Dogs and humans have been buddies for at least 20,000 years. For most of that time, it was thought that the relationship had been primarily about work—not belly rubs and games of fetch. Early dogs had jobs, like pulling sleds in the tundra or hunting with early humans in Jordan. At least, that’s what archaeologists suspected based on a spinal condition in ancient canine bones called spondylosis deformans, which for decades has been interpreted as a sign that a dog engaged in carrying or pulling. But a new study published in the journal PLOS One calls that idea into question, suggesting that the spine issues are a sign the dogs lived long, healthy lives.
Anthropologist Katherine Latham of the University of Alberta, the study’s lead author, says it’s been difficult for archaeologists to figure out the details of how humans used early dogs as pack animals since any harnesses or sleds were made of material that doesn’t readily survive in the archaeological record. Decades ago, researchers began using the presence of spondylosis deformans, in which bony spurs or bridges form around discs and spinal joints, as an indicator that a dog was used to drag or carry loads.
“Since at least the 1970s, many archaeologists have assumed the condition is a telltale sign that early dogs pulled heavy loads,” she tells David Grimm at Science. “But there was no empirical evidence. It’s an idea that has become perpetuated in literature without anyone going back and testing it.”
So Latham decided to investigate the condition. Over the course of five months, she traveled to museums and university collections in North America and Europe to examine canid bones found in archaeological digs, including 136 non-transport dogs, 19 sled dogs and 241 sets of wolf remains.
Latham found that the spinal condition was common in all the dogs and wolves, even the non-working dogs. In fact, she found it was primarily correlated to age rather than labor. By three to five years old, half of the dogs had some degree of the disease, and by age nine, all the animals had it.
“To find that the condition is common in archeological dogs, then, does not suggest they were being overworked and injured,” Robert Losey, co-author and expert on the human-dog relationship also from the University of Alberta, says in a press release. “Instead, it suggests the dogs were living to old ages, which makes the condition appear very common in the archeological samples.”
The new study means archaeologists need to rethink some of their assumptions about how prevalent working dogs were in the past. That doesn’t mean ancient dogs didn’t carry loads, but tracing the origin of the practice can be challenging. On the Great Plains of North America, Native American tribes employed dogs for centuries, outfitting them with a load-bearing frame called a travois that the animals pulled behind them. Losey told Kristin Romey at National Geographic in 2016 that there's evidence the tradition of dogs pulling sleds in the Arctic is at least 2,000 years old, though he believes it could be much older.
While the study makes the history of working dogs more muddled, it does clarify some things about the bond between dogs and humans. “Ancient dogs with a lot of spondylosis deformans are probably older dogs,” Latham tells Grimm. “And in order for them to have reached that age, someone must have been taking care of them. Humans were likely giving them food and sharing the warmth of their fires and the protection of their shelters.”
So maybe dogs were more than just four-legged porters and hunting guides to our ancestors after all.