When Did Dogs Start Changing Their Shape?

Dogs are famous for their variety, from tiny Chihuahuas to massive Great Danes. But when did this transformation begin? A recent study posted on arXiv examined 643 canid skulls dating back 50,000 years using 3D geometric morphometrics. The findings reveal that a distinctive dog shape emerged about 11,000 years ago, during the Holocene. Even then, early dogs already displayed a remarkable range of sizes and outlines, long before humans started breeding specific breeds in the 19th century. This means the diversity we love today isn’t just a recent product of selective breeding, but has deep roots in our ancient hunter‑gatherer partners. Researchers faced two big hurdles: few Pleistocene specimens and the difficulty of telling early dogs apart from wolves based solely on skulls. With 3D technology, they could compare shapes and sizes precisely, uncovering that canine morphological diversity began thousands of years before modern times. In short, our four‑legged friends started “customizing” themselves long before we did.

The study employed three‑dimensional geometric morphometrics (3DGM), a technique that quantifies complex shapes using coordinates of anatomical landmarks on digital models. The 643 skulls examined include specimens of wolves, ancient dogs, and modern dogs, spanning a 50,000‑year timeframe. After digitization via structured‑light scanning, researchers aligned the data using Procrustes superimposition, removing differences in scale, rotation, and translation to isolate shape variation. Principal component analysis (PCA) revealed that early dogs, from about 11,000 years ago, occupy a distinct region of morphospace separate from wolves, indicating significant divergence. Moreover, the intra‑group variance among ancient dogs is already high, suggesting a rapid exploration of diverse morphologies, likely linked to different ecological roles (hunting, guarding, transport). Calibrated dating was achieved through radiocarbon (C‑14) and stratigraphy, with errors of ±200 years. The results challenge the view that canine diversity is solely a recent phenomenon driven by 19th‑century artificial selection. Instead, natural and cultural selection by early farmers likely favored useful morphological traits, creating a variability foundation for later breeders. This work shows how integrating advanced imaging techniques with statistical analysis can resolve long‑standing evolutionary questions, paving the way for further research on other domesticated animals.