Animals

A Family Tree for Dogs Reveals How Different Breeds Emerged Around the World

The most comprehensive evolutionary tree of dogs could help improve canine health — as well as our own.

NIH Dog Genome Project

Before we began adopting dogs to keep us company, our ancestors bred them for a very different reason: work. Today, researchers published the largest evolutionary tree of dogs to date, which reveals how various types of dogs were bred for specific tasks, like keeping predators at bay or herding livestock.

In order to construct the evolutionary tree, published in the journal Cell Reports, the researchers sequenced the genes of 161 breeds.

“What we [found] is four different groups of herders that developed in different parts of the world at different points in time,” said Elaine Ostrander of the Cancer Genetics and Comparative Genomics Branch at the National Human Genome Research Institute.

“It makes sense,” she added, “because the dogs that you would need to drive bison on the plains have to have a different set of skills than those who herd goats on rocky territory, which is going to be different than what you use to move sheep in a pastoral setting.”

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The findings are significant because they provide a complete framework for mapping breed behavior, something that Ostrander is often asked about in her line of work.

“The question I get asked most often is ‘when are you going to map genes for breed behavior?’” Ostrander said. “[But] no one has really had any luck doing that and partly it’s because we’ve grouped everything together and now we know that’s not the right way to go. We need to consider these herders separately because their underlying genetics are going to be different.”

This photograph shows a toy xoloitzcuintlel, a dog breed that likely descended from dogs that crossed the Bering Land Bridge with Native Americans ancestors. | Penny Inman

The study also found evidence that as humans began to migrate, so did their canine companions. The “New World Dog,” an ancient canine subspecies, is known to have migrated across the Bering Land Bridge with the ancestors of Native Americans. The study shows that some modern breeds from Central and South America, including the Peruvian hairless dog and the Xoloitzcuintle, share genes with the New World Dog, providing the first link between ancient and modern dogs.

“The community has had hints of [the New World Dog] before from looking at mitochondrial DNA,” Ostrander said, “but this is really the first extensive nuclear study that shows it and digs down to show you which breeds and which times [in history].”

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Perhaps the most practical implication of the study is the insight into the likelihood of disease development among certain breeds. Dogs suffer from many of the same medical conditions as humans, including cancer, kidney disease, and diabetes, and the prevalence varies greatly among different breeds. The data set allowed scientists to track the migration of disease alleles in order to better predict where they are likely to show up next.

“This [discovery] enormously simplifies the problem of finding disease genes in dogs,” Ostrander explained. “It gives us a pathway that we can walk along and hopefully find the things that are important for human health as well as canine health.”

This evolutionary tree shows the relationships between dog breeds. | NIH Dog Genome Project

The model used by Ostrander and her colleagues in the study could likely be applied to disease alleles in humans as well, allowing for a more accurate prediction of which human populations are at-risk for the same conditions.

“Sometimes it’s the same gene, sometimes the same mutation, sometimes it just reveals a pathway we hadn’t thought about before as being important in human disease,” Ostrander said. “[It’s] a great way to get insight into the missing pieces of the human gene puzzle.”

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