The largest study of dog DNA to date tracks how dog breeds changed due to time and human migration.

Researchers at the National Institutes of Health published the results of their genetic study on April 25 in Cell Reports. The analysis stems from 1,346 dogs representing 161 breeds. DNA was collected from across the world. Collecting so many samples and mapping them out has allowed the researchers to make connections they hadn’t before and get a better sense of what breeds have close ties to each other.

The genetic dataset researchers collected combines genetic distance, migration, and genome-wide haplotype sharing analyses to reveal geographic patterns of developments and independent origins of common traits. Previous studies have addressed the genomic makeup of breeds on a smaller scale, but none of them accounted for the ways in which modern breeds may have developed, like geographic separation and the timeline of breed formation.

One benefit of the study is to be able to track disease-causing genetic mutations, as Elaine Ostrander, one of the lead researchers, told NBC News. For instance, collie eye anomaly is a disease that affects several herding breeds, including Border collies and Australian shepherds in the UK. Collie eye anomaly has also shown up in the Nova Scotia duck tolling retriever in Canada, and this presented a puzzle as the two groups of dogs were seemingly unrelated. Analysis from this study, however, shows that the collie and/or Shetland sheepdog were strong, but undocumented, contributors to the formation of the Nova Scotia duck tolling retriever.

Some other findings in the study include the following discoveries:

• The pug’s early exportation from Asia means it contributed to many other small breeds, shown by its shared haplotypes with other Asian toy breeds and other small dog breeds like the European Brussel griffon.
• Many terriers and mastiffs were bred in different combinations when dog fighting was popular. Analysis shows that bull and terrier crosses relate to the terriers of Ireland and date to the mid-1800s. This finding fits with the historical description of dog fighting and breeding in Ireland.
• Dogs came to the Americas with the first humans, but those dogs were almost entirely replaced through European contact. Native hairless breeds of South and Central American show ties to herding dogs, likely developed from cross breeding of dogs starting in the 16th century. However, some of the older American breeds do show signs that they retain some of the original genetic make-up of native American dogs.
• Some dogs with similar traits do not show a mixing, which suggests that the same traits arose independently of each other based on need. One example is Mediterranean and European mastiffs, which both guard flocks, but they do not share a common genetic makeup. This means that the two breeds of mastiff likely developed the trait independently.

People have been breeding dogs for thousands of years, but the research shows that a round of hybridization and selection has been applied within the last 200 years, creating many of the modern breeds we have today.

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