After that domestication event, some things seem to have remained constant. According to the team’s findings, after dogs separated from wolves over 11,000 years ago, wolves never made a major re-entry into dog populations (until, perhaps, the contemporary wolf dog craze). Given that dogs and wolves belong to the same species and produce perfectly healthy offspring, this discovery came as a surprise to the authors. They deduced this result from the observation that some wolves are equally related to all ancient and modern dogs, which indicates that all dogs have the same amount of wolf ancestors. The logical explanation is that wolves did not contribute substantially to the dog’s gene pool after domestication. If, on the other hand, wolves had continued to interbreed with dogs, the team would have expected to observe that all wolves were more closely related. some dogs – who had wolves in their family trees after domestication – compared to others, who only had dog ancestors.
But, for some reason, the opposite has happened when it comes to the wolf genome: Dogs are universally more related to some wolves than others, indicating that dogs have actually contributed genetic material to wolf populations. This asymmetry between dogs and wolves can have a simple explanation: humans. “It shows us,” Lindblad-Toh says, “that people probably kept their dogs and looked after them and made sure they didn’t let wolves in.” Wolves had no such guardians.
But Liisa Loog, a postdoctoral researcher in Cambridge University’s Department of Genetics who was not involved in the study, believes it’s important to keep this finding in perspective. Note that the authors’ argument hinges on some specific hypothesis about how ancient wolves relate to modern wolves, which is impossible to confirm without studying ancient wolves directly. “The authors here are based on the assumption that this happened on a now extinct wolf population that was not sampled, and that is equally related to all modern day wolf populations,” he says. “This may be the case, but it may also not be the case.”
This hypothesis, and the hypotheses about geographic and climatic coherence that underlie the commercial hypothesis of Bergström and Frantz, mean that their findings and their theories cannot be confirmed without further research, such as similar studies of ancient wolf DNA. But, in the end, 27 dog genomes are a narrow window into the past: when working with such a small amount of data, assumptions become necessary. “DNA itself is just DNA,” says Bergström. “It needs that broader context of interpretation.”
The paucity of evidence, coupled with the difficulty of extracting high-quality DNA from such ancient bones, could make ancient DNA research seem like a rash effort: why not just get genetic samples from modern dogs and figure out the family tree from there? But ancient DNA also has some distinct advantages over modern DNA, especially when it comes to dogs. Many contemporary dogs owe their genetic profiles to the Victorian dog breeding craze, so signatures from their more distant past may be difficult to discern. Looking for evidence of ancient dogs in the genome of modern ones is like “looking for a needle in a haystack,” Loog says. So it can be helpful to go straight to the source. “Ancient DNA,” Loog says, “literally gives us this genetic picture of the past with timestamps.”
So while it may be difficult to learn about prehistoric dogs by studying their modern descendants, the special insights offered by ancient DNA can provide invaluable context for understanding how humans relate to dogs today. “Dogs are unique as predators, carnivores. And they were domesticated by hunter-gatherers, long before agriculture, and they were also able to spread so quickly to most groups, “Bergström says.” Somehow it’s surprisingly suitable for the human species to assume this animal as companion, although, a priori, it seems an unlikely candidate for domestication. “If Bergström and his colleagues are right, the human tradition of coexisting, breeding and protecting dogs and treating dogs not only as useful tools but as sources of social connection and emotional support, it may have a history of 11,000 years.Even before they figured out how to grow crops, humans may have known very well how to care for their animals and be looked after.
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