A study of dog DNA has shown that our "best friend" in the animal world may also be our oldest one.
The analysis reveals that dog domestication can be traced back 11,000 years, to the end of the last Ice Age.
This confirms that dogs were domesticated before any other known species.
Our canine companions were widespread across the northern hemisphere at this time, and had already split into five different types.
Despite the expansion of European dogs during the colonial era, traces of these ancient indigenous breeds survive today in the Americas, Asia, Africa and Oceania.
The research fills in some of the gaps in the natural history of our close animal companions.
Dr Pontus Skoglund, co-author of the study and group leader of the Ancient Genomics laboratory at London's Crick Institute, told BBC News: "Dogs are really unique in being this quite strange thing if you think about it, when all people were still hunter gatherers, they domesticate what is really a wild carnivore - wolves are pretty frightening in many parts of the world.
"The question of why did people do that? How did that come about? That's what we're ultimately interested in."
To some extent, dog genetic patterns mirror human ones, because people took their animal companions with them when they moved. But there were also important differences.
For example, early European dogs were initially diverse, appearing to originate from two very distinct populations, one related to Near Eastern dogs and another to Siberian dogs.
But at some point, perhaps after the onset of the Bronze Age, a single dog lineage spread widely and replaced all other dog populations on the continent. This pattern has no counterpart in the genetic patterns of people from Europe.
Anders Bergström, lead author and post-doctoral researcher at the Crick, said: "If we look back more than four or five thousand years ago, we can see that Europe was a very diverse place when it came to dogs. Although the European dogs we see today come in such an extraordinary array of shapes and forms, genetically they derive from only a very narrow subset of the diversity that used to exist."
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