Where humans go, dogs follow

“Man’s best friend” is the phrase most often wheeled out to describe dogs’ thousands of years as a human companion animal, and a new study reveals details about dogs’ ancestry and their long and complex relationship with us.

“The dog is the oldest domesticated animal and has a very long relationship with humans,” says lead author Anders Bergström, in a video accompanying the study, published in Science. “Therefore, understanding the history of dogs teaches us not just about their history, but also about our history.”

A team led by Bergström, of the Francis Crick Institute, UK, sequenced 27 whole ancient dog genomes and found five original dog lineages that date back to the Palaeolithic era, from which all our current dogs descended.

Analysing these new data alongside other ancient and modern dog genomes, the authors found that all dogs share a common ancestry distinct from present-day wolves. The evidence suggested limited gene flow from wolves since domestication but substantial dog-to-wolf gene flow.

Modern dogs have significantly diversified from their original lineages over the last 11,000 years, but the way dogs intermingled and changed to form new breeds closely reflects human migration – where humans went, dogs went too.

For example, the paper shows that European dogs have ancestry from Palaeolithic West Eurasia and Southwest Asia, which is the same as European people. As people came together, so did their dogs.

Bizarrely, they found some dog genes evolved at the same times as similar genes in humans. Humans have the ability to break down starch due to an enzyme called amylase, which we have more of than other apes due to farming high-starch foods. Dogs also carry extra copies of amylase genes compared to wolves, suggesting humans and dogs gained this trait by eating the same food.

However, the researchers found that not all dogs showed a pattern of following humans. Some appeared to move between groups as well, possibly due to humans trading dogs with each other, or because some dogs turned semi-feral and migrated before being domesticated again.

For instance, the dogs of Anatolian farmers appeared to have been adopted from people in Germany and Ireland and taken home to West Asia. The movement might be explained by the trading or gifting of dogs.

The study also compared the ancient dog genomes to wolves to see whether dogs and wolves were breeding. Despite the five lineages being completely distinct from modern wolves, the team did see some evidence of this.

Interestingly, the greatest gene flow was from dogs to wolves. For example, black wolf coats seem to be a trait passed from North American dogs, and other genes that originated in dogs could be found in wolves but not vice versa.

One possible reason for this one-sided gene flow is that a male dog’s and female wolf’s offspring may have been more likely to survive to continue breeding, whereas humans may not have favoured wolf-like traits in puppies born from female dogs, and stopped them breeding.

Domestic dogs’ biggest mystery remains elusive.

“We find that the modern and ancient genomic data are consistent with a single origin for dogs, though a scenario involving multiple closely related wolf populations remains possible,” write the authors, in conclusion.

“However, in our view, the geographical origin of dogs remains unknown. Previously suggested points of origin based upon present-day patterns of genomic diversity or affinities to modern wolf populations are sensitive to the obscuring effects of more recent population dynamics and gene flow.

“Ultimately, integrating DNA from dogs and wolves even older than those analysed here with archaeology, anthropology, ethology, and other disciplines is needed to determine where and in which environmental and cultural context the first dogs originated.”