How Dogs (Eventually) Became Our Best Friends

How Dogs (Eventually) Became Our Best Friends

It was the summer of 2018 in Siberia, and a patch of permafrost near the Indigirka River had melted enough to uncover the body of a two-month-old puppy. After its almost perfectly preserved remains were discovered, scientists determined that the puppy was an astonishing 18,000 years old. The frozen animal was nicknamed “Dogor” - not only the word for ‘friend’ in the local language, but also a clever play on words: is it a dog, or…? Something else? And, despite its age, it still had most of its fur, teeth, and even a cute little nose preserved.

But while Dogor was in really good condition for a nearly 20,000-year-old pup, scientists were unable to confirm what species it belonged to. Was it a dog or was it a wolf? Or was it something in between? Dogor comes from the period of time when scientists think wolves were becoming domesticated, so knowing whether it was a wolf or a dog could help us better understand the specific time, and maybe even the place, that domestication occurred. Because, there’s still a lot we don’t know about how wolves went from fairy tale villains to our canine companions.

Like, when did they first become domesticated? Where did this happen? And what did the process look like, in terms of genetics and anatomy? We’re still figuring out the details, but most scientists agree that it took thousands of years of interactions to develop our deep bond with these good boys and girls. Modern dogs… like my good friend Abby here… belong to the subspecies known as Canis lupus familiaris. And we can trace their origins back to a now-extinct species of wolf from the Pleistocene, an ancestor they share with the modern grey wolf, called Canis lupus. But the exact species of this ancestor is still unknown.

While some potential ancestral wolf species - like the extinct species from which the Taimyr wolf, a specimen discovered in Northern Siberia, is from - have been identified, genetic analysis has shown that they’re not direct ancestors to what would become Canis lupus familiaris. What we can say from studies of dog and wolf genomes is that wolves and dogs began to genetically diverge from each other sometime between about 40,000 and 27,000 years ago. And figuring out the exact timing is tough, because it looks like the split happened over a very short period of time, and there was probably interbreeding between domestic dogs and wild wolves along human migration routes. So dogs still looked pretty wolf-like at the start of domestication.

It’s also complicated because these two species diverging genetically isn’t necessarily the same thing as domestication; one’s just a split in the gene pool, while the other’s the whole behavioral and genetic process that humans were involved in. But one of the key genetic traits wolves and modern dogs share, that has been really strongly selected for in modern dogs, seems to be hypersociability, which is the tendency for adult animals to initiate social contact even with members of other species. And for some wolves, this tendency, along with other behaviors, like scavenging for food, could’ve made them a better fit for eventual domestication. These traits also would’ve been useful as human settlements became more widespread, with resources that these canines definitely would have wanted.

This is known as the commensal pathway to domestication, where an animal benefits from a relationship with humans, but there’s little to no benefit for the humans themselves... well you know at least at first. In this case, proto-dogs were drawn to the discarded human food, which also likely attracted other animals that they could’ve preyed on, too. And there seems to be some evidence that this was probably happening around 28,500 years ago. A new paper published in 2020 was able to distinguish between two different types of canids from a site in the Czech Republic based on the microscopic wear on their teeth. One group had wear that better matched a diet with more meat in it, while the other group had wear that suggested they’d been chomping on harder, more brittle foods - things like bone. And the researchers think the difference means that the bone-chewing group was hanging around this human settlement more and eating their scraps.

Eventually, humans realized that wolves - once domesticated - could be useful: they could be guards, work with hunters, and even help with domesticating other livestock species.

And after that, wherever humans went, their canine companions followed. In fact, we can actually track the spread of agriculture through a particular genetic adaptation in dogs! In 2013, scientists were able to isolate the gene associated with the change from the carnivorous diet of wolves to a more starchy diet in dogs. Domestic dogs have more copies of the gene known as AMY2B than wolves do. AMY2B codes for an enzyme that’s secreted by the pancreas that breaks down starch. An increase in starch consumption in people is often associated with agriculture - like growing wheat and rice. And domesticated dogs living in human settlements would’ve been fed the kinds of things that people were eating, too.

Along with the difficulties in figuring out when dogs were domesticated, there’s also been some debate about whether it happened once or more than once. Like cats, dogs were once thought to have been domesticated twice, because in 2016 researchers showed that the genetic divergence between European and Asian dogs seemed to happen after dogs were found in these areas, suggesting domestication happened in both Europe and Asia. However, another study from 2017 suggests that dogs may only have been domesticated once. This research on the genomes of two really old dog specimens from Germany shows that this might’ve happened as far back as 20,000 to 40,000 years ago!

One set of dog remains was 7,200 years old and the other 4,700 years old. And by comparing them to modern wolves and dogs, scientists were able to find that they both had between 70-80% of European ancestry within their genetic makeup. And this study found a much older date for the genetic divergence between European and Asian dogs than the 2016 study did - old enough to suggest that domestication happened just the one time. So it seems there was one continuous lineage of domesticated dogs, instead of two separate domestication events.

While we’re still figuring out when all of this took place and how it happened, it didn’t seem to take that long before people were deeply attached to their pups. And we can see this bond in the archaeological record with burials. Across Europe, Asia, Africa, and North America, dog burials can be found spanning the Late Pleistocene to the Mid-Holocene Epoch. What makes these dog burials special is that many of them were treated and deposited in ways that are really similar to how humans are buried. This implies that these dogs were seen as very close companions, even in death.

For example, the remains of a male dog were recovered by archaeologists at the 9,000 or so years old cemetery in Siberia alongside other artifacts, like a spoon made from a large antler. This dog was an older adult, with evidence of wounds that were partially healed by the time he died, showing that he had been cared for during his life. An analysis of the chemistry of one of his vertebra showed that his diet included both terrestrial and aquatic resources, similar to the diets of the people at the site. This might mean that these dogs and humans lived in close proximity, even sharing food.

We also see mixed burials in some cultures, where both dogs and humans are laid to rest together. In fact, the earliest known burial of a dog -- a puppy that was buried around 16,000 years ago in Germany -- was actually found alongside two human bodies! Dogs were also buried alongside their humans in Egypt, where dogs were often used in hunting and guarding. This may have been the case for a mummified dog found in a tomb at Valley of the Kings, which may have been a favorite hunting dog of one of the rulers buried nearby.

Over thousands of years, domestication created both physical and genetic changes in dogs. While many early dogs looked pretty similar to each other, new breeds were developed to meet a variety of human needs, and coat colors and textures became more diverse. Many of these changes can be traced to the cross-breeding and hybridization of individual dog populations, as humans moved around the planet with their canine companions and came across new groups of canids.

Today, there are hundreds of dog breeds, and most of them aren’t actually that old. They came about because of the introduction of dog shows during the Victorian era in Britain. So dogs were originally drawn to our ancestors for food, but they eventually bonded with us, working and living alongside us for thousands of years. And this bond continued even after death, based on the archaeological record of human and dog burials. But the origins of this relationship are still more complicated than scientists originally thought, with new discoveries changing the history of dog domestication all the time

And we’re still waiting to find out the DNA results of Dogor, that 18,000-year-old puppy from Siberia. The hope is that it can shed some light on the early days of domestication. But, at the very least, we can say that dogs have been our species’ best friend, for a very, very long time.

Gotta give a quick shoutout to David Howe, the ethnocynology guru, for making sure what had our “pups” in a row.

Big high fives to this month’s Paws-itively awesome Eontologists: Patrick Seifert, Jake Hart, Jon Davison Ng, Sean Dennis, Konstantin Haase, and Steve!

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