Barking up a big tree. (Credit: Ahmed Mateo, Wikimedia Commons)

Dogs vary more in size than any other mammal on earth, from teacup-sized Chihuahuas to towering Great Danes. Most of this extreme variation has arisen over the past two centuries with the rise of modern dog breeding.  But Victorian dog fanciers didn’t create these breeds out of whole cloth, a new study finds. Instead, they hijacked two tiny genetic changes that have been present in the ancestors of dogs since at least the last Ice Age.  The study, which I cover this week in Science,  doesn’t just help explain why dogs are among the most malleable creatures on the planet. It may also elucidate how and why the sizes of wolves and their relatives have changed over evolutionary history.

A 19th-century sketch of the Japanese wolf. (Credit: Wikimedia Commons)

Where and when did dogs arise? It’s one of the greatest mysteries of domestication, and one that remains unresolved despite decades of study.

Scientists know that all modern dogs descend from a population of gray wolves. But exactly who these wolves were and where they lived has been unclear. And thus, so has the origins of dogs.

Now, a new study of Japanese wolves may be providing some answers. This mysterious animal lived in Japan for thousands of years, but humans wiped it out about a century ago. In a new study, a team of Japanese researchers sequenced ancient DNA from nine Japanese wolves and 11 dogs, and compared them to the sequences of a variety of other canids. The data suggest that Japanese wolves are more closely related to dogs than are any other wolves. More importantly, the DNA suggests that the ancestor of the dog and the Japanese wolf was the same: A population of gray wolves that lived in East Asia, and which has likely vanished.

In all, the study suggests that dogs arose in East Asia, though the timing is still unclear. The location jibes with two proposed locations of dog domestication: Northeastern Siberia and Southeast Asia. It also seems to rule out a European or Middle Eastern origin, which some researchers had posited.

More work will be needed to seal the deal, and to say whether this is one canine case that’s finally been closed.

The Chinese mountain cat. (Credit: https://commons.wikimedia.org/w/index.php?curid=31346955)

Unlike the ongoing mystery of where and when dogs arose, the history of cats is a less convoluted affair. Most scholars agree–based on both archaeological and genetic evidence–that domestic cats likely arose in the Middle East some 10,000 years ago.

Still, there have been hints that the cat story may not be as simple as it seems. In 2016, scientists reported evidence of a possible second domestication of cats–one that took place thousands of years later in China. Unlike the first cats, which descend from the African wildcat, these Asian kitties appear to have evolved from the leopard cat. Whatever happened, they didn’t last long; there’s no trace of them in today’s housecats. But the study did raise the intriguing possibility that cats may have been independently domesticated in Asia, as some argue happened with dogs.

New research appears to put that notion to rest. The largest genetic analysis of Chinese cats–including domestic cats, the Asiatic wildcat, and the mysterious Chinese mountain cat–finds that all domestic cats in the country are genetically indistinguishable from those elsewhere in the world. The researchers did find some Chinese mountain cat DNA in domestic cats, but that’s likely because the two have begun to interbreed as more and humans (and their cats) have shown up in the Tibetan Plateau–the realm of the Chinese mountain cat.

If the new study does have anything to say about domestic cats it’s that they may pose a threat to local wildcats. If domestic cat DNA begins to show up in the DNA of the Chinese mountain cat–an animal already considered vulnerable because of its low numbers and threats from humans–it could corrupt the genome of this unique creature, eventually scrubbing it from existence. A similar situation played out with the Scottish wildcat, which some now consider “functionally extinct” due to interbreeding with domestic cats.

Efforts are underway to save the Chinse mountain cats. But it remains to be seen if these felines will stand the test of time.

A cat wearing a bronze collar found in the Berenice pet cemetery. (Credit: M. Osypinska)

Ancient pet cemeteries are rare. Archaeologists do find dog and cat burials, sometimes dating back 10,000 years or more. But these creatures are typically interred alone, or with people, in one-offs–not in a dedicated burial ground. Researchers have also unearthed dozens of cat mummies and hundreds of dogs in single locations, but these appear to have been ritualistic burials; the animals were sacrificed or being honored for some sort of spiritual reason.

So a new find of nearly 600 cats and dogs buried in southwestern Egypt in what appears to be a bona-fide pet cemetery is exceptional. The animals were interred in single graves over the course of about a hundred years–from the mid 1st century to the mid 2nd century CE–and they were not sacrificed nor mummified. Instead, they appear to have been lovingly buried, often with collars or other jewelry, and protected by textiles or pieces of pottery. Many also appear to have survived sometimes serious injuries and disease, implying that people at this site–known as Berenice–may have cared for them much like we care for our pets today.

That’s especially remarkable, because this is a period of human history when pets are typically seen as working animals. And the residents of Berenice–merchants, slaves, and soldiers–would seem to have had little time for pet keeping, especially in this rough, isolated region. Did they love their cats and dogs because they hunted mice or guarded their homes? Or did they have a deeper, non-utilitarian connection with them, like many of us do today? With more research, such questions may not be lost to the sands of time.

Photo by PIXNIO

Given our deep and enduring relationship with dogs, it’s remarkable that scientists still don’t know where our canine pals came from, or when they arose. Researchers have speculated that dogs evolved everywhere from Southeast Asia to the Middle East, and that they may even have been domesticated more than once.

Now scientists are proposing a new time and place: Northeast Siberia, around 23,000 years ago. The work is based on mitochondrial DNA recovered from ancient dogs, which the researchers then compared to DNA from ancient humans. Where the patterns matched, the team was able to reconstruct the history of dogs all the way–possibly–to the beginning.

The study resolves several mysteries around doggy origins. Not only does it give a putative time and place, it also helps explain why dogs seem to appear in Europe and the Americas around the same time–15,000 years ago–which has led some to propose multiple domestications. The idea is that a group of people known as the Ancient North Siberians domesticated dogs and then traded them to people traveling both east and west. These animals would have been invaluable as hunters, guardians, and–perhaps most importantly–sled dogs, helping people travel vast distances and carry heavy kills back to camp.

The study also addresses another big canine conundrum: How dogs were domesticated in the first place. The prevailing idea has been that gray wolves inched closer and closer to human campsites to scavenge food, with the least timid ones evolving—over hundreds or thousands of years—into the gentle pups we know today. But the scenario doesn’t work if humans are traveling so far and wide that they’re always encountering different populations of wolves. It just so happens that the Ancient North Siberians were stuck in northeastern Siberia for thousands of years, because the harsh climate of the last Ice Age prevented them from traveling too far east or west. That may have given these humans time to turn the wolf into the dog–or for wolves to turn themselves into dogs, as many believe that dogs self-domesticated.

This isn’t likely to be the last word on where dogs came from. But for now, it’s an intriguing piece of the puzzle.