Dogs hold the remarkable distinction of being the most physically diverse mammal species on Earth, a fact that new research reveals has much deeper roots than previously believed.
The Ancient Origins of Canine Diversity
While Victorian kennel clubs that emerged approximately 200 years ago are often credited with creating the extraordinary variety of modern dog breeds through selective breeding, a groundbreaking study published in Science demonstrates that canine diversity existed millennia earlier. Dogs already exhibited remarkable variation in skull size and shape more than 10,000 years ago, long before the establishment of formal breeding programs.
This discovery fundamentally challenges the long-held assumption that directed breeding alone created the physical diversity we see in dogs today. Instead, the research indicates that early dogs had evolved an extraordinary range of forms soon after domestication, with this diversity being continually shaped by thousands of years of shared history with humans.
Tracking Domestication Through Skull Analysis
Archaeologists and geneticists have long grappled with the deceptively simple question of when wolves became dogs. As the first species humans domesticated - preceding plants or livestock by significant margins - dogs represent a crucial milestone in human history. However, the similarity between wolves and dogs has made tracking domestication in the archaeological record particularly challenging.
The research team employed an innovative technique called geometric morphometrics, which maps and measures shape variation in three dimensions, to analyze 643 skulls of ancient and modern dogs and wolves spanning 50,000 years. The specimens came mainly from sites across the northern hemisphere, allowing researchers to track the emergence and diversification of domestic dogs across both time and space.
The findings were striking: the earliest skulls with clearly domestic shapes in their dataset date to approximately 11,000 years ago from the Mesolithic site of Veretye in Russia. By this period, dogs had not only diverged in skull shape from wolves but had already begun diversifying among themselves.
Regional Lineages and Lost Morphologies
These early dogs weren't uniform but exhibited skulls of different sizes and shapes, likely reflecting the influence of local environments, population histories, and human preferences. Intriguingly, some early dogs displayed skull forms not found in any modern breeds, suggesting lineages and morphologies that may have since vanished.
While the most extreme forms seen in modern breeds like pugs or bull terriers weren't present, the variation observed by the Mesolithic period already represented half the total variation seen in modern breeds. This finding complements genetic studies revealing deep splits among early dog populations.
By the Neolithic period (approximately 8,000-5,000 years ago), dogs had formed regionally distinct lineages across Europe, the Near East, and Asia. Some of these ancient lineages survive in modern breeds, while others appear to have gone extinct, possibly replaced or diluted through interbreeding and human migrations.
The research team examined 17 Late Pleistocene skulls (dating from 126,000 to 11,700 years ago) and found no evidence of domesticated dogs among them, suggesting domestication may not reach as far back as the 30,000 years proposed by some studies. However, the researchers acknowledge that the earliest dogs would have closely resembled wolves, making identification challenging.
To deepen understanding of this critical period in human-canine history, the study emphasizes the need for more specimens from the window between 25,000 and 11,000 years ago, particularly from underrepresented regions like central and south-west Asia.
Ultimately, this research reinforces that dogs serve as a mirror of human history. Their story is inextricably intertwined with ours, shaped by shared migrations, changing environments, and evolving societies. As the first domesticated species - and still our most enduring companion - dogs offer a unique window into how humans have shaped the natural world and how the natural world has shaped us in return.
