS) — The beloved dog that snores on your couch or sticks its nose under your arm during dinner comes from a much wilder creature. At some point, dogs evolved from gray wolves under the direction of domestication and evolved into a variety of furry creatures that fill our homes and hearts with such joy today.

However, when and how exactly this process occurred remains a mystery. Now, ancient DNA, including that of wolves preserved in the permafrost for tens of thousands of years, is shedding light on how wild wolves became some of our best non-human friends.

“Through this project, we have significantly increased the number of sequenced genomes of ancient wolves, which allowed us to create a detailed picture of the origin of wolves over time, including at the time of the origin of dogs,” explains geneticist Anders Bergström from the Francis Crick Institute in the UK.

“In trying to fit the dog into this picture, we found that dogs are descended from at least two separate wolf populations – an eastern source from which all dogs are descended, and a separate more western source from which some dogs are descended.”

Today, all domestic dogs, from the smallest Chihuahua to the mightiest mastiff, belong to the same species – Canis familiaris.

And they are all descended from wolf ancestors in common with the modern gray wolf (Canis lupus). However, the chronology of events is obscure and hotly disputed. Some scientists controversially suggest that this process began over 100,000 years ago.

A recent paper by Bergström and colleagues examined the DNA of 32 dogs dating from 100 to 32,000 years ago. They found that dogs diversified as early as 11,000 years ago, so it must have happened earlier.

It is generally accepted that domestication, and therefore diversification, began sometime between 40,000 and 20,000 years ago, and probably more than once, in different parts of the world.

The new work is based on 72 ancient wolf genomes, 66 of which were rescanned for this analysis and date back 100,000 years ago, spanning approximately 30,000 generations of wolves across Europe, Siberia and North America.

They were compared with 68 genomes of modern wolves, ancient and modern dogs, and other canid species such as coyotes.

Specimens included famous recent finds, including a near-perfectly preserved baby Dogor locked up for 18,000 years in Siberian permafrost, and a 32,000-year-old wolf head, also from Siberian permafrost.

Genomes have shown that both ancient and modern dogs are more closely related to the ancient wolves of Asia than to those that lived in Europe. This suggests that domestication and diversification may have started in the East rather than the West.

However, something was strange. Early dogs in northeastern Europe, Siberia and America are 100 percent descended from the eastern wolf population. Early dogs from the Middle East, Africa, and southern Europe have DNA contributions from wolves related to modern populations in Southeast Eurasia.

This may confirm previous findings that dogs were domesticated more than once, in different parts of the world. However, this could also mean that dogs were domesticated first in the East and then mixed with the wild wolf population.

It is not yet clear which of these scenarios could have taken place; none of the genomes in the study are direct matches, so more information is needed.

The research also allowed the team to learn more about ancient wolves and their evolution. In particular, they traced a gene variant that went from very rare to almost ubiquitous over a period of about 10,000 years.

This mutation affects a gene called IFT88, which is involved in the development of the head and jaw bones, which is still present in almost all dogs and wolves today.

The team does not know why this mutation has become so common, but it may be due to natural selection; perhaps the types of loot available made the changes brought about by the mutation especially beneficial. It’s also possible that the gene does something we don’t know about, and the mutation did some unknown benefit.

“For the first time, scientists have directly traced natural selection in a large animal over 100,000 years, watching evolution in real time, rather than trying to reconstruct it from DNA today,” says geneticist and senior author Pontus Skoglund, also from Crick.

“We found a few cases where the mutations spread across the entire wolf species, which was possible because the species was highly related over long distances. It may be due to this connection that the wolves managed to survive the ice age, while many other large predators disappeared.”

These results suggest that such temporal large-scale studies of whole genomes can give us much more detailed insight into how species move and change over time.

The next stage of the study will be an attempt to determine even more precisely which wolves were the ancestors of modern dogs. The team is expanding their study to regions of the world not covered by this analysis.

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