New archaeological evidence shows that the size of domestic dogs doubled between 8,000 and 2,000 years ago when early European farmers began breeding large livestock guardian dogs (similar to today’s Anatolian Shepard Dog and Great Pyrenees breeds).

Dog domestication goes as far back as 30,000 years ago, and these early dogs were likely the size of small wolves. Over time, dogs were bred up or down in size, depending on their function.

Archaeologists studied the remains of dogs found at early human settlement sites in the eastern Adriatic region of Europe. These remains date from the late Stone Age to the Roman period.

They found that the earliest of these dogs were around the size of modern Border Collies, but as livestock herding developed, the size of the dogs increased from around 30 pounds to nearly 40 pounds in the Bronze Age and reached 50-70 pounds by the Roman era.

A report on the study in Science notes that these large dogs accompanied flocks of sheep and other livestock as they grazed further away from human settlements and were at increased risk from predators like wolves and bears.

The AKC notes that today’s livestock guardian breeds are working dogs, separate from the herding dog group, and most have ancestry that goes back thousands of years in Europe and the Middle East.