Researchers present new insights into the age-old common history of dogs and humans: They have examined the genetic makeup of 27 dog skeletons that are up to 11,000 years old. It showed that even then there were at least five different lineages of dogs, whose inheritance was mixed in different proportions in later breeds. The spread of the dogs is closely related to the migration movements of humans.
Dogs are considered to be man’s “best friends”. They were probably domesticated 25,000 to 40,000 years ago – as the very first animal species. In contrast to pigs, for example, which were domesticated several times independently of one another in different parts of the world, according to the current state of knowledge, all dogs go back to a single line of wolves, which is now probably extinct. Nevertheless, there was considerable genetic diversity as early as 11,000 years ago, as an international team led by Anders Bergström from the Francis Crick Institute in London has now shown.
Bone samples from all over the world
To do this, the researchers examined genetic material from the skeletons of 27 dogs. “The dog samples were collected from museums and other collections around the world and by several members of this team,” says co-author Anna Linderholm of Texas A&M University. The oldest samples were almost 11,000 years old, so they come from a time when humans still lived as hunters and gatherers and had not yet domesticated any other animals apart from dogs.
Even then, the dogs evidently exhibited considerable genetic diversity: the researchers identified five different lineages that were represented in different proportions in later breeds. “Some of the differences that you see in dogs today had their origins in the Ice Age. By the end of this period, dogs were already common all over the world, ”says Bergström’s colleague Pontus Skoglund.
Diversity used to be greater than it is today
Using bone samples from different eras, the researchers were able to trace how the genetic makeup of the early dogs mixed and spread. The first European dogs, for example, came from two very different dog populations from the Middle East and Siberia. However, over the millennia, diversity has decreased. “If we look back over four or five thousand years, we can see that Europe was a very diverse region when it came to dogs. Although the European dogs as we know them today have such an extraordinary variety of shapes and forms, genetically speaking they only descend from a very limited subset of the diversity of that time, ”explains Bergström.
Common history with humans
Many of the events that can be read off in the genetic history of dogs are closely related to human influences. The researchers proved this by also including old genomes of people from the same period in the study. For example, when the first Neolithic farmers from Anatolia came to Europe, they apparently brought their dogs with them, so that from then on their genetic material spread throughout Europe. “We see a clear link between the movement of people and the introduction of a new breed of dog,” says Linderholm.
In other cases, however, dogs seem to have spread independently of their human companions. A lineage of dogs from southern Sweden established itself in large parts of Europe without any knowledge of human migration. Conversely, not all peoples brought their dogs with them to new regions.
Gene flow from dog to wolf
According to the genome data, intermingling with wolves took place several times. In the genomes of today’s wolves from different regions of the world, clear influences from dogs from the same regions can be found. Apparently the exchange was only going in one direction. None of the dog breeds examined showed relevant traces of wolf genes. One reason for this could be that mixed breeds between dogs and wolves were accepted in wolf packs and were able to reproduce while they were weeded by humans.
In further studies, the authors now want to address the question of when and where exactly dogs were domesticated for the first time. “Just as the old DNA revolutionized research into our own ancestors, it is now doing the same for dogs and other domesticated animals,” says co-author Ron Pinhasi from the University of Vienna. “This adds another level to our understanding of human history.”
Source: Anders Bergström (Francis Crick Institute, London) et al., Science, doi: 10.1126 / science.aba9572