A global study by an international team of archeologists has found that there were five different types of dogs more than 11,000 years ago in the period immediately following the Ice Age, a discovery which sheds light on the origin of the many different lineages of humanity's best friend.
The research, published in the journal Science, sequenced ancient DNA from 27 dogs, some of which lived up to nearly 11,000 years ago, across Europe and Siberia.
The scientists, including those from Francis Crick Institute in the UK, found that that by this point in history, just after the Ice Age and before any other animal had been domesticated, there were already at least five different types of dogs with distinct genetic ancestries.
The findings suggest that the diversity observed between dogs in different parts of the world today originated when humans were still hunters and gatherers.
"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," said Pontus Skoglund, study co-author from Francis Crick Institute.
In the study, the scientists extracted and analysed the genetic material DNA from skeletal material of the dogs.
The team showed that over the last 10,000 years, these early dog lineages mixed and moved to give rise to the dogs we know today.
Citing an example, 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.
However, they said this diversity was lost at some point as it is not present in European dogs today.
"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," said Anders Bergstrom, lead author of the study from Francis Crick Institute.
Although the European dogs we see today come in such an extraordinary array of shapes and forms, the scientists said they derive genetically from only a very narrow subset of the diversity that used to exist.
They also compared the history of these dogs to changes in human evolution, lifestyles and migrations.
In many cases, comparable changes took place, likely reflecting how humans would bring their dogs with them as they migrated across the world, the study noted.
But the scientists said there were also cases when human and dog histories did not mirror each other.
They said the loss of diversity that existed in dogs in early Europe was caused by the spread of a single dog ancestry that replaced other populations.
This dramatic event is not mirrored in human populations, and it remains to be determined what caused this turnover in European dog ancestry, the study noted.
"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," said Greger Larson, another co-author of the study from the University of Oxford.
While this study provides fresh insights into the early history of dog populations, the scientists said they are still trying to uncover where and in which human cultural context, dogs were first domesticated.