While the range of physical diversity dogs show is often thought to be the result of intense breeding over the last 200 years, a new study – based on tracing 50,000 years of canid skull evolution – suggests domestic dogs began developing their distinctive forms thousands of years before humans started shaping modern breeds. Dogs at this time were shaped by early human influence, environmental shifts, and changing food sources. The origins and early diversification of domestic dogs are among the most debated topics in archaeology. Previous studies indicate that dogs first appeared during the Late Pleistocene, with major distinct genetic lineages appearing by at least 11,000 years before present. Because of their long association with humans, modern dogs exhibit an exceptional range of physical diversity, in both size and shape. It's thought that much of this diversity is the direct result of intense breeding that happened in recent centuries. However, exactly when distinct dog variation first began to take shape is poorly understood and has been limited by the scarcity of Pleistocene specimens, the fragmentary condition of available remains, and the challenge of distinguishing early dogs from wolves based solely on skeletal morphology.
To trace how the physical forms of domestic dogs developed and diversified over time, Allowen Evin and colleagues used advanced 3D morphometric analysis to examine 643 canid skulls spanning 50,000 years, allowing them to measure subtle differences in skull shape and size with exceptional precision. By creating digital 3D models through laser scanning or photogrammetry, Evin et al. compared specific cranial features across ancient and modern dogs and their wild relatives. The findings show that distinct dog-like skull traits first appeared during the early Holocene, evidenced by 10,800-year-old remains recovered in Russia. Notably, all of the Ice Age canid skulls examined closely resembled wolves, suggesting that although visible domestication traits appeared only after 11,000 years ago, the process of domestication likely began earlier during the late Pleistocene, which is consistent with genetic evidence. The oldest known dogs from the Mesolithic and Neolithic possessed skulls that fell within the modern range of sizes but were typically smaller and less varied, lacking exaggerated traits that characterize many present-day breeds. Even so, their diversity was surprising; early Holocene dogs exhibited roughly half the morphological range seen in modern dogs and twice that of their Pleistocene wolf ancestors, suggesting that notable variation in dog form had already emerged millennia before modern breeding practices. The retention of wolf-like characteristics in some modern breeds highlights the gradual and complex evolution of the dog from their wild wolf ancestors. Evin et al. also found that ancient wolves were more varied in skull shape and size than they are today. "The domestication of dogs has captivated attention because of the close bonds that many humans share with dogs," Melanie Fillios writes in a related Perspective. "[Evin et al.'s] research contributes to the wider understanding of domestication as a complex, multifaceted biological and cultural process in which thousands of years of human and animal history are intertwined."
