By Dr. Becker
In the modern day, we typically group dogs into breed categories like working dogs or herding dogs, with the assumption that those within any given category share similar traits. An analysis of canine genomes — the most diverse dataset of dog breeds to date — reveals that this may not necessarily be the case, however, along with other intriguing insights into how modern-day dog breeds came to be.
There are close to 400 domestic dog breeds in the world, each with a storied history and unique genetic profile. The researchers examined the genomes of nearly 1,350 dogs, including 161 breeds, to reveal the ancient and often-surprising origins of and relationships between breeds. Meanwhile, the analysis revealed very different lineages among herding dogs, likely because such dogs were bred at different times and in different places.
U.S. National Institutes of Health (NIH) biologist and study author Elaine Ostrander, Ph.D., explained in Nature, "In retrospect, that makes sense … What qualities you'd want in a dog that herds bison are different from mountain goats, which are different from sheep, and so on."1
'New World Dog' Revealed
Among the most intriguing discoveries revealed by the canine genome map is a New World dog within some modern-day breeds. These dogs likely entered the Americas with humans who crossed the Bering land bridge between Alaska and Siberia, then eventually disappeared after the introduction of European and Asian dogs (where most dogs in the study came from).2,3 The researchers explained in the journal Cell Reports:4
"Dogs have been in the Americas for more than 10,000 years, likely traveling from East Asia with the first humans. However, studies of mitochondrial DNA suggest that the original New World dogs were almost entirely replaced through European contact and additional Asian migrations. As colonists came to the Americas from the 16th to the 19th centuries, they brought Old World livestock, and therefore the dogs required to manage and tend the livestock, to the New World.
Many of the newly introduced animals outcompeted the native animals, which may explain the surprising and very strong herding dog signature in the native hairless breeds of South and Central America that were not developed to herd. In this analysis, we observe that the ancient hairless breeds show extensive hybridization with herding dogs from Europe and, to a lesser extent, with each other."
Previous research revealed that Chinese Cresteds, Xolos and Peruvian hairless breeds share the same dominant gene mutation, which may give clues to the dogs' origins and possible relation, with the researchers noting it could be due to early trade between Asia and the new world or prehistoric migration from Asia across the Bering Strait.5 The ancient Aztecs in Mexico considered Xolos to be sacred guides for souls in the afterlife, while Peruvian hairless dogs lived during the Incan Empire.
It's thought that Chinese Cresteds may have come from African hairless dogs. However, although these breeds were "derived from or crossed with each other prior to breed establishment," each has very different traits today. The featured study also revealed two major diversification periods for dogs — one that occurred thousands of years ago, during which dogs were selected for their skills, and one that occurred just a few hundred years ago, in which dogs were bred primarily for physical traits.6
Studying Dog DNA May Unlock Secrets of Human Disease
Studying the origins of different dog breeds is fascinating, especially since they're the only species that's been so intensely and deliberately bred by humans, however canine DNA also has the potential to shed light on genetic mutations that could influence human disease. Because humans are so genetically diverse, it can be difficult to reveal genetic links to diseases in human studies. "Dogs, however, are more genetically homogeneous," Nature reported, which makes them ideal for studying genetic variants.7
In one project called Darwin's Dogs, researchers are gathering data from thousands of dogs. Owners answer detailed questionnaires and send in a saliva sample, which will be used to collect the dog's DNA. The researchers then plan to analyze the DNA samples and compare each dog's genetics to its behaviors.
Likewise, because dogs and people share so much similar DNA and develop similar types of cancer, treatments that prove to be successful in dogs often prove to be successful in people as well. The field of comparative oncology has since been created, which teams veterinary and medical oncologists who study naturally occurring cancers in animals to further human and animal cancer treatment. Other diseases, like epilepsy, may be similarly studied, as reported by Nature:8
" … [Be]cause dog breeds are relatively genetically isolated, each breed might carry only one or two of the genes involved in epilepsy, says Ostrander. 'By studying dogs, we can we look at each [gene] individually. It's much more efficient.'"
As genetic analysis becomes more common and widely done, we're likely to learn even more about the origins of domestic dog breeds and how they relate to humans. Of note, it's becoming clear that many modern dog breeds weren't likely developed from one lineage but, rather, popular traits such as herding or large size were probably developed multiple times and in multiple locations during their history.