Every dog lover has, at one time or another, marveled at the variety of one dog breed compared to another. From the massive St. Bernard to the tiniest Pomeranian, it can be hard to fathom just how canines branched out from their wolfish roots into an array of retrievers, poodles, and pugs.
That's why a team of researchers spent more than 20 years creating the first genomic "family tree" of dog breeds, identifying genetic traits that are shared among some breeds and not included in others.
The new study provides insight into breeding processes that have been conducted, with the help humans, for thousands of years. Dog breeding represents one of the earliest and longest-running genetic experiments in human history, producing more than 350 distinct varieties of man's best friend. The new study provides valuable insight into this millennia-old process, sometimes confirming what humans have known for centuries – but also revealing a few surprises along the way. One new discovery pertains to the many breeds of dogs used to herd livestock, according to Heidi Parker, one of the co-authors of the study.
"You would think that all working dogs or all herding dogs are related, but that isn't the case," Dr. Parker told Nature magazine.
The researchers found that some breeds of herding dogs actually came around at multiple times and in different places, depending on the needs of humans in different geographical locations. Ancient humans would breed dogs based on specific, useful attributes that specialized varieties of canines for hunting, protection, and even as a source of meat.
"When humans started living with dogs, much about life itself was less about the aesthetics and more about survival and making life easier for ourselves," said Dayna Dreger, another author of the study, told The Guardian.
All that changed in the past 300 years or so, when dog breeding began to be influenced by fashion, giving rise to "less useful" canine companions. The introduction of Chinese pugs into European breeding programs, for instance, had the effect of shrinking other dog breeds, leading to some of the smaller, more decorative canines we know today.
But despite physical differences between breeds, dogs are all extremely similar genetically, making constructing a "family tree" like this one a challenge for researchers. The new study, which was published in the journal Cell Reports on Tuesday, was based on genetic data points from 1,346 dogs representing 161 breeds, a little under half of all dog types. The researchers could then group these 161 breeds into 23 confirmed clades, which are groups of breeds that come from a common ancestor. With this information in hand, researchers could track the movement of dogs from region to region across history – and sometimes even across continents.
One interesting discovery in this vein relates to the "New World Dog," which likely crossed into the Americas on a land bridge some 13,000 years ago with early human settlers in the region. When dogs began to trickle in from Europe and the rest of the world, the New World Dog seemed to disappear from the archaeological record completely – until the researchers noticed what appeared to be unique DNA hidden in two dog breeds: the Mexican Hairless and the Peruvian Hairless dog, possible descendants of the old American breed.
"What we noticed is that there are groups of American dogs that separated somewhat from the European breeds," Parker told NBC. "We've been looking for some kind of signature of the New World Dog, and these dogs have New World Dogs hidden in their genome."
The new genetic research reveals details about dogs that could never be determined simply by observing physical traits, since the team also found that certain traits, such as large size, would often develop independently in breeds in different parts of the world. As a result, the new research corrects many incorrect assumptions that humans have had about dogs for centuries and uncovers new questions scientists have never known to ask until now.
Of course, over half of all dog breeds are not covered in the new family tree, so there's still a lot of work to be done to fully understand man's best friend – at least, as far as genetics are concerned. For the family tree researchers, this study is only the beginning.
"We had reached a point where we could begin to do some of the things we wanted to do," Elaine Ostrander, study co-author said in a statement from the journal Science. "By no means are we done."