Subspeciation in the Meadow Mouse, Microtus Montanus, in Wyoming and Colorado

A meticulous monograph born from years of fieldwork across the mountain valleys and plains of Wyoming and Colorado. Sydney Anderson examined 1,187 specimens of Microtus montanus, measuring skulls, teeth, and pelage with painstaking precision to draw the invisible boundaries between populations. What emerges is a portrait of evolution in motion: how the Rocky Mountains, the Great Plains, and a thousand subtle gradients of moisture and altitude have sculpted distinct subspecies over millennia. Anderson documents 19 subspecies, several previously unrecognized, revealing that even tiny mammals like the meadow mouse are not uniform creatures but living mosaics shaped by their geography. The study stands as a foundational text in mammalogy, demonstrating how rigorous specimen-based research can illuminate the processes that generate biodiversity. For students of evolutionary biology, field ecologists, and anyone fascinated by the hidden architecture of life on Earth, this monograph offers a master class in asking nature's oldest question: where do species come from, and what keeps them apart?