Dogs and Humans Didn’t Become Best Friends Overnight

First, we feared and ate them, a new isotope analysis reveals

When it comes to ancient remains, isotope analysis could help scientists separate dogs from wolves. Anja Seibert / Alamy

Dogs may be man’s best friend, but new research on ancient canine remains shows that the relationship didn’t develop overnight. For long periods of time, humans lived in tension with their canine companions, often eating them and skinning them for pelts. Theirs was a relationship of necessity and convenience.

“At that time (the relationship) obviously fluctuated,” says Stefan Ziegler, a scientist with the World Wildlife Fund and the coauthor of a study published recently in the Journal of Archaeological Science: Reports. “Sometimes people ate their dogs and sometimes they just used them as guard dogs and maybe even pets.”

Researchers learned this by analyzing the stable isotopes in the remains of dogs found in Western Europe. (Stable isotopes are forms of atoms that leave behind signatures in biological samples, revealing details about diet, environment and other conditions.) As the diet and lifestyle of humans shifted between the Middle and Late Stone Age, when dogs had already been domesticated, those of their dogs shifted right along with them.

The discovery tells us something about the changing nature of the relationship between humans and dogs. Domestication, after all, is rarely a tidy affair; it took cats 9,000 years to conquer the world, while the domestication of fluffy bunnies is a complicated affair full of dead ends and false turns. But the recent study could provide a new tool for archaeologists to sort out the level of domestication between the remains of ancient wolves and dogs.

Traditionally, archaeologists have determined whether remains are from dogs or wolves by relying on the size of their bones. Smaller width, shorter snouts and smaller teeth have generally been understood to mean the samples were dogs, according to Angela Perri, an archaeology research fellow at Durham University in the U.K. who was not involved with Ziegler’s study. But dividing samples based on morphological traits doesn’t take into account the small wolves or large dogs that might be exceptions to the rule. “It’s super subjective—that’s the problem,” says Perri.

Ziegler and his coauthors took a different tack. First, they examined the bones—which came from canines found from 36 sites spanning from modern day Denmark to Switzerland, dating from roughly 4500 B.C.E. to 2300 B.C.E—for marks that indicated the canines had been butchered and skinned for their pelts. These details would suggest that the remains were dogs, which could be used for meat or for their pelts when times were hard, rather than wolves which are more difficult to hunt. 

Lateral view of a lumbar vertebra
Lateral view of a lumbar vertebra of a Late Mesolithic dog from Germany with several cut marks by a flint knife. Jörg Ewersen

But they also took the analysis a step further. They reasoned that domestic dogs would share a similar diet to the humans they lived alongside, but different from their wild cousins. Through an examination of collagen from the bone fragments, the team found that the domestic dogs had higher levels of nitrogen and carbon isotopes, an indication that they were eating more seafood and certain grasses associated with human agriculture. Wolves, on the other hand, would show a varied but more strictly carnivorous diet.

“The data show that dogs and wolves must generally have had a different diet, which is reflected in the altered isotope ratios. Dogs could occasionally access human food sources and their diet must have been either more omnivorous or monotonous than that of wolves, depending on the feeding regime,” the authors say in the study.

Previous dog vs. wolf designations based only on the size of the bones were correct about 80 to 85 percent of the time, says Ziegler. The stable isotope analysis was more accurate, and even revealed a few mistaken identities among the earlier analyses.

Ziegler’s study shows some variation based on geography: dogs that lived near coastlines had more nitrogen isotopes, which indicates a higher intake of fish and seafood. The authors also found that the diet of the domestic dogs went through a change along the rough date lines of the Mesolithic and Neolithic, or from the middle to late Stone Age – a period when humans were starting to adopt some agricultural and shifting away from relying on hunting large animals and marine resources. 

Perri says that some of this is also evident in the visible remains from archaeological sites. She says that during the late Stone Age when agriculture began to take, people begin burying domestic dogs with special distinction less than they did when the dogs were valuable hunting companions. “They become pests, these things you have to feed and figure out what to do with,” she says.

This didn’t always turn out well for the dogs. Ziegler says that when food was scarce due to a frozen Baltic Sea and lack of other resources, domestic dogs would sometimes end up on the dinner table rather than underneath it. “Sometimes it really helps people to survive,” he says.

Perri says that she is excited that someone is looking at new techniques to solve the heated debate over the domestication of dogs. Most researchers agree that by 20,000 years ago we almost certainly had domestic dogs and that domestication first occurred somewhere in Eurasia. But there is a lot of debate on whether this first happened in Asia and spread west or the opposite. Some researchers even believe domestication began much earlier.

“People in our field, we need all of the help we can get to figure out this dog versus wolf thing,” she says. Perri was a coauthor on a paper which theorizes a dual origin, with domestic dogs appearing both in East Asia and Europe between 14,000 and 6,400 years ago.

Part of the problem with distinguishing between wolves and dogs is that both types of bones turn up relatively frequently at archaeological sites across the board. Perri says that in the glacial periods, evidence of skinning marks on bones discovered suggests humans would sometimes hunt wolves for the valuable insulation offered by their pelts.

Interspecies competition which led to dead wolves also occurred, with humans stealing freshly killed meal from a pack and vice versa. “It’s essentially a scene from The Revenant,” she says.

As a result, Perri believes that the diet of wolves would not have been that different from humans and the dogs that ate their scraps in the Paleolithic—which would make it difficult to use nitrogen or carbon isotope studies to mark any difference between wolves and their sellout cousins.

However, other isotopes—such as oxygen or strontium—could hold the key to separating wolf from dog, since their signatures can be traced to the subtly different environmental conditions. Scientists could see how far a canine moved and through which kinds of environments, knowing that domestic dogs would likely be less mobile and stick closer to humans.

“Isotopes are an interesting way forward,” she says. 

Get the latest Science stories in your inbox.