At least five different types of dog with distinct genetic ancestries existed in Europe around 11,000 years ago when humans were still hunters and gatherers, scientists have found.
The analysis is based on DNA sequenced from 27 ancient canine specimens from across Europe, the Near East and Siberia.
Researchers say the findings, published in the journal Science, could shed light on the “inextricable bond between dogs and humans”.
Lead author Anders Bergstrom, a post-doctoral researcher in the Ancient Genomics laboratory at the Francis Crick Institute, said: “The dog is the oldest domesticated animal and has a very long relationship with humans.
“Therefore, understanding the history of dogs teaches us not just about their history, but also about our history.”
DNA analysis indicates early dog lineages mixed and moved to give rise to the dogs we know today, the researchers said.
They said early European dogs were initially diverse, appearing to originate from two highly distinct populations, one related to Near Eastern dogs and another to Siberian dogs.
But at some point this diversity was lost as it is not present in European dogs today, they added.
Mr Bergstrom 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.”
Pontus Skoglund, group leader of the Ancient Genomics laboratory, who was also an author on the study, said: “Some of the variation you see between dogs walking down the street today originated in the Ice Age.
“By the end of this period, dogs were already widespread across the northern hemisphere.”
The researchers also compared the changes in canine and human histories.
They found that changes in human lifestyles and migrations were mostly reflected in some dog populations, but there were also instances when human and dog histories did not mirror each other.
For example, the researchers said, a single dog ancestry may have caused the loss of diversity that existed in dogs in early Europe but this “dramatic event” is not reflected in the human populations.
Study author Greger Larson, director of the Palaeogenomics and Bio-Archaeology Research Network at the University of Oxford, said: “Dogs are our oldest and closest animal partner.
“Using DNA from ancient dogs is showing us just how far back our shared history goes and will ultimately help us understand when and where this deep relationship began.”