Dog DNA study maps breeds across the world

Mapping the relationships between different dog breeds is rough (get it?), but a team of scientists at the National Institutes of Health did just that using the DNA of 1,346 dogs from 161 breeds. Their analysis, which appears April 25 in Cell Reports, offers a lot to chew on.

Here are five key findings from the work:

Dogs were bred for specific jobs, and this shows in their genes.
As human lifestyles shifted from hunting and gathering to herding to agriculture and finally urbanization, humans bred dogs (Canis familiaris) accordingly. Then over the last 200 years, more and more breeds emerged within those categories. Humans crossed breeds to create hybrids based on appearance and temperament, and those hybrids eventually became new breeds.

DNA from hybrid dogs backs up historical records.
Genetic backtracking indicates that, for example, mixing between bulldogs and terriers traces back to Ireland between 1860 and 1870. That timeframe and location coincides with historical records indicating a dog-fighting fad that’s linked with crossing breeds to make better fighters.

Geography also matters.
While herder dog breeds showed a lot of genetic diversity, they fall into two general groups from the rural United Kingdom and the Mediterranean on the breed family tree. When humans switched from hunting to farming, herding breeds may have emerged independently in different areas. Geography could also explain why these two groups use different herding tactics.

New World dogs aren’t all immigrants.
A genetic legacy of America’s early canine inhabitants lives on in some of today’s breeds. Dogs trekked to the Americas from Asia with people more than 10,000 years ago, but when European groups started to colonize the Americas, they brought European dog breeds with them. Past studies suggest that outside breeds largely replaced New World dogs, but the new dataset shows New World dog DNA actually does persist in a few modern New World breeds, such as Chihuahuas.

Big dogs evolved independently to be big.
European mastiffs and Mediterranean sheepdogs don’t share recent changes in their DNA, meaning their size traits arose separately and for different reasons. While both breed groups specialize in guarding things, mastiffs use their size to intimidate humans, while sheepdogs use their size to overpower animal predators. Larger size may have been one of the first traits that human breeders zeroed in on, the researchers suspect.